2 CONSIDERATION OF ALTERNATIVES
2.1.1.1
Several options and alternatives have been considered in the
development, refinement and selection of the scheme of the Trunk Road T2 to be
taken forward for environmental assessment and detailed design. This section of the report provides the
details of the alignment options considered and the constraints and
considerations assessed in adopting the recommended scheme.
2.1.1.2
In addition, as part of this process, the various
construction methodology options available have been reviewed in order to
determine the most effective means of building the Project. The review has taken into account engineering
feasibility, site conditions, programme constraints and environmental considerations. Details of the construction method
alternatives are, also, provided below.
2.2 Alignment Option Review and Selection
2.2.1 Background
2.2.1.1
As a part of the strategic road
network within the South East Kowloon Development, Route 6 forms an east west
express link between
2.2.1.2 Details of the development of the Trunk Road T2 alignment and the options considered are presented below.
2.2.2 Development of Previous Alignment Options for Trunk Road T2
2.2.2.1 Under the previous study, the South East Kowloon Development Comprehensive Feasibility Study (SEKD CFS), commissioned in 1999, Trunk Road T2 was proposed to link up the Central Kowloon Route and Trunk Road T1 (no longer being considered) at the western end and the Western Coast Road (WCR), now renamed as the Tseung Kwan O - Lam Tin Tunnel (TKL-LTT)) at the eastern end. The western portion of the Trunk Road T2 was proposed to be an at-grade road which descended with a gentle gradient into the tunnel section. Elevated viaduct was proposed at the eastern part of Trunk Road T2 for the portion near the existing Kwun Tong Ferry Pier to allow the road to pass over other proposed roads. The alignment then crossed over Tsui Ping Nullah and turned down to join with the proposed WCR (TKO-LTT).
2.2.2.2 The study proposed extensive reclamation in the Harbour resulting in strong criticism from the public and resulted in a re-study for the South East Kowloon Development. This SEKD CFS alignment option was, therefore, not considered further as a result.
2.2.2.3 Following the SEKD CFS, the Kai Tak Planning Review (KTPR) was conducted in January 2004 with the objective of reviewing the planning basis of SEKD CFS and formulating a preliminary outline development plan (PODP), starting on the basis of no reclamation. The PODP developed under KTPR proposed the Trunk Road T2 to be in form of tunnel that would be fully embedded into the seabed of Kwun Tong Typhoon Shelter (KTTS) and the Harbour in order to avoid reclamation. This tunnel option of Trunk Road T2 and the PODP was generally accepted by the public during the public consultation undertaken at that time.
2.2.2.4 Subsequently, the Kai Tak Development Engineering Study (KTDES) was undertaken in 2007 and this study reviewed the PODP and undertook detailed engineering feasibility studies, including for the proposed Trunk Road T2 alignment. Based on the alignment constraints arising from the necessary connections with CKR and TKO-LTT, the layout of Trunk Road T2 was developed.
2.2.2.5 In the KTDES scheme, it was proposed that about 2.6 km of Trunk Road T2 would be in the form of tunnel and about 2.0 km of the tunnel was to be in the form of an immersed tube tunnel placed under the seabed. After its connection with CKR, the Trunk Road T2 alignment would run mostly at-grade along the South Apron, starting from the mouth of the Kai Tak Nullah. After crossing the Jordan Valley Box Culvert (JVBC), Trunk Road T2 starts to depress and then descends into tunnel under the Road D4 towards the seabed in the Kai Tak Typhoon Shelter (KTTS). Within the KTTS, the Trunk Road T2 scheme comprised a fully embedded tunnel in the seabed that passed through and under the KTTS, breakwaters and sewage subsea outfall of the Kwun Tong Preliminary Treatment Works (KTPTW) at a gentle gradient before making landfall at Cha Kwo Ling (CKL). At CKL the Trunk Road T2 comprised a depressed open section to allow connection with the TKO-LTT.
2.2.2.6 The alignment of Trunk Road T2 developed by the KTDES is shown in Figure 2.1 and this is the scheme which was included in the Study Brief for this Assignment.
2.2.2.7
Since the
period from the development of the KTDES alignment in 2007, a number of key items have
changed and these have influenced the potential Trunk Road T2 alignment
options, specifically;
·
After consideration of different options
and alignments, the alignment of CKR was updated to cope with the public
concern and, therefore, the interface of the Trunk Road T2 has had to be fine
tuned to accommodate;
·
After consideration of different
horizontal and vertical alignments for Route 6 as it passed through
·
New techniques in tunnel construction have
reduced the risks associated with TBM works within the soft and mixed ground
conditions anticipated for the trunk Road T2 alignment;
·
Similar Hong Kong highway projects have
now adopted TBM tunnelling for similar ground conditions to those encountered
in the Trunk Road T2 alignment, significantly increasing the knowledge and
experience in handling this form of construction; and
·
The timing of the construction of the
Trunk Road T2 has been reprogrammed for commencement to end of 2015 (from
2012), resulting in a different set of project interfaces to those anticipated
at the time of the KTDES.
2.2.2.8
The key constraints on defining the Trunk
Road T2 alignment options are discussed in Section
2.2.3 below.
2.2.3 Constraints on Trunk Road T2 Alignment
2.2.3.1
Environmental considerations are key to the
development and assessment of the alignment options and all key environmental
parameters during both the construction and operational phases of the project
have been considered. Thus, the guiding
principle in establishing the final preferred alignment for the Trunk Road T2
has been to produce an effective highway alignment that would comply with
the constraints identified in Section
2.2.3.2 below, meet the statutory obligations under the Protection of the
Harbour Ordinance (PHO), since the alignment is located within the boundary of
Victoria Harbour (see Figure 2.1), minimise the impact on
the KTTS and present the best environmental option.
2.2.3.2
In addition to the
environmental issues, the key physical constraints that must be considered in
developing the horizontal alignment and vertical profile of the Trunk Road T2
alignment are given in Table
2.1 below and discussed in the sections below.
Table 2.1 Summary
of Physical Constraints on Alignment Development
|
Natural Constraints |
Existing Man-Made Constraints |
Future Man-Made Constraints |
|
·
Sea Bed level (PHO) ·
Geological profile |
·
·
Kerry Dangerous
Goods Godown ·
Public Works
Central Laboratory ·
Breakwater of
KTTS ·
Kwun Tong Bypass ·
·
Eastern Harbour
Crossing (EHC) ·
Existing
properties in Kwun Tong District |
·
At-grade
developments on South Apron for the Kai Tak Development (KTD) ·
Hospital developments
on South Apron ·
Environmentally
friendly linkage system for KTD (EFLS) ·
At-grade
developments on the former ·
Cruise terminal
on the former ·
Interface with ·
Interface with
Tseung Kwan O – Lam Tin Tunnel (TKO-LTT) |
Seabed Level/PHO
2.2.3.3
In 1997, the PHO, Cap.531, was brought into law, preserving the
(1)
“The harbour is to
be protected and preserved as a special public asset and a natural heritage of
(2)
All public officers and public
bodies shall have regard to the principle stated in subsection (1) for guidance
in the exercise of any powers vested in them.”
2.2.3.4
In compliance with the statutory requirements of the PHO, any structure
has to be designed and constructed without exploitation of the Harbour.
Geological Profile
2.2.3.5
The geological profile has been established through research on previous
site investigations and through the project specific site investigation carried
out under this Assignment.
2.2.3.6
Alignment options
passing through the South Apron and former Kai Tak airport runway are
anticipated to encounter fill materials from 11m to 20m thick underlain by thin
layers of marine muds varying from 2m to 10m in thickness. Under the muds, a layer of silty alluvium with thicknesses varying from 12m to 25m is
present, followed by a layer of completely decomposed granite (CDG) that varies
from 15m to 40m in thickness. Rockhead in the form of grade III or better granite is
encountered at between -45mPD to -70mPD. The geological long sections relevant
to these alignment options are presented in Figures 2.2a, b, c
and d.
2.2.3.7
Alignment options
passing through the KTTS are anticipated to encounter thin layers of marine
muds varying from 2m to 10m in thickness.
Under the muds, a layer of silty alluvium with
thicknesses varying from 8m to 30m will be encountered, followed by a layer of
completely decomposed granite (CDG) that varies from 5m to 30m in
thickness. Rockhead
in the form of grade III or better granite is encountered at between -30mPD to
-60mPD.
2.2.3.8
In respect of
alignment options passing through the Kwun Tong area,
parallel to the existing Kwun Tong Bypass, they would
be expected to encounter fill materials up to 15m thick underlain by layers of
marine muds varying from 5m to 15m in thickness. Under the muds, a layer of silty alluvium with thicknesses varying from 5m to 20m is
present, followed by a layer of completely decomposed granite (CDG) that varies
from 10m to 50m in thickness. Rockhead in the form of grade III or better granite is
encountered at between -25mPD to -80mPD.
2.2.3.9
The existing Jordan Valley Box Culvert is located within the South Apron
of the former Kai Tak Airport, as shown in Figure 2.3. The culvert is a multi-cell drainage culvert which
drains all of the hinterland behind the Kwun Tong
district and is a critical element of the drainage for the
area.
2.2.3.10
The culvert is
located very close to the existing ground level in the South Apron. Therefore, any Trunk Road T2 option which
crosses the alignment of the culvert must pass over the culvert
without imposing additional loading on the culvert or must pass under the
culvert. Any construction works and new
infrastructure constructed on or below the culvert should seek to minimise the
risk of imposing additional loading on the culvert and avoiding damage or
settlement of the culvert.
Kerry Dangerous Goods Godown
2.2.3.11
The existing Kerry Dangerous Goods Godown
(KDGG) is a 6 storey building of 71.2m by 41.2m and founded on bored piles toed
into bed rock and is located at the southern edge of the South Apron landfall (Figure
2.4).
2.2.3.12
A planning application (Application No. A/K22/13 (Appendix 2A)) for residential
development at the site was approved by the Town Planning Board in March
2012. It has been advised that the
residential development will be in place towards the end of 2016 (see
Concurrent Project summary table in Appendix 3C). Any encroachment of permanent and
temporary works on this lot, therefore, needs to be avoided.
Public Works Central Laboratory
(PWCL)
2.2.3.13
As there are some sensitive equipment in the existing PWCL building, the
alignment of Trunk Road T2 needs to be designed to maximise the separation from
the existing PWCL building, while still maintaining a minimum 2m clearance with
the building area of the Commercial Site 3E-1 (C(2) shown on OZP) in Figure 9.5.5. While impacts to the PWCL facility could be
avoided by relocating it before construction, this might take about 6-8 years
for site selection, construction of a new building and relocation of equipment
(approximately 18 months) and, thus, could affect the implementation programme
for the Trunk Road T2. Thus, in order to
meet the proposed construction programme, it has been recommended that the
building be retained in-situ during the construction of the Trunk Road T2.
2.2.3.14
Further careful consideration has to be
given to restrictions on construction vibration that may be imposed on the
building’s sensitive test equipment. As
such, the selection of the alignment options needed to consider the potential
impact on the operation of the PWCL building to within its acceptable operating
levels.
Breakwaters of Kwun
Tong Typhoon Shelter (KTTS)
2.2.3.15
There are two breakwaters located at the entrance of the Kwun Tong Typhoon Shelter. These breakwaters, depending on
the alignment, may have to be partially demolished. The vertical alignment of
the Trunk Road T2 tunnel would need to be at a level such that adequate
foundations for the re-instated breakwaters, if so required, can be provided or
not impacted at all. The typhoon shelter
should be maintained with uninterrupted operation during the construction stage
of the Trunk Road T2 and, therefore, a temporary breakwater may need to be
provided to provide wave protection for the typhoon shelter in the event that
the existing breakwaters need to be removed to allow access for the
construction of the Trunk Road T2, for example in the case of Immersed Tube
(IMT) tunnel construction. The typical details for the existing breakwaters can
be seen in Figure 2.5.
Kwun Tong Bypass (KTBP)
2.2.3.16
The KTBP is a precast segmental viaduct running along the promenade of Kwun Tong Area. Both the vertical and horizontal alignment
of any inland Trunk Road T2 option would be constrained by the existing KTBP
from a safety and traffic point of view.
A typical section for the viaduct is shown in Figure 2.6.
Sewage
2.2.3.17
The existing sewage subsea outfall consists of a pair of subsea precast
concrete pipes of 2.1m diameter. These pipes function as an emergency sewage
outfall from the Kwun Tong Sewage Treatment Works to
the Harbour and the whole pipeline is fully embedded into the seabed. The vertical alignment of the tunnel must
allow for the future operation of the outfall for any proposed Trunk Road T2
alignment option that would cut across the subsea outfall. For instance, for
IMT tunnel options, a temporary diversion would be required. The arrangement of
the sewage subsea outfall can be seen in Figure 2.7.
Eastern Harbour Crossing
2.2.3.18
The existing Eastern Harbour Crossing (EHC) is located near the southern boundary of the
Trunk Road T2 alignments options being considered, close to the interface with
the Tseung Kwan O –
Lam Tin Tunnel. Running from Tai Koo Shing on
Existing Properties in Kwun Tong District
2.2.3.19 The Kwun Tong District is a densely developed area with medium to high-rise industrial, commercial, residential properties. The industrial buildings, some constructed in the 1950s are mainly located within the Kowloon Bay, Kwun Tong (to the southwest of Kwun Tong Road), and Yau Tong areas with the main roads within the area under consideration, such as Wai Yip Street, constrained on both sides by industrial properties.
At-grade developments on South
Apron for the Kai Tak Development
2.2.3.20
The infrastructure for the south apron is currently under construction
and will continue to be developed over the duration of the Trunk Road T2
construction period. The planning for
the Kai Tak Development (KTD) has taken Trunk Road T2 into account and defined a corridor within
which the alignment can pass and it is anticipated that this corridor could
only be changed where there would be significant benefits to be gained by the
change. In developing the alignment options, the
development areas have been considered in terms of what impact a change in the
planned alignment may have but have not been taken as fixed constraints. However, those alignment options that work
within the space identified in the KTDES and/or have minimum interface with the
planned developments would be preferable.
Hospital Developments on South Apron
2.2.3.21
The development plan for the South Apron identifies that a Centre of Excellence
for Paediatrics (CEP) will be located on the Site C of Site 3C1 at the South
Apron.
2.2.3.22
The planning for the South Apron, also,
identifies that the Site A of Site 3C1, next to Site C
will be allocated for a hospital development in the form of a Centre of Excellence for Neuroscience and
2.2.3.23
As with the
interfaces with the other developments in the KTD, alignment options that work
within the space identified in the KTDES and/or have minimum interface with the
planned hospital developments would score higher in the assessment.
Environmentally Friendly Linkage
System for Kai Tak Development
2.2.3.24
An Environmentally
Friendly Linkage System (EFLS) is planned in the Kai Tak Development as illustrated in Figure
2.8. The elevated EFLS is
proposed to comprise a 9-kilometre 12-station line linking the MTR Kowloon Bay
Station, through
2.2.3.25
The EFLS is envisaged as a primarily
elevated transportation system which connects the Kai Tak development and the Kwun Tong hinterland.
The current planning for the EFTS may constrain the alignments of the
Trunk Road T2 as follows:
·
Horizontal - along the main road link of
the former Kai Tak Runway of KTD; and
·
Vertical - at the KTTS the Kwun Tong transportation link.
2.2.3.26
Similar to the assessment for the
developments on the South Apron, those alignments that work within space
identified in the KTDES and/or have minimum interface with the planned EFLS
would score higher in the assessment.
At-grade Developments on the
2.2.3.27
The planning for the development of the former runway includes for the
EFLS and the new cruise terminal along with the infrastructure (utilities,
roads etc) necessary to support the development, the most significant being
Road D3 (Shing Fung Road) which is to be constructed along the length of and
between the planned developments along the runway.
2.2.3.28
Trunk Road T2 alignments options that have
minimum or no interface with the indicated developments on the former Kai Tak
Airport runway would be preferred and would score higher in the assessment.
Cruise Terminal on the
2.2.3.29
Located to the south of the runway of the former Kai Tak airport, the
new cruise terminal, which is due to open the first berth in 2013, will have
two alongside berths of lengths of 450m and 400m for Berth I and Berth II,
respectively, and disembark a total of 5,400 passengers and 1,200 crew, as well
as anticipating the future demands of cruise liners.
2.2.3.30
The location of the terminal and its
foundations, shown in Figure 2.9, will impose a constraint
on the potential Trunk Road T2 alignments.
As with the other items on the runway, the alignment options that have
minimum or no interface with the planned cruise terminal score higher in the
assessment.
Interface with
2.2.3.31
The Trunk Road T2 alignment is required to connect with the CKR mainline
on the South Apron where the CKR has defined the interchange and slip roads for
connection to the at-grade road networks and to serve the Kwun
Tong area, including the Kai Tak development.
The proposed Kai Tak Interchange is an at-grade interchange and is
located within the KTD area. The eastern side of the interchange is the
depressed road emerging from or leading to the CKR tunnel portal while the
western side of the interchange is the at grade road section of the Trunk Road
T2, see Figure 2.10.
2.2.3.32
The Kai Tak Interchange has been optimised to
suit alignment, statutory and operational constraints and thus, the Trunk Road
T2 interface with the CKR is taken as fixed, for major issues,
but minor adjustments may be made to facilitate highway design, interface
details or minimise potential temporary reclamations.
Interface with Tseung Kwan O – Lam
Tin Tunnel
2.2.3.33
The Trunk Road T2 alignment is required to connect with the Tseung Kwan O – Lam Tin Tunnel (TKO-LTT) at the Cha Kwo Ling area, where the TKO-LTT has already completed a
detailed preliminary design and public consultation process to arrive at their
current preferred alignment.
2.2.3.34
According to the TKO study, the Lam Tin
Interchange (LTI) of the TKO – LTT is proposed to be located at the
existing FEHD vehicular depot in Kwun Tong adjacent
to the Eastern Harbour Crossing (EHC).
The LTI would be the major interchange of TKO-LT Tunnel and other
adjoining roads in Kwun Tong, including the future
proposed Trunk Road T2, EHC and local road network. Moreover, the proposed LTI
will provide connections between Tseung Kwan O and Kwun
Tong/ Yau Tong /Lei Yue Mun area on the
2.2.3.35
The connection with the TKO-LTT has been
taken as fixed, for major issues, but minor adjustments may be made to
facilitate highway design, interface details or minimise potential temporary
reclamations as required.
2.3.1.1
In order to fully evaluate the potential alignments options for the
Trunk Road T2 with a view to identifying the Recommended Scheme to be assessed in
the EIA Report, a comprehensive assessment has been undertaken, taking into
account the numerous design requirements, constraints and interface items
identified in the Section 2.2, above
along with the key project issues of environmental impact, cost and
programme.
2.3.1.2
Initially, potential horizontal alignments
have been identified and each horizontal alignment has then been reviewed
against the following vertical alignment scenarios, which consider the feasible methods of construction predominating along the
alignments:
·
High Level Scenario – adopting
predominantly viaduct structures to support the alignment with at-grade or
embankment works at the ends to tie-in with the adjacent CKR and TKO-LTT
alignments;
·
Low Level Scenario – adopting combinations
of at-grade, open trough, cut and cover or immersed tube tunnel forms of
construction as suited to the site constraints; and
·
Deep Level Scenario – adopting soft ground
or rock tunnelling methods such as drill and blast, drill and break or TBM
depending on the particular ground conditions prevalent in the section of
alignment.
2.3.1.3
Having identified the possible alignment
arrangements available, the relative merits of each possible alignment has been
assessed and alignment options that are considered not to be preferred due to
readily identifiable project constraints or project key issues are then
eliminated at this stage.
2.3.1.4
The assessment of the alignment options
will adopt a qualitative assessment of the impact of each of the alignment
options, as compared to the original KTDES
alignment described in Section 2.2.2
above, by applying the grading in Table 2.2 below to each of the project specific
constraints and key issues.
Table 2.2 Summary of Option Grading for Comparison with KTDES Alignment
|
Grading |
Description |
|
3 |
Significantly less impact than KTDES
alignment |
|
2 |
Moderately less impact than KTDES alignment |
|
1 |
Mildly more less impact than KTDES
alignment |
|
0 |
Having no significant greater or lesser impact
than KTDES alignment |
|
-1 |
Mildly more impact than KTDES alignment |
|
-2 |
Moderately more impact than KTDES alignment |
|
-3 |
Significantly more impact than KTDES
alignment |
2.3.1.5
Two categories of weighting have been applied
to each of the project specific constraints and key issues that can influence
the Trunk Road T2 alignment as described Section
2.2.3 above. The weighting factors have been
selected to place emphasis on the key
issues affecting the feasibility of the alignment options, as follows:
·
Weighting Value of 1 – For items that, although important for the
project, do not have as high a priority as other items and, thus,
are regarded as having normal priority on the Trunk Road T2 project; and
·
Weighting Value of 2 – For items regarded
as having particularly high priority for the Trunk Road T2 project.
2.3.1.6
The weighting values assigned to each of
the key constraints and issues are summarised in Table 2.3 below:
Table 2.3 Weightings Assigned to Key Constraints and Issues
|
Category |
Key Constraints and Issues |
Weighting |
|
Impact on Existing Constraints |
Impact on Sea Bed i.e. PHO and Harbour users |
2 |
|
Geological profile and related technical
difficulty |
2 |
|
|
|
1 |
|
|
Kerry Dangerous Goods Godown |
1 |
|
|
Public Works Central Laboratory |
1 |
|
|
Breakwater of KTTS |
1 |
|
|
Kwun Tong Bypass |
1 |
|
|
|
1 |
|
|
Eastern Harbour Crossing (EHC) |
1 |
|
|
Existing properties in Kwun Tong District |
1 |
|
|
Impact on Interfaces |
At-grade developments on South Apron for the Kai
Tak Development (KTD) |
2 |
|
Hospital developments on South Apron |
2 |
|
|
Environmentally friendly linkage system for KTD
(EFLS) |
1 |
|
|
At-grade developments on the former |
2 |
|
|
At-grade roads and public thoroughfares in Kwun
Tong area |
2 |
|
|
Cruise terminal on the former |
1 |
|
|
Interface with |
2 |
|
|
Interface with Tseung Kwan O – Lam Tin Tunnel
(TKO-LTT) |
2 |
|
|
Highway Design |
Highway Design |
2 |
|
Impact
on Environment |
Air Quality Impact |
2 |
|
Noise Impact |
2 |
|
|
Water Quality Impact |
2 |
|
|
Waste Management |
2 |
|
|
Landscape and Visual Impact |
2 |
|
|
Cultural impact |
2 |
|
|
Marine Ecology Impact |
2 |
|
|
Fisheries Impact |
2 |
2.3.1.7
The weighted results for each of the categories
are then summed to generate a sub-total for each of the alignment
scenarios. The sub-totals are taken
forward to produce a total score.
2.4
Alignment Options and Scenarios
2.4.1
Background
2.4.1.1
In developing the potential feasible alignment options for the Trunk
Road T2, possible horizontal alignments have been first identified.
2.4.1.2 Based upon the constraints of the area, eight potential horizontal alignments have been identified and these are illustrated in Figure 2.12. These eight alignments are described below with reference to the three potential vertical alignments for each.
2.4.2
Option 1 Alignment
2.4.2.1
Option 1 comprises the original
KTDES horizontal
alignment but incorporates developments in the alignment at Cha Kwo Ling defined under
the TKO-LTT assignment. The option ties
in with CKR at the
High Level Scenario
2.4.2.2
This scenario would start at-grade at the interface with CKR rising on
elevated structure towards the end of the South Apron. In order to provide adequate vertical
clearances to the ground level roads on the South Apron development, the
alignment will be required to be between 10 to 12m above the ground level
depending on the form of structure and support arrangements.
2.4.2.3
As the alignment would pass directly over
the Road D4, the supports for the elevated structure would have to be either
single piers running along a median strip introduced in the Road D4, which
would widen the Road D4, or, alternatively the deck could be supported on
portal frames with foundations located at either side of the Road D4.
2.4.2.4
The alignment would then continue at high
level through the KTTS and towards the CKL interface with the TKO-LTT. Typical pier spacing may range from 50 to
100m depending on the balance between economy/visual intrusion of large decks
and the need to minimise the impact on the KTTS. The alternative option of a single large span
is considered not practical due to the length of structure involved, i.e. 2000m
between South Apron and CKL seawalls.
2.4.2.5
In order to provide clearance similar to
that proposed for the EFTS planned over the KTTS, a clearance to the structure
from High Water level of at least 21m is required. Typical structure depths of 4m for a 100m
span would require a level at the top of the alignment of approximately +25mPD. This level can of course reduce as the alignment
approaches the CKL seawall.
2.4.2.6
The level of the alignment will reduce as
it approaches the CKL down to the interface level of -26mPD. However, based on the absolute maximum
gradient of 8% and the fact that the space available within the former PCWA is
only approximately 150m between the tie-in point and the edge of the harbour,
the alignment would only be at -14m when it passed the existing seawall
line. This means that the alignment
would have to be contained within a structure/embankment until it reached high
water level and then transitioned onto viaduct.
This will require further permanent reclamation of the harbour to allow
for the alignment.
2.4.2.7
The Option 1 High Level alignment
would cross the alignment of the EFTS link bridge and either the link bridge or
the High Level alignment would be required to adopt an alignment high enough to
provide operational clearances to the other structure.
Low Level Scenario
2.4.2.8
This option is effectively the developed KTDES alignment, incorporating
the developments in the alignment from TKO-LTT.
The alignment is at-grade from the interface with CKR until it passes
over the Jordan Valley Box Culvert, and then descends down into cut and cover
to pass under the South Apron seawall.
Immersed tube tunnel is envisaged for the section of alignment from the
South Apron to the interface with the TKO-LTT at CKL. Due to the changes at the TKO-LTT, the
alignment will drop down more than previously anticipated at CKL to tie-in with
the -26.9mPD level at the interface between the contracts. This option will serve as a base option for
comparison with other alignment passing through the assessment.
2.4.2.9
The TKO-LTT is anticipated to adopt a
drill and break tunnelling approach in the section to the east of the
2.4.2.10
The adoption of this alignment would
result in the following major impacts:
·
Dredging works for the removal of the marine mud and alluvium;
·
Impact on the use of the KTTS;
·
Demolition and re-provision of the breakwaters for the KTTS;
·
Provision of temporary breakwater to allow the KTTS to continue
operating;
·
Temporary diversion and reinstatement of the subsea outfall from the DSD
Kwun Tong pumping station; and
·
Breaking down of the existing seawalls at the South Apron and CKL.
2.4.2.11
It should be noted that all alignment
options that adopt IMT construction include the issues:
·
The need for a casting basin (currently planned for shared use of the
Shek O casting Basin);
·
Need for a temporary mooring point at Junk bay to store units following
casting; and
·
The need to dredge and access channel for delivery of the IMT units to
the alignment.
Deep Level Scenario
2.4.2.12
This scenario would adopt the similar at-grade alignment developed in
the KTDES from the interface with CKR until it passes over the Jordan Valley
Box Culvert. The alignment would then
descend down at a gradient of up to 5% (a steeper gradient to that in the
KTDES) into cut and cover to pass under the South Apron seawall. With the increase in depth of tunnel as it
passes under the seawall, the tunnel is planned to be constructed using the TBM
method.
2.4.2.13
Implementation of this alignment requires
the use of a climbing lane for the sections of alignment that have gradients
>3% over a length to 500m.
Investigation of the space necessary for the additional lane has
identified that this option is feasible within the space available for the
Trunk Road T2 works, as illustrated in Figures 2.13 to 2.18.
2.4.3
Option 2 Alignment
2.4.3.1
Option 2 ties in with the CKR in
Kowloon Bay Interchange, turning south through the South Apron to reach the former runway,
running along the runway to the end of the KTTS and then turns east to cross
over from the end of the runway to Cha Kwo Ling to
tie in with the TKO-LTT at Lam Tin Interchange.
High Level Scenario
2.4.3.2
A high level scenario would adopt a profile rising from the interface
with CKR up to levels similar to the nearby Kwun Tong Bypass. The alignment would continue at or close to
ground level as it turns southward to cross the Kai Tak Approach Channel. As the access to the Kai Tak Approach Channel
is strictly limited by the existing old taxi-way bridge, the viaduct structure
would adopt a similar minimum soffit level.
However, the alignment would rise up as it crosses the Channel to ensure
that the viaduct could provide sufficient headroom clearance to the at-grade
roads for the developments on the former runway. This would place the alignment at
approximately 10 to 12m above the ground level, depending on the form of
structure and support arrangements.
2.4.3.3
As the alignment would pass
directly over the Road D3, the supports for the elevated structure would have
to be either single piers running along a median strip introduced to the Road
D3, which would widen the Road D3 impacting on the development areas adjacent
to the road. Alternatively the deck
could be supported on portal frames with foundations located on either side of
the Road D3.
2.4.3.4
Upon reaching the end of
the former runway the alignment would turn eastward and curve towards the
interface with TKO-LTT at the Cha Kwo Ling road
descending towards CKL to tie-in with TKO-LTT alignment at a level of
-26.9mPD. This will face similar issues
to those described in paragraph 4.2.8 and therefore this option will not be
developed further in view of the non-compliance with the PHO.
Low Level Scenario
2.4.3.5
This scenario would start at-grade at the tie-in with the CKR but then
immediately start descending into, first, open trough and, then, cut-and cover
tunnel in order to descend below the seabed level in the Kai Tak Approach
Channel. Use of an IMT for this section
is considered not to be feasible due to the constraints imposed on access by
the taxi-way bridge across the channel.
2.4.3.6
The alignment would then
turn to run down the alignment of the Road D3 in cut and cover tunnel to the
end of the former runway. From the end of the runway the alignment turns
eastward to run to CKL to tie-in with the TKO-LTT.
2.4.3.7
The option of cut and cover
for the construction of the tunnel from the end of the runway to the CKL will
not be considered further since this would require significant amounts of
temporary reclamation for the platforms necessary to construct the cut and
cover tunnel. As there are other
feasible options for construction in line with the PHO, this option has not
been developed further.
2.4.3.8
Even with the IMT
construction, a minimal amount of reclamation is anticipated at the end of the
former runway to match the proposed cut-and-cover tunnel section, which is a
similar scenario to the Option 2 Low Level alignment option of which the
reclaimed portion is near the end of South Apron.
Deep Level Scenario
2.4.3.9
This Option 2
Deep Level scenario would start at-grade at the tie-in with the CKR but then
immediately start descending into, first, open trough and, then, cut-and cover
tunnel in order to descend below the seabed level in the Kai Tak Approach
Channel.
2.4.3.10
The potential for
implementing a TBM from the South Apron has been considered. However, based on a TBM of 14m diameter (D)
and using a 1D cover to the tunnel, this would require a road level of
approximately -27mPD. The tie-in level
with the CKR is approximately +6.5mPD.
As the distance from the interface with the CKR to the seawall at the
south apron is approximately 350m, this would require a gradient for the trunk
road of 9.4% which exceeds the stated absolute maximum for the vertical
alignment and hence is considered not to be a feasible option.
2.4.3.11
Once the alignment passes
into the former runway it is anticipated that a TBM would be used to construct
the tunnel along the runway and then turn towards CKL and the interface with
TKO-LTT.
2.4.4
Option 3 Alignment
2.4.4.1
Option 3 is similar to Option 1, with
the horizontal alignment tying in with CKR at the
High Level Scenario
2.4.4.2
The issues associated with this option are the same as that described
for Option 1 with only a minor variation in the horizontal alignment which only
has a significant effects for the low level option, as described below.
Low Level Scenario
2.4.4.3
The engineering aspects associated with this option are the same as that
described for Option 1 with only a minor variation in the horizontal alignment
such as to reduce the extent of the breakwaters for the KTTS that would require
demolition and reconstruction during construction of the Low Level (IMT
option).
Deep Level Scenario
2.4.4.4
The issues associated with this option are the same as that described
for the Option 1 with only a minor variation in the horizontal alignment which
only has significant effects for the Low Level option, as described above.
2.4.5
Option 4 Alignment
2.4.5.1
The horizontal alignment
for Option 4 ties in with CKR at the
High Level Scenario
2.4.5.2
This high level scenario would start at-grade at the interface with CKR
rising on elevated structure towards Petrol station located at the edge of the
South Apron. In order for the alignment
to pass over the Kwun Tong Bypass it would need to reach a level of
approximately +23mPD.
2.4.5.3
Once over the Kwun Tong
Bypass the alignment would continue on viaduct.
In order for the structure supporting the alignment to provide adequate
vertical clearances to the ground level roads on the south apron development,
the alignment will be required to be between 10 to 12m above the ground level
depending on the form of structure and support arrangements.
2.4.5.4
As the alignment would pass
directly over
Low Level Scenario
2.4.5.5
This Option 4 Low
Level
scenario would start at-grade at the interface with CKR and then descend in
trough and cut and cover tunnel to pass under the
Deep Level Scenario
2.4.5.6
This Option 4 Deep
Level
scenario would follow the same alignment as the Option 4 Low Level from Sheung Yee Road to Wai Yip Street. In order to avoid conflict and to minimise the impacts on the foundations of the existing buildings,
the alignment would have to be descended to a level of approximately -40mPD for
TBM construction until it ties in with the TKO-LTT alignment and details at Lam
Tin Interchange.
2.4.6
Option 5 Alignment
2.4.6.1
Similar to Option 4, the horizontal alignment of Option 5, also, passes
along an inland route which ties in with CKR at the
High Level Scenario
2.4.6.2
This high level scenario would start at-grade at the interface with CKR
and continue down the South Apron at grade until it reached the north end of
the Road D4. The alignment would turn
eastward and rise on viaduct structure until it met the edge of the Kwun Tong
bypass viaduct. The alignment would then
follow the alignment of the Kwun Tong bypass down the east side of the KTTS
until it reached the Nullah next to
2.4.6.3
The viaduct is anticipated
to be a separate structure to the KTB with pier and foundation positions in
harmony with the existing KTB. Due to
the anticipated size and positioning of the new viaduct the piers would be
located within the KTTS (Figure 2.6). From this location, this option would
continue on viaduct across the Nullah and begins to
turn inland and descend down to the interface with TKO-LTT.
Low Level Scenario
2.4.6.4
This Option 5 Low Level scenario would start at-grade at the interface
with CKR and maintain at-grade level until it passed over the Jordan Valley Box
Culvert. It would then turn eastward
towards the pacific trade centre and descend in trough and cut and cover tunnel
to pass under cargo handling areas and sea wall of the KTTS. Once the alignment had reached Cha Kwo Ling, it turns eastward in cut and cover section to
tie-in with the TKO-LTT.
Deep Level Scenario
2.4.6.5
This deep level scenario would start at-grade at the interface with CKR
and maintain at-grade level until it passed over the Jordan Valley Box
Culvert. It would then turn eastward
towards the pacific trade centre and descend in trough by cut and cover tunnel
until it reached the launching shaft for TBM tunnelling
at the Pacific Trade Centre. At this point, the tunnel would progress in TBM
under cargo handling areas and sea wall of the KTTS. Once the alignment had reached Cha Kwo Ling, it turns eastward in cut and cover section to
tie-in with the TKO-LTT.
2.4.7
Option 6 Alignment
2.4.7.1
Option 6 ties in with CKR at
Kowloon Bay Typhoon Shelter and turns southeast to run along the previous Kai
Tak airport runway to the end of the KTTS and then turns east to cross over
from the end of the runway to Cha Kwo ling to tie in
with the TKO-LTT at Lam Tin Interchange.
High Level Scenario
2.4.7.2
With the alignment for CKR fixed, this alignment option would commence
with a section of cut and cover tunnel for the lanes merging with the CKR. Merging lanes of the high level alignment
would adopt a profile rising from the interface with CKR up to levels similar
to the nearby Kwun Tong Bypass. The
alignment would continue on elevated structures over the south apron to the
KTTS and then continue on viaduct through the KTTS and on until landing at the
Cha Kwo Ling area to descend to meet the alignment
from the TKO-LTT at a level of approximately -26.9mPD.
Upon reaching the
end of the former runway the alignment would turn eastward and curve towards
the interface with TKO-LTT at the Cha Kwo Ling road
descending towards CKL to tie-in with TKO-LTT alignment
Low Level Scenario
2.4.7.3
As noted above, the alignment for CKR fixed this Low Level alignment option would, also,
commence with a section of cut and cover tunnel for the lanes merging with the
CKR. The Low Level alignment would then
turn down and run along the old runway, continuing in a cut and cover tunnel
section long the length of the old runway.
As previously described, use of the cut and cover method for the
construction of the tunnel from the end of the old runway is considered not to
be an option since this would significant amounts of temporary reclamation for the
platforms necessary to construct the cut and cover tunnel. Thus, the low level
tunnel section between the end of the runway and the CKL would consist of
IMT. Once at the CKL, the tunnel would
continue at low level in cut and cover until the tie-in point with TKO-LTT.
Deep Level Scenario
2.4.7.4
The Deep Level scenario, also, commences with a section of cut and cover
tunnel and then turns down and aligns to follow the line of the old
runway. At this point a launching shaft
would be constructed and TBM operations would commence. The TBM would follow the alignment of the
runway to the end of the runway and then turn eastward and cross to CKL. The alignment would then continue in cut and
cover section to the tie-in point with the TKO-LTT.
2.4.8
Option 7 Alignment
2.4.8.1
The horizontal alignment of Option 7 ties in with the CKR at Kowloon Bay
Interchange and then runs along to about the midway of South Apron, turning
south at this point to run along the previous Kai Tak airport runway, then,
similar to Option 2, tying in with the TKO-LTT at Lam Tin Interchange.
High Level Scenario
2.4.8.2
Similar to Option 2, this Option 7 High Level scenario would be at-grade
at the interface with CKR, but would then run along the south apron until after
the Kai Tak taxiway bridge where it turns to cross the Kai Tak Approach
Channel. In order for the structure
supporting the alignment to provide adequate vertical clearances to the Road
D4, which it crosses just before turning towards the old runway, the alignment
will be required to be between 10 to 12m above the ground level.
2.4.8.3
As the alignment would pass
through the South Apron Site C, which is designated for the development of the
Centre of Excellence in Pediatrics (due for operation in 2018), this alignment
would be in direct conflict with the development potential of the Kai Tak Site.
2.4.8.4
The alignment would then
continue at high level across the Kai Tak Approach Channel on viaduct structure
with typical pier spacing of 40 to 50m.
An alternative option would be to have a single large span, but this
would require a span of around 250m making this a very visually intrusive
structure. The
alignment would then turn down to follow the alignment of the old runway and
continue along the same alignment as that for Option 6 as described above.
Low Level Scenario
2.4.8.5
This Option 7 Low Level scenario would adopt the profile similar to the
alignment developed in the KTDES being at-grade from the interface with CKR
until it passes over the
2.4.8.6
Use of a cut and cover for the
construction of the tunnel from the South Apron to the KTTS is considered not
to be an option since this would significant amount of temporary reclamation
for the platforms necessary to construct the cut and cover tunnel.
Deep Level Scenario
2.4.8.7
As with the Low Level, this Option 7 Deep Level scenario would adopt the
profile similar to the alignment developed in the KTDES being at-grade from the
interface with CKR until it passes over the
2.4.8.8
Implementation of this alignment requires
confirmation that there is sufficient space for climbing lane required for
alignments that have gradients >3% over a length to 500m. Investigation of the space necessary for the
additional lane has identified that the option is feasible within the space
available for the Trunk Road T2 works.
2.4.9
Option 8 Alignment
2.4.9.1
Similar to Option 2, this horizontal alignment ties in with the CKR at
the Kowloon Bay Interchange, runs along the end of the south Apron before
turning south to reach the near end of the former runway, and then crossing
over the KTTS to tie in with the TKO-LTT at Lam Tin Interchange.
High Level Scenario
2.4.9.2
Similar to Option 2, this Option 8 High Level scenario would be at-grade
from the section at the interface with CKR rising on elevated structure towards
the end of the South Apron. In order for
the structure supporting the alignment to provide adequate vertical clearances
to the ground level roads on the south apron development, the alignment will be
required to be between 10 to 12m above the ground level
2.4.9.3
As the alignment would pass
directly over the Road D4, the supports for the elevated structure would have
to be either single piers running along a median strip introduced in to the
Road D4 which would widen the Road D4.
Alternatively the deck could be supported on portal frames with
foundations located either side of the Road D4.
2.4.9.4
The piers for the High
Level scenario would adopt a profile rising from the interface with CKR up to
levels similar to the nearby Kwun Tong Bypass.
The alignment would continue on elevated structures over the South
Apron, across the north-west corner of the KTTS on viaduct structure with
typical pier spacing of 40 to 50m. On
landing at the Cha Kwo Ling area to descend to meet
the alignment from the TKO-LTT.
Low Level Scenario
2.4.9.5
This Low Level scenario would adopt a profile similar to the alignment
developed in the KTDES, being at-grade from the interface with CKR until it
passes over the
2.4.9.6
Use of a cut and cover for
the construction of the tunnel from the South Apron to the KTTS is not
considered to be an option since this would significant amounts of temporary reclamation
for the platforms necessary to construct the cut and cover tunnel.
Deep Level Scenario
2.4.9.7
Between the interface with CKR and the
2.4.9.8
Implementation of this
alignment requires confirmation that there is sufficient space for climbing
lane required for alignments that have gradients >3% over a length to
500m. Investigation of the space
necessary for the additional lane has identified that the option is feasible
within the space available for the Trunk Road T2 works.
2.5.1 Background
2.5.1.1
Each of the alignment options described in Section 2.4 above would be technically feasible but would have their
own advantages and disadvantages in terms of the constraints and key issues
identified. The detailed assessment
scoring for each of the horizontal alignments and their three vertical
scenarios are presented in Appendix 2B, and the advantages
and disadvantages of each discussed in the sections below from an engineering
constraints perspective and in terms of potential impacts to the
environment.
2.5.2
Option 1 Alignment
Engineering Aspects
Project
Constraints
2.5.2.1
Within the assessment in Appendix 2B, it can be seen that
High Level scenario performs better in some key items than the Low Level or
Deep Level scenarios by having a very small “footprint”, but overall the high
level scenario performs less well than either of the other two scenarios. The High Level scenario would have lower
at-grade impacts on the South apron structures i.e. Kerry DG Godown and PWCL due to the viaduct for the High Level
option using discrete foundations (approx 40 to 50 m spacing between
foundations) and which will be located further away from these buildings, as
compared with the approximately 25m wide cut and cover trench section necessary
for the Low and Deep Level scenarios.
However, a critical point is that the High Level scenario would require
piers located within the harbour area, resulting in a form of permanent
reclamation which has PHO implications.
2.5.2.2
The Low Level scenario is the selected option under
the KTDES and the effects on the impacts on the Kerry DG Godown,
PWCL, breakwaters and subsea outfall are taken as the base case for this
assessment. Thus, the scenarios, such as
the High and Deep Level scenarios and Inland options (Options 4 and 5), that
avoid impacts on these are seen to score higher. It is envisaged that the High Level scenario
would span over the breakwater and outfall, with foundations set to avoid
impact on these structures. The Deep Level
scenario would pass under the breakwater and outfall, avoiding any impact on
these structures.
2.5.2.3
In the case of the Deep Level scenario, the
eastbound and westbound tunnel sections are separated by approximately 14m
resulting in an increase in tunnel section from approximately 27m to 42m and
the edges of the tunnels moving closer to the KGDG and PWCL boundaries imposing
greater constraints on the working methods for construction of the cut and
cover tunnel sections next to these boundaries.
2.5.2.4
Although the TBM tunnelling (envisaged for the Deep
Level scenario) is now a common construction method within
Project
Interfaces
2.5.2.5
Due to most of the interfaces being on land the Deep and Low Level
scenarios for this alignment option are assessed as being the same since the
construction method anticipated in these land sections would be a cut and cover
tunnel method for both of these scenarios.
For the High Level scenario, the alignment would be carried on a viaduct
structure that would pass close to the boundary of the adjacent Hospital site,
resulting in air, visual and noise impacts on the lower floors of the Hospital
development. This is further reflected
in the assessment of the potential environmental impact of this alignment
scenario below.
2.5.2.6
A High Level scenario would, also, have an impact
on the possible alignment for the future EFLS with the alignments crossing and
certain locations on the South Apron, potentially requiring one of the
alignments to be raised by up to 10m to ensure adequate clearances, resulting
in a higher visual impact closer to the harbour front area.
Environmental Aspects
Air Quality
and Noise
2.5.2.7
Based upon a construction commencement in 2015,
some of the future sensitive receivers would also be under construction and
occupied prior to the completion of the Trunk Road T2 in 2020. Given the alignment passes would be mainly on
viaduct directly adjacent to future sensitive developments, with a minimal
separation distance of 10 to 15m, both construction noise and dust would be a
key issue at the South Apron Area.
2.5.2.8
In terms of the Cha Kwo
Ling end, the High Level scenario would mainly involve all above ground works
until it reached the CKL and then descend to tie-in with the TKO-LTT tunnel,
thus there would be the potential to affect the village residents, some 150m
away from the elevated section in terms of dust and noise impact.
2.5.2.9
The Low Level scenario involving an IMT tunnel
would involve a cut and cover section of tunnel in the PWCA which would involve
more excavation than that for viaduct piers.
Thus, in terms of construction dust, the low level option may not be
preferred in this location.
2.5.2.10
The Deep Level scenario would, however, includes a
subsea tunnel constructed by TBM method and noise and dust from this operation
would be contained underground from the point of the launching shaft,
minimising construction phase impacts to the environment on the South Apron,
particularly for exisiting sensitive receivers (SRs)
at the southern end of the alignment in Cha Kwo Ling, such as the
proposed Kerry Godown residential development.
2.5.2.11
Operationally, the High Level scenario has the
potential for the highest air and noise impacts with the viaduct structure
being elevated by 10 to 12m from the ground in this area (rising to about 21m
in height in the marine section). There
will be no opportunities to control vehicle emissions which would affect the
adjacent SRs on the South Apron predominately.
The elevated viaduct will also increase the noise impacts to the sensitive
receivers and would likely need extensive mitigation in the form of a noise
enclosure on the South Apron and a cantilevered or semi-enclosure at Cha Kwo Ling to screen the noise from the high rise
developments on either side and the village houses, respectively.
2.5.2.12
The operational air emissions from the Low and Deep
Level tunnel scenarios would be vented via a high level shaft from the
ventilation buildings, enhancing dispersion and resulting in low level impacts
at the SRs at both the South Apron and Cha Kwo Ling.
Water
Quality
2.5.2.13
All scenarios have the potential for construction run-off from the land
based works and while no streams are present in the area, such run-off could
affect the marine waters. The High Level scenario would have the least
excavation for the bridge piers limiting the potential for construction
run-off. It is anticipated that the High Level scenario would affect only about
1400m2 of seabed for the 35 piers envisaged.
2.5.2.14
The IMT will require a large trench to be
constructed of in the region of 100m wide and 16m deep. The dredging has the
potential to cause increases in suspended solids and other contaminants (the
sediment has been shown to have varying levels of chemical and biological
contamination) in the marine waters which will affect water quality and could
impact on marine life. The Low Level IMT
scenario may, also, require temporary reclamations at either end of the subsea
tunnel which could affect the hydrology and flows in the
2.5.2.15
In terms of the marine part of the alignment, the
High Level scenario will require some dredging in the marine environment for
the bridge piers but the disturbance to the seabed would not be as significant
as the Low Level scenario which will required extensive dredging for the
construction of the immersed tube tunnel.
2.5.2.16
The Deep Level scenario would involve a TBM
constructed tunnel which would be deep enough to avoid the seabed and marine
deposits, tunnelling through alluvium, CDG and Grade II/III rock material. The
TBM would be deep enough to pass under the existing breakwaters to the KTTS and
the existing twin subsea outfalls of the KTSTW and hence avoid the need to
excavate and temporarily reprovide both of these features
and thus reduce further disturbance to the seabed and marine sediment
deposits. The TBM would also be launched
and received from shafts on land which would also avoid any disturbance to the
seawalls and marine environment.
Waste
Management
2.5.2.17
In terms of construction and demolition waste, the High Level scenario
is likely to produce the least material as excavation for pier foundations only
would be required and it is likely that 50% of this material could be reused on
site. However, this scenario would also
result in some contaminated marine sediment needing to be dredged and removed
from the construction works for the marine piers. Site investigation works have shown the
marine sediment in the KTTS and beyond contains Cat L, M and H sediment in accordance
with ETWB TCW No.34/2002 and, therefore, this material would need to be handled
in accordance with the Dumping at Sea Ordinance (DASO) and would require
disposal at open sea or confined marine disposal pits, all of which are rapidly
filling up.
2.5.2.18
As noted above, the Low Level scenario would
require extensive dredging and would result in the removal of an estimated
310,000m3 of Class M, H and H+ contaminated marine sediment for
treatment and proper disposal. This
scenario would also result in land based C&D material but it is unlikely
all could be used on site and some surplus would have to be removed off-site to
a fill bank.
2.5.2.19
While the Deep Level scenario will, also, generate
notably more waste than the high level scenario, the bulk of the material (in the
region of 630,000m3) will be alluvial material from the sub-sea
tunnel construction by TBM, material which is not contaminated and can be
reused in other projects once dewatered.
Marine
Ecology and Fisheries
2.5.2.20
As the majority of alignment will be constrained within the seabed and
the effect on the ecology and fisheries is considered to be minimal amongst the
3 scenarios. In terms of the terrestrial elements of the alignment, the project
has avoided key habitats as far as possible.
The land based works for all three scenarios are to be undertaken in
areas that have been previously developed and are of low ecology value. The exception to this is a small area of
plantation located where the eastern ventilation building will be constructed
but the loss of this area would be small and common to all three scenarios.
2.5.2.21
In terms of marine ecology, as described in the
water quality section above, the Low Level scenario would result in significant
disturbance to the marine environment and has the greatest potential to affect
marine ecology. The latest Port Survey
of 2006 did not record any fishing operations or fisheries production in the
KTAC and inner KTTS, showing that this immediate area around the Trunk Road T2
project has no, or very limited, value in terms of capture fisheries. However, sampans do fish in this area and the
dredging could affect these activities, subject to the fisheries moratorium
from December 2012, and fish resources in the area.
Landscape
and Visual
2.5.2.22
As noted from for terrestrial ecology, little landscape will be affected
by any of the three scenarios due to the already development nature of the
site. However, visually, during the
operational phase, the high level scenario comprising a viaduct of up to 21m
high, would be highly visible to the existing and future developments in the
study area. While the viaduct could be
made more visually attractive through design and would blend into the
surrounding development to some extent, this scenario would result in increased
permanent impacts compared to the two low and deep level tunnel options, where
only small sections of at–grade and depressed road would be visible.
2.5.2.23
During the construction stage, all scenarios would
be effectively comparable given the extent of construction works being undertaken
in the vicinity for the CKR, KTD and TKO-LTT, with the Deep Level scenario
being preferred due to the extent of underground works.
Cultural
Heritage
2.5.2.24
Study of the marine and terrestrial archaeology did not reveal any areas
of archaeological potential in the Trunk Road T2 area and as such no impacts
are expected from either of the three scenarios. In terms of built heritage,
the only resources are located in the
Summary
2.5.2.25
With reference to the preceding paragraphs, the critical consideration
to Low Level Option 1 scenario is that the construction of piers and permanent
reclamation at the interface with TKO-LTT located within the harbour is not in
compliance with the PHO and the potential dust and noise impact to the
surrounding NSRs. As there are other feasible options, this alignment option
can be seen to score very poorly in the assessment. The Low Level scenario could, also, give
rise to potential impacts during the construction phase associated with the cut
and cover tunnel sections. Similar to the High Level option, given the distance
of about 30m to the closest properties, this would, also, require extensive
mitigation to minimise impacts.
2.5.2.26
However, it should also be noted that the use of a
cut and cover for the construction of the tunnel from the South Apron to the
KTTS is considered not to be practical since this would require significant
amount of temporary reclamation for the platforms necessary to construct the
cut and cover tunnel and since there are other feasible options, this would not
comply with the PHO and unlikely to be the best environmental solution.
2.5.2.27
Apart from the similar cultural heritage impact to
the Low Level option, the Deep Level TBM scenario alone has the potential for
ground-borne noise impacts during construction but these are expected not to be
significant given the over 100m separation distance from the closest
property. Notwithstanding the large amounts
of waste material that would be generated but taking into account the fact that
the majority of the material could be reused, the Deep Level scenario would
result in the least environmental implications, as it avoids impacts on the
marine environment during the construction phase, therefore, protecting the
water quality, marine ecology and fisheries.
The TBM tunnel also minimises noise and air quality impacts during both
the construction and operational phases.
2.5.3
Option 2 Alignment
Engineering
Aspects
Project
Constraints
2.5.3.1
By adopting an alignment along the runway, all of the options avoid
adverse impacts on the breakwaters, but the Low Level scenario would still
impact on the subsea outfall and thus performs less well when compared with the
High/Deep Level scenarios which can be designed to avoid impacting on the
outfall.
2.5.3.2
As with all of the other alignment options in this
section, the High Level scenario for Option 2 is rated poorly due to the need
for the use of piers located within the harbour area and thus results in a form
of permanent reclamation. Low and Deep
Level scenarios avoid this issue by ensuring no permanent change in the seabed
level.
2.5.3.3
However, as Option 1 Low Level scenario would
require the temporary demolition of the existing KTTS breakwaters it would be necessary
to provide a temporary breakwater to maintain the operation of the KTTS. This would be classified as a form of
temporary reclamation, and thus to be avoided if possible. By taking an
alignment that passes along the runway the Low Level scenario passes outside of
the breakwaters and so is regarded as performing the same as the Deep Level
scenario.
The Deep Level
scenario can be seen to perform better than the High and Low scenarios in
regard to the reduced disturbance of the seabed and impact on the constraints
on the South Apron. However, due to
vertical gradient limitations this is balanced by the need to adopt a cut and
cover tunnel section across the Kai Tak Approach Channel (KTAC) with resulting
temporary reclamation needed for the construction for this section.
Project
Interfaces
2.5.3.4
With the alignment passing across the area of potential Kai Tak
development and then along the runway the alignment scenarios have
significantly more potential for adverse impacts than that of the Option 1
alignment, which passes down the planned corridor for the Trunk Road T2
project. This is identified by the low
scores for the interface with the cruise terminal, EFLS and at-grade
developments on the former runway.
Further, by cutting across the KTAC, the alignment passes under
potential development areas on the South Apron.
Environmental Aspects
Air Quality
and Noise
2.5.3.5
The former runway of the Kai Tak airport has been designated for
development including commercial, government, institutional and community and
residential. Given that the cruise
terminal stages 1 and 2, including hotels and commercial properties, would be
constructed between 2010 to 2015, for occupation between 2014 and 2016, this
development would be sensitive to air quality and noise impacts during both the
construction and operational phases, given the construction period for Trunk
Road T2 of 2015 to 2020. The residential
and community developments, however, are not proposed to be completed before
2021, the same time as Trunk Road T2 is implemented, and as such will be
sensitive to only operational noise and air quality.
2.5.3.6
Given that the majority of the development on the
runway would be constructed in parallel to the Trunk Road T2, this alignment
option would, also, be comparable in construction noise and dust terms to their
equivalents for Option 1, which is only requiring 1700m of land based viaduct
for the high level scenario.
2.5.3.7
As with Option 1 High Level scenario, this option
will have the potential for the highest air and noise impacts on the adjacent
runway developments based upon an elevated viaduct structure of 10 to 12m in
height running along the length of the runway. Extensive mitigation measure
would be required.
2.5.3.8
The Low Level scenario has the potential to create
the worst air and noise impacts during the construction stage as this will
comprise a long section of cut and cover tunnel in the vicinity of the cruise
terminal for a length of 800m and the major excavation involved would
potentially cause more impacts than the works for the viaduct piers for the
High Level scenario over the same length.
2.5.3.9
The Low Level IMT tunnel scenario would avoid noise
impacts for the length of the tunnel, and operational air emissions can be
better dispersed through discharge via the ventilation buildings.
2.5.3.10
The Deep Level scenario would enter a tunnel
constructed by TBM just after the alignment crosses the KTAC, 800m north of the
major cruise terminal development. As
such, the construction works directly adjacent to the cruise terminal will be
underground which would limit the dust and air-borne noise impacts during
construction at these SRs to a minimum.
The ground-borne noise implications of the TBM would need to be
considered but can be controlled readily though management of the advancing and
cutterhead speed.
The lack of residential development and the advanced point of launching
the TBM as a compared to the SRs would make this Option 2 Deep Level scenario
marginally better than Option 1, where above ground works have more potential
to affect the adjacent SRs.
2.5.3.11
The Deep Level TBM tunnel scenario would avoid
noise impacts for the length of the tunnel, and operational air emissions can
be better dispersed through discharge via the ventilation buildings.
Water
Quality
2.5.3.12
The overall design of Option 2 is similar to Option 1 in that they both
comprise a land based section, followed by a marine section. The main difference is that the marine
section of Option 1 is longer, being 2100m in length, compared to 1450m in length
for Option 2. As such, as would be the
case for Option 1, the potential for water quality impacts are largely
associated with the High and Low Level scenarios, which require dredging for
the marine piers and the IMT tunnel. However, the shorter marine alignment
would make this Option 2 slightly preferable, when compared with Option 1, in
water quality terms, with less dredging required.
2.5.3.13
The Deep Level scenarios of both Options 1 and 2
would be comparable and not cause any disturbance to the marine environment
including no reclamation or dredging of contaminated marine mud.
Waste
Management
2.5.3.14
The High Level scenario, however, would generate, not only C&D
material from the pier construction and extensive cut and cover section, but,
also, contaminated marine dredged sediment. However, less marine mud will be
generated from the marine section as compared with Option 1 Low Level scenario.
2.5.3.15
Similar to the High Level scenario, the Low Level
scenario would generate, not only C&D material from the pier construction
and extensive cut and cover section, but, also, contaminated marine dredged
sediment, with the Low Level scenario generating more waste to be handled than
the High level scenario. However, this option would produce about 50% less
marine mud than the equivalent Option 1 alignment with its longer marine
section.
2.5.3.16
The Deep Level scenario would produce both C&D
and alluvium materials which can be reused on site or transported to the fill
bank. However, as this scenario requires
a cut and cover section through the KTAC, some marine sediment will, also, be
generated.
Marine
Ecology and Fisheries
2.5.3.17
As with Option 1, with the exception of a small area of planation
located where the eastern ventilation building will be constructed, which is
common to all three scenarios, all land based works for all three Option 2
vertical scenarios are to be largely undertaken in areas that have been
previously developed and are of low ecology value. However, there are small areas of
plantation/grassland mosaic and grassland on the runway that would be affected
by the Trunk Road T2, but these habitats are not of high ecological value.
2.5.3.18
For marine environment, the Low Level scenario
would result in significant disturbance to the marine environment from the IMT
tunnel construction and has the greatest potential to affect marine ecology and
any fish resources in the KTTS, although not as much as the Option 1 Low Level
scenario.
2.5.3.19
This Deep Level scenario is considered to have the
least impact on the ecology as compared with the High and Low Level scenarios
for the same option.
Landscape
and Visual
2.5.3.20
Minimal vegetation will be affected by any of the three vertical
scenarios due to the already development nature of the site. However, visually, during the operational
phase, the high level scenario comprising a viaduct of up to 12m high, would be
highly visible to the future developments along the runway, passing through the
middle of the development sites. Given
the height of the viaduct, this will be a particular issue for the low floors
of the properties which will have views either under or directly onto the
viaduct or onto a noise barrier structure.
The viaduct along the former runway will be screened from wider views by
the properties but the marine viaduct, while shorter than the Option 1 High
Level scenario, will, also, be visible to the surrounding Kwun
Tong and
2.5.3.21
Minimal vegetation will be affected by any of the
three vertical scenarios due to the already development nature of the
site. During the construction stage, all
options would be effectively comparable, with the Deep Level scenario being
preferred due to the extent of underground works.
Cultural
Heritage
2.5.3.22
The impact is comparable with Option 1 for all vertical scenarios.
Summary
2.5.3.23
Option 2 has a shorter marine section that Option 1 with reduced
construction in the harbour waters and avoidance of the KTTS breakwaters
reducing the possible impacts on the PHO.
However, due to the alignment constraints in the South Apron the section
of alignment crossing the KTAC would have to be in cut and cover tunnel
resulting in temporary reclamation which has to be tested against other options
under the PHO. The alignment would
present some marginal benefits to potential water quality, marine ecology and
fisheries implications over the Option 1 alignment with respect to the High and
Low Level scenarios, but would be comparable in terms of air quality and noise
implications. As with Option 1, the
Option 2 Deep Level scenario presents the preferred vertical alignment
environmentally, avoiding impacts to water quality, marine ecology, fisheries
and minimising noise and air quality impacts during both the construction and
operational phases.
2.5.4
Option 3 Alignment
Engineering Aspects
Project
Constraints and Interfaces
2.5.4.1
The aspects associated with this option are the same as that described
for the Option 1, with only a minor variation in the engineering aspects in
relation to simpler construction works at the KTTS breakwaters. The interfacing aspects for this option are
identical to those for the alignment Option 1 horizontal alignment.
Environmental
Aspects
Air
Quality, Noise, Landscape and Visual and Cultural Heritage
2.5.4.2
As stated above, Option 3 is very similar to the Option 1. The environmental implications of the three vertical
Option 2 scenarios for air quality, noise, landscape and visual and cultural
heritage would be considered comparable to Option 1, as described above. Other
environmental parameters are discussed below but on balance, environmentally,
Option 3 would be equivalent to Option 1.
Water
Quality
2.5.4.3
The potential for run-off from land based works would be the same as
Option 1. In terms of marine impacts, the slightly increased length of the
marine alignment (2150m), compared to Option 1 (2100m), would marginally
increase the amount of marine dredging required for the Low Level IMT scenario,
with a slight potential increase in the potential for water quality
impacts. In terms of the high level
marine viaduct scenario, only 1 more pier would be needed and additional
impacts would be limited.
Notwithstanding, the environmental implications would be expected to be
similar to Option 1, with the Deep Level scenario having the least potential
for water quality impacts, followed by the High Level scenario and then the low
level scenario as a result of the extensive dredging for the IMT.
Waste
Management
2.5.4.4
The slightly longer marine section of Option 3 compared to Option 1, as
noted above, would result in an increase in the amount of marine sediment to be
removed, increasing to approximately 0.006Mm3 for the High Level
scenario (or by 3%) and 1.4Mm3 for the Low Level scenario. However, this is not expected to generate
significantly higher water quality impacts with the implementation of
mitigation measures. While the Deep Level scenario will, also, generate some
more waste than the equivalent Option1 scenario and more waste than the High
Level scenarios of both Option 1 and Option 3, as the material will be alluvial
material it can be reused in other projects once dewatered.
Marine
Ecology and Fisheries
2.5.4.5
While a marginal increase in dredging and marine sediment removal is
expected for Option 3 compared to Option 1, as the ecological and fishery
resources in the area of the KTTS and KTAC are not of high value, further potential
for impacts are not predicted.
Summary
2.5.4.6
In summary, Option 3 would be comparable to Option 1, with only a
slightly longer marine section having the potential for marginally more
environmental impacts to waste and the marine environment.
2.5.5
Option 4 Alignment
Engineering
Aspects
Project
Constraints
2.5.5.1
With the use of an inland alignment, all three of the alignment
scenarios have no impact on the seabed and, thus, be seen as advantageous over
any Low and High Level alignment scenarios that pass through the harbour. Further, by adopting an inland alignment, all
of the alignments avoid the constraints imposed by the KTTS, breakwaters and
subsea outfall. However, the inland
alignment results in the Trunk Road T2 alignment crossing the alignment of the Kwun Tong Bypass. In
the case of High Level scenario, it is necessary to adopt a high, very visually
obtrusive, (up to +23m PD) alignment. In
the case of a Low Level alignment, it is anticipated that alteration to the
foundations for the Kwun Tong Bypass would be
necessary to allow a section of cut and cover tunnel to be constructed under
the Bypass.
2.5.5.2
The use of the inland alignment also
avoids the small amount of temporary reclamation needed for the temporary
breakwater foreseen under the Option 1 Low Level scenario, as is the case for
all of the alignment scenarios that do not require demolition of the KTTS
breakwaters.
2.5.5.3
This inland alignment scenario brings the
alignment in conflict with the constraints for the existing buildings and
infrastructure of the Kwun Tong district
infrastructure. The High Level scenario
would pass very close to the facades of the existing buildings and virtually
enclose the street level roads and pavements.
The Low Level scenarios would require extensive cut and cover operations
along the roads of the Kwun Tong District causing
major disruption to the users of the area.
2.5.5.4
Although for the Deep Level scenario the
tunnel would pass under the foundations of the existing structures, ensuring no
adverse impact on the existing structures which would add significantly to the
inherent technical difficulties of TBM works.
Project
Interfaces
2.5.5.5
With all of the scenarios the change in the alignment would require
re-design of the CKR interchange and its connections to the local road network
at the Kai Tak Interchange, which is understood to be highly constrained. With the re-alignment of the Option 4 it is
understood that there would be associated issues of the connection of the Trunk
Road T2 with the at-grade road network
for the Kai Tak area and, thus, not achieving one of the key objectives for the
Route 6.
2.5.5.6
With the Option 4 alignment following the
alignment of the existing at-grade roads for the Kwun
Tong district the disruption to traffic during construction can be anticipated
to be very significant for the High and Low Level scenarios. For the majority of the Deep Level scenario
there would be no effect on the at-grade roads, but as the alignment approaches
the Kai Tak Interchange the tunnel would rise up to allow for the at-grade
connections in cut and cover section with resulting disruption of the ground
level roads.
Environmental
Aspects
Air Quality
and Noise
2.5.5.7
The Option 4 alignment takes an inland route through Kwun
Tong, passing for much of its alignment along
2.5.5.8
Construction of the Low Level scenario
will potentially cause dust and noise impacts than the High Level scenario
based on the need for a cut and cover tunnel for much of its length, along Sheung Yee Street and Wai Yip Street. Impacts are expected to be significant and
difficult to mitigate.
2.5.5.9
Operationally, the Low Level scenario
would be largely in tunnel and potential air quality impacts would be
restricted to the ventilation buildings at either end with high level air
dispersion from the stacks.
Notwithstanding, given that the air quality in this area is already
poor, the additional emissions could result in a deterioration of air quality
for the surrounding area.
2.5.5.10
The Deep Level scenario will present the
best scenario overall for Option 4 in the construction stage, with works being
underground for 3400m of the 3550m alignment, therefore, containing any dust
and noise. The ground-borne noise
implications of the TBM would need to be considered but can be controlled
readily though management of the advancing and cutterhead
speed. This option would have a similar impact with the low level option during
operation. The Deep Level tunnel scenario would likely to have the additional
potential issue of tunnel dewatering.
Water
Quality
2.5.5.11
As Option 4 will not interface with the marine environment, no marine
water quality impacts would be predicted for all three of the vertical
alignment scenarios. As the works will
be land based in all three cases, water quality implications would be
restricted to construction phase run-off which could be controlled through the
proper implementation of mitigation measures.
2.5.5.12
The Low Level scenario is likely to have
the highest potential for run-off from land based works as it involves the
largest extent of land base excavation for the cut and cover tunnel as compared
with the high and deep level scenarios.
2.5.5.13
The implications for land based run-off of
particularly the low level scenarios for Option 4 would be potentially worse
than Option 3 given the longer length of alignment being constructed on
land. However, this can be balanced
against the alignment avoiding water quality impacts on the marine environment.
Waste
Management
2.5.5.14
It is not anticipated that contaminated marine sediment would be
generated from the Option 4 scenarios.
2.5.5.15
Other waste streams would be C&D
material and rock from the TBM deep level scenario. The high level scenario would produce the
lowest quantity of waste material to be handled and disposed of. While the amount of C&D waste would be
more than the equivalent High Level scenarios for Options 1-3, the waste would
not include marine dredged sediment which would be preferred. The Deep Level scenario for Option 4 would
generate mostly rock from the TBM tunnel which can be reused making it
comparable in terms of waste to the equivalent scenario under Options 1-3.
Marine
Ecology and Fisheries
2.5.5.16
None of the three vertical scenarios for Option 4 will have any effect
on fisheries or marine ecology due to their purely land based alignments. In
terms of terrestrial ecology, the horizontal alignment passes through developed
areas currently subject to high levels of disturbance and with no vegetated
areas and would be considered to be of very low ecological value.
Landscape
and Visual
2.5.5.17
This option does not pass through any vegetated areas and therefore no
significant landscape impacts would be predicted. Visually, all the vertical alignment
scenarios will be contained along a confined transport corridor in a built up
area, and therefore would be not visible to any SRs other than those in close
proximity to the alignment itself.
2.5.5.18
During the construction stage, the High
Level scenarios would be highly visible to the local residents and occupants.
Operationally, the residual impacts of the 12m high viaduct high level scenario
would be significant, particularly for the lower level properties which will
have all views blocked by the deck or will look directly onto the traffic
corridor/noise barrier.
2.5.5.19
During the construction stage, the Low
Level scenario would also be highly visible to the local residents and
occupants. Operationally, the IMT tunnel scenarios would cause limited visual
impacts. The Deep Level scenario would
have the least potential for impacts, affecting only SRs close to the launching
and receiving shafts and the small sections of at-grade road and with limited
visual impact for the TBM tunnel scenarios during operation.
Cultural
Heritage
2.5.5.20
There are no built heritage resources or areas of archaeological
potential along the Option 4 alignment. Impacts to the built heritage resources
in Cha Kwo Ling would similar to Options 1-3.
Summary
2.5.5.21
Moving the Trunk Road T2 alignment inland does remove the issue related
to the works within the Harbour but to the disadvantage of the Kwun Tong district, with the Option 4 scenarios generating
permanent and temporary impacts on the existing and future developments in the
area. The Option 4 does have benefits
associated with water quality, marine ecology, fisheries and the lack of
generation of marine sediment waste, the potential for air, noise and visual
impacts during both the construction and operational phases, specifically for
the high and low levels scenarios, would be expected to be significant,
difficult to fully mitigate and not preferred compared to Option 1 Deep Level
scenario. The Deep Level scenario presents the least potential environmental
implications of the three vertical scenarios and would be graded higher
overall.
2.5.6
Option 5 Alignment
Engineering Aspects
Project
Constraints
2.5.6.1
The impacts on project constraints are similar to that for the Option 4
alignment scenarios, with the exception of the impact on the seabed and harbour
users which would be more adversely affected when compared with the full inland
alignment due to the need for the High and Low Level scenarios requiring
demolition and excavation of the existing seawall to allow for construction of
foundations or cut and cover tunnel sections.
Project
Interfaces
2.5.6.2
The impacts on project interfaces are similar to that for the Option 4
alignment options with the exception of the impact on the at-grade roads and
public thoroughfares in the Kwun Tong area which
would benefit from the alignment being shifted to the edge of the KTTS and away
from the main Kwun Tong roads. However, this is at the expense of having an
adverse impact on the seabed and harbour users, as described above.
Environmental
Aspects
Air Quality
and Noise
2.5.6.3
The alignment passes industrial buildings on the Kwun
Tong water front and these, together with the Kwun
Tong bypass would largely shield the SRs within Kwun
Tong from both construction and operational noise impacts from Option 5 and
would be preferable to Option 4 in this respect. However, the construction and operation of
the High Level viaduct scenario have the potential to affect residential and
other developments on the South Apron, and also at Cha Kwo
Ling.
2.5.6.4
The High Level scenario, however, while
not passing through Kwun Tong would pass close to the
areas of high development and the open roads will allow vehicle emissions to
pollute the surrounding area. No
mitigation would be possible.
2.5.6.5
In terms of construction air quality, the
low level scenario would involve the largest extent of excavation for the cut
and cover tunnel. However, as the majority of the alignment would be
constructed along the edge of the KTTS, partly in the water, significant dust
would not be expected.
2.5.6.6
As with Option 4, the Deep Level scenario
will present the best scenario overall for this alignment option in the
construction stage, with works being underground for 3400m of the 3550m
alignment, therefore, containing any dust and noise. The ground-borne noise implications of the
TBM would need to be considered but can be controlled readily though management
of the advancing and cutterhead speed and significant
impacts would not be expected.
Water
Quality
2.5.6.7
The viaduct piers of the High Level scenario would be constructed within
the KTTS and would involve dredging of contaminated marine mud on a similar
scale to Option 1 and, therefore, would have the potential to cause suspended
solids and other contaminants contained within the sediment to be released into
the water column.
2.5.6.8
For the Low Level scenario, the water
quality implications would be expected to be potentially worse, based upon the construction
of a long cut and cover tunnel along the length of the KTTS seawall
(1400m).
2.5.6.9
The TBM Deep Level tunnel scenario would
avoid any contact with the seabed and marine environment and would be preferred
from a water quality perspective, being similar to the equivalent scenario for
alignment Option 4.
Waste
Management
2.5.6.10
For C&D waste, the high level scenario is likely to produce the
least material as excavation for pier foundations only would be required but as
the piers long the KTTS will be constructed in the water, this scenario would
also result in contaminated marine sediment being dredged which will require
treatment and disposal.
2.5.6.11
The Low Level scenario would also require
extensive excavation for the cut and cover tunnel along the seawall and would
result in the removal of an estimated amount of 21,000m3 of
contaminated marine sediment. This
scenario would also result in large amounts of land based C&D material but
it is unlikely all could be used on site and some surplus would have to be removed
off-site to a fill bank.
2.5.6.12
While the Deep Level scenario will, also,
generate notably more waste, the bulk of the material (in the region of
931,000m3) will be rock and alluvial material from the tunnel
construction by TBM, material which is not contaminated and can be reused in
other projects.
Marine
Ecology and Fisheries
2.5.6.13
As with the equivalent option of Option 1, Option 3 and Option 4, the
land based works will be undertaken in areas that have been previously developed
and are of low ecology value. The
exception to this is a small area of plantation located where the eastern
ventilation building will be constructed but the loss of this area would be
common to all alignment options.
Landscape
and Visual
2.5.6.14
During the construction stage, works, the High Level options will be
visually intrusive to SRs looking from the South Apron, runway (Cruise
Terminal) and with distant views from across Kowloon Bay, although the viaduct
piers could be constructed to coincide with those of the elevated Kwun Tong by-pass, providing a more streamlined view of the
two roads in parallel.
2.5.6.15
As with alignment Option 4, the Low Level
tunnel scenario will not result in any significant visual impacts, with above
ground structures being limited to the ventilation buildings and some at grade
road sections. The Deep Level scenario,
comprises predominately underground works from the TBM, will cause less
landscape and visual impact.
Cultural
Heritage
2.5.6.16
While the High and Low level scenarios will affect the marine waters of
KTTS, no areas of marine archaeological potential have been found in this area
and as such, no marine archaeological impacts would be expected.
2.5.6.17
The Deep Level TBM scenario alone has the
potential for ground-borne noise impacts during construction but these are not
expected to be significant given the over 100m separation distance from the
closest property.
Summary
2.5.6.18
By moving the alignment to the edge of the KTTS some of the issues
related to the works within the Harbour are reduced but not sufficiently to
overcome issues associated with constructing the alignment next to the existing
Kwun Tong Bypass and though the existing seawall
KTTS. The High and Low level scenarios
of Option 5 have some noise benefits over Option 4 due to the increased
separation distance to the developments in Kwun
Tong. However, the high level scenario
does pass close to many air SRs, including all the industrial buildings along
the KTTS coastline, and would be similar to Option 4 in terms of operational air
quality. From a marine perspective,
concerning water quality, waste, ecology and fisheries, the potential for
impacts would be expected to be comparable to Option 1 and Option 3 based upon
a similar level of construction works in the KTTS. The deep level scenario
presents the least potential environmental implications of the three vertical
scenarios and would be graded higher overall.
2.5.7
Option 6 Alignment
Engineering Aspects
2.5.7.1
In many respects the Option 6 is similar to the inland alignments
Options 4 and 5 with the change in the interface alignment with CKR considered
to be a significant disadvantage to this option. In particular, for this Option 6, the
connection between Trunk Road T2 and CKR would occur underground with road
connections to the Kai Tak Interchange splitting from the main Route 6
alignment underground, which is not a preferred arrangement. Connectivity of the Trunk Road T2 with the Kwun Tong area would also be affected as the connection via
the Kai Tak Interchange would not be possible for west bound traffic, again not
a preferred arrangement.
Environmental Aspects
2.5.7.2
Environmentally, Option 6 is very similar to Option 2, except that the
alignment connects with CKR earlier, removing the need to pass over the KTAC as
with Option 2. All three vertical alignment scenarios for Option 6 would
commence with a short section of cut and cover tunnel at the interface with CKR
which will affect the corner of the Kowloon Bay Typhoon shelter (KBTS). After that the alignment would run along the
middle of the former Kai Tak airport runway before meeting the Option 2
alignment, some 600m down. Given the
similarity of the alignments, all vertical scenarios for Option 6 would be
comparable to the equivalent Option 2 scenarios in terms of environmental
implications, with any benefits from not affecting the KTAC associated with
Option 6, being balanced by the cut and cover tunnel impacts in the KBTS.
2.5.8
Option 7 Alignment
Engineering Aspects
Project
Constraints
2.5.8.1
In terms of the Low Level scenario, the Option 7 alignment is the same
as Option 2 and Option 6 alignments, in that it avoids any constraints imposed
by the existing KDGG and PWCL buildings and avoids the need for any temporary reclamation by passing outside
of the KTTS breakwaters.
2.5.8.2
The High Level alignment is similar to that for Option 2 with the need
for piers located within the harbour waters and, thus, is seen as not
preferred.
2.5.8.3
The Deep Level scenario is similar to Option 6 in having increased
difficulty for construction to deal with the foundations for the buildings on
the former runway. However, the Deep
Level scenario avoids impact on the harbour with no requirement for temporary
reclamation, seabed excavation or alteration of the subsea outfall. In order to achieve this, the alignment would
use a gradient of up to 5% which is more than the desirable 3%, but still less
than the permissible maximum of 8%.
Project
Interfaces
2.5.8.4
All of the Option 7 vertical scenarios would conflict with the future
at-grade and hospital developments on the South Apron as the alignment turns
towards the runway, some 500m before the end of the South Apron. Similarly, all of the scenarios would have an
impact on the future developments.
2.5.8.5
All of the scenarios would have an interface with the EFLS which is understood
to follow the similar alignment along the runway but with the Deep Level
scenario having the least impact, assuming the foundations for the EFLS can be
located to miss the Trunk Road T2 tunnel.
Similarly, the future developments for the High Level and Low level
scenarios would impact on the other developments along the runway with the Deep
Level being constrained to avoid the foundations for the developments as much
as possible, but would pass directly under the viaduct.
Environmental Aspects
2.5.8.6
Option 7 is, also, similar to
Option 2 with the majority of the alignment running down the former runway and
at the end of the runway, forming a marine section to Cha Kwo
Ling and connection with the TKO-LTT.
The main difference between these two options is the location where the
alignment crosses the KTAC from the South Apron, with Option 2 designed to
undertake this north-west of the KTAC taxiway bridge and Option 7, some 700m
further down the South Apron, south-east of the KTAC taxiway bridge but the change
in location means that different construction methods can be applied. The environmental implications of the three vertical
Option 7 scenarios for landscape and visual and cultural heritage would be
considered comparable to Option 2 as described above. The environmental implications of the other
environmental parameters are discussed below.
Air Quality
and Noise
2.5.8.7
In terms of the construction phase and potential impacts to the cruise
terminal, the only SR that would be present during the construction phase, the
High and Low Level scenarios for Option 7 would be similar to Option 2, with
the above ground viaduct pier cut and cover tunnel construction works,
respectively.
2.5.8.8
In respect of the Deep Level scenario, the TBM launching shaft for
Option 2 would be further up the runway, some 1100m from the cruise terminal,
while it will be on the South Apron for Option 7. In both cases, works near the cruise terminal
would be underground and this would minimise dust and noise during the
construction phase.
Water
Quality
2.5.8.9
The mode of crossing the KTAC on viaduct would be the same for the High
Level scenario for both Option 2 and Option 7 and, as such, water quality
implications would be expected to be similar to the Option 2 equivalent, with
some potential for the release of suspended solids during the dredging for the
marine piers, as is the case for the marine section from the end of the runway
to Cha Kwo Ling.
2.5.8.10
For the Low Level option, while cut and cover is used for this scenario
along the South Apron, the IMT tunnelling method will be used to pass under the
KTAC and then down the runway and to Cha Kwo
Ling. As the seabed would have to be
excavated in both cases, the implications to water quality would be similar.
2.5.8.11
In respect of the Deep Level scenario, the TBM launching shaft for
Option 2 would be further up the runway, some 1100m from the cruise terminal,
while it will be on the South Apron for Option 7. In both cases, works near the cruise terminal
would be underground and this would minimise dust and noise during the
construction phase.
Waste
Management
2.5.8.12
The High Level scenario would generate C&D material from the pier
construction but, also, contaminated marine dredged sediment, from the runway
to Cha Kwo Ling section and the sections of alignment
crossing the KTAC. As with Option 2, this scenario would produce less marine
mud than the equivalent Option 1 alignment with its longer marine section.
2.5.8.13
The Low Level scenarios would generate C&D material from the
extensive IMT section on land but, also, contaminated marine dredged sediment,
from the runway to Cha Kwo Ling section and the
sections of alignment crossing the KTAC. For the low level scenario, the amount
of marine mud to be generated will be increased due to the use of IMT in the
KTAC section, increasing from 90,000m3 for the Option 2 cut and
cover to 150,000m3 due to the access channel necessary for delivery
of the IMT units up the KTAC. The Low
Level scenario will generate more waste to be handled than the High Level
scenario.
2.5.8.14
The Deep Level scenario for Option 2 would produce both C&D and
alluvium materials which can be reused on site or transported to the fill
bank. The use of TBM for the KTAC
crossing section will avoid the generation of marine mud for disposal and, in
this respect, will be similar to Option 1.
However, as the overall alignment is longer than Option 1, the amount of
alluvium waste to be generated would increase leading to more surplus.
Marine
Ecology and Fisheries
2.5.8.15
The ecology and fisheries implications associated with the High and Low
Level scenarios would be expected to the comparable to Option 2.
2.5.8.16
The Deep Level scenario will avoid all disturbance to the seabed by
adopting the TBM tunnelling method throughout, avoiding water quality impacts
and, therefore, effects on marine ecology and fisheries.
Summary
2.5.8.17
Although very similar to the Option 2 alignment, the added length of
alignment on the South Apron allows the tunnel sufficient length to reach a low
enough level to pass under the KTAC using TBM and, hence, avoid the issues related
to the cut and cover section in Option 2.
The environmental implications for Option 7 would be expected to be
similar to Option 2. However, the deep
level scenario for Option 2 would have some benefits to water quality, waste
ecology and fisheries, associated with the use of the TBM under the KTAC,
avoiding the need for a cut and cover tunnel which will disturb the seabed
and generate marine sediment waste.
2.5.9
Option 8 Alignment
Engineering Aspects
Project
Constraints
2.5.9.1
Both the Options 8 and 7 alignments are very similar to the Option 2
alignment, with the advantages associated with avoiding constraints from the
buildings on the South Apron. The
significant differences being that the Option 8 alignment continues along the
South Apron to such a point where the Deep Level scenario can adopt a TBM
method of construction under the KTTS, the former runway and the Harbour from
the South Apron to CKL, thus avoiding impacts on the seabed. However, similar to Options 2, 3, 4, 5 and 7,
this alignment the Deep Level scenario would have impacts on the foundations of
existing or planned buildings.
Project
Interfaces
2.5.9.2
By following the KTDES corridor for the Trunk Road T2 alignment, this
option avoids conflicts with the South Apron infrastructure and
developments. However, as the alignment
curves to join with the former runway it potentially constrains the
developments on the runway, constrains the foundation locations for the future
EFLS and would interface with the new cruise terminal. In particular the High and Low Level
scenarios for this alignment would pass very close to the new cruise terminal
with likely interface items between the construction works for the Trunk Road
T2 tunnels and the operation of the new cruise terminal.
Environmental
Aspects
Air Quality
and Dust
2.5.9.3
As with Option 1, all three vertical scenarios for Option 8 have the
potential to cause noise and dust impacts during the construction stage to the
SRs on the South Apron which will be in place prior to the end of the Trunk
Road T2 construction period in 2020.
2.5.9.4
In respect of the High Level scenario, the construction of the viaduct
alignment would also affect the cruise terminal development on the former
runway in terms of dust and noise, as for Options 2 and 7. Operationally however, as the viaduct only
crosses the southern edge of the runway, it will be further way from the future
commercial and residential development further north-east up the runway, having
a separation distance of 250m. As such,
potential direct operational noise and air quality impacts would be reduced for
the high level Option 8 scenario compared to Options 2 and 7. The low level scenario would be similar to
Option 7, with construction phase impacts affecting both the SRs on the South
Apron and runway as a result of the IMT excavation works.
2.5.9.5
The Deep Level scenario would be similar to Options 1, 3 and 7,
comprising some at-grade and cut and cover sections on the South Apron but with
the majority of the alignment in deep tunnel, avoiding dust and construction
noise. In terms of the Cha Kwo Ling end, all scenario and options would involve
excavation works that may disturb the village and mitigation would be required
for all.
2.5.9.6
Operationally, the two tunnel scenarios would likely be similar to Option
1, both avoiding noise impacts for the length of tunnel which forms the
majority of the alignment, and with the operational air emissions from the
tunnel being vented via a high level shaft of the ventilation buildings,
enhancing dispersion and minimising low level impacts at the SRs at both the
South Apron and Cha Kwo Ling.
Water
Quality
2.5.9.7
The length of crossing from the South Apron to the runway is slightly
longer by 300m (from 300m), as compared to Option 2 or 7. As such, the High Level scenario would
require approximately 5 additional viaduct piers in the marine environment,
resulting in more dredging and disturbance to the seedbed that would result in
water quality issues. However, as the
alignment passes over the former runway, the overall amount of marine works
would be less than Options 1, 3 and 5.
2.5.9.8
For the Low Level option, the water quality implications would be
similar to Option 7, comprising IMT excavation from the point of leaving the
South Apron seawall. For the deep level
scenario, as for Option 1, 3, and 7, TBM is proposed to be used from the South
Apron and beyond, avoiding impacts to the marine environment.
Waste
Management
2.5.9.9
For the High and Low Level scenarios, waste implications would be
expected to be similar to Option 7 and involving the removal of marine
sediment. The waste generated for the
Deep Level scenario from the TBM tunnel will be about 10% more than Options 1
and 3 due to the increased curvature passing via the former runway. Notwithstanding, as with Options 1, 3, 4, 5,
6 and 7, no marine mud will be generated from this scenario and the majority of
the material produced can be reused, making this scenario preferred from a
waste perspective.
Marine
Ecology and Fisheries
2.5.9.10
As noted above, the Deep Level scenario will avoid all disturbance to
the seabed by adopting the TBM tunnelling method throughout, avoiding water
quality impacts and, therefore, effects on marine ecology and fisheries. The marine ecology and fisheries implications
associated with the Low Level scenario would be expected to be comparable to
Option 1. The High Level viaduct will
pass through an area of plantation/grassland mosaic on the southern end of the
runway, but this habitat is not considered to be of high ecological value.
Landscape
and Visual
2.5.9.11
There is little landscape resource in the area that will be affected by
any of the three scenarios due to the already development nature of the site,
with the exception of a small piece of plantation/grassland mosaic on the
runway. However, the loss of this area
would not be considered significant. However, visually, during the operational
phase, the High Level scenario comprising a viaduct of up to 12m high, would be
highly visible to the existing and future developments in the study area, both
on the South Apron, runway and beyond.
The tunnel scenarios would, therefore, be preferred.
Cultural
Heritage
2.5.9.12
There are no built heritage resources or areas of archaeological
potential along this alignment and potential impacts to the heritage resources
in the Cha Kwo Ling village are expected to be
controlled with mitigation measures, as for the other options.
Summary
2.5.9.13
Again this alignment is very similar to the Option 2 alignment and the
added length of alignment on the South Apron allows the tunnel sufficient
length to reach a Level Low enough to pass under the KTAC using TBM and hence
avoid the issues related to the cut and cover section in Option 2. The Option 8 High Level scenario has some
benefits over Options 2 and 7 in terms of operational noise and air and the
distance from the runway future residential development but otherwise would be
expected to be similar. The tunnel
scenarios are generally preferred over the High Level scenario for their
operational phase benefits but with the Deep Level scenario having the least
potential for impacts overall.
2.5.10
Summary of Option Assessment
2.5.10.1
The weighted scores for each horizontal alignment option and vertical
scenario are provided in Appendix 2B. A summary of the total results for all
criteria including both engineering and environmental is summarised in Table 2.4 below:
Table 2.4 Summary of Total Weighted Scores for Each Alignment
|
Alignment Options |
Vertical Scenario |
Total Assessment Score |
|
Option 1 |
High Level |
-20 |
|
Low Level |
0 |
|
|
Deep Level |
21 |
|
|
Option 2 |
High Level |
-22 |
|
Low Level |
-11 |
|
|
Deep Level |
2 |
|
|
Option 3 |
High Level |
-19 |
|
Low Level |
-1 |
|
|
Deep Level |
21 |
|
|
Option 4 |
High Level |
-5 |
|
Low Level |
-2 |
|
|
Deep Level |
16 |
|
|
Option 5 |
High Level |
-21 |
|
Low Level |
-21 |
|
|
Deep Level |
15 |
|
|
Option 6 |
High Level |
-15 |
|
Low Level |
-4 |
|
|
Deep Level |
8 |
|
|
Option 7 |
High Level |
-23 |
|
Low Level |
-18 |
|
|
Deep Level |
3 |
|
|
Option 8 |
High Level |
-17 |
|
Low Level |
-6 |
|
|
Deep Level |
12 |
2.5.10.2
From the total weighted scores allocated to each of the alignment options
against the constraints, interfaces design criteria and environmental impacts,
it can be seen that the Deep Level scenarios generally perform the best, the
Low Level scenarios show highly variable scores and the High Level scenarios
scoring the lowest for the particular set of conditions applicable to the Trunk
Road T2.
2.5.10.3
The High Level scenarios can be seen to perform
poorly in the assessment. This is in
part due the fact that those alignments that install foundations in the marine environment
would result in both a direct conflict with the PHO and a major disruption to
the potential uses of the KTTS.
Alignments that follow an inland route, or follow the line of the former
runway would have significant ground level impacts on the current and future
developments, along with generating a very significant visual impact again
generating lower assessment scores.
2.5.10.4
The High Level inland scenarios (Options 4 and 5),
also, perform poorly due to the structures impacting directly on the existing
densely developed Kwun Tong Area, whether via a
physical conflict requiring permanent easement, or environmentally in terms of
air, noise and visually intrusive structures conflicting with the wishes of the
local Kwun Tong users.
2.5.10.5
The Low Level scenarios demonstrate a wide range of
scores, reflecting the sensitivity of the performance of these alignment
options against the constraints and impacts on the features close to ground/sea
level along with more significant perceived environmental impacts. The Low Level options may be able to avoid
some of these issues by adopting construction methods such as cut and cover or
immersed tube tunnel methods. However,
these Low Level options still generate some degree of temporary reclamation,
large quantities of excavated material, and disruption to the use of the KTTS,
breakwaters and subsea outfall, which makes them not preferred.
2.5.10.6
The “deep” alignment scenarios consistently score
highly in the assessment due to the very much reduced impact on the existing
constraints, the avoidance of any impact in regard to the PHO and the very much
reduced environmental impacts during both the construction and operational
phases as a result of TBM underground works.
In particular the deep alignments reduce the quantity of dredged
material (in some cases contaminated) that would need to be disposed of at sea
if a low level option such as cut and cover and IMT were to be adopted.
2.5.10.7
All of the deep alignment scenarios avoid major
conflict with the constraints, meet the design criteria, cater for the future
interfaces and reduce environmental impact to surrounding sensitive
receivers. This can be seen in the high
scores obtained from the Option 1 and Option 8 alignments.
2.5.10.8
Table 2.5 below provides a summary of the optional
assessment scoring from a purely environmental perspective. It can be seen that the scoring largely
reflects the overall total scores of all criteria, which would be expected
given that the environmental parameters have been given the highest weighting
factors and will notably influence the overall scoring, therefore.
2.5.10.9
The conclusion of the environmental assessment,
matches that of the overall option assessment, with Deep Level scenarios for
Options 1 and 3 scoring highest environmentally and overall, including the
engineering criteria.
Table 2.5 Summary of Total Environmental Weighted Scores for Each Alignment
|
Environmental
Parameters |
Weighting |
Option 1 |
Option 2 |
Option 3 |
Option 4 |
Option 5 |
Option 6 |
Option 7 |
Option 8 |
||||||||||||||||
|
H |
L |
D |
H |
L |
D |
H |
L |
D |
H |
L |
D |
H |
L |
D |
H |
L |
D |
H |
L |
D |
H |
L |
D |
||
|
Air Quality Impact |
2 |
-6 |
0 |
2 |
-6 |
0 |
2 |
-6 |
0 |
2 |
-6 |
-4 |
4 |
-6 |
-4 |
2 |
-6 |
0 |
2 |
-6 |
0 |
2 |
-6 |
-2 |
2 |
|
Noise Impact |
2 |
-6 |
0 |
2 |
-6 |
0 |
2 |
-6 |
0 |
2 |
-6 |
-6 |
0 |
-6 |
-6 |
2 |
-6 |
0 |
2 |
-6 |
0 |
2 |
-6 |
-2 |
2 |
|
Water Quality Impact |
2 |
2 |
0 |
6 |
4 |
2 |
4 |
2 |
0 |
6 |
6 |
6 |
6 |
4 |
2 |
6 |
4 |
2 |
4 |
4 |
0 |
4 |
4 |
2 |
6 |
|
Waste Management |
2 |
4 |
0 |
2 |
4 |
-2 |
0 |
4 |
0 |
2 |
6 |
0 |
2 |
4 |
0 |
2 |
4 |
-2 |
0 |
4 |
-4 |
0 |
2 |
-2 |
0 |
|
Landscape and Visual Impact |
2 |
2 |
0 |
6 |
2 |
2 |
4 |
2 |
0 |
6 |
6 |
6 |
6 |
-2 |
-4 |
6 |
2 |
2 |
4 |
2 |
0 |
4 |
2 |
0 |
6 |
|
Cultural impact |
1 |
1 |
0 |
3 |
1 |
1 |
2 |
1 |
0 |
3 |
3 |
3 |
3 |
1 |
0 |
3 |
1 |
1 |
2 |
1 |
0 |
2 |
1 |
0 |
3 |
|
Marine Ecology impact |
2 |
-6 |
0 |
2 |
-6 |
0 |
2 |
-6 |
0 |
2 |
-6 |
-2 |
0 |
-4 |
0 |
0 |
-6 |
0 |
2 |
-6 |
-2 |
2 |
-6 |
0 |
2 |
|
Fisheries Impact |
1 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
|
Total Weighted Scores |
-9 |
0 |
23 |
-7 |
3 |
16 |
-9 |
0 |
23 |
3 |
3 |
21 |
-9 |
-12 |
21 |
-7 |
3 |
16 |
-7 |
-6 |
16 |
-9 |
-4 |
21 |
|
2.5.11 Alignment Selection
2.5.11.1
The results above show the Deep Level scenarios for Options 1 and 3
scoring highest environmentally and overall when including the engineering
criteria. Although Option 3 Deep Level
has scored highly in the assessment, it has not been assessed in detail as it
is considered to be identical in all real terms to Option 1 Deep Level
alignment, albeit having a slightly longer marine alignment which could cause marginally
more environmental impacts on the marine environment.
2.5.11.2
Following the assessment described in this section,
it has been concluded that the Option 1 alignment is the preferred alignment
for the Trunk Road T2 as it is seen to provide:
·
A technically feasible alignment;
·
The best environmental option resulting in
significantly less environmental impacts, including reduced quantities of
excavated material, no dredging of potentially contaminated of marine deposits,
reduced impacts on fisheries, water quality and marine ecology and operational
noise and air quality benefits;
·
Significantly less impact on the users of
the KTTS;
·
Minimised impacts to KTD developments;
·
Avoidance of impacts on the existing
subsea outfall, breakwater and seawalls; and
·
Avoidance of temporary reclamation in the
2.5.12 Ventilation Buildings
2.5.12.1 Having established the preferred alignment, the preferred arrangements for the ventilation buildings have been considered. As the locations of the ventilation buildings are driven by functional requirements, and it is essential that a tunnel such as that for the Trunk Road T2 has a ventilation system, then the items that have been considered in defining the preferred arrangement have been the location and number of the ventilation buildings.
2.5.12.2 The potential location for a western ventilation building on the South Apron is highly constrained. Planning for the development KTD already reserved land for the ventilation building at a position adjacent to the Kwun Tong Bypass (KTBP) and the proposed desilting works for the JVBC, locating it as far as practical from the future developments in the Kai Tak development. In order to accommodate the location of this ventilation building, an adit would need to be constructed form the Trunk Road T2 tunnels to connect to the ventilation building. Other locations for the ventilation building have been reviewed, including placing the building at the end of the Trunk Road T2 tunnel to avoid the need for the additional adit, but this would place it significantly closer (approximately 80m) to air and noise sensitive receivers on the South Apron. The proposed location for a western ventilation building is, also, on developed land and would not affect any natural resources.
2.5.12.3 The potential location for the eastern ventilation building has, also, been reviewed as a result of the land constraints at the CKL end of the Trunk Road T2 tunnel and the alignment changes described in Section 2.2.2.7 above. With the continuation of the Trunk Road T2 tunnel under the CKL Road to the portal at the TKO-LTT interchange, two main options existed for the location of the eastern ventilation building, namely to locate it at the CKL seafront as envisaged by the KTD studies or to locate the building at the end of the tunnel section and within the Lam Tine Interchange. The latter option has been adopted as the preferred arrangement as it is more efficient for the ventilation operation, reduces visual impact on the CKL seafront and frees up development space at the former PWCA. The proposed location is, also, further away from the CKL village by about 200m. The preferred location is, also, on land that is already developed or will be disturbed for the TKO-LTT project and as such, would not affect any natural resources.
2.5.12.4 In terms of the number of ventilation buildings, the practical options were 1, 2 or 3 buildings. The logical arrangements being:
·
A single ventilation building located at
one end of the tunnel. This could be either
at South Apron or at the Lam Tin Interchange;
·
Two ventilation buildings, one at South
Apron and one at the Lam Tin Interchange; and
· Three ventilation buildings, one at South Apron, one at the Lam Tin Interchange and one at approximately half-way along the tunnel, but located on the Kwun Tong shoreline, within the future promenade and connected to the tunnel via a ventilation adit. The ventilation adit is necessary as the third ventilation building cannot be located over the top of the tunnel under the KTTS as this would constitute a permanent reclamation and, thus, not permissible under the PHO since there are other feasible options.
2.5.12.5 The key aspect in terms of the number of ventilation buildings relates to operational phase air and fixed noise impacts to surrounding sensitive receivers, although construction phase impacts need to also be considered. A preliminary appraisal of these options is shown in Table 2.6.
Table 2.6 Potential Environmental Benefits and Dis-benefits of Different Numbers of Ventilation Buildings
|
Environmental
Issues |
No. of
Ventilation Buildings |
Commentary |
||
|
1 |
2 |
3 |
||
|
Noise and
Vibration |
X |
ü |
ü |
A single
building would generate higher noise and vibration impacts during the operational
phase due to more dispersion equipment being located in one place. Potentially less construction phase
impacts would occur with one building but, as the one building scenario would
require a larger structure, any impacts would be temporary, the environmental benefits would be considered to be
minimal. |
|
Air Quality |
X |
ü |
ü |
A single
vent building would release more emissions in one location. Dispersion from 2 or 3 ventilation shafts
would be preferred. Potentially less construction
phase impacts would occur with one building but, as the one building scenario
would require a larger structure, any impacts would be temporary, the environmental benefits would be considered to be
minimal. |
|
Water Quality |
ü |
ü |
ü |
All options
would have no water quality impacts, |
|
Marine Ecology
and Fisheries |
ü |
ü |
ü |
All options
would have no marine ecology and fisheries impacts as would be land based. |
|
Waste |
ü |
ü |
X |
As a single ventilation
building would be much larger, the construction waste would be equivalent
overall to the construction of two building Construction of a third building,
however, would generate additional construction from the building works
themselves and, also, the third ventilation building excavation on the CKL sea front would require the
additional construction of a connecting adit to the
remote Trunk Road tunnel generating about 7000m3 of material and
for this reason the 3 building option is not preferred. |
|
Landscape and
Visual |
X |
ü |
X |
A single
building would have to be a larger structure to process with all the tunnel
emission and as such would be more visually intrusive and more difficult to
screen. The possible location for 3rd ventilation
would be on Kwun Tong shoreline which would be
highly visible to the new development on the Kai Tak runway. |
2.5.12.6 It can be seen from Table 2.6 above, that the option of two ventilation buildings is overall preferred on environmental grounds and as such, two ventilation buildings are proposed at the South Apron and the TKO-LTT interchange.
2.5.13 Options for the Portal Structure
2.5.13.1 It is fundamental that tunnel portals are required for the Trunk Road T2 project, but the locations and details have been reviewed with a view to minimizing their environmental impact and the satisfy engineering requirements. Having identified the deep level tunnel for alignment Option 1 as the option with the best environmental performance overall, the potential locations for the portals are limited by the site constraints on the South Apron and at Cha Kwo Ling.
2.5.13.2 The portals have been located along the alignment in positions that minimise the environmental impacts from the tunnel emissions on the surrounding areas. In respect of the western portal at the South Apron, the engineering requirements fix the position of the portal and are determined by the Trunk Road T2 vertical profile. The Trunk Road T2 vertical profile should provide minimum soil/rock cover of the subsea tunnel with one tunnel diameter to meet the technical requirement of the TBM construction method, as well as tie in to the road level of at-grade section of CKR above the existing Jordon Valley Box Culvert. However, the portal is located as far away from the sensitive receivers, such as the CEP hospital, while providing the minimum traffic opening to the tunnel. The location and road level of the western portal are restrained by a minimum portal opening height of 7.65m which must accommodate 5.1m traffic headroom, 0.8m tunnel electrical and mechanical facilities plus traffic signs, 1.25m thick tunnel roof slab and 0.5m soil cover over the portal.
2.5.13.3 The eastern portal has followed a similar development process as the eastern ventilation building with the location being moved away from the seafront and into the Lam Tin interchange in order to reduce the visual impact of the portal and move the structure away for noise and air sensitive receivers.
2.6.1 Subsea Tunnel Construction
Background
2.6.1.1
The previous the KTDES
developed an immersed tube (IMT) tunnel
solution for the stretch of subsea tunnel but given the large extent of marine
disturbance this would cause, it was necessary to consider the possibility of
other forms of tunnel. However, other
possible means of tunnel construction include Drill and Blast / Drill and
Break, Cut and Cover and the use of tunnel boring machine (TBM).
Drill and Break
2.6.1.2 The option for using drill and blast or drill and break has been considered for the subsea tunnel. In order to adopt this form of construction, the tunnel would need to pass through Grade III rock or better to achieve an adequate depth of rock above the roof of the tunnel. However, this would require the vertical alignment of the Trunk Road T2 subsea tunnel section to adopt a gradient exceeding the absolute maximum value of 8%. It is noted that this level of gradient would, also, result in higher vehicle emissions from the vehicles climbing the steeper slope. Therefore, based on the inability to comply with the minimum highway standard, this Drill and Blast / Drill and Break option is not preferred.
Tunnel Boring Machine
2.6.1.3 Based on the internal traffic envelope and ventilation requirements, the twin bored Tunnel Boring Machine (TBM) tunnels are envisaged to have an external diameter of approximately 13.2m. The tunnels will be constructed in a parallel configuration with a typical separation of about one times the diameter of the tunnel or 13.2m.
2.6.1.4 The twin bored tunnel constructed by TBM launched from the South Apron and retrieved from a shaft located on the previous Public Cargo Works Area (PCWA) at Cha Kwo Ling. Cross passages connecting the twin tunnels will be provided at regular intervals and generally ground freezing method will be employed for the cross passage construction.
2.6.1.5 The TBM moves forward as it excavates the tunnel by extending the pushing jacks at the back. When the advancement of the machine reaches distance of the length of a ring, the excavation stops and the pushing jacks are retrieved, a concrete circular ring in the form of a numbers of segments are then put together at the tail of the shield. The pushing arms are once again extended in full contact with the concrete ring just erected and the excavation is resumed. The cycle of excavation and ring erection is repeated as the TBM is advanced to form the lining of the tunnel.
2.6.1.6 The TBM tunnelling can be executed from the existing land, behind the seawalls at either end and would, therefore, not require any reclamation, disturbance to the seawalls themselves or the marine environment.
2.6.1.7 A tunnel constructed by use of a Tunnel Boring Machine (TBM) has been considered as an alternative for four reasons:
· to minimise the disturbance to and disposal of contaminated seabed sediments that would arise from the dredged trench required for an IMT or cut and cover option;
· to minimise the re-provisioning/relocation of existing facilities within the typhoon shelter and at the CKL PCWA;
· to remove the need for temporary reclamation; and
· to tie-in with the lower vertical profile now proposed at CKL village under the TKO-LTT contract, where an IMT would require a much deeper dredged trench (causing greater disturbance and a much increased excavated volume of sediment), but has the benefit of making a TBM option more feasible.
2.6.1.8
The use of TBM for the construction of the subsea tunnel
has many environmental and engineering advantages, as summarised
below:
· involves no dredging operations;
· no impacts to marine ecology and fisheries resources;
· due to the deeper depth of boring, the excavated material will be uncontaminated alluvial or rock suitable for recycle/ re-use (on site or offsite) as public fill;
· there would be no disturbance to the marine operations in the Kwun Tong Typhoon Shelter;
· construction of TBM tunnel does not depend on the weather and can be operated with day and night shifts; and
· able to avoid all disturbance to the harbour area.
2.6.1.9
The major concern of TBM is the risk of human health and safety of
exposure to hyperbaric environment on rare occasions.
Maintenance of the TBM cutterhead is required
from time to time, particularly for changing worn or damaged cutter discs. Cutterhead tools
can be changed within the spokes of the cutterhead under
atmospheric conditions. Notwithstanding,
the possibility exists during emergency situation for entering the excavation
chamber under hyperbaric condition if such operations cannot be carried out
within the cutterhead spokes.
Immersed Tube
2.6.1.10
The IMT tunnel method of
construction involves the tunnel elements being sunk into a trench dredged into
the seabed and supported on a sand bed foundation. By virtue of their buoyancy
the tunnel elements exert less foundation pressure on the sand bed than the material removed from the
trench. In the case of Trunk Road T2,
the elements would generally be founded on alluvium. It is necessary for the
marine mud overlying the alluvium to be removed as part of the dredging
operation.
2.6.1.11
Construction of an IMT tunnel for Trunk Road T2 would, therefore,
require a dredged trench in the bed of the typhoon shelter. Typically the trench would represent the
structural depth of the tunnel element, plus the sand foundation, plus the rock
armour on the top to allow the rock armour to be flush with the existing seabed
and minimise the risk of collision with marine traffic, falling anchors etc.
2.6.1.12 In order to create access for this trench, existing installations would require to be removed, either permanently with re-provisioning elsewhere or temporarily. These include:
· breakwater at the entry/exit of the KTTS;
· sewerage subsea outfall; and
· typhoon moorings.
2.6.1.13
As the immersed tube tunnel itself consists of
numbers of prefabricated tunnel elements, these first need to be fabricated in
a casting basin. The proposed immersed
tube tunnel (IMT) would take the form of reinforced concrete rectangular box
structures of dimensions
2.6.1.14
In additional, after the tunnel elements are constructed, if they cannot
be floated to the site and installed straight away, a temporary mooring would,
also, be required which would be anchored to the seabed and have the potential
to disturb the marine environmental in its location. The preferred choice for a mooring area would
be
2.6.1.15
The major advantages of employing the IMT tube for the construction
of the subsea tunnel are summarised as follows:
· the IMT works would be principally focused on the marine areas and would have no additional impact on the shore users over that for the construction of the approach works;
· there is less risk of settlement impacts on adjacent structures;
· cross passages can be more easily provided within the internal tunnel structure;
· a shallow tunnel can achieve flatter gradients with less impact on vehicle emissions; and
· reduced construction risk as main elements are prefabricated.
2.6.1.16
However, the major disadvantage
to the technique is its increased potential for environmental impacts
associated with seabed disturbance and dredging and the associated impacts on
water quality, marine ecology and fisheries.
Dredging works for the tunnel trench (and associated temporary
reclamations) will disturb the settled sediments leading to both sediment
plumes and release of sediment bound contaminants. As the sediment in KTTS is
known to be highly contaminated with heavy metals and trace organic pollutants,
potential impacts on general water quality will be a particular concern for
this construction method. Subsequent
backfilling works will, also, lead to further sediment plumes, although as the
backfill material is generally non-contaminated and coarser, the plumes would
be more limited and secondary impacts like contaminant release is usually not a
concern.
Cut and Cover
2.6.1.17
In order to construct the subsea tunnel using cut and cover tunnel
methods, it would be necessary to construct a temporary reclamation. Although this could be constructed in a
single large length to include the whole length of the subsea tunnel, it is
envisaged that it would actually be carried out in sections of 100m to 200m
lengths in order to avoid completely disrupting the operation of the KTTS and to
reduce PHO implications. The envisaged
method for construction of the temporary reclamations is by constructing
temporary embankments within the KTTS waters up to a level of approximately
+4mPD. Diaphragm walls will then be sunk
down through the temporary full to create working cofferdam. The fill material within the cofferdam would
then be excavated to allow the tunnel section to be constructed. Following completion of the tunnel box
backfilling would take place up to finished seabed level and the cofferdam
demolished down to seabed level. This
process would be repeated in 100m to 200m long sections until the full tunnel
is constructed. Although this method
does have the advantage of allowing the use of simpler construction techniques
and potential multiple faces for working it can be seen to have much more
impact on the marine environment and the operation of the KTTS. Further, the filled material necessary for
constructing the temporary reclamations will need to be imported to the site
and exported inducing the secondary environmental impacts associated with
handling and transportation.
2.6.1.18 As with the IMT option, the cut and cover options has key environmental disadvantages associated with the extensive temporary reclamation for the working platform required for such works and the resulting adverse water quality, marine ecology, fisheries, waste and PHO implications.
2.6.1.19 The temporary reclamations for this cut and cover option will require extensive dredging and disturbance to the seabed and the release of contaminated sediment plumes that will affect water quality and potentially marine ecology and fisheries. The large temporary reclamations will, also, require import and removal of temporary fill the handling and transportation of which can cause secondary noise, air and visual impacts.
Comparative
Assessment
2.6.1.20
Drill and Blast / Drill and
Break option has the major disadvantage of being unable to comply with the
minimum highway standard. The TBM tunnel will have significant
environmental advantages over the IMT and cut and cover tunnel schemes. For the IMT tunnel construction, dredging
for the tunnel trench would be required, which would be about 140
2.6.1.21 Given the pros and cons of each tunnelling method, a comparative assessment has been undertaken. Table 2.7 evaluates the two options based upon different engineering and environmental criteria. High values indicate the higher potential for beneficial outcomes. In order to clearly separate the options, the following evaluation has been adopted:
a) Weighting: the relative importance weighting assigned to each category, as follows:
3 : item of Higher Significance
to the assignment;
2 : item of Medium Significance to the
assignment; and
1 : item of Lower Significance to the
assignment.
b) Assessed Value: relative performance of each method under each category, and taken to be:
-3 : Significantly
more adverse.
-2 : Moderately more
adverse.
-1 : Slightly more
adverse.
0 : no significant relative difference (i.e. options are relatively equal).
1 : Slightly more beneficial.
2 : Moderately more beneficial.
3 : Significantly more
beneficial.
2.6.1.22 The details in Table 2.7 below show that, the TBM method has very significant advantages in the reduction of disturbance to the marine operations in the KTTS. Similarly, the TBM may be able to avoid disturbance to the harbour bed. Although the disturbance resulting from the IMT and cut and cover works is temporary in nature and will be re-instated as part of the construction programme, the construction phase impacts would be significant. Following developments in the design and implementation of TBM projects for similar ground conditions, these two TBM advantages have been balanced against the risks of working with a very large TBM with potential mixed and difficult ground conditions.
Table 2.7 Comparative Assessment of
IMT, Cut and Cover, Drill and Break and TBM Tunnelling Methods
|
Item |
IMT |
Cut and Cover |
Drill and Break |
TBM |
Remarks |
||||||||
|
Assessed Value |
Weighting |
Weighted Result |
Assessed Value |
Weighting |
Weighted Result |
Assessed Value |
Weighting |
Weighted Result |
Assessed Value |
Weighting |
Weighted Result |
||
|
Construction
Risk |
0 |
3 |
0 |
0 |
3 |
0 |
-2 |
3 |
-6 |
-1 |
3 |
-3 |
The use of
the TBM will require workers working at pressure. For the drill and break section the tunnel
will be deeper and thus working pressure will be higher. |
|
Construction
Cost |
0 |
2 |
0 |
1 |
2 |
2 |
1 |
2 |
2 |
-1 |
2 |
-2 |
Within the
level of accuracy for this study there is no significant difference between
IMT and TBM construction costs however the potential for repeated
interventions associated with low cover and poor/unknown geological
conditions under the TBM option favours
construction by IMT methods. For the
cut and cover and drill and break methods these are generally considered to
be cheaper construction methods. |
|
Programme |
0 |
2 |
0 |
1 |
2 |
2 |
0 |
2 |
0 |
0 |
2 |
0 |
There is no
significant difference between construction programmes
except for the cut and cover, where multiple working fronts can be set
up. However, this would increase
environmental impacts and PHO issues. |
|
Environmental
Impacts |
-1 |
3 |
-3 |
-1 |
3 |
-3 |
1 |
3 |
3 |
1 |
3 |
3 |
Dredging and
handling potential contaminated fill is a significant relative disadvantage to
the IMT and cut and cover options, although some mitigation measures can be
put in place. |
|
Impact on
Marine Operations |
-1 |
3 |
-3 |
-2 |
3 |
-6 |
1 |
3 |
3 |
1 |
3 |
3 |
The IMT would
disrupt usage during towing and sinking operations. Dredgers and barges would increase the
marine traffic. However, the cut and
cover option would generate significant temporary working platforms that
would make sections of the KTTS unavailable. |
|
Reclamation
-Temporary |
-1 |
3 |
-3 |
-2 |
3 |
-6 |
1 |
3 |
3 |
1 |
3 |
3 |
Current IMT
proposals require temporary reclamation at the temporary breakwater for the
continued operation of the KTTS. The
cut and cover method would, also, require temporary working platforms. |
|
Reclamation
-Permanent |
0 |
3 |
0 |
0 |
3 |
0 |
0 |
3 |
0 |
0 |
3 |
0 |
No permanent
reclamation for alignments. |
|
Operational
costs |
0 |
1 |
0 |
0 |
1 |
0 |
0 |
1 |
0 |
0 |
1 |
0 |
There is no
significant difference between operation costs. |
|
Maintenance
items |
0 |
2 |
0 |
0 |
2 |
0 |
0 |
2 |
0 |
0 |
2 |
0 |
There is no
significant difference between maintenance costs. |
|
Impact on the
Public |
0 |
3 |
0 |
0 |
3 |
0 |
0 |
3 |
0 |
0 |
3 |
0 |
Construction
provisions for removal of spoil will need to include barging of spoil removed
from TBM launching shaft, in a similar manner to barging away of dredged
materials. |
|
Satisfy
design requirements |
1 |
2 |
2 |
1 |
2 |
2 |
-3 |
2 |
-6 |
-1 |
2 |
-2 |
Construction of
cross-passages by manual excavation cannot be entirely catered for by the
designer. Detailed geotechnical
information will assist thorough planning and help strengthen design
proposals however the ability of the contractor to carry out the works (including
pre-grouting and ground freezing) will play a major role in determining the
outcome of the works. For the drill
and break section, the tunnel would need to go deeper to reach the Grade III
rock prior to passing under the south apron.
This will generate a steep vertical alignment. |
|
Total
Weighted Score |
-7 |
-9 |
-1 |
2 |
|
||||||||
Selected Method
2.6.1.23 Considering the notable environmental and PHO benefits of the TBM method, along with the very significant reduction of impacts on the KTTS users when compared with IMT, Cut and Cover and Drill and Break construction, the TBM method is preferred and has been selected.
2.6.2 Number of Tunnel Boring Machines
2.6.2.1 Based upon the information available on the ground conditions along the tunnel alignment, engineering requirements have dictated the use of closed shield slurry TBMs. The proposed design is for a twin tunnel of 13.2m diameter constructed using two TBMs, one for each bore.
2.6.2.2 The use of a single TBM for the construction of both bores of the subsea tunnel has been considered, but this was not preferred on environmental, technical and programme grounds. In one scenario, the single TBM would be required to progress to Cha Kwo Ling and then turn around and then progress back to bore the second tunnel. This would require ancillary equipment for the tunnel to either be set up at Cha Kwo Ling or be placed on a floating platform that could be initially moored to the South Apron and then towed and moored at the Cha Kwo Ling area. This would have an increased risk to the marine environment through spillage of tunnel slurry into the KTTS, as piping would need to span from the tunnel access point to the support facilities. The TBM support facilities would, also, be located at Cha Kwo Ling and closer to the Cha Kwo Ling village. The alternative scenario would be that the TBM would be dismantled at Cha Kwo Ling after the first tunnel construction and transported back to the South Apron to repeat the process for the second tunnel. This would result in a longer construction period for the tunnelling with the potential for extended noise and air impacts.
2.6.2.3 A further option for the use of the single TBM was the use of a single 17m diameter TBM that would construct a single bore that would have sufficient space for both carriageways. This single “over under” tunnel is not preferred due to the need for the larger tunnel to be located deeper below the seabed. The increase in depth would lead to higher vehicle emissions in the tunnel due to the need to climb a steeper gradient (over 6%) and, also, results in increased risks associated with working on the tunnel at pressures greater than atmospheric. In addition, the use of such a large diameter tunnel would be at the limit of current TBM technology and is considered to pose safety, programme and commercial risks with no clear environmental benefits.
2.6.3 Depressed Road/Cut and Cover Tunnel
Background
2.6.3.1 Along the land portion of the Trunk Road T2 alignment, the road includes at-grade road, depressed road and cut and cover tunnel at the South Apron and cut and cover tunnel at the Cha Kwo Ling Public Cargo Working Area at the connection to the proposed TKO-LTT. An extensive deep excavation and lateral support (ELS) system would be required for both a depressed road and cut and cover tunnel construction. Ground settlement would be induced due to the deflection of the temporary ELS system, as well as to carry out dewatering during the ELS construction.
2.6.3.2 The key options considered for constructing the ELS system are sheet-piled wall, soldier pile wall, pipe pile wall, diaphragm wall and bored pile wall, as discussed below.
Sheet-piled Wall
2.6.3.3 Sheet-piled wall is a temporary displacement wall but with a relatively small wall stiffness. It is installed by hammering or vibration into the ground and drivability of the pile is a main concern. The ability to overcome underground obstructions such as boulders, old foundations and seawalls in fill, colluvium and weathered rocks is low and a more powerful pile hammer, heavier steel sheet pile or pre-boring may be required in order to pass through any underground obstructions. Due to its low stiffness, sheet-piling in loose sandy soils can induce settlement in adjacent ground and, therefore, it is usually applied to applications needing a lesser excavation depth. Seepage may, also, occur through the interlocking sheet-piles under difference hydraulic heads, which may induce consolidation in compressible soils. Settlement of adjacent ground may, also, occur during the extraction of sheet pile from cohesive soils.
2.6.3.4 Sheet-piling equipment is simple, usually comprising of attachment mounted onto standard excavators or vibration hammer. However, noise and vibration will be induced.
Soldier Pile Wall
2.6.3.5 A soldier pile wall serves as a temporary/permanent replacement wall. It has two components, the soldier piles (vertical component) and lagging (horizontal component). Compared to sheet-pile wall, the solider pile wall has greater stiffness. The piles provide the primary support to the retained soil by arching effect and the spacing of piles depends on the arching ability of the soil and the distance of structures sensitive to settlement. In order to have full contact with the soil, piles are either driven or placed in pre-drilled holes which are backfilled to the ground surface with concrete. The lagging provides the secondary support to the soil face and prevents progressive deterioration of the soil arching between piles.
2.6.3.6
Overcoming underground obstruction
is conventional by pre-drilling holes.
However this method is unsuitable for granular material excavation below
the groundwater level because soldier pile wall is pervious such that water
leakage would occur during excavation.
Pipe Pile Wall
2.6.3.7
A pipe pile wall is a
replacement wall, similar to the soldier pile wall. It is comprised of the steel pipe pile and
the lagging. The construction equipment
used and the effects due to the construction is similar to the soldier pipe
wall but the advantages of the pipe pile wall over the soldier pipe wall is
that the pipe pile wall usually has greater wall stiffness, as well as better
performance in groundwater with soil retaining during excavation.
Diaphragm Wall
2.6.3.8
The diaphragm wall comprises a
type of cast-in-situ replacement concrete pile wall. It is constructed by
excavating a slurry trench with a guide wall to maintain the stability of the
trench and then reinforcement cage fixing and concreting is carried out. For wall stiffness, diaphragm wall has a number of times compared
to sheetpile and pipe pile wall. For the diaphragm wall construction, the temporary
trench excavation would be supported by bentonite
slurry. The
temporary stability of the slurry filled trench would be the main concern with
this technique, although trench stability in soft clay can be improved by
reducing the panel length or increasing the slurry pressure (either increasing
the density of the slurry or raising the slurry level above ground level). Horizontal movement of the diaphragm wall due
to the swelling of weathered granite layer can be controlled by increasing the
net slurry pressure. Therefore, it is a beneficial technique for excavation
near to sensitive structures.
Bored Pile Wall
2.6.3.9 The bored pile wall is another type of cast-in-situ replacement concrete pile wall. It is a non-percussive piling method at which the circular casing is installed to the design depth. Soil and rock will be excavated out, with subsequent installation of steel reinforcement cage. Concreting will be carried out with tremie method and the casing will be extracted during the course of concreting.
2.6.3.10
Wall deflection and settlement
can properly be controlled and minimized due to the improved wall stiffness,
again, making this technique beneficial for excavation near to sensitive
structures. It also has greater ability to overcome underground obstruction
when compared with other types of pile wall.
However, this requires workmanship and comprehensive detailing to control
water leakage during excavation. The
construction cost will, also, be relatively higher.
Selected Method
2.6.3.11 Selection of the ELS system for the cut and cover tunnel needs to be based upon the depth and extent for depressed road / cut and cover tunnel construction, site-specific geology, groundwater conditions, adjacent existing and proposed structures which are sensitive to settlement, the available working area, environmental impact to the surroundings, cost and time.
2.6.3.12 From an environmental perspective, compared with the diaphragm and bored pile wall method, sheet, pipe and soldier piling would reduce the amount of excavated material generated since these are typically driven solutions. However, driving piles into position can result in higher noise impacts when compared with diaphragm or bored pile solutions. Quiet driving techniques can be implemented to reduce the noise impacts and vibration associated with driven pile installation, but where the works are adjacent to vibration sensitive structures or facilities then other forms of temporary wall must be adopted.
2.6.3.13 The diaphragm and bored pile methods adopt a drilling fluid to stabilise the pile shaft which will generate waste to be disposed of and site management measures will be needed to be in place to control the water in site around all the piling works. The diaphragm and bored piling will use water mixed with the bentonite solution to progress the works and, thus, will have a higher water demand.
2.6.3.14 Visually all of the methods of construction require similar forms of equipment for installation.
2.6.3.15 In terms of air quality, the sheet pipe and soldier piling may be up to 2 to 3 times faster for installation than the diaphragm and bored pile walls and, thus, the duration of air impacts would be reduced. However, all options would be part of excavation works which can create dust and would need to be controlled.
2.6.3.16 A preliminary appraisal of the available construction methodology options is shown in Table 2.8.
Table 2.8 Potential Environmental Benefits and Dis-benefits of ELS Construction Methodology Options
|
Environmental Issues |
Sheet
Pile Wall |
Soldier
Pile Wall |
Pipe Pile Wall |
Diaphragm
Wall |
Bored Piled Wall |
|
Noise and
Vibration |
X |
X |
X |
ü |
ü |
|
Air Quality |
- |
- |
- |
- |
- |
|
Water Quality |
ü |
ü |
ü |
X |
X |
|
Waste |
ü |
ü |
ü |
X |
X |
|
Landscape and
Visual |
- |
- |
- |
- |
- |
Note: “ü” =
Potential reduced environmental impacts; “X” = Potentially
higher environmental impacts; “-” = No significant environmental difference
2.6.3.17 The benefits and dis-benefits concerning dust and landscape and visual are not significantly different between the techniques and can be adequately controlled in both cases. The driven piling techniques, sheet, soldier and pipe piling, are less preferable from a noise perspective but do have some dust and water quality advantages over the diaphragm and bored piling techniques. However, overall, there is only a marginal difference between all the techniques environmentally and, therefore, the best engineering methods for the site situation have been selected, as discussed below.
2.6.3.18 The maximum excavation depth will be approximately 30m. For excavations up to 10m, and where settlement is not a concern, it is recommended to adopt sheet-pile wall as the ELS system because it is conventional and faster to install. The works will be undertaken in an open space area such that settlement is not the main concern. However, as the excavation depth increases, pipe pile wall or diaphragm walls are recommended for forming the cofferdam for the construction of the tunnel.
2.6.3.19 For the area where a greater depth of excavation is needed and the alignment is adjacent to the existing PWCL building with its sensitive equipment, diaphragm wall or bored pile wall would need to be adopted to minimize the lateral wall movement and building settlement. Ground treatment to strengthen the ground may, also, be needed to further minimise the construction adverse impact to the surroundings if found necessary.
2.6.3.20
As such the type of ELS system
for the depressed and cut and cover sections of the alignment will vary
depending upon the location. A schematic
ELS design along the land portion of Trunk Road T2 alignment is summarised as
follows.
· CH5850 – 6050 (including depressed road portion) (up to 8m excavation): Open cut and sheet-pile wall with 3 layers of struts;
· CH6050 – 6230 (up to 15m excavation): Pipe pile wall with 4 layers of struts;
· CH6230 – 6475 (up to 23m excavation): Diaphragm wall with 6 layers of struts;
· CH6475 – 6544 (influence zone to existing PWCL building) (max 30m excavation): Bored pile wall / T-shaped diaphragm wall with maximum 9 layers of preloading struts;
· CH6544 – 6630 (seabed chainage) (up to 35m excavation): Diaphragm wall with 10 layers of struts; and
· Cha Kwo Ling Portion (up to 35m excavation): Diaphragm wall with 6 layers of struts.
2.6.4 Others
2.6.4.1
Based on the selection of the TBM tunnelling methods, no reclamations or
dredging works are required and as such no comparison of alternative
construction techniques has been undertaken.
2.6.5 Sequencing of Construction Works
2.6.5.1 The sequencing of the construction works has been investigated with a view to achieving a minimum export of materials from site, in particular the marine deposits and alluvium. The phasing has been planned to allow for stockpiling of the marine deposits for treatment on site and re-use in the backfilling over the cut and cover tunnels. Similarly, the phasing has been designed to allow for use of the alluvium materials after all of the marine deposits have been used. The proposed phasing, also, avoids the importation of materials to the site and uses only materials generated from the Trunk Road T2 contract for the backfilling of excavations. This is considered a notable environmental benefit of the proposed construction programme.
2.6.5.2 Programmes with shorter overall durations for the construction works have been considered but these resulted in the generation of larger quantities of excavation in the early phases of the Trunk Road T2 project, far exceeding the capacity of the stockpile area and requiring more export of all the types of excavated materials. The option of increased early excavation, also, increased the amount of road and marine transport movements needed to and from the site for removal of the spoil materials and, also, resulted in the need for the import of fill materials to the site to complete the backfilling operations. On this basis, the shorter durations were not preferred. Notwithstanding the proposed construction sequence is longer and would not be expected to result in notably more environmental nuisance.
2.6.6 Works Areas
2.6.6.1 The Works Areas have been selected with a view to reduce the impact of transporting materials to and from the site and reducing the impacts on the natural environment. Based upon this, the current locations are all located on already disturbed or developed land and are not vegetated. Notwithstanding that available sites on the South Apron are limited by the planned developments in this area, the selection of suitable Works Areas have been located as close to the construction works as possible to reduce transportation and its associated visual, air and noise impacts. The potential volume of materials to be transported to and from the working fronts are such that there would be a very high transport demand resulting in increased air and noise impacts if the Works Areas where located further away and closer to sensitive receivers.
2.6.7 Barging Point Selection
2.6.7.1 According to preliminary estimates, the volume of material to be extracted from the works is estimated to be in the order of approximately 1,070 construction vehicles per day.
2.6.7.2 With an assumption of 8 working hours a day, this works out to be 134 construction vehicles per hour. Each delivery is assumed to have an inbound movement for empty construction trucks, and an outbound movement for filled construction trucks to go to the designated fill deposit point, understood to be in Tseung Kwan O Area 137 at the moment. That means there are 134 veh/hr of inbound movements, and 134 veh/hr of outbound movements. In pcu/hr terms, this is equivalent to roughly 335 pcu/hr per direction (based on pcu factor of 2.5 for construction vehicles), i.e. 335-in and 335-out.
2.6.7.3 Given the muck-out point’s location at Kai Tak South Apron near Cheung Yip Street (Refer to Figure 3.8), and the fill materials deposit point at TKO Area 137, the most logical haul route would be as follows:
· Outbound: Cheung Yip Street -> Sheung Yee Road -> Wang Chiu Road slip road to Kwun Tong Bypass -> Kwun Tong Bypass -> Tseung Kwan O Tunnel -> Wan Po Road -> TKO Area 137; and
· Inbound, assuming return of construction trucks from TKO Area 137 back to muck-out point:
- Route 1 - TKO Area 137 -> Wan Po Road -> Tseung Kwan O Tunnel -> Kwun Tong Bypass -> Slip road to Wai Fat Road -> Wai Yip Street -> How Ming Street -> Hoi Bun Road -> Cheung Yip Street; or
- Route 2 - TKO Area 137 -> Wan Po Road -> Tseung Kwan O Tunnel -> Kwun Tong Bypass -> Slip road to Wang Chiu Road -> Lam Fung Street -> Sheung Yee Road -> Cheung Yip Street.
2.6.7.4
Minor variation of the haul
routes may be possible, but travelling along the close block of
2.6.7.5 Should the material be removed by road, the following traffic constraints would be expected to limit the viability of allowing any sizeable volumes of land-based deliveries of spoil materials along the haul route:
Concurrent
Traffic Generation from Cruise Terminal and Hospital Sites
2.6.7.6 The Kai Tak Cruise Terminal and the two hospitals at Site A (New Acute Hospital (NAH), Centre of Excellence in Neuroscience (CEN)) and the hospital at Site C (Centre of Excellence in Paediatrics (CEP)) are envisaged to be operational in 2017 and 2018 respectively. The estimated traffic volumes from these three major developments as documented in the “Traffic and Transport Impact Assessment for Establishment of Centre of Excellence in Paediatrics and Neuroscience and a New Acute Hospital in Kai Tak Development” commissioned by Architectural Services Department (ArchSD), are detailed in Table 2.9 below.
Table 2.9 Traffic and Transport Impact Assessment for Establishment of Centre of Excellence in Paediatrics and Neuroscience and a New Acute Hospital in Kai Tak Development.
|
Development |
AM Generation (pcu/hr) |
AM Attraction (pcu/hr) |
PM Generation (pcu/hr) |
PM Attraction (pcu/hr) |
|
Cruise Terminal |
972 |
969 |
691 |
705 |
|
NAH + CEN + CEP combined |
272 |
335 |
306 |
235 |
2.6.7.7 Prior to the completion of CKR and the associated slip roads S5 and S6 scheduled for the first year of operation in 2021, the only external road connection for the Kai Tak South Apron and Cruise Terminal would be via Road D3 (to/from Kai Tak North and Kowloon Central), Road D4 and Cheung Yip Street (to/from Kowloon East and Tseung Kwan O) which forms part of the Advance Works 2 (AW2) that is scheduled for commissioning in 2018. Before 2018, Roads D3 and D4 would comprise single-2 carriageways and the road capacity would be even more constrained.
2.6.7.8
Based on the construction
programme for T2 of 2017-2021, the worst case would be 2018 when the cruise
terminal and hospital developments are completed but AW2 is not commissioned
yet, and thus traffic is handled by the single carriageways of Roads TD3 and
TD4. As demonstrated by the aformentioned study, the
road and junction capacities along Road D4 and
Constraints in
Surrounding Junctions
2.6.7.9
The traffic handling capacity
in the Trunk Road T2 area, also, hinges upon the junction capacities of Cheung
Yip Street/Hoi Bun Road, with all inbound/outbound traffic for the hospital
sites and Cruise Terminal having to go through this, prior to commissioning of
the CKR and its slip roads. Any
construction traffic for spoil removal to Tseung Kwan O would, also, have to
pass through this junction and other critical junctions, namely
Table 2.10 Junction Capacity at Critical Junctions
|
Scenario |
R.C.
of |
R.C.
of J/O
Wan |
||
|
AM |
PM |
AM |
PM |
|
|
Without Construction Vehicle |
-17% |
8% |
21% |
23% |
|
With
Construction Vehicle (335pcu-in and 335pcu-out) |
-39% |
-32% |
2% |
0% |
Note: Reserve Capacity (R.C.) indicated in
%, provides an indication of signal junction performance. Positive RC indicates
the junction is operating satisfactorily, negative RC indicates the junction is
overloaded.
2.6.7.10
As shown in Table 2.10, the
results indicated that the affected junction of Wang Chiu Road/ Sheung Yee Road along the haul route would be seriously overloaded with the
construction traffic during construction while the junction of Wan Po Road/
Shek Kok Road would be worsened significantly to a marginal condition. Based on
the above comparison results, the junction of
Traffic
conditions at strategic links of Kwun Tong Bypass, Tseung Kwan O Tunnel and Wan Po Road
2.6.7.11
The traffic capacities on the
strategic links of Kwun Tong Bypass, Tseung Kwan O Tunnel and
Table 2.11 Link Capacity at Strategic Road Links
|
Scenario |
V/C ratio of
Kwun
Tong Bypass |
V/C ratio of
Tseung Kwan O Tunnel |
V/C
ratio of Wan
Po Road Flyover near Chiu Shun Road |
|||||||||
|
EB |
WB |
EB |
WB |
EB |
WB |
|||||||
|
AM |
PM |
AM |
PM |
AM |
PM |
AM |
PM |
AM |
PM |
AM |
PM |
|
|
Without Construction Vehicle |
1.1 |
0.9 |
1.2 |
0.9 |
0.7 |
1.0 |
1.3 |
0.8 |
0.5 |
0.6 |
0.6 |
0.5 |
|
With Construction Vehicle (335pcu-in and 335pcu-out) |
1.2 |
0.9 |
1.2 |
1.0 |
0.8 |
1.1 |
1.3 |
0.9 |
0.7 |
0.8 |
0.8 |
0.7 |
2.6.7.12 As shown in Table 2.11, the results indicated that the affected road links along the haul route would be worsened with the construction traffic during construction.
2.6.7.13 Summarising from the capacity assessment results, it can be seen that the identified road network constraint points would be seriously overloaded based on the full extent of spoil delivery by land-based transport (i.e. 335 pcu/hr) and only if the construction traffic was reduced to about 5% of the original volume assumed in Table 2.10 and 2.11 above, would the affected road sections operate without any significant worsening in traffic conditions. In a test scenario in which the land-based delivery could be scaled back by delivering some spoil materials by other means (e.g. barging), and the construction truck volume is reduced to about 5% of the original volume to 7 veh/hr (7-in and 7-out), or equivalent to 18 pcu/hr (18-in and 18-out), the resulting capacity assessment results are shown in Tables 2.12 and 2.13.
Table 2.12 Junction Capacity at Critical Junctions
|
Scenario |
R.C.
of Junction
of |
R.C.
of Junction
of Wan |
||
|
AM |
PM |
AM |
PM |
|
|
Without Construction Vehicle |
-17% |
8% |
21% |
23% |
|
With
Construction Vehicle (18pcu-in and 18pcu-out) |
-19% |
8% |
20% |
22% |
Note: Reserve Capacity (R.C.) indicated in %, provides an indication of signal junction performance. Positive RC indicates the junction is operating satisfactorily, negative RC indicates the junction is overloaded.
Table 2.13 Link Capacity at Strategic Road Links
|
Scenario |
V/C ratio of Kwun
Tong Bypass |
V/C ratio of Tseung Kwan O Tunnel |
V/C ratio of Wan Po Road Flyover near
Chiu Shun Road |
|||||||||
|
EB |
WB |
EB |
WB |
EB |
WB |
|||||||
|
AM |
PM |
AM |
PM |
AM |
PM |
AM |
PM |
AM |
PM |
AM |
PM |
|
|
Without Construction Vehicle |
1.1 |
0.9 |
1.2 |
0.9 |
0.7 |
1.0 |
1.3 |
0.8 |
0.5 |
0.6 |
0.6 |
0.5 |
|
With Construction Vehicle (18pcu-in and
18pcu-out) |
1.1 |
0.9 |
1.2 |
0.9 |
0.7 |
1.0 |
1.3 |
0.8 |
0.5 |
0.6 |
0.6 |
0.5 |
2.6.7.14 It can be seen that only in such arrangement, that the affected road section would operate without any significant worsening in traffic conditions.
2.6.7.15 From the above findings, it can be seen that the junctions and road links along the likely delivery routes for spoil materials between Kai Tak and Tseung Kwan O Area 137 are already or would likely be operating at above capacity even without any addition of the T2 construction traffic. Any significant amount of additional traffic generation from the construction of T2 would bring about additional adverse impacts onto these roads and junctions. Therefore, from a traffic perspective, means of marine transport (e.g. by barges) has been explored for delivering most, if not all, of the spoil materials generated.
2.6.7.16 The Barging Point location has been selected to minimise environmental impacts, minimise disruption to current projects on the KTD and minmise impacts on the Kwun Tong area, in particular the local road network. The Barging Point is planned to be located close to the TBM launching shaft (which will, also, serve as the subsea tunnel mucking out shaft) to minimise the distance for the transport of spoil from the subsea tunnel working area to its export point from the site. The option of locating the Barging Point closer to the stockpile area at WA4 was considered, but rejected as this would bring the barging point closer to the CEP hospital (within 25m rather than the planned 225m), with resulting noise and air impacts on this sensitive receiver. Also, the placing of the Barging Point close to WA4 would have required a 500m longer conveyor belt system for the TBM spoil to be delivered to the barging point, resulting in a potential increase in noise impacts. It was, also, noted that in order for barges to access closer to the works area WA4, there may have been a requirement for limited dredging to provide sufficient navigable water depth for the assumed 500m3 barges, resulting in water and marine ecology impacts. The planned Barging Point location, however, has recently been used as a cargo handling point with hard standing and, thus, would have no impact on existing vegetated areas. There would, also, be no marine impacts as works below the waterline to prepare the Barging Point for use would not be required.
2.6.7.17 Brief consideration was, also, given to using a barging point at the Cha Kwo Ling end of the tunnel, but this would have meant starting the TBM works from the CKL end of the subsea tunnel and having the TBM ancillary equipment located close to the Cha Kwo Ling village with potential for increased noise and air impacts. It would, also, have meant that any spoil generated from the cut and cover tunnel sections that could not be used on site would have to be exported via the local road network to the barging point or to the fill banks resulting in secondary noise and air impacts from the increased construction traffic.