2.1
Various options and alternatives of project
design and construction methods have been reviewed and considered in the course
of the development and selection of preferred scheme for SCL (HUH-ADM), taking account
of engineering feasibility, site constraints, programme and environmental
aspects. This section presents the details of the options and alternatives
considered, and the constraints and considerations assessed in adopting the
preferred scheme and construction method.
Purpose
and Objective of the Project
2.2
The SCL is strategically important for
connecting the existing railway lines into an integrated rail network. The
east-west connection, will allow the creation of a 57km east-west corridor
across the city connecting Wu Kai Sha with Tuen Mun via
2.3
As part of the
SCL, the objective of the SCL (HUH-ADM) (which is the Project being considered in this EIA Report)
is to extend the existing East Rail Line from Hung Hom Station (HUH) to the north shore of Hong Kong Island and
the Central Business District, providing convenient interchanges at HUH,
Exhibition Station (EXH) and ADM.
Brief
Description of the Project
2.4
The proposed SCL is an extension of the
existing Ma On Shan Line via East Kowloon and connect
to West Rail Line at Hung Hom, and an extension of the existing East Rail Line
from Hung Hom to Admiralty crossing
2.5
The SCL (HUH-ADM) is an approximately 6km long East Rail Line extension from HUH across the harbour to new EXH and ADM, with
provisions to facilitate a possible station at Central in the longer term. This
section of SCL alignment will be entirely underground while the associated
ventilation building, ventilation shafts, plant rooms and station entrances
will form aboveground structures.
Scope
of the Project
2.6
The Project comprises the following key
elements:
Ÿ An approximately 6km extension of the East Rail Line including a rail harbour crossing from Hung Hom to Admiralty on Hong Kong Island;
Ÿ A new EXH located near the Hong Kong Convention and Exhibition Centre (HKCEC);
Ÿ An integrated ADM for the existing urban lines, the future SCL and South Island Line (East) (SIL(E));
Ÿ Ventilation buildings, ventilation shafts, smoke extraction facilities and other associated works of the Project; and
Ÿ Demolition of the existing
2.7
Apart from the above key elements, barging
facilities, supporting works areas and access roads will be required to support
the construction of the Project.
2.8
It should be noted
that the works at the HUH would be within the scope of SCL (MKK-HUH). The design and construction of the ADM including associated structures
for the SCL (HUH-ADM) will be carried out by the SIL(E)
whilst the construction of the overrun tunnel beyond ADM and minor building
works will be carried out under SCL (HUH-ADM).
2.9
The SCL is an
important strategic rail corridor purposed for forming an expanded railway
network in
Ÿ Providing a fast, reliable and convenient mode of transport running
through the northern
Ÿ Redistributing railway passenger
flows to relieve the existing railway lines in urban
Ÿ Improving the coverage of the railway network by placing 70% of the population and 80% of the workforce within one km of a railway station, and also by crossing the Harbour to interchange with the the Tsuen Wan Lin, Island Lin and SIL(E) at ADM;
Ÿ Stimulating the redevelopment of Hung Hom and Waterfront areas; and
Ÿ Relieving reliance on road-based transport, resulting in significant reductions in roadside air pollutants, respirable suspended particulates and carbon dioxide, and providing a more environmentally-friendly public transport option in terms of energy conservation.
2.10
The Project provides Hong Kong with the fourth Rail Harbour Crossing
which essentially relieves the existing congestion on the Tsuen Wan Line
through redistributing railway passengers, and connects the new development
areas in Kai Tak with
2.11
More importantly,
the expansion in railway network can gradually conduce
a significant modal shift in passengers’ travel behaviours from road-based
transport to railway system, and thereby soothing the burgeoning reliance on
cross harbour road tunnels, especially the demand on the Hung Hom Cross Harbour
Tunnel, as well as alleviating environmental nuisance from existing road
networks.
2.12
From the environmental
perspective, the rail will be powered electrically. Rail is widely
recognized as a more sustainable form of transport
than road transport in terms of carrying capacity and energy effectiveness, adverse
environmental implications such as roadside air pollution associated with
electrically-powered rail are far less in comparing to vehicle fleets. Having
anticipated that the Project will increase public transport patronage and
reduce the overall road traffic volumes through providing a more convenient and
easily accessible transport option, the Project will bring improvements in air
quality, noise pollution, on-road safety and the overall quality of the ambient
environment. As the most of the rail line is underground, the visual quality, landscape
character and land amenity can also be maintained whilst still providing
convenient access to areas by the public.
Scenario Without the Project
2.13
If the Project is not to be put forth,
passengers will be forced to rely on road-based transport between areas along
the SCL corridor, and there would be a significant increase in road traffic
volumes and hence air and noise pollution as a result of the increased vehicles
travelling similar distances. It is expected that the increased congestion
would also be negatively impact Hong Kong’s competitive advantage.
2.14
In addition to the pivotal role of the Project in traffic congestion and
environmental impacts relief, the Project will also improve accessibility to
the harbour by providing a direct link between Hung Hom and
2.15
The construction and operation of the SCL
will also create numerous new employment opportunities within Hong Kong SAR.
Construction of new stations and redevelopment of current stations will also
create commercial opportunities within the stations and enhanced economic
development of the areas they serve.
Considerations for Alternatives/Options
2.16
The following
sections present the consideration of the alternatives for the following key
elements of the Project:
(a)
Alignment;
(b)
Stations/platforms;
(c)
Ventilation
buildings/ventilation shifts;
(d)
Entrances/exits;
and
(e)
Train system.
Alignment
Criteria
for Options Development
2.17
To assess the
suitability of the alternative alignment options, a range of environmental,
engineering, safety and general community disruption considerations were
developed to help the decision making process. These considerations are
presented in Table 2.1 below.
Table 2.1 Considerations
in Determining Preferred Alignment and Construction Method
|
Considerations |
Description |
|
Engineering Factors |
|
|
Implementation
Programme |
Minimisation of construction period. Shorter
construction period is preferable in order to minimise the disturbance to the
community. |
|
Interface with Existing Facilities |
The preferred railway alignment connecting the
HUH and the new EXH should be a direct connection with minimal distance to
reduce construction costs, maintain operational efficiency and minimise
passenger travelling time between stations. Specific consideration in relation to HUH and EXH
included: ·
minimum impact
on the operation of the existing stations; and ·
ensuring an efficient
interchanges between the SCL and SIL(E). Other specific interfacing issues that were taken
into account during selection of alignment options including: the need for
the SCL crossing under the Hung Hom Bypass piers and the fender piles that
have a depth of up to -20mPD; the need to minimise impacts to the existing
freight pier and to avoid impacting on the Cross Harbour Tunnel and tension
anchors. There are also important interfacing issues with
the Central Wanchai Bypass (CWB) and Wan Chai Development Phase II (WDII)
projects. Protection works to these projects are required to ensure
construction works can be carried out more efficiently with fewer
disturbances to the environment. The operational impacts to the CBTS
including the existing breakwater and existing moorings/anchorages within the
Typhoon Shelter are also required to be minimised. |
|
Construction/Operational Safety, Flexibility and Maintenance
Requirements |
A number of safety, flexibility and maintenance
requirements in the design and construction of railway lines constrain
certain alignment options. Particular
constraints identified within this Project included: ·
horizontal curve
radius for a rail track; ·
a maximum
vertical gradient of 3% should be achieved, with minimum gradients for long
lengths of track to improve energy efficiency; ·
tunnel ventilation
and emergency access points for a tunnel ; and ·
Factories and
Industrial Undertakings Ordinance limits the maximum compressed air pressure
at work to protect tunnel personnel from being unnecessarily exposed to
unacceptable hazardous conditions to health and safety. |
|
Constructability and Implication on |
Constructability is primarily related to concerns
surrounding destabilising structures already present or to be built. Concerns identified in the SCL
include: ·
allowing for
practical construction under existing aboveground buildings; ·
avoidance/minimisation
of constructing soft ground tunnel due to safety and building settlement
issues; and ·
avoidance/minimisation on
construction risks due to uncertain ground condition and long tunnel. Reclamations within the boundaries of |
|
Land Acquisition |
This issue is considered in order to minimise
area of land that may need to be acquired so as to minimise disruption to the
local community. |
|
Environmental Factors |
|
|
Water Quality and Ecology/Fishery |
The associated water quality and
ecological/fishery implications when marine works are required for the cross
harbour section are considered. |
|
Air Quality |
Dust generated during the construction of the SCL
and its impact on human health and the environment is considered. |
|
Noise |
Ground-borne rail noise impact associated with
the train pass-bys, together with noise impact on nearby residents during the
construction phase of the SCL are considered. |
|
Other Environmental
Considerations |
Other environmental factors that are considered
include: ·
the avoidance or
minimisation of landscape and visual impacts associated with the above-ground
structures; ·
preservation of
mature trees; ·
C&D / Waste
generation (e.g. contaminated soil/sediment); and ·
minimisation of fuel usage. |
|
Other Factors |
|
|
Avoidance/Minimisation
of Issues/Constraints |
This includes minimisation of project areas encroaching into developed
area, and interface issues with other projects currently being planned or
constructed. |
|
Disruption to the
Community |
Minimisation of disruption to the community, e.g. residential
households, business operations and potential structural impacts along the
alignment, are considered. |
2.18
A preliminary
design for the SCL was conducted from 2008 to 2009, in which comprehensive studies
have been carried out to investigate various alignment options. The alignment
options developed for the Project would need to meet the requirements of the
Protection of the Harbour Ordinance (PHO), and the need to prepare Cogent and
Convincing Material where reclamation is required to prove such reclamation can
satisfy “overriding public need test”.
Compliance
with the Protection of Harbour Ordinance (PHO)
2.19
The PHO Cap 531 recognizes the harbour as a
special public asset and a natural heritage of
2.20
The presumption against reclamation can only
be rebutted by establishing an overriding public need for the reclamation work.
Guidance for addressing the public need for reclamation (referred to as “the
overriding public need test”) is provided in the Housing, Planning and Lands
Bureau Technical Circular No. 1/04 (HPLB TC 1/04). This applies to all
reclamations within the boundaries of
2.21
The HPLB TC No. 1/04 states that a “no
reclamation” scenario must be taken as the starting point in considering
alternatives and that it is imperative to examine if an overriding public need
can be met without reclamation through a reasonable alternative. It further
states that all circumstances should be considered in determining whether there
is a reasonable alternative to reclamation, including the economic, social and
environmental implications, cost and time incurred, and other relevant
considerations, including technical feasibility and safety considerations.
2.23
As detailed in the CCM Report, the three
tests in rebutting the presumption against the reclamation as set out in the
PHO have been satisfied:
·
In facilitating the construction of the SCL and
therefore in meeting the overriding public need for the railway, there is
consequently a compelling and present need for the reclamation in the CBTS and
adjacent to Hung Hom landfalls. All of the reclamation is essentially temporary
and will be removed upon completion of construction, with the seabed reinstated
to the original level.
·
No reasonable alternative to temporary
reclamation is found for constructing the SCL (HUH-ADM) (known as SCL Cross
Harbour Section in the CCM Report).
·
The extent of reclamation has been determined
to be the minimum required.
Alignment Options
2.24
In general, two broad groups of engineering
design have been considered for the Project, namely the “No Reclamation
Options” and “Alternative Options Requiring Reclamation” and are described in
the sections below. Details of the options are described in the CCM Report.
“No Reclamation” Options
2.25
Three “no-reclamation” options have been
investigated as a part of the engineering design of the Project, however each
of these options are considered to be either not viable or not a reasonable
alternative to reclamation. These options include:
·
Bridge Option;
·
Shallow Bored Tunnel Option; and
·
Deep Tunnel Option.
Bridge
Option
2.26
The Bridge Option would have huge impacts on
existing infrastructure and buildings on both sides of the harbour as well as
significant visual impact. The problems arise from the need to provide
sufficient navigation clearance under the bridge deck and the limiting 3%
gradient for the railway. The approach ramps on other side of the harbour would
have to be 1km long for every 30m of clearance.
2.27
On the
2.28
On the Hong Kong side the approach ramp would
have to extend a significant distance along the north shore on Hong Kong
Island, including sections at grade and in trough and would fail to provide
acceptable interchange stations at EXH and ADM because of the significant level
differences involved. This option is therefore not considered to be viable.
Shallow
Bored Tunnel Option
2.29
The Shallow Bored Tunnel Option would have to
be constructed by Tunnel Boring Machines (TBM) in view of the anticipated
ground conditions along the alignment corridor (Figure 2.1 of Appendix
2.1). The alignment of these options is driven
by the need to pass under the CWB tunnels with adequate clearance to avoid
damaging the CWB tunnels during SCL tunnel construction and also to maintain
adequate cover under the seabed, particularly below a large depression in the
seabed near the HUH seawall in order to allow the TBM to operate.
2.30
In order to adopt the Shallow Bored Tunnel
Option, sufficient ground cover is required over the TBM to enable ground
control and steering so as to meet safety requirements. The absolute minimum
ground cover above the tunnel is generally one TBM diameter and preferably two
diameters. It is expected that an internal diameter of 9m would be required for
a single track SCL tunnel with ventilation duct. The external diameter of the
TBM would be about 10.35m. Accordingly, to allow for sufficient ground cover,
the tunnel would require an absolute minimum depth below seabed of 10.35m and
preferably more than 20m clearance from the top of the tunnel to the seabed.
2.31
Due to these constraints, this option
involving twin bored TBM tunnel would require an invert level of approximately
-50 mPD, at the lowest point under the CWB tunnel, and a general depth below
-44 mPD within the remaining areas of the Harbour. At these levels the tunnel
would pass in and out of rockhead several times and significantly increase both
the likelihood of corestones being encountered and the general engineering
difficulty of the alignment.
2.32
The particularly onerous tunnelling
conditions demand the TBM to be capable of operating in mixed face conditions
at deep tunnel depths. Based on previous experience, and in view of the
expected high cutter wear and risk of damage to the cutterhead, daily
interventions would be required at the tunnel face for inspection, maintenance
and repair. These works would require workers to enter the pressurised
cutterhead via air locks in the pressure bulkhead of the TBM, and would be
undertaken in a small and confined space at deep tunnel depths under the
harbour at pressures exceeding 50 pounds per square inch (psi) (approximately
3.45 bar) (Figure 2.2
of Appendix 2.1).
2.33
In
2.34
This limit is in place to protect tunnel
personnel from being unnecessarily exposed to more hazardous conditions to
health and safety than necessary. In all such cases the objective must be to
keep the risk as low as reasonably practicable to these personnel. This,
therefore, means that any requirement to exceed the current regulated level
must be supported by an argument that there is no reasonable, safer way of
carrying out the construction.
2.35
The deeper alignment across the harbour would
mean that a cross platform interchange could not be provided at EXH resulting
in a poorer level of service to passengers.
2.36
This TBM tunnel option also has significant
disadvantages for connecting with stations and achieving operation
requirements. Due to the tunnel depth requirements for the TBM, the platforms
at HUH for the SCL (HUH-ADM) would need to be up to 15m lower than an option
using immersed tube tunnel construction with the following implications:
·
Approximately 2km of the existing East Rail
north of HUH would have to be lowered to tie into the deeper platforms at the
station.
·
Impacts on the Hong Kong Coliseum may occur
due to increased volumes of rock excavation adjacent to and under it.
·
Increased construction risks and costs
associated with construction adjacent to the existing station foundations and
under the Hong Kong Coliseum.
·
Increased interchange times, as the vertical
separation between the east-west and north-south corridor platforms would be
increased.
2.37
It is considered that the risks to health,
life and the project associated with this Shallow Bored Tunnel Option cannot be
justified. There are alternative ways of constructing the project which avoid
these risks. It would also cost more, provide a considerably poorer level of
service to rail users and has increased impacts on the community which extend
over a wider area.
2.38
As such the Shallow Bored Tunnel Option is
not considered to be a reasonable alternative to options which require
reclamation.
Deep
Tunnel Option
2.39
Stations are preferably kept as shallow as
possible in order to make them as easily accessible as possible for passengers.
This dictates that the tunnels between them generally be kept shallow. However,
the problems with the Shallow Bored Tunnel Option listed above dictate that
deeper tunnels in rock be considered.
2.40
Previous and currently planned drainage
projects have deep tunnels under the harbour which are located in rock. These
are aimed at avoiding the need for pressurized face interventions.
2.41
For the SCL (HUH-ADM), this would mean that
the tunnels would have to be lowered to approximately 80m below sea level in
bedrock. The problems are that the stations would also have to be deepened
significantly, i.e. HUH would have to be approximately 50m deep and EXH 43m
deep. Cross platform interchange would not be possible at EXH. This option has
not been taken forward as it would provide an unacceptable level of service for
passengers entering or leaving these stations and an impractical interchange
due to the level difference. This does not satisfy the project objectives to
provide efficient interchanges.
2.42
There would also be a knock on effect to the
alignment to the west of EXH to ADM and also particularly along East Rail Line
north of Hung Hom. A significant length of East Rail Line would have to be
lowered to suit this new level including Mong Kok East Station. Tunnelling at
depths with intervention pressures greater than 50 psi would also be required
along this section as the tunnel climbs above rockhead.
2.43
This is therefore not considered to be a
viable option.
2.44
To conclude, there is no acceptable
“no-reclamation” option for the Project. It must be accepted that some
reclamation will be required to enable its construction.
Alternative Options Requiring
Reclamation
2.45
The Immersed Tube Tunnel (IMT) construction
method has been adopted for all existing cross-harbour transport tunnels in
Hong Kong, including the Eastern Harbour Crossing, Western Harbour Crossing and
Central Harbour Crossing transport tunnels across
2.46
The standard practice for IMT construction is
to dredge a trench in the seabed to remove soft materials, provide a foundation
base within the trench, float in precast tube tunnels in sections, sink the
precast units into place within the seabed using a floating pontoon system or
from a barge and finally connect and backfill the tunnel with a rock blanket or
other suitable material to protect and anchor the tunnels. This approach would
raise some sections of sea-bed but does not result in any dry surface or land
formed. Nonetheless, the raising of the sea-bed level would not affect the use
or access to that part of the harbour.
2.47
The maximum depth and portion of IMT
extending above the seabed is generally dictated by marine clearance
requirements. The top level of a short section of the IMT at the north of the
CBTS will be slightly above the Cross Harbour Tunnel but the slightly reduced
water depth should have no impact to the marine users and it will not affect
the main fairway.
2.48
An envelope covering various alignment
options of the Project is shown on Figure 2.4 of Appendix 2.1. This is bounded by the existing Cross
Harbour Tunnel on the west and the need to identify a suitable landfall on
2.49
As the SCL tunnels would clash with CWB Slip
Road No. 8, which extends above the main CWB Tunnel Box, alignment options
along the central part of the corridor on
Eastern and Western Corridor
Options
2.50
For both the Eastern and Western Alignment
Corridors, the requirements at the Hung Hom landfall are common. At the Hung
Hom landfall, the SCL tunnels would need to pass under the Hung Hom Bypass.
During construction of the SCL tunnels, some of the fender piles for protecting
the Hung Hom Bypass would need to be removed and reprovisioned in a slightly
different form. The reprovisioned fender piles are considered to be permanent
reclamation but are not considered to affect the use or enjoyment of the
Harbour.
Eastern Corridor Options
2.51
The Eastern Corridor options are shown on Figures 2.5 to 2.8 of Appendix 2.1 and the key characteristics are summarised
below:
·
Option 1A:
Alignment runs under CWB tunnels along the same corridor as far as possible.
·
Option 1B:
Alignment runs partly under the CWB tunnels and then to the south of the
tension anchor zone at the Cross Harbour Tunnel and then parallel to and just
to the south of the CWB tunnels.
·
Option 1C
non-stacked: This is a similar alignment to Option 1B through the CBTS but then
follows a non-stacked inland alignment to EXH. A similar alignment option to
provide a cross platform at EXH was also considered but found to be
unfeasible.
·
Option 1D:
Shallow alignment above the CWB tunnels.
2.52
Options 1A to 1C would require construction
of the SCL tunnels beneath the CWB tunnels within the CBTS. These works would have
to be carried out under the CWB contract. Due to the extra depth of
construction and complexity, completion of the CWB tunnels is expected to be
delayed for 3 years, which hence prolongs the period of disruption in the CBTS.
2.53
The assessment of Option 1D has shown that
the currently proposed CWB tunnels would have to be lowered to avoid the SCL
tunnels from either clashing with the CWB Slip Road No. 8 or protruding above
the seabed at this location, and in the eastern part of CBTS as shown on Figure 2.8 of
Appendix 2.1. The
CWB project team has advised that deeper CWB alignment would result in the CWB
tunnel portal being moved further east towards North Point. This would increase
the permanent reclamation in North Point from 3.3 hectares to approximately 10
hectares.
2.54
All options would require temporary
reclamation of up to 2ha while Option 1B would also require additional
permanent reclamation to allow the Project to be constructed parallel to the
CWB tunnels adjacent to the Wanchai East Screening Plant and Hong Kong Electric
Sub-station.
2.55
The Eastern Alignment Options are therefore
not favoured because of a combination of the need for permanent reclamation and
the prolonged period of construction required in CBTS. In addition, the route
length for the alignment within the Eastern Corridor would be extended
resulting in greater construction impacts and longer journey times during
operation.
Western Corridor Option
2.56
The horizontal alignment of the Western
Corridor Option is shown on Figure 2.9 of Appendix 2.1. At the location where the Project crosses
the CWB, the SCL tunnels will pass over the CWB tunnels.
2.57
After passing through the Hung Hom landfall
section, the alignment will run in a southerly direction towards the CBTS, to
the east and generally parallel to the existing Cross Harbour Tunnel. South of
the CBTS breakwater, the alignment will then run in a south westerly direction
towards the Police Officers’ Club site where a ventilation building will be
located.
2.58
The tunnel between the Hung Hom landfall and
a point approximately 72m north of the breakwater will be constructed using the
IMT method. South of the IMT section, the cut and cover construction method
will be adopted. The cut-and-cover section requires temporary reclamation, with
a total area of approximately 2.2ha, including the temporary reprovisioned
jetty for the Royal Hong Kong Yacht Club.
2.59
The existing breakwater will be removed after
the surrounding area has been temporarily reclaimed. The breakwater will be
reinstated at the existing location and in a similar form after completion of
the SCL tunnels below. The typhoon shelter will be protected at all times by the
temporary seawalls and reclamation provided while the existing breakwater is
removed for the SCL tunnel construction.
2.60
There are several challenges with
constructing the Project through the CBTS section, these include:
·
The need to
reduce disturbance to the moorings and operations of the typhoon shelter as
much as possible and ensure the works are undertaken as quickly as possible to
avoid prolongation of any impacts.
·
Ensuring the
tunnels are placed at a sufficient depth to reduce the potential risk of damage
from ship impact, anchors, etc. and are not exposed, whilst minimising the
amount of materials to be dredged from within the typhoon shelter during
construction, due to the expected high levels of contaminants in the sediment,
and ensuring that contaminants are contained as best as possible when removed.
·
Interfacing
with the CWB project construction at this area which will commence earlier than
the SCL.
2.61
The above requirements contribute to the need
for temporary reclamation to be undertaken for construction works. In
particular, the most significant implication to the Project is the interface
requirements with CWB.
Other Alternative Considerations
2.62
Other alternative alignment
options to the west of the Cross Harbour Tunnel and to the east of CBTS were
studied but considered not preferable for the reasons given below.
Alternative Alignment to West of
2.63
These options would require the
SCL tunnels to pass under the Cross Harbour Tunnel on the
2.64
There are a number of major challenges
with this alignment which renders it unfeasible. These include conflicts with
the Hong Kong Coliseum foundations, retaining structures or footings for the
East Rail Line tunnels and the adjacent flyover. Mined tunnelling under the
existing Cross Harbour Tunnel on
2.65
The tunnel across the harbour
would be particularly deep (approximately 40m below sea level) as it would have
to pass below the CWB tunnels. This would lead to excessive dredging and
significant areas of temporary reclamation. EXH Station would have to be much
deeper and a cross platform interchange could not be provided.
2.66
The risks associated with this
alignment, the impacts of construction and less favourable EXH Station
interchange mean that this option is unacceptable.
Alternative Alignment to East of CBTS
2.67
This alignment option will shift
towards eastern side of
2.68
The key destinations for rail
users crossing the harbour through SCL would be Central, Admiralty Wanchai and
2.69
In terms of station capacity,
North Point Station is currently providing for interchange between the Tseung
Kwan O Line and the Island Line. The interchange capacity is already stretched
as the original platform tunnels have limited width and thus there is limited
flexibility to enhance this capacity. Fortress Hill station is configured as
two platforms connected by a number of adits which in turn connect to a single
principal bank of escalators connecting to the concourse level. The platforms
are limited in width.
2.70
Due to the insufficient capacity at these existing stations,
neither of them would
be able to cope with the large numbers of passengers crossing the harbour, and
having to interchange with the Island Line, and total reconstruction of the
station would be necessary. The adjacent Island Line tunnels would also have to
be realigned causing major disruption to the Island Line services and the
community. There would be huge space, cost and programme implications.
2.71
As most people would eventually
travel to central business district in the morning peak, a large number of passengers
would be trying to board the Island Line. The Island Line would be overloaded
by the number of SCL passengers.
Conclusions of Options Reviewed
2.72
A number of “no-reclamation” options have
been investigated and are considered to be not viable or not a reasonable
alternative to reclamation. These options include: (i) Bridge Option; (ii)
Shallow Bored Tunnel Option; and (iii) Deep Tunnel Option.
2.73
The Bridge Option would cause very
significant adverse impacts on both sides of the Harbour. It is not possible to
engineer a scheme which meets the SCL project objective. This option is
therefore rejected.
2.74
The Deep Tunnel Option is not considered to
be viable because of the impractical interchanges created and the need for
tunnelling at pressures greater than 50 psi.
2.75
The Shallow Bored Tunnel Option would require
working in high pressures exceeding the statutory limit of 50 psi. The MTR
Corporation are not prepared to accept the risks to health, life and the
project with this option when there is an acceptable alternative option
available which avoids these risks. Also, the poor interchange arrangement
would not meet the SCL project objective.
2.76
For the “Options Requiring Reclamation”, the
Immersed Tube and Cut-and-Cover Tunnel option have been adopted as the approach
for the construction of tunnels, thanks to the well established technology and
construction process for this method and the relatively little risk involved.
2.77
Based on the analysis of the alignment
options for the IMT, it has been concluded that the IMT alignment should follow
the Western Corridor Option as it minimises interfaces with CBTS and is the
most direct railway alignment. The Eastern Corridor Options have more
significant adverse impacts on reclamation durations and greater construction
risks.
2.78
Permanent reclamation would not be required
under the Western Corridor option by the IMT and cut-and-cover tunnel, as all
permanent works would be below seabed or lowest astronomic tide level, other
than the reprovisioned fender piles for the Hung Hom Bypass. However, temporary
reclamation will be required to construct the cut-and-cover tunnel to connect
with the IMT and inside the CBTS.
2.79
In light of the above reasons, it is
concluded that there is no reasonable alternative to the IMT tunnel option
which requires temporary reclamation for construction at the Hung Hom landfall
and adjacent to and in the CBTS and replacement of the fender piles for the
Hung Hom Bypass. This option is the most appropriate option that can achieve
the Project requirements and benefits
to the public and be constructed safely with
proven technology, lower costs and less risk to programme.
2.80
A comparison of the key aspects
of each alignment is presented in Table 2.2
below.
2.81
Based on feedback from the public
consultation process particularly from the Professional Forum and taking into
account construction risks and programme, the Western Corridor Option is
considered to be a better option than the Eastern Corridor Options.
Table 2.2 Comparison
of Alignment Design Options
|
Construction alignments/ Aspects |
“No
Reclamation” Options |
Alternative
Options Requiring Reclamation |
|||||||
|
Bridge Option |
Deep Tunnel Option |
Shallow Bored Tunnel Option |
IMT Eastern Corridor |
IMT Western Corridor |
|||||
|
Option 1A (below CWB) |
Option 1B (below CWB) |
Option 1C (below CWB) |
Option 1D (above CWB) |
||||||
|
Engineering Factors |
|||||||||
|
Implementation Programme |
- |
+ 2 further years as compared to IMT. |
+ 2 further years as compared to IMT. |
Extended 3 years of works in CBTS
& cause delay to CWB |
Extended 3 years of works in CBTS
& cause delay to CWB |
Extended 3 years of works in CBTS
& cause delay to CWB |
Extended 3 years of works in CBTS
& cause delay to CWB |
Extended 1.5 years of works in CBTS but no delay to CWB |
|
|
Interface with Existing Facilities |
Major impact on the East Rail Line, existing roads and other
infrastructure on Major resumption of land on The Hong Kong Coliseum would also have to be demolished. |
- |
- |
Prolonged occupation of moorings at CBTS and major interaction
with CWB. |
Limited mooring affected. |
||||
|
Construction/ Operation Safety, Flexibility and Maintainability |
The approach ramps on either sides of
the harbour need to be 1km long for every 30m of clearance due to the
limiting 3% gradient for the railway. On the |
Use of face interventions at greater than the maximum 50 psi
pressure as currently set in the Factories and Industrial Undertakings
Ordinance (Cap 59) is not permitted. It is considered that the
Health & Safety risks associated with these options cannot be justified. |
Increased construction complexity and risk, particularly for the construction under the Cross Harbour Tunnel, Adverse impact on interchange at EXH |
Increased construction complexity and risk, particularly for the construction of the combined CWB and SCL
tunnels under the Cross Harbour Tunnel. |
Much simpler construction method. Size and duration of temporary
reclamation would be significantly reduced. All permanent works would be
below seabed or lowest astronomic tide level |
||||
|
High risk |
High risk |
High risk |
Medium risk |
Low risk |
|||||
|
Temporary / Permanent Reclamation |
Nil |
Nil |
Nil |
0.6ha Temporary Reclamation + Permanent reclamation required for the reprovision of fender pier
piles for Hung Hom Bypass (not considered to affect the enjoyment of the
Harbour) |
2ha Temporary Reclamation + Permanent reclamation required for the reprovision of fender
pier piles for Hung Hom Bypass (not considered to affect the enjoyment of the Harbour) |
2ha Temporary Reclamation + Permanent reclamation required for the reprovision of fender pier piles for
Hung Hom Bypass (not considered to affect the enjoyment of the Harbour) |
0.6ha Temporary Reclamation + Permanent reclamation required for the reprovision of fender pier piles for
Hung Hom Bypass (not considered to affect the enjoyment of the Harbour) + additional 6.7ha Permanent
reclamation for CWB. |
2.2ha Temporary Reclamation Required. + Permanent Reclamation required for the reprovision of fender pier piles
for Hung Hom Bypass. (not considered to affect the enjoyment of the Harbour) |
|
|
Land Acquisition & Railway
Operation |
Bridge extends a significant distance along the north Cross-platform interchange not engineered practical at the
stations. |
80m below sea level in bedrock; HUH Station at 50m deep and EXH at 43m deep Cross-platform interchange not possible
and unacceptable level of service for passenger entering or leaving stations. |
Deep Station; Cross-platform interchange not
possible. |
Longer tunnels; Cross-platform interchange at EXH not possible. |
Longer tunnels; Cross-platform interchange at EXH not possible. |
Longer tunnels; Cross-platform interchange at EXH not possible. |
Longer tunnels; Cross-platform interchange at EXH not possible. |
Min length; Cross-platform interchange at EXH possible. |
|
|
Environmental Factors |
|||||||||
|
Environmental Considerations |
· Significant visual impact · Water and ecology/fishery impacts would be
concerns. |
· Much more sediment/C&D will be generated due
to a longer alignment. |
· Much more sediment/C&D will be generated due
to a longer alignment. · Construction noise and dust would be a concern at
the cut-and-cover section at the landing points. · Water and ecology/fishery impacts would be
concerns. |
· Localised construction noise and dust impact at
the cut-and-cover section at the landing points. · Water and ecology / fishery impacts would be
concerns. |
|||||
|
Other Factors |
|||||||||
|
Avoidance of Issues/Constraints |
Marine traffic would be a major concern.
|
Tunnelling for the Project would be a major concern on Health
& Safety risks. |
Engineering constraints cannot be resolved. |
Avoidance of engineering and environmental
constraints has largely been investigated and resolved. |
|||||
|
Disruption to the Community |
Significant impacts on existing infrastructure and buildings on
both sides of the harbour |
Significant traffic and other disruption to the north of HUH |
Significant traffic and other disruption to the north of HUH |
Long interfacing/ disruption at CBTS. |
Limited interfacing/ disruption at CBTS. |
||||
Preferred Alignment Option
2.82
As discussed, the IMT along the Western
Corridor option is considered as the most appropriate option that can both
achieve the objective of the Project and benefit to the public while it will be
constructed with proven technology, at lower costs and less risk to the
programme. It minimises interfaces with CBTS and is the most direct railway
alignment. The Eastern Corridor options have more significant adverse impacts
on reclamation duration and much greater construction risks. Other alternative considerations have been deemed to be
infeasible.
Stations/Platforms
Exhibition
Station (EXH)
2.83
EXH will be an interchange
station and is the first station after the harbour crossing section of the
Project. EXH passengers can continue to Admiralty. Passengers will also be able
to interchange with the Island Line via ADM, which will be extended by the West
Island Line and SIL(E) via ADM.
2.84
EXH is expected to handle
passengers to and from the north Wan Chai district, visitors to the HKCEC and
related facilities, and also allows for interchange with the Public Transport
Interchange (PTI) located directly above the station bounded by
2.85
Three location options have been
identified for the EXH:
·
EXH Option 1 – North of Great
Eagle and Harbour Centre
·
EXH Option 2 – Harbour Road
Alignment Option
·
EXH Option
EXH Option 1 - North of Great Eagle and Harbour Centre
2.86
The EXH location in this option
(as shown in Figure
2.10 of Appendix 2.1)
is on the site occupied by the North Wan Chai PTI, Wan Chai Swimming Pool and
Harbour Road Sports Centre.
2.87
This EXH is located next to the
new WDII/CWB temporary reclamation area to the north, Harbour Road Sports
Ground to the east, hotels to the west, and commercial/residential buildings to
the south. A fair setback distance can be allowed between station and nearby
buildings to minimise any environmental implication due to the construction
works. Except the residential building to the south, other buildings are
provided with centralised air-conditioning system with fresh air intake at high
level which is not sensitive to noise and less sensitive to dust in general.
With the provision of good site practices and mitigation measures, the
environmental impacts can be kept to an acceptable level.
EXH Option 2 - Harbour Road Alignment
Option
2.88
An alternative EXH location at
·
The unacceptable construction constraints
imposed by the alignment across the critical Fleming Road / Harbour Road
junction, which are deemed to be virtually unbuildable.
·
The insufficient width remaining for a
station in
·
The unfeasibility of constructing a launch
chamber for a TBM at the junction of
·
The need for a major 1800mm diameter sewer to
be diverted out of
·
The unsatisfactory alignment that results in
having a station at this location including curves with radii of 250m back to
back on the approach to ADM.
·
The requirement to demolish part of the
podium and basement structures of the Great Eagle and Harbour Centres.
·
The requirement for modifications to the
foundations of
·
The lack of available space to undertake
support works to Fenwick Pier Street Flyover.
·
The severe disruption caused to traffic in
·
Increased noise and vibration levels on the
HKAPA.
·
Permanent resumption of part of
2.89
Under this option, the proposed
EXH would be surrounded by hotels and commercial buildings on four sides. Owing
to the site constraints, the setback distance to the nearby buildings are
fairly close or even underneath existing building foundation. Ground-borne
construction noise and dust would be key concerns. Extensive controlled
measures shall be kept in place to minimise the environmental impacts.
EXH Option
2.90
This option is similar to the
2.91
Under this option, the proposed
EXH would be located at the middle of the
2.92
The tunnels would also clash with
the foundations of the HKAPA and require major cut and cover construction under
Conclusion to review of
Alternative Locations for EXH
2.93
Based on the constraints listed above
and the aim to provide a direct connection with minimal distance to reduce
construction costs, maintain operational efficiency and to minimise the
passenger travelling time between HUH and EXH, it is proposed that the new EXH
will be constructed at North of Great Eagle and Harbour Centre (Option 1). In
adopting this location the EXH platforms can be connected at strategic
positions.
2.94
In terms of environmental issues,
a fair setback distance can be allowed for scheme at North of Great Eagle and
Harbour Centre to nearby buildings so that environmental implication can be
minimised. With the provision of good site practices and mitigation measures,
the environmental impacts can be kept to the lowest as compared to other two
schemes.
Admiralty
Station (ADM)
2.95
The whole SCL will terminate at
Admiralty in its southern end for the sake of convenient interchange between
Tsuen Wan Line, Island Line and the proposed SIL(E). A
modified ADM is proposed as an interchange station under
2.96
The proposed ADM including
station structures and protection works for interchange with SCL would be
designed and constructed under the SIL(E) project with the aim to minimise
disruption in the area especially Harcourt Garden.
Ventilation
Buildings/Ventilation Shafts
Ventilation
Buildings
Principal Functions
2.97
Ventilation buildings/Ventilation
shafts will serve multiple purposes during the operation of the railway. In
normal operation, they will be the air exchange route for the railway system;
while under emergency circumstances, they will become essential components of
the tunnel smoke control system. As no air
pollutant emissions would be generated from the electrical trains, the
ventilation shafts connecting to the ventilation system of the station would
only emit carbon dioxide (CO2) generated from the breathing of the
passengers and staff. The ventilation
system will be designed for an air exchange rate of 5 litre/person/second in
accordance with MTR Design Manual. As a
result, all CO2 would be exhaled by normal air exchange. Similar to other electrical rail projects
with substantial underground sections (e.g. Kowloon Southern Link), air quality
impact from the operations of ventilation shafts would not be a concern.
2.98
In addition, the ventilation
building can serve as an Emergency Access Point (EAP) and Emergency Egress
Point (EEP). EAPs will be activated in the event of train fire or incident
inside tunnel and will serve as the access points for firemen and police to
access into the rail tunnels, whereas EEP will be the assembly point for
emergency evacuation. Parking areas are provided next to the ventilation
buildings for parking of emergency vehicles. A permanent Emergency Vehicle
Access (EVA) connecting the existing road networks together with the
ventilation building will be used for access by Fire Services Department (FSD)
and police vehicles in case of incident inside the rail tunnels. All these provisions are safety measures for
protection of the SCL passengers. Design criteria developed for ventilation
building are presented in Table 2.3.
Table 2.3 Design
Criteria for Ventilation Building
|
Criteria |
Description |
|
Functional requirements |
·
Location and
orientation within the site of the Tunnel Ventilation Fan (TVF) will be determined
by the connection to the tunnels below the TVF shafts. ·
Allow vehicular
access by relevant authorities, such as FSD, police in case of emergency; and
MTR for maintenance of the railway related facilities to the building. ·
Allow access
from the building into the rail tunnel underground. |
|
Accessibility |
·
Suitable EVA for
fire appliances with water supply and street fire hydrant. Access road should also be capable of
allowing vehicular access and parking for relevant parties, such as FSD,
ambulance, MTR. |
|
Constructability |
·
Avoidance/minimization
of constructing soft ground tunnel due to safety and building settlement
issues. ·
Avoidance/minimization
on construction risks due to uncertain ground condition and long tunnel. |
|
Land Acquisition |
·
Minimization of
affected areas to avoid disruption to local community. ·
Avoidance of
incompatible land use in urban planning |
|
Site Formation Levels |
·
Adequate site
formation level to protect the building and rail tunnels underneath from
flooding. |
|
Environmental |
·
Minimization of
visual and landscape impacts on built-up urban environment. ·
Sufficient
setback distance away from sensitive receivers to minimise fixed source noise
impact on nearby residential premises. |
|
Operational
requirements |
·
Functional
requirements include ventilation provision for the tunnel, power provision
for tunnels, telecom provision and fire service provision. ·
Adequate size of
E&M and building services plantrooms to avoid overheating of mechanical
equipment. ·
Provision of EAP
and EEP. ·
Minimal impact
to adjacent buildings during operation of tunnel ventilation system. ·
Easy maintenance
with heavy plantrooms located on G/F. |
Selection of Ventilation Buildings
Location
2.99
Ventilation facilities are
essential components of a railway providing the necessary air exchange for the
stations and tunnels. However, heavy development in city areas has made
suitable locations for ventilation building increasingly scarce, given that
land selection for ventilation building shall avoid incompatible land use and
private lands as much as possible to achieve minimum land requirement for
ventilation building. Total footprint and height of the ventilation building
should also be minimised as far as practicable. The form, finishing and
plantation around ventilation building should be optimized to eliminate any
landscape and visual impacts. Integrated form of design should be considered
wherever feasible.
2.100
Due to the length of the cross
harbour tunnel, two ventilation buildings are proposed at the northern and
southern end of the harbour crossing tunnel to provide
track ventilation.
The ventilation building on
2.101
After determining the preferred alignment
of the tunnel sections and locations of the stations, careful consideration has
been given to the locations and design of the required ventilation facilities,
cooling systems and other fixed plants to ensure that they are situated away
from sensitive receivers as far as practicable and sufficient mitigation
measures have been incorporated into the design.
Location of South Ventilation Shafts, Plant
Rooms and Emergency Access (SOV)
2.102
The location of the SOV has been
selected to address the following key issues:
·
In view of the court decisions
relating to the PHO, it is considered not justifiable to locate the SOV in
reclamation on the south west corner of the CBTS as envisaged in the “MergeCo
SCL Project Proposal”. An alternative location for the SOV had to be found.
·
The SOV serves the cross harbour
section of the SCL tunnels. It should be located as close as possible to the
point where the tunnels cross the
·
The SOV will accommodate a range
of facilities including tunnel ventilation, emergency access, traction power
and floodgates. The orientation of the floodgates will be perpendicular to the
alignment of the SCL tunnels.
2.103
In order to meet the above
criteria, the SOV is proposed to be located at the Police Officers’ Club (POC)
site in
2.104
As the SOV is co-located with the
POC on the existing POC site, the POC would be demolished and reinstated back
on its present site after the completion of SCL. The design of the SOV should
therefore be integrated with the re-provisioned POC.
2.105
Additionally, the proposed SOV
will serve as an EAP/EEP area. Owing to the relatively large setback distance
with the nearby residential premises, potential environmental concerns such as
noise during construction and operational phases could be minimised.
Location of
2.106
The proposed NOV will be located
at the southern end of the HUH, and just north of the existing
2.107
Due to the simplicity of the NOV,
there is only one proposed scheme which is described above.
Ventilation Shafts
2.108
Ventilation shafts are integral
parts of the ventilation facilities providing for air exchange for the railway
system. As mentioned earlier, alternative locations for ventilation facilities
are subjected to significant site and technical constraints. Land resumption
should be avoided yet the ventilation shafts could not be situated too far away
from the stations and tunnel alignment, otherwise the efficiency of ventilation
would be significantly affected and additional plants and conduits would be
required. The footprint of the whole ventilation facility will need to be
expanded as a consequence.
2.109
The general concerns for
ventilation shafts are the operational noise, height and shape of the shaft and
the effect it has on the surrounding areas. The following possibilities can be
considered when rationalizing the shape and size of the ventilation shafts:
·
Direct noise mitigation measures
including silencers, acoustic louvers and acoustic enclosure where necessary;
·
Use upward discharge louvers
where possible so that louvers can be located 3 meters above ground level,
reducing the overall height of the ventilation shafts;
·
Use architectural fins instead of
louvers so that the required ventilation area can be further reduced;
·
Use top discharge ventilation
shafts for ventilations with horizontal transfers with no direct connection to
the plant rooms, hence possible omission of louvers;
·
Re-shape the ventilation shafts
in order to maximize the louver area and minimizing the height of the
ventilation shafts; and
·
Omit the louver separation
requirement for intake ventilation shafts only.
Ventilation Shafts for EXH
2.110
The ventilation shafts design for
EXH has taken into consideration the urban setting and the sensitive receivers
surrounding the station. Since the ventilation shafts will be visible from
across the harbour, careful consideration and studies have been conducted to
achieve a sculptural form and shape that would be both functional and
aesthetically pleasing.
2.111
Having considered the above
concerns, all the ventilation shafts for the EXH would be located to stand back
from the Great Eagle and Harbour Centre. Amongst them, four top discharge
ventilation shafts would be sited on the west of
Ventilation Shafts for ADM
2.112
Since the new ADM to be designed
and constructed under SIL(E) would contain the
interchange for SCL as well, the associated structures such as ventilation
shafts for SCL would also be provided in the station prior to the commencement
of the SCL tunnel construction. These ventilation shafts would be located at
the north part of the station adjacent to the
Conclusion to the selection of Ventilation Buildings/Vent Shafts
Location
2.113
The site selection for both the
NOV and SOV has avoided incompatible land use and minimised the use of private
lands. Total footprint and height of the ventilation buildings have also been
downsized as far as practicable to prune visual impacts, whereas the form,
finishing and plantation around ventilation buildings and ventilation shafts
have been optimized to enrich aesthetic pleasing. Figure Nos NEX2213/C/331/ENS/M50/21 and NEX2213/C/331/ENS/M50/23 shows the locations of the NOV and SOV,
respectively.
2.114
All the ancillary ventilation
shafts of the EXH and ADM would be situated within the station footprints where
disturbance to nearby sensitive receivers can be reduced to the greatest extent
with the implementation of suitable mitigation measures.
Entrances/Exits
2.115
The new EXH to be constructed
under the Project is anticipated to handle a huge amount of passengers both to
and from streets and interchanging. Passenger movement modelling has been
carried out to test the layout of the station to ensure that localized congestion
areas are avoided.
2.116
Since the EXH would be situated
within a densely developed urban area, the selection of entrance locations
would thus be heavily constrained by the availability of land given that
avoiding resumption of private land shall also be prioritized. Two principal
entrances are developed accordingly for the station given the site constraints
and modelling results of the passenger movement:
·
Entrance A is located on the
south western side of the station box.
·
Entrance B is located at the
eastern end of the station.
2.117
These two entrances (see Appendix 3.2),
both with exits at street level, are also planned for the onward connections to
the WDII landscape deck across
Train System
2.118
Currently, a mixed fleet of MLR
and SP1900 trains are running on the East Rail Line. After the completion of
SCL (HUH-ADM), 9-car SP1900 or equivalent will be adopted. With the shorter
train length, length of platforms and stations can be reduced accordingly. In
general, this will reduce the potential environmental impact (in terms of
extent and/or duration) that would be generated from the Project during both
the construction and operation phases.
2.119 The
selection of trackform types will be based on environmental, operational and
maintenance considerations. Special trackform will be required as mitigation measure
along sections where sensitive receivers of ground-borne noise are present.
These areas include the Harbourfront Horizon in Kowloon Side, Hoi King Court,
Elizabeth House Block C, Renaissance Harbour View Hotel, Grand Hyatt Hotel,
HKAPA and Island Shangri-La Hotel in
Construction Methodologies
2.120 This
section describes the planning of the construction of the project, covering the
key aspects including the envisaged methods
of tunnel construction, works site
requirements and locations,
requirements on barging points for handling excavated
materials, and the sequence of works.
Construction Method for
Land-based Section
2.121
There are several tunnel
construction methods that have been undertaken in
·
bored tunnelling
construction;
·
cut-and-cover
construction;
·
drill and blast
construction;
·
sequential
excavation method; and
·
mini and
Micro-tunnelling
Bored Tunnelling Construction Method
2.122
Tunnel boring machines (TBM) can
be utilised for the soft and mixed ground tunnels with adequate ground cover. The
construction methodology eliminates the need for surface access except at
launching and retrieval shafts thus minimising surface disruption. The machine
can be utilised for short rock sections in the tunnels but is not as efficient
or flexible as traditional drill and blast techniques.
2.123
The selection of the appropriate
tunnelling machine will depend on many issues, including the ground conditions,
contractor’s experience, tunnel size and tunnel
alignment. Given the ground conditions anticipated, a shielded TBM erecting an
un-drained (i.e. sealed) segmental lining would be specified to ensure the
stability of the tunnel face, safety of the workers, minimising the impact to
the groundwater regime and limit surface settlement.
Cut-and-Cover (C&C) Construction Method
2.125
In urban areas, the trench can be
covered with a temporary deck following excavation to maintain traffic
management, if required.
Drill and Blast Construction Method
2.126
Drill and blast methods are the
conventional method of excavation for large face area hard rock tunnels within
2.127
The use of explosive for the bulk
excavation of hard rock is the most efficient method available in the
market. As compared to the cut-and-cover
method, drill and blast construction will involve less construction plant items
and reduce the duration of overall long term noise from the works, thus reduce
impacts on residents living adjacent to the tunnel route, whilst minimising spoil.
2.128
With careful control of the
quantity of explosives, the generated vibration levels on existing structures
(buildings, roads, utilities etc) can be well controlled. In addition, the
duration of a blast is very short (less than 6 seconds) and infrequent (every
12 to 16 hours). With sufficient depth of rock head between the blasting
section and the above ground/hill structure, both airborne and ground-borne
noise impact induced by blasting would not be a concern as compared to the use
of power mechanical plant. Drill and blast is well proven technology for tunnel
construction in hard rock.
Sequential Mining Construction
2.129
Sequential Excavation Method,
also known as the New Austrian Tunnelling Method (NATM), entails dividing the
space to be excavated into segments, then mining the segments sequentially, one
portion at a time, using supports.
Mining equipment, such as backhoes and roadheaders, are used to excavate
the tunnels. This method is slow, but it is especially effective in certain
areas, for example, around a subway or a sewer that cannot be relocated where
special care is required to protect it.
2.130
Whereas TBMs can excavate only a
fixed, generally circular shape, the sequential excavation method allows a
tunnel of any shape to be excavated. The
method is especially applicable for areas, such as cross-over and bifurcation,
in which the tunnel shape or size needs to change.
2.131
To use the sequential excavation
method, the ground must be completely dry and it will be generally necessary to
dewater the ground prior to excavation.
Ground modifications, to strengthen and prepare the soil for tunnelling,
are also common with this method. These
include various types of grouting (injection of chemical or cementing agent
into the soil), ground freezing, and other such treatment. Potential environmental impacts of ground
treatment would mainly relate to construction noise impacts arising from the
use of powered mechanical equipment such as drill rig, grout pump and grout
mixer.
Mini and Micro-tunnelling
2.132
This
method is usually adopted in small scale tunnelling works that would not cause major disturbance to any
above ground operation. As
such, it is usually applied by drainage, sewerage and utility works along or across busy roads, where Temporary Traffic
Management (TTM)
is very difficult.
2.133
Nonetheless,
this construction method is very slow and can only be applicable under small tunnel
diameter limited to 2 to
3 metres only. In general, it is usually
adopted with soft
ground condition. Given that the size of the rail tunnel would be more than 5m in diameter,
mini and micro-tunnelling is considered not applicable to the Project.
Construction Methods for
Marine-based Section
Immersed Tube Tunnel
2.134
The construction of tunnels using Immersed
Tube Tunnel (IMT) method has been the approach used for all existing
cross-harbour transport tunnels in Hong Kong, including the Eastern Harbour
Crossing, Western Harbour Crossing, Airport Railway and the Cross Harbour
Tunnel across
2.135 The standard practice for IMT construction is to dredge a trench in the seabed to remove soft materials, provide a foundation base within the trench, float in precast tunnel units, sink the precast units into the trench and backfill the trench with a rock blanket or other suitable material for protection and anchoring the tunnels. Neither permanent nor temporary reclamation would be required in this method.
Deep/Shallow Bored Tunnel by TBM
2.136
As mentioned in the Bored
Tunnelling Method by TBM for land-based section, selection of TBM depends
largely upon the ground conditions, size and depth of tunnel required. Due to
the particularly onerous tunnelling conditions in the harbour area, the type of
TBM would generally be limited to either an Earth Pressure Balance or a slurry
type shielded TBM, which can be applied to the mixed face conditions that are
present along the cross harbour alignment.
2.137
Based on previous experiences,
high cutter wearing and damage to cutterhead of the TBM would be expected
during the tunnelling works. Daily interventions would thus be required at the
tunnel face for inspection, maintenance and repair, which could only be
performed manually through entering into the pressurized cutterhead by worker
via air locks in the pressure bulkhead of the TBM. The pressure inside this
small and confined space at deep tunnel depths is anticipated to exceed the
safety threshold of 50 psi as stipulated in the Factories and Industrial
Undertakings Ordinance (Cap. 59). Workers working under a pressure exceeding
this limit would be exposed to more hazardous conditions to health and safety.
2.138
Both the Deep and Shallow Bored
Tunnel approach would bear these similar risks to health, life and the Project.
Hence this is an approach that employers, tunnel designers and contractors try
to avoid.
Cut-and-Cover Construction Method
2.139
Slightly differing from the
land-based approach, the C&C method for harbour section would involve
construction of a temporary reclamation area to provide a dry working platform
and the installation of temporary walls propped by steel struts. The soil
between the temporary walls would then be excavated and a reinforced concrete
tunnel box would be constructed to form the permanent structure. Backfilling
would then be undertaken on top of the tunnel and the temporary reclamation
materials would then be removed.
2.140
The width of temporary
reclamation is driven by a few factors, including but not limited to, width of
tunnels plus ventilation ducts, working space for construction of tunnels,
temporary walls and the need to minimise conflicts between the seawall
foundation and temporary wall construction.
Environmental Considerations of
Construction Methods
2.141
Potential environmental issues
associated with each construction method have been reviewed and a summary of
the benefits and dis-benefits of construction methods is presented in Table 2.4.
Table
2.4 Benefits and Dis-benefits of
Construction Methods
|
Construction
Method |
Benefits |
Dis-benefits |
|
Land-Based
Section |
||
|
Cut-and-cover
construction (C & C) method |
·
Accommodation of different
sizes of works areas ·
Can undertake both shallow and
relatively deep tunnelling |
·
More
construction plants will be involved working at-grade such that this is
likely to generate relatively more noise and dust impacts ·
Sensitive receivers will be affected over a longer
construction period ·
Require recycling of bentonite for diaphragm wall
construction ·
Larger amount of spoil required to be disposed
of. Possibility for spoil reuse,
subject to availability of stockpiling space and site conditions |
|
Bored tunnelling construction method |
·
All works underground to minimise the
disturbance to land, wildlife and public activities at ground level
throughout the period of construction ·
Less spoil to be disposed of, as
compared to C&C method ·
Noise impact could be minimised by
provision of temporary decks over the portal ·
Above-ground works only required for
construction of retrieval and launching shafts ·
Comparatively lower vibration impact ·
Less impact on groundwater level with
the installation of water tight concrete tunnel lining in pre-cast segments |
· Requires
additional land for the handling of slurry that needs processing before
disposal ·
Potential adverse ground-borne noise
impact when excavating in rock below existing buildings ·
Higher engineering difficulties ·
Complex interface with existing building
foundation /structures |
|
Drill and blast construction method |
·
All works underground to minimise the
disturbance to land and public activities at ground level throughout the
period of construction; especially when there is a great rock head depth ·
Duration of blasting would be short
(less than 6 seconds) and infrequent ·
Lesser spoil to be disposed of, as
compared with C&C method ·
Above-ground works only required for
portal construction ·
Noise impact could be minimised with the
provision of temporary doors and barriers at the portals and shafts |
·
Vibration might be a concern if
sensitive receivers located in close proximity of the source. It could be
mitigated through blast design and careful monitoring ·
Provision of site explosives magazines
for storage of explosives may be required ·
Transportation of explosives on public
roads |
|
Sequential Mining Construction |
·
Applicable for cross-over and
bifurcation, in which the tunnel shape or size needs to change |
·
Slow ·
The ground must be completely dry and it
will be generally necessary to dewater the ground prior to excavation ·
Ground modifications, to strengthen and
prepare the soil for tunnelling, are also common with this method ·
Potential environmental impacts of
ground treatment would mainly relate to construction noise impacts arising
from the use of powered mechanical equipment such as drill rig, grout pump
and grout mixer |
|
Mini and Micro-tunnelling |
·
Small scale tunnelling that would not
affect any above ground operation ·
No need to apply TTM; especially for
works along/across busy roads |
·
Slow ·
Only applicable to very small scale
utility projects, with tunnel
diameter usually limited to 2 to 3 metres only ·
Usually
adopted at soft ground ·
Tunnelling
from two ends might be required. If there is any failure in the system,
construction of rescue pit might be required at the middle section of the
alignment |
|
Marine-based
Section |
||
|
Immersed
Tube Tunnel (IMT) |
·
No permanent / temporary reclamation would
be required ·
Well established techniques and less
engineering risks compared to Bored Tunnelling |
·
Larger extent of dredging might be
required to ensure sufficient depth for marine traffic |
|
Deep/Shallow
Bored Tunnel by TBM |
·
No permanent / temporary reclamation
would be required ·
Less spoil to be disposed of, as
compared to IMT and C&C method |
·
Higher engineering difficulties. ·
Working in high pressures exceeding the
statutory limit of 50psi would be required ·
Severe risks to health and safety of workers
and project |
|
Cut-and-cover
construction (C & C) method |
·
Accommodation of different
sizes of works areas ·
Can undertake both shallow and
relatively deep tunnelling |
·
Temporary reclamation would be required
in the ·
Larger amount of spoil required to be disposed of |
Selection
of Preferred Construction Methods
2.142
Different approaches would be
selected for different sections of the tunnel alignment with respect to the site-specific
geological conditions and constraints such as the type of soil, rock and the
presence of water, as well as the cost-effectiveness of the tunnelling
methods.
2.143
For the land-based tunnel
sections, sections at Hung Hom Landfall and the west of EXH along with the new
EXH would be constructed by the C&C method. Due to site constraints for
instance significant interfacing with other utilities and structures, choices
of construction method are largely limited by the corresponding engineering difficulties.
In this fashion, C&C method is considered to be the most feasible option
that can allow adequate flexibility to accommodate works area of various sizes
and tunnelling of different depths. Besides, this conventional method will be suitable for some
areas to construct ventilation buildings, ventilation shafts and station boxes.
As land-based excavation as well as the associated dewatering works may result
in the potential drawdown in soil and aquifer layers, preventive measures, such
as installation of groundwater recharge well, use of closed face boring machine with sealed
cutter head, etc, would be taken to minimise the
drawdown of groundwater during the
land-based excavation.
2.144
Starting from south of the IMT
section (ie, breakwater of the CBTS) all the way to the SOV cutting across the
CBTS, C&C method will be adopted. This section will interface heavily with
the CWB project which will commence earlier. In this connection, the two
projects would be integrated with the aims to reduce disturbance to the moorings
and operations of the CBTS as much as possible and minimise impacts on its
users. Use of the temporary reclamation provided by CWB contractor could be
optimized such that repeated dredging and temporary reclamation activities
could be avoided.
2.145
Bored tunnelling method by TBM
would be selected from sections between SOV to EXH and west-end of HKCEC Phase
I to ADM. The advantages of excavation by TBM in rock tunnelling include
relatively higher daily production rates, a more controlled excavation profile
and lower vibration and noise generation as compared with drill and blast
method. However, the TBM
tunnelling would generally involve continuous operation, which would often be
the main source of ground-borne construction noise impact. On
the other hand, due to limited number of suppliers, shortage of manufacturing
capability and overall global demand within the buoyant tunnelling market,
procurement of TBM is expected to take 18 months. In comparison, the daily
production rate of TBM will be relatively higher than that of blasting but the
overall production rate will be lower for short tunnel sections.
2.146
The rock tunnels at the ADM
overrun section would be constructed by drill and blasting method. This method
is not a continuous operation and in general has lower daily production rates
than TBM tunnelling, yet it requires less lead time and is thus more flexible
in terms of programme management. Excavation by this method in rock face is
better in managing ground risk issues but ventilation adits will be required
for supporting the blasting activity.
2.147
For the marine-based tunnel, the
cross harbour section between southern boundary of the Hung Hom landfall and a
point approximately 70m north of the breakwater of CBTS will be constructed
using the IMT method. The reinstated seabed above the IMT would be at a similar
but generally lower level than the adjacent Cross Harbour Tunnel to ensure that
sufficient water depth for marine traffic is achieved whilst reducing the
amount of dredging for installation of the IMT units. Permanent or temporary
reclamation could be avoided along this section.
2.148
The
construction methods for different sections have therefore been selected, based
on engineering, site constraints and environmental considerations. The
preferred construction are summarised in Table 2.5 below and
illustrated in Figure No. NEX2213/C/331/ENS/M50/011. More
detailed descriptions on the construction methods for the alignment from HUH to
ADM are presented in Section 3 of
this Report.
Table
2.5 Preferred Construction
methods
|
Construction
Method |
Sections |
Selection
Reasons |
|
Cut-and-Cover Construction Method |
· From Hung
Hom NOV to Hung Hom Landfall · From the
breakwater of CBTS to SOV · EXH Station
to |
· Engineering
constraints; in particular interfacing with existing buildings/structures
closed to the alignment · Interfacing
with CWB project in the CBTS where the CWB tunnel would be constructed by
C&C method such that environmental impacts and disturbances
to the existing facilities, users and sensitive receivers could be minimised · Protection
to the moorings in CBTS can be maintained |
|
Bored Tunnelling Construction Method |
· From SOV to
EXH Station/Wanchai Sports Ground · From |
· Geological
and engineering considerations · Comparatively shorter construction period · Minimization of works areas so as to minimise
potential disturbance to the environment · Minimization of potential environmental impacts to
the public such as construction dust, airborne noise, and landscape and
visual impacts |
|
Drill
and Blast Construction Method |
· ADM Overrun |
· Great Rock
Head Depth - Geological and engineering considerations · Minimisation of works areas · Minimisation of potential environmental impacts to
the public such as construction dust, airborne noise, and landscape and
visual impacts |
|
Immersed
Tube Tunnel Method |
· From
southern boundary of the Hung Hom Landfall to approximately 70m north of the
breakwater of the CBTS |
· Permanent /
Temporary reclamation can be avoided · Comparatively
well-established method with less engineering risks · Minimization
of potential disturbance to the public |
Works Area(s) / Site Requirements and
Locations
2.149
Generally, works areas/ sites will be
required for the construction and operation of:
·
Stations and entrances;
·
Cut-and-Cover tunnel;
·
IMT tunnel fabrication and
mobilisation;
·
Ventilation buildings and
ventilation shafts;
·
Spoil Disposal Systems;
·
Tunnel Launch / Reception Shafts;
·
Reprovisioning works;
·
Diversion of affected utilities;
·
Underpinning and removal of the
foundations of affected buildings and infrastructure;
·
Temporary traffic management
schemes;
·
Temporary site accommodation and
facilities.
2.150
Since the SCL (HUH - ADM) will
pass along the condensed northern shore of Hong Kong Island, the lack of space available
at the surface for locating entrances and railway facilities and for working
space poses great constraints to the planning, design and construction of the
railway. Identification of available works areas/sites hence represents a
significant challenge to the Project.
2.151
The proposed location and size of
works areas/sites are
wherever possible confined to the site of permanent works, and are selected
based on their accessibility and suitability for construction works and future
permanent structures. The above-ground works areas/sites have been minimised to
reduce land take as far as practicable and avoid the potential environmentally
sensitive areas, such as green belt, coastal protection area,
2.152
To support the construction of
the Project, additional temporary works areas/sites would be required for the
provision of site office, storage of materials, utility, traffic diversion and
barging points for efficient removal of spoil. With a view to minimising
road-based traffic and stress on existing road networks, barging points have to
be set up at waterfront sites to remove the excavated materials generated from
tunnelling and earth works by sea. This will significantly reduce the impact on
road traffic in particular the burden on routes in Wan Chai, Causeway Bay as
well as in the Kowloon side, and hence the impact on nearby environment.
2.153
Details of the works areas/sites requirements and locations
for the Project are presented in Section
3.
Sequence
of works
2.154
It should be understood that the
sequence of construction works carried out under this Project is largely
defined by the need to meet the constraints of the overall programme as well as
engineering requirements. In brief, two approaches are usually adopted for
arranging the sequences of works, namely the concurrent construction sequence and
phased construction sequence.
2.155
Concurrent construction sequence
involves various construction activities occurring at the same time. The
environmental benefit of this approach would result in a shorter construction
period and hence the duration of impact due to the construction activities.
However, the magnitude of the overall environmental impact could be
intensified. Whereas the phased construction sequence involves construction
activities being carried out one followed by another. This would help reduce
the magnitude of the overall impacts, yet at the expense of prolonged
construction period.
2.156
As the two approaches have their
environmental benefits and drawbacks, a balancing approach with a combination
of both will be adopted in different stages of the construction period to
alleviate the potential environmental impact and to meet the target
commissioning date.
2.157
Amidst the multiple construction
activities to be undertaken, the sequence of the tunnelling works in the CBTS
are particularly critical, not only to the determination of the overall
construction programme, but also to the cumulative environmental impacts on
surrounding receivers due to its interfacing with the CWB project in the
region.
Sequence of Works at CBTS
2.158
It has been concluded in Section
2.82 above that the IMT along the Western Corridor option, which passes through
the CBTS and lands on Hong Kong Island at the SOV, would be the most preferable
alignment option for the SCL (HUH – ADM) based on all-round considerations. One
of the key aspects under this scheme would be the coordination of interfaces
between the SCL tunnel works and the CWB project in the CBTS area.
2.159 In determining the sequence of SCL tunnelling works
adjacent to and within the CBTS, due consideration has been taken of views expressed
in consultation with the District Councils, the public and affected
stakeholders. The principal concerns were:
·
The SCL works should be integrated with the CWB works
where possible with a view to minimizing the duration of construction.
·
Stakeholders do not want to have any more moorings
reprovisioned out of the CBTS (i.e. over what CWB has already proposed).
·
Adequate
separation should be provided between moorings and construction equipment for
the required marine works. The level of protection provided by the existing
breakwater should be maintained.
2.160 The construction of the SCL tunnels through the CBTS
would be carried out in stages, using the same approach to dealing with the
moorings as developed under the CWB project.
Whilst it is envisaged that the SCL works within the CBTS can be
completed within 18 months of completion of the CWB works within the CBTS, the
full area of temporary reclamation would not be in place up until that time.
Illustrative construction staging plans for the works through the CBTS are
shown in Appendix 2.2.
2.161 Key aspects of the staging are:
·
The section of
SCL tunnels which run above the CWB tunnel and to the south of the CWB tunnel within
the CBTS will be constructed under the CWB construction contract.
·
Construction of
the SCL tunnels immediately to the north of the existing breakwater will
commence during Stage 3 of the CWB construction to allow the connection between the immersed tube tunnel and the cut-and cover-tunnel to be
completed.
·
Construction of
the SCL tunnels through the breakwater and into the northern part of the CBTS
would commence once the CWB Stage 3 works are completed. These works will extend as far as possible
into the CBTS without affecting CWB construction or requiring additional
moorings to be relocated out of CBTS. Earlier commencement of these works is
not possible without additional moorings being relocated out of CBTS.
·
The final stage
of SCL construction would commence once all of the CWB works within the CBTS
are completed. These would take a
further 18 months to complete.
2.162 The durations of the temporary reclamation staging for
SCL works from the time of starting seawall construction and filling above the
seabed to the time when the temporary reclamation is removed and the seabed
reinstated will vary from 15 months to 28 months, except for a small area near
the shoreline (Area SCL 1.4 in Appendix 2.2) which
will stay for a longer period.
2.163 Upon completion of each stage, the temporary
reclamation would be removed and the seabed reinstated. There would be some overlapping of temporary
reclamation between stages. At any one
time the maximum area of temporary reclamation for SCL would be around 1.6ha
(excluding temporary reclamation for CWB).
2.164 Therefore, whilst the overall area of temporary
reclamation required for SCL construction at the CBTS is approximately 2.2ha,
the additional affected area of the harbour in respect of temporary reclamation
in the CBTS will only be around 1.6ha for approximately 8 months. This would be reduced to approximately 0.8ha
for the final 10 months of SCL construction after completion of the CWB.