Construction of Site Reclamation Works for the
B1 Construction of Site Reclamation Works
In order to construct the proposed LNG Receiving Terminal facility
it is necessary to form at least 25ha of
land area. Where the available land
area, even with excavation is insufficient it is necessary to undertake
reclamation to make up the difference. A
comparison of the reclamation requirements for the three different layout options
at
At all locations the reclamation areas are expected to be underlain by a significant thickness of compressible marine deposits. Using the partially dredged method these clays will be largely left in place during the reclamation process.
The
B1.2 Assessment Parameters
In order to create a cost effective and sustainable site formation, a balance between cut and fill quantities is required. A combination of on-shore cutting and off-shore reclamation is typically adopted unless other considerations do not permit this. Generally for each layout a level platform of +6mPD will be created to be sufficiently above the high tide level. The formation of the reclamation will involve the filling of significant quantities of soil and rock material which will need to be sourced either from the land excavation works or from external sources depending upon the balance achieved. In order to assess the engineering implications of the off-shore reclamation at each of the sites the following assessment parameters have been considered: -
· Area of sea reclaimed.
· Volume of dredging material.
· Volume of filling material and how much is imported.
· Length of coastline affected.
· Length of seawall required.
· Time for dredging and filling and for consolidation.
· Ground improvement measures.
B2 Area of Sea Reclaimed
B2.1 Option 1 – Base Case
Land will be reclaimed immediately to the west of the existing platform previously formed for the Vietnamese Refugee Detention camp for the proposed Utility Pier, and to the east of the platform for the proposed loading and unloading berth.
The total area to be reclaimed is estimated to be about 16,700 m².
B2.2 Option 2 – Full Reclamation
A significant area will be reclaimed to the west of the existing platform to house the proposed turbine substation, utility area and layout area. The area to the east of the platform will be for the loading and unloading berth.
The total area to be reclaimed is estimated to be about 130,000 m².
B2.3 Option 3 – SE Jetty
The reclamation profile is identical to Option 1.
The total area to be reclaimed is estimated to be about 16,700 m².
B3 Volume of Dredging and Filling Materials
B3.1 Option 1 – Base Case
The estimated total volume of dredging and subsequent reclamation fill required to form the terminal area including the seawall are as follows: -
Volume of dredging = 0.18 x 106 m³
Volume of reclamation fill = 0.52 x 106 m³
B3.2 Option 2 – Full Reclamation
The estimated total volume of dredging and subsequent reclamation fill required to form the terminal area including the seawall are as follows: -
Volume of dredging = 0.22 x 106 m³
Volume of reclamation fill = 0.79 x 106 m³
B3.3 Option 3 – SE Jetty
The estimated total volume of dredging and subsequent reclamation fill required to form the terminal area including the seawall are as follows: -
Volume of dredging = 0.18 x 106 m³
Volume of reclamation fill = 0.52 x 106 m³
B4 Reuse of Excavated Material
For the use of excavated materials within the reclamation refer to Annex A1.
The reclamation can be formed using the excavated material from the site formation works, which are expected to comprise largely moderately to slightly decomposed granite material. However, in order to achieve the required grading for reclamation standards it will be necessary for the material to undergo primary, secondary and possibly tertiary crushing with associated sorting and mixing off-site at an appropriate stockpile site.
B5 Length of Seawall and Natural Coastline Affected
B5.1 Option 1 – Base Case
The site formation will require a total seawall length of 1,100m only to form the boundary of the proposed terminal. A total of 1,370m of existing coastline, of which 450m is natural coastline, will be affected by this construction.
B5.2 Option 2 – Full Reclamation
The site formation will require a total seawall length of 1,360m only to form the boundary of the proposed terminal. A total of 1,520m of existing coastline, of which 600m is natural coastline, will be affected by this construction
B5.3 Option 3 – SE Jetty
The site formation will require a total seawall length of 1,100m for the boundary of the proposed terminal. A total of 1,370m of existing coastline, of which 450m is natural coastline, will be affected by this construction.
B6 Time for Construction
B6.1 Option 1 – Base Case
It is estimated 11 months will be required to complete the dredging and filling operation for the reclamation works.
B6.2 Option 2 – Full Reclamation
It is estimated that the dredging and filling operation will be completed within 14 months.
B6.3 Option 3 – SE Jetty
It is estimated 11 months will be required to complete the dredging and filling operation for the reclamation works.
B7 Ground Improvement and Time for Consolidation
Since the marine deposits are largely left in place under the reclamation, ground improvement work will be required in the form of vertical drains plus surcharge pre-loading. This significantly reduces the ongoing creep settlement within the sand fill layer and speed up the consolidation process.
B7.1 Option 1 – Base Case
It is estimated 4 months will be required to complete the surcharging and consolidation process for the reclamation works.
B7.2 Option 2 – Full Reclamation
It is estimated that the surcharging and consolidation process will be completed within 14 months.
B7.3 Option 3 – SE Jetty
It is estimated 4 months will be required to complete the surcharging and consolidation process for the reclamation works.
B8
Summary for Site Reclamation
Construction
A summary of the parameter values and relative scores assigned to each from the engineering assessment for the site reclamation construction is given in Table B1 below.
Table B1 - Summary for Site Reclamation
Construction
|
Parameter |
Option 1 |
Option 2 |
Option 3 |
|
Area of reclamation |
RS = 3 (16.7) |
RS = 1 (130) |
RS = 3 (16.7) |
|
Volume of dredging material (106 m³) |
RS = 3 (0.18) |
RS = 1 (0.22) |
RS = 3 (0.18) |
|
Total volume of fill material required |
RS = 3 (0.52) |
RS = 1 (0.79) |
RS = 3 (0.52) |
|
Volume of imported fill |
RS = 3 (0) |
RS = 1 (0.18) |
RS = 3 (0) |
|
Length of natural coastline affected (m) |
RS = 3 (450) |
RS = 1 (600) |
RS = 3 (450) |
|
Length of artificial coastline affected (m) |
RS = 3 (920) |
RS = 3 (920) |
RS = 3 (920) |
|
Length of seawall required (m) |
RS = 3 (1,100) |
RS = 1 (1,360) |
RS = 3 (1,100) |
|
Construction time for dredging and filling |
RS = 3 (11) |
RS = 2 (14) |
RS = 3 (11) |
|
Time for consolidation after construction |
RS = 3 (4) |
RS = 1 (14) |
RS = 3 (4) |
|
Need for ground improvement |
RS = 3 |
RS = 3 |
RS = 3 |
RS = Relative Score
B9 Scoring for Site Reclamation Construction
Each of the parameters summarised above in Table B1 have been scored in accordance with the procedure described in Section 2.1. 3. The results for each of the layout options are shown below in TableB3. The table also shows the total score for each layout derived using the relative weightings given in Table 2.4.
Table B3 – Scoring for Each Layout
Option for Site Reclamation Construction
|
Parameter |
Weight |
Option 1 |
Option 2 |
Option 3 |
|||
|
Score |
WS |
Score |
WS |
Score |
WS |
||
|
Area of reclamation |
0.10 |
3 |
0.30 |
1 |
0.10 |
3 |
0.30 |
|
Volume of dredging material |
0.20 |
3 |
0.60 |
1 |
0.20 |
3 |
0.60 |
|
Total volume of fill material |
0.05 |
3 |
0.15 |
1 |
0.05 |
3 |
0.15 |
|
Volume of imported fill |
0.20 |
3 |
0.60 |
1 |
0.20 |
3 |
0.60 |
|
Length of natural coastline |
0.15 |
3 |
0.45 |
1 |
0.15 |
3 |
0.45 |
|
Length of artificial coastline |
0.05 |
3 |
0.15 |
3 |
0.15 |
3 |
0.15 |
|
Length of seawall required |
0.10 |
3 |
0.30 |
1 |
0.10 |
3 |
0.30 |
|
Construction time for dredging &
filling |
0.05 |
3 |
0.15 |
2 |
0.10 |
3 |
0.15 |
|
Time for consolidation after construction |
0.05 |
3 |
0.15 |
1 |
0.05 |
3 |
0.15 |
|
Need for ground improvement |
0.05 |
3 |
0.15 |
3 |
0.15 |
3 |
0.15 |
|
Total Weighted Score |
|
3.00 |
|
1.25 |
|
3.00 |
|
|
Normalised Score |
5.00 |
2.08 |
5.00 |
||||
From the result of the assessment of all parameters for site reclamation construction, it is clear that layout options 1 and 3 are preferred.