Comparison of the SE Jetty Options for the South Soko Location

F1 Construction of Site Formation Works

F1.1 Assessment Parameters

In order to assess the engineering implications of the on-land formation works at Option 3 and 3D at South Soko the following engineering assessment parameters have been considered: -

· Volume of excavation in soil

· Volume of excavation in rock

· Volume of soil and rock to be removed from site

· Impact of formation works on the overall construction programme

· Extent of slope stabilisation measures required

· Slope maintenance requirements

· Potential future hazard from slopes

· Blasting restrictions

F2 Volume of Excavation in Soil and Rock

F2.1 Option 3 – SE Jetty (3 Tanks Within Cuttings)

An estimated total volume of 0.52 x 10⁶m³ of soil and 1.77 x 10⁶m³ of rock material will be excavated from the existing slope cuttings. The total excavated volume will be about 2.29 x 10⁶ m³.

F2.2 Option 3D – SE Jetty (2 Tanks Within Cuttings)

The relocation of the provisional third tank to the platform area to the south of the northern hill will reduce the amount of cutting required. This however will be slightly offset by the excavation needed at the hillside near the loading and unloading berth for the purpose for siting the maintenance workshop, control room and administration building.

It is estimated that a total volume of 0.50 x 10⁶ m³ of soil and 1.56 x 10⁶ m³ of rock material will be excavated from the existing slope cuttings. The total excavated volume will be about 2.06 x 10⁶ m³.

F3 Volume of Spoil to be Removed from Site

F3.1 Option 3 – SE Jetty (3 Tanks Within Cuttings)

A minimum surplus of approximately 0.12 x 10⁶ m³ will be created from the site formation works.

F3.2 Option 3D – SE Jetty (2 Tanks Within Cuttings)

Due to the reduced quantity of excavated material generated, the quantity of spoil to be removed is approximately 0.10 x 10⁶ m³.

F4 Extent of Slope Stabilisation Measures

F4.1 Option 3 – SE Jetty (3 Tanks Within Cuttings)

The cuttings for the tank structures will extend to a height of approximately 72m and will be predominantly in rock. The face area of the slope is estimated to be approximately 22,000 m². The cuttings for the pipe trestle will extend to a height of approximately 20m and the face area of the slope is estimated to be approximately 10,000 m². The rock mass forming the hillside will likely be jointed and fractured for which extensive stabilisation measures will be required including rock bolting, dowelling and buttressing as necessary to prevent toppling, wedge and sliding failures. The soil slopes will be similarly stabilised with soil nails. The natural slope above the cut slope will also require inspection and possibly some stabilising works. Appropriate drainage measures will be required to drain surface run-off away to reduce infiltration into the slopes which could otherwise lead to high water pressure build up and potential failure.

F4.2 Option 3D – SE Jetty (2 Tanks Within Cuttings)

The cuttings for the tank structures will extend to a height of approximately 72m and will be predominantly in rock. The face area of the slope is estimated to be approximately 14,000 m². The cuttings for the pipe trestle will extend to a height of approximately 20m and the face area of the slope is estimated to be approximately 10,000 m². The stabilisation measures required for the soil and rock slopes will be similar to Option 3, albeit in a much smaller scale.

F5 Slope Maintenance Requirements

The cut slopes created for the site formation works are large and extensive i.e., >5m height and will therefore be subject to registration with the government. The slopes will be categorised as Category 1 in view of their consequence to life. As such the slopes will be subject to Routine Maintenance Inspections each year and Engineer Inspections for Maintenance every 5 years. The slope maintenance requirements may therefore be considered as being similar for both options, with Option 3D having the lower risk of the two as the slope area involved in smaller due to the relocation of the provisional third tank.

F6 Long Term Slope Hazard

The terminal facility will be located adjacent to a high cut slope in soil and rock with an extensive natural slope above it. Even with the slope stabilisation measures and long term maintenance activities there is a risk of future instability. The risk is classified as being similar for both options, with Option 3D having the lower risk of the two as the slope area involved in smaller due to the relocation of the provisional third tank.

F7 Impact of Site Formation Works on Construction Programme

F7.1 Option 3 – SE Jetty (3 Tanks Within Cuttings)

The construction of the storage tanks is on the critical path for the construction of the receiving terminal facility. The excavation within the hillside to create the formation for the tanks is therefore also on the critical path. Assuming an excavation rate of 42,000m³ per week the excavation works will take approximately 290 days.

F7.2 Option 3D – SE Jetty (2 Tanks Within Cuttings)

Similar to Option 3, the excavation within the hillside to create the formation for the tanks is on the critical path. Assuming an excavation rate of 42,000m³ per week the excavation works will take approximately 250 days. The impact on the programme is therefore classified as lower than of Option 3.

F8 Blasting Restrictions

The South Soko Island site is approximately 6km south of Lantau Island. There are no significant residential areas near to the site. The only restriction to blasting will be with the supply of emulsion explosive to the site, which is controlled by the Mines and Quarries Department of Hong Kong. However, given the remoteness of the site it is likely that a magazine storage and explosive manufacturing plant will be established on the site, which will overcome this issue. Restrictions to blasting are therefore considered to be low for both options.

F9 Summary for Site Formation Construction

A summary of the parameter values and relative scores derived from the engineering assessment for the site formation construction is given in Table A1 below.

Table F1 - Summary for Site Formation Construction

Parameter	Option 3 (SE Jetty – 3 Tanks Within Cuttings)	Option 3D (SE Jetty – 2 Tanks Within Cuttings)
Volume of excavation in soil (10^6m³)	RS = 3 (0.52)	RS = 4 (0.50)
Volume of excavation in rock (10^6m³)	RS = 3 (1.77)	RS = 4 (1.56)
Volume of soil to be disposed of (10^6m³)	RS = 3 (0.12)	RS = 4 (0.10)
Volume of rock to be disposal of (10^6m³)	RS = 3 (0.)	RS = 3 (0)
Impact on construction programme (months)	RS = 3 (10)	RS = 4 (8)
Slope stabilisation measures required	RS = 3	RS = 5
Slope maintenance	RS = 3	RS = 5
Future slope hazard	RS = 3	RS = 5
Blasting Risks	RS = 3	RS = 5

F10 Conclusion for Site Formation Construction

It is clear by directly comparing the results of the parameters for each layout in Table F1 above that Option 3D would generate less excavated material and have a smaller impact on the construction programme. Hence Option 3D is the preferred layout.

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