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Advisory Council on the Environment

Strategic Sewage Disposal Scheme - Stage I Information Note on the Progress of the Tunnelling Works

 

(ACE Paper 31/99)
for information by circulation

This information note summarizes the progress of the tunnelling works under Strategic Sewage Disposal Scheme - Stage I for the quarter ending on 30 June 1999. The progress of the tunnelling works up to end June 1999 is as follows :

 

Tunnel Length of Tunnel(m) Excavation
completed up
to last quarter
Excavation
completed in
this quarter
Excavation
completed up to date
Western Tunnels
Tunnel from Kwai
Chung to Tsing Yi
779 779 (100%) N/A 779 (100%)
Tunnel from Tsing
Yi to Stonecutters
Island
3580 1255 (35%) 722 (20%) 1977 (55%)
Eastern Tunnels
Tunnel from
Tseung Kwan O to
Kwun Tong
5332 1642 (31%) 1560 (29%) 3202 (60%)
Tunnel from Chai
Wan to Kwun Tong
4830 903 (19%) 261 (5%) 1164 (24%)
Tunnel from Kwun
Tong to To Kwa
Wan
3572 1294 (36%) 527 (15%) 1821 (51%)
Tunnel from To
Kwa Wan to
Stonecutters Island
5495 1005 (18%) 785 (14%) 1790 (32%)

2.In total, 10.7km (45.5%) of the 23.6km tunnel system has been excavated up to end June 1999. The tunnelling works continue to pick up progress steadily and a total of 3.8 km (16.5%) has been excavated during the last quarter.

3.Progress in the tunnel from Chai Wan to Kwun Tong has been slow during this quarter. The contractor is excavating through a stretch of difficult ground with large water inflow and this has slowed down the progress. This stretch of difficult ground was first encountered in mid March 1999. The excess inflow of water has caused some minor subsidence at a small section of seawall and an adjoining road in Chai Wan. Immediate actions were taken by the contractor and the subsidence was quickly stabilized in early April 1999. The contractor is making great efforts to improve his working methodology to deal with the difficult geological conditions. Progress is expected to pick up after going through this area of difficult ground.

4.Steady progress has been maintained in the excavation of the tunnel from Kwun Tong to To Kwa Wan during the first two months of this quarter and the tunnel is now about 51% completed. However, a major mechanical problem with the tunnel boring machine occurred on 3 June 99 and excavation in this tunnel has stopped since then. It is estimated to require about four to five months to rectify the problem. Whether the delay will affect the completion date of the SSDS Stage I will depend on the actual time eventually used for repairing the machine.

5.Although there remains the risk of encountering difficulties as the works proceed, we are confident to be able to handle the difficulties as they arise. We are working hard to achieve the completion of the Strategic Sewage Disposal Scheme - Stage I project as a whole in the year 2000. The problem with the tunnel boring machine in the tunnel from Kwun Tong to To Kwa Wan may cause some slight delay to this target completion date. We are actively exploring means to mitigate the impact.



Drainage Services Department
August 1999


 

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