Hong Kong is a Special Economic Region of China. The population has increased rapidly and is set to grow from 6.81M in 1999 to 8.1M in 2011. To cater for this increasing popula-tion, new towns have been constructed in the New Territories. The West Rail Phase 1 project will improve transport and communication between the central business district in Hong Kong and Kowloon and the residential areas in the New Territories.
General manager of West Rail construction for the KCRC Jaya Jesudason put the project into historical context. From 1888 to 1910, approximately 50km of railway was constructed followed by a gap of 60 years when no new railway infrastructure was built. Since 1974, there has been an increasing provision and a further 155km has been constructed, of which West Rail represents around 20%.
The scheme requires nine new stations of which Nam Cheong and Mei Foo interchange with Mass Transit Railway (MTR) and Yeung Long and Siu Hong with the North West New Territories light rail system. The urban nature of Hong Kong, coupled with the mountainous relief, has resulted in limited open surface alignment as shown below.
The project management team was assembled in 1998 to look after construction and to clear 382 hectares of land, including demolishing large multi-storey buildings. The project estimate is HK$64bn (US$8.21bn) and the out-turn cost is targeted to be HK$57bn (US$7.31bn) The project represents the largest single infra-structure investment in Hong Kong to date.
Construction started in October 1998 and by January 2001 was over 40% complete. The first key date, access for track, is August 2001.
The construction contracts included: Nam Cheong Interchange station, a Balfour Beatty-led joint venture. A key aspect of this contract was the construction of the station below an existing elevated operational railway; Mei Foo station, a Kier-led joint venture. The main constraint was the limited space available for construction in the urban environment and the environmental restrictions caused by proximity to residential areas; Tsuen Wan West station, a Kier joint venture and a cut and cover station within reclaimed land; Yeong Long station, Amec Construction. An elevated station which is adjacent to a high-rise housing estate. The station was founded in marble and required the construction of bored piles up to 100m deep. Piling is almost complete and the structure is about to commence; Long Ping which is located over a storm water channel with construction limited to the dry winter months between October and March; and Siu Hong station, constructed over a drainage channel (Nullah) foundation, which needs to be completed in the six-month dry season.
The 13.4km of viaduct runs between six elevated structures through residential areas and noise abatement measures are required. This is in glued segments cast in China and transported by road.
Jesudason explained the construction management organisation. The employer delegated powers to the KCRC project management team based on site. The detailed design consultant (DDC) had both design responsibility and acted as the engineer under the contract. The resident site staff included employees from KCRC’s project management team and the consultant’s resident site staff. KCRC were keen to promote a partnering approach between KCRC, the designer and the contractors to resolve problems as they arise.
The main tunnels are: the 5.5km long Tai Lam tunnel, which is the longest transportation tunnel in Hong Kong and is being excavated by drill and blast; and the 3.6km long Kwai Tsing tunnels.
Tai Lam Tunnel DB 320
The 5.5km long rock tunnel is being constructed by a Nishimatsu/Dragages joint venture. The contract value is HK$1790M ($230M) and was awarded as design and build. It includes two ventilation buildings and 350m of cut and cover tunnel.
The conforming design comprised a twin bore with emergency cross passages at 60m centres. The joint venture proposed an alternative which comprised a 13.5m wide tunnel with a central dividing wall. An extensive site investigation was undertaken prior to tender. This had located the 50m wide Ho Pui Fault. This was negotiated using arch rings and shotcrete.
Some 550m of the tunnel has a span of up to 17m to accommodate crossovers. There are cross passages and side niches and lining generally comprises 300mm of un-reinforced sprayed concrete.
Nishimatsu started construction from the north portal using two three-boom Atlas Copco drilling jumbos and dump trucks to remove excavated material. Dragages started from the south portal.
Before they were able to start the rock drive a section of cut and cover tunnel had to be constructed. This went under an existing viaduct through the existing foundations. These were replaced with a beam supported on new bored piles. The preparatory works took a year before rock tunnel excavation could start using two three-boom Montabert drill jumbos, a crawler mounted mobile crusher and a conveyor to remove the rock material.
The two methods achieved similar production rates of 50m/week with the rock crusher and conveyor system having a shorter cycle time but being more prone to breakdowns. Breakthrough occurred in April 2001.
Charles Perrier spoke on Contract KCRC DB 320 – Kwai Tsing Tunnels and credited Atkins China as the designer and Ove Arup and Partners as the checking engineer for the contract.
Kwai Tsing tunnels comprise three sections of tunnel: Ha Kwai Chung tunnel, 1.7km constructed in rock using drill and blast; Tsing Tsuen Tunnel, 1.78km constructed in soft/rock using a TBM; Tsing Tsuen tunnel, 0.12km as a cut and cover tunnel.
The conforming design required:
The JV successfully proposed an alternative TBM solution which:
The ground level along the alignment was approximately 5m AOD. The reclaimed ground was 20 years old with a water table 2m above, overlying alluvium which overlay completely decomposed granite. Sections of the tunnel were to be excavated in ground ranging from soft alluvial marine sands and clays, a full face of granite with a UCS strength of 80 to 250 MPa and mixed face conditions in between. The tender investigation confirmed the feasibility and viability of a TBM solution.
The successful tender scheme increased the length of the twin bore 7.625m internal diameter Tsing Tsuen tunnel to 1.84km and the cross passage spacing was revised to 90m following risk assessments. The tunnel lining comprised 400mm thick by 1.8m long reinforced pre-cast concrete segments, cast on site using grade 50 concrete with a design life of 120 years.
An earth pressure balance TBM (EPBM) was used to cater for the range of ground conditions envisaged. The machine was designed to work in open mode for full face rock conditions with a belt conveyor and closed EPBM mode in soft ground using a screw conveyor. The changeover took two to three days. The TBM was designed by NFM under licence from Mitsubishi, and the main components manufactured in France and Europe. All steel structure fabrication and assembly of the TBM was undertaken in Shanghai by SHMP. The 7.5m dia TBM was transported from Shanghai to the site by sea as the site was close to the harbour.
The screw conveyor removed spoil from the base of the cutterhead and the belt conveyor from the centre of the face. The TBM operation was controlled electronically with parameters and pressures to monitor the operation of the machine displayed and recorded. A special guidance system was used to control the alignment. The work site had stringent environmental controls applied with a night time noise level limit of 45dB(A). The working shaft was acoustically covered to meet the noise and dust limits.
The programme for TBM manufacture included contract award to NFM, 20 November 1998; start manufacture in Shanghai, April 1999; arrival in Hong Kong, 10 February 2000; start first drive 6 April 2000, completed 13 December 2000; start second drive, March 2001; completion forecast September 2001.
The production rates for the first drive are: overall average progress 220m/ month; in rock (open mode) best week 115m, best month 410m; in soft (closed mode), best week 106m, best month 320m.
A breakdown of the production figures for open and closed mode TBM operation is given in the pi charts (below). The high level of intervention required under closed mode 27% was due to the greater cutter wear when going through mixed face conditions in the closed mode.
Related Files
Comparison of open mode and closed mode TBM
Route and main construction types along West Rail
Railway development in Hong Kong
