West Rail – Part 5 Construction – Southern Section
Tymon Mellor: With the approval of the environmental impact assessment in March, 1998 and endorsement of the Project Agreement in September 1998, work on the construction of West Rail could commence. The West Rail project management team had already started tendering the key construction packages and with the approval of the scheme, the initial packages were awarded allowing a ground breaking ceremony to be held in October, 1998. Now all they had to do was build one of the most complex projects implemented in Hong Kong and open the railway before December 2003, all within budget.
Construction of a new metro requires many different technical skills and each party must implement their own works while coordinating with adjacent parties. It is not possible to resolve all these interfaces at the design stage as some relate to methods of construction, while others relate to equipment selection, design of software or coordination of multiple parties, all of which can only be determined once the relevant contractors are on board. Many clients see each one of these interfaces as a potential commercial dispute and try to minimise the associated risks by reducing the number of packages by increasing their multidisciplinary scope of works, transferring the responsibility of resolving interfaces to the contractors and their respective sub-contractors. This approach is popular in the middle east and Australia where typically less than five packages are awarded for the construction of a metro.
This approach reduces client managed interfaces but removes the client from the selection process and obscures transparency on progress, particularly when key elements of the works are undertaken off-site. An alternative approach is to split the works into multiple packages, typically infrastructure or civil works and the respective specialist electrical and mechanical systems works. The civil works are then divided in to geographical packages of a size suitable for the local contracting market. Where consistency is required across the line for operational and maintenance reasons, separate line wide supply and installation packages can be utilised for equipment and systems such as lifts, escalators, master key system and door locks, electronic access control etc.
Within the civil works packages, two implementation approaches were adopted on West Rail. For the tunnelling works, where the construction methodology influences the tunnel design, the contractor was made responsible for the design of the works, i.e. a design and build approach. For the remaining packages, KCRC undertook the design and the contractors were responsible just for the construction along with their temporary works design. This approach provided design consistency across the line and ensured sufficient time for the design of the complex stations to meet the operator’s needs, passenger expectations and statutory requirements. The civil works were broken down into 17 construction contracts and the system/supply works into 20 packages.
West Rail Civil Works Packages
West Rail Systems and Procurement Packages
In addition to the main packages, several specialist packages were identified to support the works.
West Rail Specialist Packages
The project required the mobilisation of thousands of people to design and construct the works. Fortunately, with the corresponding completion of the Airport Core Programme, there was significant capacity within the industry to support West Rail. This resulted in competitive tender prices and the availability of experienced design and construction teams.
West Rail Project Manpower (Feb 2002)
Tunnelling is notoriously dangerous and risky. It has been described as an art rather than a science due to its complexity and variability, and it is thus a very specialist field in the construction industry. Tunnelling in Hong Kong is particularly difficult and with a chequered history due to the highly variable ground conditions and the potential for large quantities of ground water. Where tunnels were required through competent rock, a traditional drill and blast approach had been adopted. This involved drilling holes in the rock and blasting the material, and this approach was used for most of the territories water and road tunnels. Where the tunnel was in soft material and at a relatively shallow depth, a cut and cover approach was usually adopted, requiring a large surface excavation to allow the construction of the tunnel box using in situ concrete. In some areas, this approach was not practical and soft ground mining had been adopted. This required the use of grouting and compressed air to stabilise the ground to prevent water ingress. Both these methods were used on the original MTR line with mixed results.
In the mid-1990s, the tunnelling industry was going through a period of evolution as the benefit of improved engineering methods, materials development, and computer controls were changing the way tunnels were constructed. As noted at the time by the KCRC construction manager for tunnels Howard Mckay, “In the last 20 years we have gone from the old airlegs and handheld drills and stick gelignite; now it is normal to have mobile jumbos and to use slurry explosives, which has improved the production.” With the new equipment and explosives, the West Rail contractors planned to excavate the large 110m2 face at a rate of 150m/month, compared to 80m/month for the Lion Rock Tunnel with a face area of 77m2 which had been constructed 30 years earlier.
DB-350 Drilling Jumbos
For West Rail, the biggest change was in the area of soft and mixed ground tunnelling as a result of the development of the Earth Pressure Balance (EPB) tunnelling machines by the Japanese. This approach to tunnelling had been developed during the 1980s and came to international attention when in 1988 a Mitsubishi EPB Tunnel Boring Machine (TBM) was selected for the Channel Tunnel. The machine used a screw conveyor to remove material from the cutter head; by controlling the rate of material removal and the advance of the machine it was possible to support the surrounding ground and avoid water ingress. Although this technology had been around for many years, a number of new developments including the use of reliable computer controls and in particular the adoption of ground conditioners to modify the properties of the spoil, allowed tunnels to be constructed safely in the cohesive ground typically found in Hong Kong.
DB-320 TBM ‘Mulan’
Two tunnelling contracts were procured, DB-320 between Mei Foo and Tsuen Wan West consisting of 3.6km of rock tunnel and cut and cover tunnel, and DB-350 from Tsuen Wan West to Kam Tin, a rock tunnel 5.5km long. The alignment was fixed but the contractors could choose their methods of construction.
D&B Contract Advert (November 1997)
CC-402 Nam Cheong Station & Tunnels
Nam Cheong Station was the southern terminus for West Rail Phase I, located on the West Kowloon Reclamation, a recently completed ‘sand pit’ with no established community. The station was designed as an integrated KCR and MTR station with at-grade side platforms and a common underground concourse. It was the first combined station between different railway operators, providing convenient passenger interchange between West Rail and the recently completed MTR Tung Chung Line.
Proposed Location for Nam Cheong Station (1998)
During the construction of the MTR Tung Chung Line, a 1m deep slab was cast below the MTR tracks as enabling works to support the construction of the future station. The West Rail contractor had to connect into the slab and support it, allowing excavation for the station box below.
Cross Section Nam Cheong Station
The station overlies a deep rock head profile of up to 100m in depth. Piling to this depth was a risk for traditional end bearing bore piles and so the contractor proposed a grouted friction barrette solution as an alternative. This approach was a cost-effective foundation solution and the ﬁrst time that grouted barrettes had been used in Hong Kong. The KCRC design for the basement utilised a diaphragm wall to form the basement cofferdam, but the contractor also proposed an alternative top-down construction method with a sheet pile wall for the 10m deep basement.
Nam Cheong Top-Down Construction
A cast in-situ reinforced concrete frame and slab superstructure was built above the basement two storeys high, and the top level was to form the podium of a proposed residential development. The MTR tracks were located below the West Kowloon Expressway, limiting construction headroom above the tracks and forcing the adoption of the basement to connect between the two railway networks.
As part of the works, several new utilities needed to be installed. To avoid surface disruption, it was agreed that the method of pipe jacking would be adopted. Given that the ground was a new sand reclamation, it would be ideal for this method to be employed where a pipe is pushed behind a cutterhead. Unfortunately, the construction records for the reclamation did not record that a sunken barge had been left in the reclamation, and was only discovered when the pipe jack hit a steel object many metres below the ground surface. The obstruction was overcome and the pipe jack completed though, but many months later than planned.
Adjacent to the station, around 1,500 steel piles were driven for future property development, and these would later prove to be problematic in a number of ways. In early 2003, the ICAC arrested nine people, including an employee of the KCRC for allegedly falsifying piling test records. The ICAC identified that records of 700 piles had been tampered with. A senior manager of KCRC confirmed that all “complete [railway project] piles have passed all of the statutory inspections, load tests and approval process”. After further review, the piles were deemed to be acceptable.
The future property development did not materialise and in 2008, an alignment was developed for the Express Rail Link that would pass through the piles, requiring the removal of 289 steel H piles and their associated pile caps.
Removal of Nam Cheong Pile for Express Rail Link
To the south of the station, an operational overrun tunnel of 440 metres was provided in the form of a concrete box. To avoid long term settlement of the structure on the new reclamation, piles were provided to support the tunnel box. At the southern end of the platforms a scissors crossover was located to allow the trains to change from one track to the other and to provide storage for an out-of-service 9-car train. A further 20 metres of tunnel was provided to facilitate later construction of an extension to the south.
CC-403 Mei Foo to Nam Cheong Tunnel
The track alignment between Nam Cheong station and Mei Foo station followed parallel to the expressway at ground level, allowing the track to pass over the top of existing DSD drainage culverts. To avoid the visual and cumulative noise disturbance of the existing MTR and West Rail, the tracks were accommodated within a piled concrete box. The structure was then externally landscaped to soften its visual impact.
CC-404 Mei Foo Station
Mei Foo Station is located within Lai Chi Kok Park and provides an important interchange station with MTR Tsuen Wan Line via an underground pedestrian link to the existing MTR Mei Foo Station. The station is of a fully enclosed side-platform configuration and partly constructed below Lai Chi Kok Bridge. The key to its design is its integration with the park environment featuring an innovative rooftop public parkland.
Proposed Location for Mei Foo Station
In addition to the two West Rail tracks, the station includes provision for the Port Rail Line, a future freight line to the adjacent container terminal. The northern approach structure and station include space for the freight tracks to bypass the station and to continue to the port. The freight spur was used during construction by the track works contractor to supply materials from a works site close to the container terminals into the tunnels.
Mei Foo Station Construction
The station design was the winner of the 2004 Building Construction Industry Awards International Category.
Completed Mei Foo Station and parkland above
DB-320 Kwai Tsing Tunnels
To the north of Mei Foo station, the ground level rises requiring the adoption of a rock tunnel as it passes through Lai King Hill. The DB-320 works consisted of a 1.8km of the hard rock Ha Kwai Chung tunnel before passing through reclamation and soft ground associated with Gin Drinkers Bay. It then transitioned back into rock and a final section of cut and cover through reclamation to connect to the Tsuen Wan station contract. The original construction method envisaged that the tunnel through the central reclamation would adopt a cut and cover approach. This would have been very disruptive to surface users requiring complex traffic management along Kwai Fuk Road.
DB-320 Kwai Tsing Tunnels
With the return of the tenders in mid-1998, two alternative tunnelling proposals were submitted. One tenderer proposed a deeper alignment allowing the use of a rock TBM to construct the tunnels, while the other proposed a state-of-the-art mixed ground TBM. The deeper alignment proposal required the alignment to be lowered to avoid the mixed ground and allow the use of a large diameter rock machine. Hard rock TBMs had been successfully used in Hong Kong, but they were of a smaller diameter through known ground conditions. In this case there was still a length of poor ground that would need to be treated to allow safe passage. The second proposal was to excavate through the northern section, consisting of soft, mixed and rock, with an EPB TBM. There were concerns within KCRC, as Howard noted “We had some misgivings when the bid came in, as we didn’t have a lot of experience of this type of machine which has never been used in Hong Kong.” Senior managers of the MTR also expressed concern, considering it too high a risk for the project. However, the General Manager Construction, Jayananda Jesudason (aka ‘Jesu’) had experience with similar machines on the Channel Tunnel and when the bidder introduced his team and presented their recent experience in Sydney and Lyons, all were happy with the proposal. Thus, in October 1998 the Dragages-Zen Pacific Joint Venture was awarded the DB-320 contract.
DB-320 TBM Launch Shaft and Site of Former Commercial Buildings
The TBM, to be named Mulan, was licensed from Mitsubishi and fabricated by NFM, a French machine supplier with the backup equipment fabricated in Shanghai. This was the ﬁrst time in Hong Kong that a mixed ground TBM had been used to excavate through both strong rock and soft/loose soil deposits. The 8.75m diameter machine was especially designed to operate in different ‘modes’ to correspond to the varying ground and groundwater conditions. For excavation in competent rock where the stability of the ground was assured, an Open Mode at atmospheric pressure was used. For sections of the tunnel with the potential for high water inﬂows or where soft deposits were encountered in the excavation face, Compressed Air Mode (CAM) or Earth Pressure Balance Mode (EPBM) was adopted. To ensure a constant face pressure, a foam conditioner was used to improve the spoil properties and to minimise ground disturbance and related ground settlement. Behind the cutter head, precast concrete segments were erected within the tail of the machine and grouted in place.
Mulan TBM During Erection (2000)
DB-320 TBM Assembly
The TBM was shipped to Hong Kong in early 2000 and begun driving the first of the 1.78-km Tsing Tsuen twin-bore tunnel in April 2000. Advancing at over 11m/day, the first drive was completed by December 2000, after which, the TBM was dismantled and resembled for the second bore. With the experience gained from the first drive, Mulan completed the second drive in less than five months, breaking through in early July 2001 advancing at an average daily rate of 12.6m. Following the passage of the TBM, ground settlement in the most sensitive areas was recorded above the tunnels and these varied between 10mm and 30mm compared with initial surface settlement predictions of approximately 26mm. With only the need for a launch and retrieval shaft, Mulan demonstrated that mixed ground tunnelling was a viable method in Hong Kong ground, minimising the impact on traffic and the surrounding community.
DB-320 TBM Cutter Head
With the diameter of the tunnel being determined by vertical dimensions of the track form, train and overhead line requirements, the internal dimension of 7.625m allowed for a wider evacuation walkway of 1.3m, twice the normal. This wider walkway would support a greater flow of evacuating passengers, allowing the cross passage spacing to be increased from 60m to 90m intervals. Nineteen cross passages were required to be formed between the two tubes of the tunnels. Sixteen of the cross passages were located wholly within rock and were formed using conventional hand excavation techniques. The remaining three cross passages were located within the section of the tunnels excavated wholly within the soft and loose Marine and Alluvial deposits. For the formation of these cross passages, grout treatment, in the form of jet grouting was undertaken to ensure the stability of both the cross passage during excavation and, in the temporary case, the completed segmentally lined tunnels.
Completed DB-320 Tunnel
The TBM launch shaft was located on the site of two former commercial buildings, Wah Kai and Paul Y Industrial Buildings. The owners of the buildings objected to the demolition of the structures, arguing that construction of the railway could be undertaken without the need for the site. This argument ended up in court and in March 2000, the court rejected the argument allowing the buildings to be repossessed and demolition works to commence. With the demolition of the buildings not due to be completed until the summer of 2000, the initial TBM drive had to be undertaken with the buildings still in place, working from a reduced site area to the north. Measures were put in place to ensure the safety of the building as the tunnelling works passed below.
DB320 Typical Tunnel Cross Section
CC-300 Tsuen Wan West Station and Approach Tunnels
The CC-300 contract was located between the DB-320 tunnels to the south and the DB-350 rock tunnel to the north. It consisted of a 408m long and 41m wide Tsuen Wan station box and 300m of approach tunnel at each end. The latter had to be constructed below large DSD culverts while maintaining water flows from the Tsuen Wan hinterland.
The station was located within a new reclamation that had to be staged to allow the existing Tsuen Wan Ferry Pier to be relocated before the full site was available. The staging also had to maintain temporary flow channels for the discharges from existing culverts while the new culvert extensions through the reclamation were under construction. To the west of the station was the elevated Tsuen Wan Bypass and an existing salt water pumping station that had to be maintained.
Proposed Site for Tsuen Wan West Station
The station utilised a two-level underground box, a 17m deep with side platform configuration. A loop track in a separate tunnel passed by on the west side, providing a track for service reversing and temporary storage of defective or out-of-service trains. To allow the loop track to be used for detrainment, a narrow platform or wide walkway was provided with exit doors to the northbound platform. To the north and south of the station, crossovers were provided for operational flexibility.
As a major facility nearest to the long Tai Lam tunnel, the station was the prime access for the emergency services to enter the underground section of the line. At the north end of the station a short siding was provided to accommodate a self-powered rail vehicle for the Fire Services to transport personnel and heavy equipment into the tunnel. The vehicle was also available for use by the maintenance departments during non-service hours, thus helping to keep this vehicle in working order as well as being useful for maintenance work.
Tsuen Wan West Construction Adjacent to Elevated Bypass
The station was envisaged to be constructed using a ‘top-down’ method within diaphragm walls, but the winning contractor decided to adopt the traditional ‘bottom-up’ method, excavating the cofferdam and casting the base slab first. The lowest level contained the platforms and tracks with the concourse level above. A two-level superstructure accommodated the entrances and plant rooms above the station. The foundation for the station comprised of large diameter bored piles with sufficient capacity for a future property development above.
Tsuen Wan West Station and Tunnel Construction
With the station located below the water table, great emphasis was placed on ensuring the station box was water tight. This was achieved through the specification of the concrete and water proofing details. The contractor proposed an alternative approach using a concrete additive that would seal any micro-fracturing within the concrete that may lead to future leakage. Trials indicated that the additive would work and the proposed concrete mix and the material was used for all the structural walls and roof. Unfortunately, as the concrete dried, micro cracking occurred allowing saline water to drip into the station box, equipment rooms and the approach tunnels. After waiting to see if the additive would self-heal, the leakage had not reduced and the contractor had to undertake an extensive grouting operation to seal the leaks.
Tsuen Wan West Grouting Gantry (2003)
Contract DB-350 Tai Lam Tunnel
North of Tsuen Wan, the alignment passed below the escarpment of Ha Fa Shan in a rock tunnel and northwards into the New Territories. At the interface with CC-300, a 350m length of cut and cover tunnel was required, passing below roads and utilities. Complex diversions were required to allow construction of the tunnel and access to the tunnel portal. Once into the rock, the tunnel passed close to an unlined WSD water supply tunnel, with the use of explosives banned within 60m of the water tunnel. A detailed assessment and monitoring were required to ensure the supply tunnel was not impacted. Along the length of the tunnel were several known faults, the biggest being the Sham Tseng and Ho Pui faults, the latter being below the Ho Pui Reservoir, with possible high flows under pressure.
Longitudinal Geological Section
A Japanese-French consortium, Nishimatsu-Dragages Joint Venture, was awarded the contract in September 1998 using their previous experience in constructing the adjacent Route 3 (Tai Lam Country Park Section) road tunnel to construct the tunnel.
DB-350 South Portal
The original conforming tender was for the provision of two single track tube bored tunnels with interconnecting emergency cross passage adits every 60 m. The contractor proposed an alternative design utilising a single bored tunnel with a central diving wall to separate the up-track and down-track. In lieu of the cross passages, cross passage doors were installed along the centre partition wall at 60 m centres.
DB350 Tunnel Cross Sections, Twin and Triple Track
To meet the operational requirements, a crossover was located midway along the tunnel, and this requirement was primarily a need to accommodate future freight operations where extended operating hours were anticipated and single line working would be required to support maintenance operations. The crossover required the installation of a large sliding ﬁre protection door, one of only two of its kind in the world to maintain ventilation separation between the tunnels in normal operation.
The tunnel was formed using conventional drill and blast techniques and was driven from the southern portal by Nishimatsu, and from the northern portal by Dragages through granitic and volcanic rocks. At the north end, to provide a highspeed bifurcation of the up-track to the depot, the initial 500m of the tunnel was constructed as a triple track tunnel.
Tai Lam Tunnel Waterproof Membrane
The average monthly production for the twin track tunnel was typically in the range of 170 m to 210 m. The cross-sectional area of the excavated face was 107 m2 for the twin track tunnel, and 168 m2 for the triple track tunnel. For the southern section, mucking out was carried out by loading tunnel spoil into vehicles at the face of the excavation. In the northern section of the tunnel however, a conveyor system was used to remove tunnel spoil to the northern portal where it was then crushed and subsequently used for the site formation and at-grade works.
DB-350 Cross Over Door
The northern portal of the tunnel was located on escarpment above the Kam Tin valley. A number of graves had to be relocated from the hillside and private land acquired. Once knowledge of the project became public, abandoned farm land was re-activated to attract a higher resumption compensation.
DB-350 North Tunnel Portal
From the tunnel portal, the alignment continued north into the site for the new Pat Heung depot and the northern section of the works
- Legislative Council Panel on Transport, West Rail Project Update, 18 Feb 2000 ↑
2. KCRC Projects Updated, Issue 17, Nov 2000 and Issue 26 May 2002 ↑
3. Tsing Tsuen and Ha Kwai Chung Tunnels DB-320, Hong Kong West Rail, NCE, 1999
4. History of Modern Tunnelling 1825 to Today, The 2010 Harding Lecture, Dr Alastair Biggart, British Tunnelling Society, 15 Apr 2010 ↑
5. KCRC Man Among 9 Arrested for Alleged Piling Scam, SCMP, 17 Jan 2003 ↑
6. Tsing Tsuen and Ha Kwai Chung Tunnels DB-320, Hong Kong West Rail, NCE, 1999
7. KCRC Projects Update, Issue 21, Jul 2001 ↑
8. Court gives green light for West Rail project, SCMP, 2 Mar 2000 ↑
9. Tsuen Wan Station, Hong Kong West Rail, ICE, 1999 ↑
10. KCRC West Rail Phase 1, Contract DB350 – Tai Lam Tunnel Hong Kong SAR, Robert D Gould, Dr Leonard John Endicott, Joseph Y C Lo ↑
This article was first posted on 5th September 2023.
Related Indhhk articles:
- West Rail – Part 1 In the Beginning
- West Rail – Part 2 Detailed Feasibility Study
- West Rail – Part 3 Technical Studies
- West Rail – Part 4 Detailed Design