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High speed squeeze

Hong Kong’s high speed rail link to China is hurtling towards its 2015 completion date, overcoming unforeseen obstacles and logistical constraints on the way.

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MTR’s largest and possibly most complex project is the 26km underground high speed link between the border with China and a huge purpose built terminus next to busy downtown Kowloon. The £5.47bn project, known as the Express Rail Link (XRL), combines a range of tunneling disciplines with the need to build the vast, underground terminus.

“The biggest challenge is the quantities in terms of the excavated material we have to get out and the volume of concrete you have to put in”

Calum Smith, XRL terminus project manager

Three years since the project got the go-ahead, civil work is underway on all fronts. “All the E&M contracts have been awarded,” says XRL general manager Antonio Choi. The project is approaching peak with MTR alone employing a project team of around 800 while the project as a whole is expected to be employing around 11,000 people this year (2013).

The most visible part of the project is the 11ha West Kowloon terminus, which has transformed from a site bristling with piling rigs, to a massive excavation over the last two years.

The terminus will house 15 platforms and will be contained within four basement levels, parts of which will open out to a roof whose glazed steel superstructure will bring natural light to lower levels. The roof itself will shape a landscaped urban park above the station.

The site covers a vast area and there is intensive activity wherever you look. Three major civil contracts are now underway, splitting the terminus into three adjoining slices. At the southern end, a Laing O’Rourke/Paul Y/Hsin Chong joint venture has completed the floor slab for the second basement level. This helps support three sides of the diaphragm wall around the site’s southern perimeter, allowing excavations for two more basement levels to take place underneath.

The neighbouring contract combines a mixture of top down and bottom up construction. There, contractor Leighton-Gammon joint venture has excavated four levels down to track level in the centre of the site, and has cast top down floor slabs around the edges. The idea here is to use embankments of unexcavated material to support the diaphragm walls while the track level basement slab is cast in the centre of the site. This slab will then be slowly extended across to the diaphragm wall.

On the adjoining contract, to the north, Gammon-Leighton joint venture is working on a top down basement construction.

Coordinating these three contracts is a major challenge for MTR’s project managers, not least because of the combination of top down and bottom up construction.

“We want the roof up as soon as possible, so we can provide a dry environment for the electrical and mechanical work”

Antonio Choi, XRL general manager, MTR

Unforeseen ground conditions have also complicated the challenges, slowing down some work on the site which is in an area of reclaimed land.

“We found more marine clay and boulders than anticipated and the material was not as homogenous as we expected,” says MTR’s projects director TC Chew. In addition, excavation work was delayed by the need to move uncharted utilities.

Excavated material from all three contracts has to be removed to a barging point in the Harbour.

Although contractors can use different routes to the barging point, there are some points where they must share. This means coordinating the movements of the armies of trucks assigned to each contractor. “We have regular meetings and have set up task forces at working level,” says MTR’s XRL terminus project manager Calum Smith. “There is also high level coordination and we have steering groups to look at the issues.”

“The biggest challenge is the quantities in terms of the excavated material we have to get out and the volume of concrete you have to put in,” says Smith.

At present he and his team are trying to accelerate the amount of excavation work on Laing O’Rourke/Paul Y/Hsin Chong’s top down contract from 15,000m3 a week to around 20,000m3 as a way of evening out difference in level with Leighton-Gammon’s neighbouring bottom up contract. Concrete volumes are also huge. Leighton- Gammon’s contract alone includesinvolves pouring 600,000m3.

The challenges have been greater than anticipated, which is perhaps not surprising given the size of the site, the intensity of activity and the different construction methods.

In response, Chew has beefed up the XRL project management team, drafting in his chief civil construction engineer Alan Myers to add the role of general manager for the terminus to his range of responsibilities. Myers’ main role is to work across all five MTR major projects, taking an independent view and resolving conflicts in priorities. He is now taking a more hands on role at the terminus site as the project reaches its peak and civil teams start working alongside structures and electrical and mechanical teams.

“One of the challenges is the interface between the civil work and the E&M,” says MTR’s XRL general manager Antonio Choi. He is keen to get the ground floor slab in as quickly as possible so that work can begin on the steel and glass roof. “We want the roof up as soon as possible so we can provide a dry environment for the electrical and mechanical work,” he adds.

To smooth out interfaces between the disciplines and to help coordinate the activities of the various contractors, the team is developing a computerised delivery system. “We are in the process of setting up a logistics software package so that we can deliver materials through the site straight to hook or hoist,” says Smith.

MTR has also been using building information modeling (BIM) to help anticipate and iron out problems before they arise. “We have been using it for clash analysis and to try to identify problems,” says Smith. “We have found a lot of things which could have caused us problems as a result.”

This included a potential headroom problem, which, had it not been tackled, could have led to the imposition of a height restriction on one of the underground roads which will serve the completed terminus.

North of the terminus, tunneling has progressed relatively smoothly, albeit with some tweaks to the programme to accommodate unforeseen issues.

At Nam Cheong, the contractor Dragages-Bouygues joint venture has almost finished tunnelling the down track to the north and to the south of a 160m long, 30m wide, 40m deep tunnel boring machine launch trench excavated on the site of a bus station using two Herrenknecht slurry shield tunnel boring machines to take the line under the densely populated areas of north Kowloon. These machines will be taken back to the Nam Cheong shaft and reused on the up-track tunnels.

Tunnelling for the first two 9.3m diameter bores was initially supposed to start on the southbound section which runs through reclaimed land from Nam Cheong to the terminus. But work to remove the deep piles from old marine structures buried along the alignment had hit problems, so it was decided to press on with the northbound bore first. This bore was due to break through into the adjoining drill and blast section which takes the line through the mountains north of Kowloon in December 2012, while the southbound bore is also due to break through at the approach tunnels in West Kowloon.

The southbound drive towards the terminus from Nam Cheong has had it challenges too.

One section had to thread over a sewer and then squeeze under tunnels carrying MTR’s live West Rail Line. Space was extremely tight and the alignment demanded that the water sump under the West Rail Line invert be cut into to allow the TBM through. All this had to happen without interrupting the West Rail Line services. Extensive monitoring equipment was used to check for movement in the live tunnel and, as an extra reassurance, project team members sat in the train cabs as they passed above the tunneling site.

Another part of the southbound section had to run through mixed ground, with the crown just 8m below the piled foundations of a 50 year old housing estate, whose residents were worried about disruption and noise caused by TBM’s cutter head repairs. This would have involved reducing compressed air pressure at the tunnel face and then grouting the surrounding ground to support it during maintenance work.

“We wanted to reduce the need for disruption caused by cutter head interventions, so we created safe havens nearby where we could reduce the pressure in the machine and could refit the cutter head so we didn’t need to do it under the estate,” says XRL project manager Bill Clowes.

A similar approach is being used for the bored tunnel drives immediately south of the border with Mainland China. Here the TBMs must pass beneath protected wetlands and contractors will not be allowed to dig an access shaft to rescue a machine if it gets stuck. It is planned to stop the TBMs for maintenance just before the protected area. Choi does not expect the TBMs in the section to get stuck, however. “The high risk comes from the cross passages,” he says. To reduce this, the contractor is to excavate the highest risk of the five cross passages in this area during a ground freezing operation.

Concession approach

Normally MTR builds its own lines in Hong Kong, often funding construction with revenue from associated property developments.

But the high speed line is being funded by the Hong Kong Special Administrative Region government. It asked MTR to manage the design and construction of the project with an option to operate it on completion. As such MTR is acting as project manager for the civil, structural and E&M works, to oversee the management of work awarded to contractors and consultants.

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