Work on Hong Kong’s high speed link to mainland China is gathering pace with construction activity focused at the terminus in Kowloon. Andrew Bolton reports.
A vast forest of piling rigs and diaphragm wall plant has sprouted in an area of reclaimed land just east of downtown Kowloon in mainland Hong Kong. On weekdays, the upwards of 50 cranes and rigs add to the roar of traffic as they go about the business of creating the Special Administrative Region’s first high speed rail terminus.
Over the last 12 months, work on the high speed line, which is being managed on behalf of the Hong Kong government by metro operator MTR, has gathered pace. The HK$66.9bn (£5.47bn) project will provide a 26km wholly underground link between the Kowloon terminus to Huanggang in Shenzhen, connecting in to the Mainland’s rapidly growing high speed rail network.
All of the 10 main tunnelling contracts were awarded during 2010 and contractors have ordered the six tunnel boring machines (TBMs) they need for the bored tunnel sections. In the meantime, preparations for the tunnelling work are getting underway.
Bachy Soletanche/Laing O’Rourke JV and Gammon Leighton JV have begun work on two separate contracts to build the cut and cover approaches to the terminus, and further north, Australian contractor Leighton has also begun work on a 400m long drill and blast adit to give it access to the alignment of a section of running tunnel on the outskirts of north Kowloon.
But the main focus of work has been the vast Kowloon terminus site, which accounts for around 40% of the value of the whole project. So far, piling contracts worth HK$2bn (£168M) have been awarded. The vast 11ha, 15 platform terminus station will be sunk below sea level into reclaimed land within a massive diaphragm wall, with its glazed upper concourses tucked under a landscaped area above the platforms.
Since the beginning of last year, Bachy Soletanche has been pushing hard on the diaphragm walling for the terminus around the site perimeter. Bachy Soletanche, Tsyan Foundations and Vibro/Chun Wo JV have been working on four separate piling contracts within it.
“We have made a very big deal of the need for interface management in the tender documents”
Calum Smith, MTR
For the terminus, 1.6km of diaphragm wall is being sunk around the periphery using both traditional and massive Hydrofraise diaphragm wall rigs excavating down to rock which is anywhere between 25m and 55m below ground.
By January this year, 70% of the piles on the site had been put in, and 75% of the diaphragm wall was complete. In all the terminus site will have 540 bored piles and 3,412 socketed H-piles.
Getting the project ready for the start of the tender process at the end of 2009 was a major challenge in itself.
The Hong Kong government had set an ambitious six year programme to get the project from drawing board and onto site and finished by 2015. As a result, preliminary route designs had to be produced at breakneck speed by an Arup/Atkins joint venture. “We had two to three months for the scheme design,” says Atkins associate technical director Lau Pak Wai. “Then three months after that we had to have the first drawings ready for internal approval,” he adds. “We had up to 100 people working full time in MTR’s offices with back up from head office.”
Atkins director John Blackwood says: “The key thing was that the government and the consultant worked as a team to get through the approvals process”.
The size of the project and its pull on resources have presented challenges to MTR’s project team in terms of marshalling the resources of the local construction industry. MTR has split the ground engineering work at the terminal into four packages to avoid placing too much risk in the hands of one contractor.
“We were concerned about contractors having adequate resources and did not want to give all of the work to one contractor,” says MTR’s terminus project manager Calum Smith.
Splitting the contracts also meant that more firms could compete for the work. “The terminus was originally to be built under a single contract, but we split it into two to get more bidders,” says MTR projects director TC Chew.
But MTR also anticipated that dividing the work up in this way would also mean that interfaces between the different contracts would have to be managed carefully. The site is extremely busy with such a high concentration of plant making manoeuvring plant and equipment a huge logistical challenge. “We made a very big deal of the need for interface management in the tender documents,” says Smith. “We expect them to have a very large interface management team,” he adds.
The project has had its own external interfaces to deal with too. The terminus’ vast footprint needs to be built within the confines of the existing surrounding road layout, so MTR has had to reroute a major north-south road, splitting its north and southbound carriageways to run either side of the terminus site.
In addition, it has had to relocate some underground storm drains to make way for the track alignment north of the terminus.
Another obstruction is a 250m long footbridge connecting Austin West Rail station with the high rise property development on the other side of the site around the Kowloon Airport Express station. The footbridge runs along a road which will have to be relocated to allow foundations and diaphragm walling to take place.
North of the terminus, but still in built up Kowloon, Dragages Bouygues JV is preparing a launch shaft for the TBM which will drive south towards the terminus and also north towards Australian contractor Leighton’s drill and blast contract, which will take the tunnels through the first of three mountains.
For once in Hong Kong the contractor has the luxury of some space, as part of the alignment crosses flat ground which had been used as a car park. Consequently, there is room to excavate a 30m wide, 120m long rectangular box along the alignment. This will allow the contractor to assemble the TBMs and back up trains online without having to lower individual sections through an access shaft.
Just up the road, Leighton has been pushing a 400m long drill and blast access adit into the side of Hong Kong’s tallest mountain to connect with the alignment of its 7.6km drill and blast running tunnel.
“We were concerned about contractors having adequate resources and did not want to give all of the work to one contractor”
Calum Smith, MTR
While progress on the high speed line project has undoubtedly been rapid over the last year, there have been some unexpected problems. Stubborn piles have presented challenges to MTR and initial works contractor Hsin Chong as they seek to remove them from the tunnel alignment.
The piles in question are around 360 steel H-piles originally installed in the early 2000s to support a future property development at MTR’s West Rail station at Nam Cheong, which runs along the western boundary of one of the tunnel sites. The property development has yet to happen, but around 60 of the H piles plus a 2m diameter reinforced concrete bored piles are on the down track alignment with the rest on the up track.
The piles are between 40m and 50m deep and some appear to have deflected deep underground, making removal extremely difficult using vibratory or hydraulic jacking methods. In the end a special technique, and what amounts to a high powered Japanese torque wrench plant, supplied by Japanese firm SNE, were brought in to twist, snap and yank them out.
The technique involves rotating a pile casing with sharp tungsten carbide teeth into the ground around the H-pile. Within the casing, ground around the pile is then excavated before the wrench grips the pile, twisting and pulling it upwards to remove it. The powerful wrench, attached to the top of the casing can apply up to 200t/m of torque.
Piles like corkscrews
Removed piles are so twisted they resemble giant corkscrews.
“The casing goes down fairly quickly assuming the pile is straight,” says MTR’s XRL tunnels project manager Alan Morris.
Typically it takes four days to remove one of these piles, but sometimes it can take longer if there is a serious deflection at the pile base. In such cases the casing has to be re-sunk repeatedly with ground inside it removed until the end of the pile can be located.
Aside from this, work is progressing rapidly with most of major civil engineering contracts along the high speed route awarded. As 2011 progresses, foundation and diaphragm walling work at the terminus site will give way to the start of station construction.
By the end of the year, tunnelling sites along the length of the route will start to open up ready for the main tunnelling phase to begin in earnest within 2011 and 2012.