From an almost standing start in 2007, Hong Kong is starting construction of a 26km underground high speed rail line. Andy Bolton reports.
More from: Going the distance: Hong Kong's MTR projects
By 2015, Hong Kong will have entered the age of the high speed train as it meshes its transport infrastructure to the expanding networks of the Mainland of China.
Contractors are gearing up for the start of work on the HK $66.9bn (£5.47bn), 26km Hong Kong section of the Guangzhou- Shenzhen-Hong Kong Express Rail Link (the Express Rail Link, XRL) which will connect into the mainland’s rapidly growing high speed rail network.
Work is starting now and is expected to be in full swing by early next year. The Express Rail Link is the fi rst high speed rail project by the MTR Corporation, which has traditionally built and operated metro systems in Hong Kong, and the Mainland of China.
“At the moment we have about 200 staff, but at peak we will be up to 800”
Paul Lo, MTR Corporation’s XRL general manager
MTR Corporation is currently building up its team as the project, dubbed XRL in Hong Kong, goes into construction phase. “At the moment we have about 200 staff , but at peak we will be up to 800,” says MTR Corporation’s XRL general manager Paul Lo.
The project was kick started by Hong Kong’s chief executive Donald Tsang in 2007 when he named it as one of 10 key infrastructure projects in support of the future development of Hong Kong.
The massive underground link will run between a huge landscaped underground terminus in Kowloon and the boundary with the Mainland of China where it will connect with the country’s high speed network. After completion, it will reduce the travelling time from Hong Kong to Guangzhou from the present 100 minutes to just 48 minutes.
Tunnelling is to be divided into eight major contracts, reflecting degrees of complexity and differing ground conditions. From the boundary at the Shenzhen River, mixed ground earth pressure balance or slurry shield tunnel boring machines (TBMs) will drive the running tunnels beneath marshes and up to the foot of Kai Kung Ling mountain.
This gives way to a 2.56km drill and blast contract which will take the tunnel through Kai Kung Ling and on to another mixed ground bored tunnel. This in turn gives way to a cut and cover section through the Kam Tin Valley.
This section also includes an emergency rescue siding 30m below ground and an at-grade stabling siding. The emergency rescue siding will be in open cut. It is compared by MTR Corporation’s engineers to the box which now houses Stratford International station on the High Speed 1 line between London and the Channel Tunnel.
From the emergency rescue station a short TBM bored mixed ground tunnel section then gives way to a challenging 7.2km drill and blast tunnel taking the line under the Tai Mo Shan mountain, where there will be up to 600m of rock cover, and under the smaller Kam Shan mountain (Golden Hill) from where it will emerge into a mixed ground TBM section through congested north Kowloon and into a short cut and cover section before entering the terminus.
The bored tunnel section under the south-western part of Kowloon is the most complex and challenging of the tunnelling contracts because of the various obstacles which must be negotiated.
Tunnels will run through reclaimed land areas containing buried jetties, piers, sea walls and drainage culverts which are still in use.
In the Lai Chi Kok district, TBMs must squeeze beneath MTR subway tunnels with just 2.8m clearance before passing either side of pairs of 2.5m diameter bored piles supporting the elevated Lai Chi Kok road interchange.
The tunnels will also thread 2m above a water transfer tunnel and then close to the piled foundations of high rise estates as they approach the cut and cover section running into the terminus.
Risks presented by the soft ground at the north end of the tunnel by the border with the mainland of China are different, but also present big challenges. Here earth pressure balance machines or slurry shield TBMs will have to drive through faulted ground under protected wetlands where access shafts are banned.
Client: Hong Kong Government
Project managment: MTR Corporation
Operator: MTR Corporation
Tunnelling consultants: Arup (North) and Atkins (South)
Terminus consultant: Aecom
“The TBMs must be fully repairable underground,” says MTR tunnels project manager Alan Morris. “If a TBM gets stuck we won’t be able to simply dig a hole to get it out.”
Part of this section also runs through an area of marble where the potential for infilled voids at tunnel invert level exists. “There could be voids and we might need to grout them to prevent the TBM alignment being affected resulting in cracking of the segment lining at the back of the tail skin,” he says. Contractors will need to probe ahead of the TBM to detect voids and so flag up the need for advance grouting.
Excavation of the tunnels and the terminus will generate 25Mt of spoil and because of pressure to limit the amount of lorry movements on Hong Kong’s roads, much if it will be transported by sea from seven barging points close to the route alignment. It is also hoped that some of the spoil can be reused within the project, or at least on other projects in Hong Kong or the Mainland of China which need spoil.
“The TBMs must be fully repairable underground. If one gets stuck we won’t be able to simply dig a hole to get it out.”
Alan Morris, MTR tunnels project manager
In addition the volume of drill and blast tunnelling has meant that the project will have to build its own explosives magazines for storing initiating materials (detonators, cartridge boosters and detonating cord), normally delivered from Hong Kong’s main explosives depot.
The other challenge has been to break the work on the vast station down into manageable packages for a contracting sector which is about to be swamped with major civils contracts.
“Because of the scale of the works, we have had to split the work up,” says Smith. “As a result, dealing with interfaces between contracts will be a major issue.”
The underground terminus will be a major 15-platform station with platforms for short distance commuter services and also for long distance trains.
An arched, landscaped roof will envelope all but the southern end of the station, with a multilevel glazed entrance structure providing pedestrian access.
The extensive use of glazing will also help to channel natural light into the building and down to the departure level.
The station’s platforms, arrivals and departure halls on separate levels with immigration, customs and quarantine facilities, passenger waiting areas, ticketing, taxi ranks, car parks and back-of-house offices and plant rooms will all be housed within a 1.5m thick, 1.5km long, 30m deep reinforced concrete diaphragm wall.
The five-level structure will incorporate large open spaces to enable it to handle 130,000 passengers per day.
“The total floor area is similar to Hong Kong International Airport Chek Lap Kok terminal 1 - but underground,” says MTR Corporation’s XRL general manager David Sorton, responsible for the civil construction works.
The XRL project is being built under a concession arrangement between MTR and the Hong Kong government, with the project funded directly by the Hong Kong taxpayer.
MTR Corporation will manage the construction work and anticipates operating the completed infrastructure as well as sharing the train service operation.