Busy Ma Tau Wai Road in Kowloon City is presenting one of the first major challenges to the MTR team working on phase one of the 17km, £5bn Shatin to Central Link.
Diaphragm wall rigs have sprung up along the busy road in the last 12 months, squeezing themselves between three lanes of traffic, bus stops, schools and shops. Some of the works are also taking place beneath a major flyover.
This has been one of the first visible signs that the Shatin to Central Link is moving ahead over the last 12 months.
The works on the six lane Ma Tau Wai Road is to create the 300m long Ma Tau Wai Station under the road within diaphragm walls.
The need to keep the road open means that contractor Samsung/Hsin Chong joint venture must form the diaphragm walls on the east side of the road first, before moving across to the west.
The station, which will incorporate two stacked running tunnels beneath a station concourse within a 30m deep box, will then be created using top down construction, underneath a reinstated road surface on which traffic will run.
Work here is very sensitive as some of the neighbouring residential buildings are more than 30 years old and there is concern among people who live there that excavation work could damage them.
Noise impact from works in congested areas is critical, while complaints about unexpected vibrations can lead to the site being shut down while they are investigated. As a result a good relationship with the local community, established by communicating the nature of the work and its impact has been vital to efforts to keep the project moving.
Dealing with the traffic is also a challenge. The road is a busy through route and is served by about 30 bus and mini-bus routes. There are also several schools in the area, so maintaining access and transport routes to these is vital.
“Ma Tau Wai Road is very congested on both sides and there are also six lanes of traffic so it was quite difficult to convince stakeholders to let us close off all of the lanes,” says MTR Shatin to Central Link general manager Philco Wong.
As a result of local consultation it was decided instead to divert some of the traffic through neighbouring streets under a four year temporary traffic management programme.
The viaduct carries the dual carriageway East Kowloon Corridor across Ma Tau Wai Road. This imposes headroom limit on the trench cutter rigs, limiting the height of reinforcement cages to 6m, compared with 12m elsewhere at the site
Meanwhile, work is progressing. “We expect to complete the diaphragm wall works on the east side of the road in the next two to three months,” says Wong.
Works are further complicated by the fact that the station is being built in mixed ground including some very hard core stone, which is hard to cut through, thus hampering the diaphragm wall excavation work.
To complicate matters further, underground services must be relocated. “We have to divert a water main which runs along Ma Tau Wai Road,” says Wong.
“The main is over 30 years old and contains asbestos cement, so after it is temporarily diverted, it will have to be replaced.
A major electricity cable has also had to be relocated as it cuts across the line of the diaphragm wall.
Then there is the viaduct carrying the dual carriageway East Kowloon Corridor across Ma Tau Wai Road. This imposes headroom limit on the trench cutter rigs, limiting the height of reinforcement cages to 6m.
MTR’s Shatin to Central Link team has used a building information modelling (BIM) system developed by consultant Atkins to help contractors get a better understanding of the designs for parts of the Shatin to Central Link route.
Using BIM helped contractors interrogate designs for the Hung Hom Station reconfiguration in three dimensions.
“It also helped them understand the construction sequences,” says MTR Shatin to Central Link chief design manager Clement Ngai.
Using computer modeling also meant contractors could visualize the work more quickly than if they had to wade through thousands of individual engineering drawings, saving time and resources.
Other works are now underway along the length of the 11km first phase of the Shatin to Central Link, which is due for completion in 2018.
Phase 1 includes an upgrade of the existing Ma On Shan line, which will splice into the northern end of the new Shatin to Central Link. This above ground line is being adapted to accommodate eight car trains, although construction works are mainly related to extending platforms for its nine stations.
To the south, the line will run through drill and blast and then bored tunnel.
Work on the access shafts for the tunnels has already begun after contractor Vinci started work last year.
In addition, Vinci is expected to launch a tunnel boring machine (TBM) to start on a section of bored tunnel between the Lion Rock tunnel and Diamond Hill station in north Kowloon where there will be an interchange with the existing Kwun Tong Line.
The TBM of contractor Chun Wo/Seli joint venture’s neighbouring section running south to Kai Tak Station is due to start work the following month.
Diamond Hill interchange
Works are also underway at the Diamond Hill interchange site. Here, MTR’s contractor Sembawang Leader joint venture is creating diaphragm walls next to the existing station before building the station box inside.
Less visible, but more challenging are the works at the southern end of the line near the existing Hung Hom Station within an area which had been occupied by the former railway freight yard.
In a tightly constrained 6m high space underneath the station, specially adapted low clearance diaphragm wall rigs are at work.
In between the rows of structural columns supporting the station above, the rigs are creating more diaphragm walls, this time for the cut-and-cover tunnels and the new 300m long platform and tunnel box which contain Shatin to Central Link and East Rail Line platforms, which will be relocated from the west side of the station, making it easier for passengers to change lines.
These walls are between 20m and 50m deep depending on the depth of bedrock, and the height constraints mean that the reinforcement cages can be no more than 4m tall.
The concourse is having to be remodeled with new escalator openings cut in the existing floor slab, to give access to the new platforms
MTR is using some of the freight yard area to set up a soundproofed reinforcement threading production yard, complete with lifting gantry which runs on the overhead rails originally attached to the structural columns to support a freight yard gantry.
The factory is currently producing 1,000 threaded rebars cages per day, but this is expected to rise to around 1,500 threaded rebars as concrete production rises to a peak of around 500m3 per day.
Remodelling the Hung Hom interchange is a major challenge as the station must stay in service while construction works arecarried out.
The concourse is having to be remodeled with new escalator openings cut in the existing floor slab, to give access to the new platforms, so close coordination with the station operators is vital.
Some work is also taking place next to live track. Positioning of the Shatin to Central Link Hung Hom Station will enable it to connect with the immersed tube tunnel which will be built to take it across Hong Kong Victoria Harbour under phase two, which is due for completion in 2020.