Section 1: Eastern Harbour Crossing to Black Hill tunnel via Yau Tong
Building an underground junction between a new and existing tunnel is one of the trickiest civil engineering challenges on the whole Tseung Kwan O project.
Right next to the eastern end of the busy Eastern Harbour Crossing is one of the most critical parts of the whole Tseung Kwan O project. It is here that Kvaerner subsidiary Gammon China Harbour Joint Venture has to connect an existing section of the MTR system to the new Tseung Kwan O line.
Work involves creating ajunction between the cut and cover EHC approach tunnel, currently used by the Kwun Tong line, and the new Tseung Kwan O tunnel.
Disruption to the Kwun Tong line and road traffic using the EHC has to be minimsed, so the contractor is keeping demolition work inside the existing tunnel box to a minimum. Sections of the central wall and southern outer wall will be demolished toallow the twin tracks to branch off. But roof slab above the demolished wall will be retained by tying it into a new slab cast above it.
Night possession work will be needed to enable to contractor to insert 66 ground anchors into the existing tunnel floor. These are to counter uplift forces resulting from demolition of the existing tunnel walls to form the junction with the new line.
Gammon China Harbour is also building a 700m drill and blast tunnel further north, beneath the motorway which feeds into the EHC. This will carry a new section of the Kwun Tong line which is being diverted to the new Tseung Kwan O station at Yau Tong.
The contractor is also doing blasting work to carve the two level Yau Tong interchange station site out of a hillside as well as blasting pad supports for housing developments around the station.
Blasting work is heavily regulated and involves extensive use of steel framed cages to contain fly rock thrown up by explosives.
Section 2: Tiu Keng Leng to Po Lam via Tseung Kwan O and Hang Hau
Piling work is under way in the shadow of densely populated housing estates.
Building cut and cover tunnels through densely populated Po Lam and Hang Hau has presented a major community relations challenge to contractors and client alike.
'The problem with Hang Hau and Po Lam is that they are in the middle of an area of occupied housing,' says Section 2 project manager Roger Bettiss.
Piling work now under way is the biggest headache. Section 2 runs through reclaimed land and extensive and noisy piling down to bedrock is needed to stablilise track and stations. More piling is required to create foundations for associated high rise housing developments, profits from which will help fund the new line.
At Hang Hau station, Dragages et Travaux Publics has one of the biggest piling jobs. It has to construct 122 bored piles to depths of around 30m for the station as well as another 133 for six neighbouring high rise blocks.
Trenches for diaphragm walls also have to go down to bedrock, and all within a tight, 40m wide site packed with plant.
Dragages has been helping MTRC by talking to residents and listening to their concerns about noise, dust and subsidence. MTRC has also held regular residents' meetings to explain how the apparent chaos on site will deliver a live railway by 2002.
The southern end of the Dragages contract takes in a bifucation tunnel where the line branches off to the depot, passing under a series of roads and a huge box culvert storm water sewer which has to be propped temporarily while the tunnel box is built underneath.
Tseung Kwan O and Tiu Keng Leng stations are relatively straightforward as they are much futher away from inhabited housing estates. Tiu Keng Leng station is being built in a massive cutting created as part of an advance works contract under which Gammon shifted 1.3M3 of rock from Black Hill to create the station site, and levelled pads for 23 blocks of flats.