Possibly some of the most interesting engineering on the Tseung Kwan O line will be hidden in the four bore 1.7km Black Hill tunnel between Yau Tong and Tiu Keng Leng.
When complete it will take track for the Tseung Kwan O line and the extended Kwun Tong line. Three of the four bores change their positions relative to the others from one end to the other.
At each end of the tunnels are the Yau Tong and Tiu Keng Leng interchange stations. They will have two levels of platforms and are designed to allow passengers a convenient cross-platform switch between lines, reducing the need for people to change levels to change trains.
This is why the tunnel configurations have to change. To complicate matters further the Black Hill tunnels incorporate crossovers.
Technically the 2.2km Pak Shing Kok tunnels are more complicated. Contractor Hyundai Kier has to contend with a mixture of granite and decomposed volcanic material. Drill and blast is being used for most of the excavation work.
Steel arches and spray concrete are being used to support excavations where short sections of soft ground tunnelling are being carried out.
Work at the 13.4ha depot has so far focussed on the massive foundations for the 15 blocks of flats, five schools and shopping centre to be built above the train shed.
Contractor Gammon has to construct 820 cast insitu piles with diameters ranging from 1.2m to 2.8m bored through reclaimed marine muds and alluvium to bedrock. Work has progressed rapidly with the contractor producing 100 piles a month at peak. At one point the contractor had around 50 piles on the go at once.