Client: Land Transport Authority
Engineer: Design & Build
Main Contractor: Nishimatsu-Lum Chang-BSS JV
Contractors Engineer: Maunsell Asia

Diaphragm Wall: 22,200m2
Thickness: 1200mm
Max. Depth: 50m
Barrettes: 5,900m2
Size: 1200x2800mm
Max. depth: 41m
Bored Piles: 173 piles
Diameters: 900mm, 1000, 1100 & 1200mm
Total length: 4,722m
Techniques: Secant & Contiguous Walls, Isolated Foundations
Jet Grouting: Soil Treated: 11,500m3

Project Duration: 14 months

The North East Line construction packages were let as Design & Build contracts. For Contract 708 Clarke Quay Station & Tunnels, the station box was built adjacent to the Singapore River and the geotechnical conditions were difficult with a significant layer of marine clay to overcome and heavy foundations to be constructed for the commercial development above the station. As a member of the Main Contractor Joint venture, Bachy Soletanche were heavily involved in the alternative of an alternative foundation scheme to simplify the station construction and propose economic methods for the Station's geotechnical works.

In the event the piled foundations of the station were deleted and the whole station box lowered to found directly on good soil. However, due to the presence of the particularly thick layer of marine clay, it was necessary to use Jet Grouting in some areas to improve the soil and therefore increase the bearing capacity. Jet Grouting was also used at the station tunnel break in and break outs and at two of the pedestrian access tunnels. Additionally, bored pile foundations were required for the station entrances and secant piles were used at Dhoby Ghaut for future access.

The Clarke Quay station box was formed with a 1200mm thick diaphragm wall, excavated using a combination of conventional grabs and the KS3000 hydraulic grab. Complex traffic management was required to allow the busy city centre traffic to flow smoothly at all times. The works programme was tight with many areas critical to the success of the overall project. During the excavation of the wall there were unforeseen difficulties to overcome, particularly old driven concrete and timber piles and debris from an old shipyard located by the Singapore River. However, the experienced site team and the modern equipment were able to cope with the surprises in the ground.

Some heavily loaded foundations were required outside the station for a future commercial development above. Barrette foundations were chosen given the high loads involved.