Contract C824 is being tackled by Nishimatsu-Lum Chang JV on a design and build, lump sum payment basis. It is understood Nishimatsu has undertaken all temporary works design in-house.
The contractor opted for a cut and cover tunnelling solution that is widely used in Singapore - but not normally for excavations as deep as that at Nicoll Highway, or in such difficult ground conditions.
Singapore engineers said that where the collapse occurred the tunnel was to eventually accommodate a twin track underground railway.
The excavation at the collapse site is some 15m wide and is 33m deep. Nishimatsu-Lum Chang had reached a depth of 30m when the collapse occurred.