Construction of North East Line tunnels at Singapore River Crossing

The construction of a twin 70 m long North East Line tunnels, under the Singapore River, was the second such crossing of the MRT system under the Singapore River. The Singapore River Crossing work was identified as a high-risk operation mainly because as the cover to the river bed was only 10m, any blow out or sudden ground loss could cause the tunnels to be inundated with sea-water causing a serious set-back to the North East Line Project. The presence of a transition zone where the ground changes from hard weathered sandstone to soft marine clay midway through the tunnel route, increased the potential for a blow-out or cave-in. This paper briefly describes these challenges that had to be overcome in the construction phase of the Singapore River crossing.