Performance of Excavations for Depressed Expressway in Singapore

The construction of the tunnels in the Central Expressway (CTE) Phase II of Singapore involved deep excavations. An extensive instrumentation program was carried out alongside the excavations to monitor the behavior of the temporary support systems. In this paper, the performance of the deep excavations in mixed-soil profiles in the construction of the CTE Phase II is presented and discussed. Emphasis will be given to the lateral wall deflections, soil settlements, and prop loads. The instrumentation resultings from the construction of the CTE Phase II shows that for excavations with a combined thickness of soft-soil layers (including fillor top-soil layer) of less than 0.9H and 0.6H overlying stiff soils, generally, the movements were less than 0.5% of H and 0.35% of H, respectively, where H is the depth of excavation. For excavations with a combined thickness of soft-soil layers of less than 0.9, 0.8, and 0.6H overlying stiff soils, the observed maximum apparent earth pressure was about 0.6, 0.4, and 0.25γH, respectively, where γ is the average total unit weight of the soils.