2D and 3D FEM Assessment of “Trouser Leg” Diaphragm Wall Panels in a Deep Excavation in Singapore Soft Clay

摘要

A unique first-of-its-kind “Trouser Leg” diaphragm wall panel was constructed in one of the pastrnSingapore underground tunnel contracts. The tunnel was supported by 2.8m wide barrettes (longrndiaphragm wall panels) at 12m intervals and socketed into the hard stratum of Fort Canning BoulderrnBed (FCBB) while the intermediate short diaphragm wall panels floated in soft marine clays. The shortrnpanels were supported horizontally by a continuous 4m thick jet grouted slab below the tunnel base.rnThe detailed analyses of these complex long and short diaphragm wall panels were initially carried outrnusing FEM Plaxis 2D version 8.6. Two different cross-sections were examined, one representing thernshort panels, and the other the long panels. This paper describes how the separate analyses wererncarried out for the short and long panels. Field measurements are compared with the analyses inrnorder to examine the performance of the walls and review the two models. It also aims to address thernvalidity of the simplifying assumptions in the 2D models by comparing it with a 3D model of the longrnand short diaphragm wall panels with Plaxis 3D Foundation version 2.2. The 2D results are found tornbe in good agreement with the 3D results in various aspects. A parametric study was furtherrnconducted to review the effects of 3D long panel spacing to determine the conditions under which arn2D model would be significantly different from the 3D model. It is found that the complex long andrnshort wall panels can be modelled in 2D models to simulate a full 3D model with simplifyingrnassumptions.