Three-Dimensional One Strut Failure Soil-structure Interaction Analysis for Strutted Diaphragm Wall Design by a New Mathematical Model - Two-Dimensional Plane Strain Finite Element Analysis combined with Plate Bending Theory

摘要

After a section of the Nicoll Highway diaphragm wall (D-wall) construction collapsed in 2004, thernSingapore authority require strutted D-wall designs to consider one strut failure (OSF) load cases –rnfailure of a single strut or anchor at each construction stage. OSF is 3-dimensional (3D) and non-planernstrain. It redistributes the lost strut load horizontally and vertically with arching effects. Rigorous OSFrnanalyses would need 3D finite element method (OSF/3D FE), which takes huge amounts of computingrntime and memory space. Thus OSF is often analysed in 2-dimensional finite element (OSF/2D FE)rnmodels assuming either the whole layer of struts removed (WSF/2D) or their axial stiffness reduced.rnHowever, the soil-structure interaction is complex and the design bending moments (BM) and shearsrnare often under-estimated. This paper presents a new and generic mathematical model to solve thernOSF problem by applying the orthotropic plate bending theory (PB) to OSF/2D Plaxis models.rnFictitious “rigidity factors” are introduced to solve the PB governing equations (eqn) and determine thernstrut loads, wall BMs and shears. The OSF/2D–PB model is then applied to the strutted D-wall designrnat Upper Changi Station, Singapore Downtown Line Stage 3 MRT extension Package C. This is arnnew railway line linking the Stage 1 Chinatown Station to airport with 9km tunnels and 6 stations eachrnabout 30m wide, 200m long and 30m underground. The results are compared with the OSF/3D Plaxisrnresults. The OSF/2D–PB model and its benefits over the OSF/3D and the WSF/2D are discussed.