Numerical study of a large diameter shaft in old alluvium

Abstract

Consolidation finite element analysis was performed using PLAXIS to simulate the excavation and construction of a large diameter circular shaft in Old Alluvium at the Changi Water Reclamation Plant. The excavation support system consisted of a diaphragm wall and internal ring walls. PLAXFLOW was used in conjunction with PLAXIS to perform axisymmetrical groundwater flow computations. The Hardening-Soil model was employed to represent the constitutive behaviour of Old Alluvium. The duration of each excavation and construction stage was considered in the finite element model. A method was proposed to account for the temperature effects during the casting of internal ring walls on the behaviour of the diaphragm wall. The numerical hoop strains agreed well with instrumentation results. Extensive parametric studies were conducted to investigate the influence of various parameters on the behaviour of the circular shaft.