Time-Effect Analysis Of Deep Excavations In Soft Clay

In process of deep excavation in soft ground,the support system's deformation,external loads and internal forces are various with time. Creep effects are detectable. Meanwhile,the unloading induced by the excavation leads to the dissipation of excess pore water. In other words,consolidation effects occur. While much effort has been made in each area,this paper is a research of coupled effect of both consolidation and creep.Based on the available rule of variation in undrained shear strength during excavation,and the basic idea of the MERCHANT model,this paper presents a constitutive relationship for saturated cohesive soils,capable of taking into account both stress path and time-dependent effect. It's named by the author as modified MERCHANT model. The resulting nonlinear modulus equations make the excavation analysis more reasonable.Plane strain finite element method is applied to incorporate the constitutive law. The code is able to simulate the coupled effect of consolidation and creep,interaction between soil and structure,and the complicated procedure of staged excavation. And this code utilizes a calculation method more reasonable than conventional ones. Four types of constitutive models are provided by the code:linear elastic model,Duncan-Chung model,nonlinear elastic model taking stress path into account and modified three-element model. Contact element is used to simulate possible sliding between soil and structure.With this code,analysis is made concerning the pore pressure dissipation,lateral deformation of the support,ground settlement,bottom heave,and variation in earth pressure and support forces;Both effects of consolidation and coupled effects of consolidation and creep are considered;Furthermore,different combinations of cohesion,permeability and excavation width are elaborated.Finally,a real example is given and comparison between computation and observation is made. The result indicates that this code is good for simulating time-dependent behaviors of excavation in soft ground. In addition,time series method is also applied in this paper for analyzing and predicting the time-dependent behavior.