Evaluating Pile Setup Using Numerical Simulation and Introducing an Elastoplastic Constitutive Model for Clays

Abstract

An elastoplastic constitutive model was developed to define cohesive soil behavior. During pile installation in saturated ground, the soil adjacent to the pile disturbs causing large displacements and numerous variation in the porewater pressure in the soil-pile interface zone. Therefore, the soil disturbance and the corresponding decline in the soil shear strength were included in the developed constitutive model. After end of pile driving (EOD), the surrounding disturbed soil tends to regain its strength over time due to both consolidation and thixotropic effects. In this paper, the soil thixotropy was simulated by applying a time-dependent reduction parameter, β, which affects both the interface friction and the soil shear strength parameters. In order to examine the proposed model, numerical simulation of pile installation and the following increase in the pile capacity over time (pile setup) was performed for a full-scale pile load test case study. Finite element (FE) software Abaqus utilized to simulate the pile installation and following pile load tests. Dissipation of the induced excess porewater pressure was modeled through applying conventional consolidation theory. The proposed model was developed based on disturbed state concept and application of the modified Cam-Clay model. Pile installation was modeled by combination of two phases in an axisymmetric FE model: creating a volumetric cavity expansion followed by applying a vertical shear displacement (penetration). The FE simulation results included: (1)-developed excess porewater pressure in the soil body during pile installation and its dissipation over time after EOD, (2)-increase in effective lateral stresses at the pile-soil interface, and (3)-the pile setup values attributed to both the soil consolidation and its thixotropic responses. Comparison of the FE simulation results with the measured values obtained from load tests conducted on a full-scale instrumented pile indicated that the developed constitutive model is able to appropriately predict pile installation and following setup.