Modeling the Pile Cycle of an Axially Loaded Pile in Sensitive Natural Clay

Abstract

The pile cycle of an axially loaded displacement pile in a sensitive natural clay has been modeled using a coupled finite-element code for large deformations. The originality lies in the effective stress–based analysis with a consistent set of model parameters that considers all necessary soft soil features, i.e., anisotropy, destructuration, and rate dependency. Furthermore, the modeling approach is successfully benchmarked at all stages of the pile cycle (initialization, installation, equalization, loading). The benchmarking consisted of model calibration at element level, model selection using simulated and measured cone penetration test (CPTu) data, comparisons of measured and computed radial and shear stress during pile installation, and pile load testing. The results indicate that, with the exception of the absolute magnitude of the excess pore-water pressures generated during installation, the trends observed in the experimental data were captured well at all stages. Furthermore, several aspects of large deformation modeling of CPTu penetration, and pile installation were discussed. Most importantly, the difficulty in modeling the postpeak softening behavior and the balancing effects of the viscoplastic response (rate dependence) and strain-softening (destructuration) was highlighted. Finally, the empirical relation between the CPTu response and the bearing capacity of pile could be numerically confirmed. In conclusion, a first step is provided for the inclusion of the spatiotemporal response of sensitive natural clay over the full pile cycle in system-level geotechnical finite-element analysis.