During pile installation, the stresses and void ratios in the surrounding soils change significantly, creating large displacements, large strains, soil disturbance and the development of excess porewater pressures. The surrounding disturbed soil tends to regain its strength with time due to both consolidation and thixotropic effects. In this paper, the pile installation process and the subsequent consolidation, thixotropy and load tests conducted at different times after end of driving (EOD) were modeled for the test piles at Bayou Laccassine Bridge site, Louisiana. In the FE model, the pile was considered as an elastic material and the anisotropic modified cam-clay model (AMCCM) was used to describe the behavior of the surrounding clayey soils. Pile installation was modeled by applying prescribed radial and vertical displacements on the nodes at the soil-pile interface (volumetric cavity explanation), followed by vertical deformation to activate the soil-pile interface friction and to simulate static load tests. The thixotropic effect was incorporated by applying a time-dependent reduction parameter, β, which affects both the interface friction and the material properties. The results from the FE numerical simulation included the development of excess porewater pressure during pile installation and its dissipation with time, the increase in effective lateral stress at the pile-soil interface, changes on stress state of surrounding soil, and the setup attributed to both the soil consolidation and thixotropy at different times. The FE results are compared with the measured values obtained from the fullscale instrumented pile load tests, which showed good agreement between measured and FE predicted results.

The lateral resistance of three pile group configurations was investigated using three dimensional (3-D) finite element modeling. The three pile groups considered in the study were a vertical pile group, a battered pile group, and a mix of vertical and battered piles in a group. The study was motivated by the full-scale static load test that was conducted on the M19 pier foundation in the I-10 twin span bridge in Louisiana. The static lateral resistance of the M19 battered pile group was investigated previously using a 3-D finite element simulation and verified with the aid of experimental results. In the present study, the M19 battered pile group model was used as the basis for the vertical and mixed pile groups for developing their 3-D finite element models. The nonlinear material behavior was accounted for using elastoplastic constitutive models such as the concrete damaged plasticity model and the anisotropic modified Cam clay model. The lateral resistance of the pile groups was investigated in terms of load–displacement, axial load, bending moment, pile damage, soil resistance, and p-multipliers. The results show that the battered pile group had the largest lateral resistance, followed by the mixed and vertical pile groups, respectively. The largest lateral load share was carried by the two middle rows in the battered pile group, while it was in the leading row in the vertical and mixed pile groups. The soil resistance profiles show that the vertical pile group mobilized greater soil resistance than the battered and mixed pile groups at the same lateral load. The back-calculated p-multipliers are the highest in the battered pile group case, followed by the mixed and vertical pile groups, respectively.

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