Analysis of pile deformations during static load tests

Results of static load tests on two cast in place concrete piles in a soil composed of sand and gravel are compared to those obtained in a nonlinear numerical analysis. A finite element analysis was performed using an elasto-plastic kinematic hardening constitutive model to describe the soil shear stiffness degradation from very small to large strains. The very small strain shear modulus was obtained from shear wave velocities measured on the test site, the degradation curve was deduced from published test data on sands, and SPT blow counts were used for strength parameters. Computed values correlate very well with measured pile load displacement data. Computed axial load distribution along the pile shaft matches measured data for both piles only if negative skin friction and the associated residual forces are taken into account. This was done by lowering the ground water table prior to the load tests.