Simplified approaches for predicting the nonlinear load-displacement response of single pile and pile groups in unsaturated soils

A simplified analytical approach is proposed for predicting the load-displacement behavior of single piles in unsaturated soils considering the contribution from the nonlinear shear strength and soil stiffness influenced by matric suction. This approach includes a Modified Load Transfer Model (MLTM) that can predict the nonlinear relationships between the shear stress and pile-soil relative displacement along the pile shaft, and between the pile base resistance and base settlement. The proposed model is also extended for pile groups to incorporate the interaction effects between individual piles. The analytical approach is validated through a comparative analysis with the measurements from two single pile tests and one pile group test. In addition, a finite element analysis using 3D modeling is carried out to investigate the behavior of pile groups in various unsaturated conditions. This is accomplished with a user-defined subroutine that is written and implemented in ABAQUS to simulate the nonlinear mechanical behavior of unsaturated soils. The predictions derived from the proposed analytical and numerical methods compare well with the measurements of a published experimental study. The proposed methodologies have the potential to be applied in geotechnical engineering practice for the rational design of single piles and pile groups in unsaturated soils.