Modified β-method for Pile Design in Partially Saturated Soils: Theoretical Considerations for an Effective Stress Framework

This study presents a theoretical approach to calculate the axial capacity of deep foundations in partially saturated soils. The β-method for deep foundation side resistance has been modified to include the effects of matric suction and varying water contents within an effective stress framework. This includes considerations for suction stresses along the length of the foundation element and a reduction in K_0 due to tension cracking near the surface. For coarse-grained soils, side resistance calculated from the conventional and modified β-method share close agreement. This is not the case for fine-grained soils, which are sensitive to suction stresses and tension cracking. Fine-grained soils with low Poisson’s ratio are highly influenced by tension cracking, resulting in predicted side resistances that are considerably lower than the conventional approach. With high Poisson’s ratio, tension cracking is reduced, and the foundation accumulates more suction stresses, increasing the predicted side resistance.