Physical Model Test and Theoretical Study on the Bearing Behavior of Pile in Expansive Soil Subjected to Water Infiltration

Abstract A loading test device with infiltration function is developed to conduct model tests on the bearing behavior of single piles in expansive soil. The infiltration observation test and vertical static-load test before and after infiltration are carried out. Meanwhile, a two-phase nonlinear analysis approach is put forward to research the bearing characteristics of single piles in expansive soil by considering the influence of water infiltration. The method is divided into two phases: the infiltration phase and post-infiltration loading phase. In the infiltration stage, based on a load transfer function that can simultaneously describe the distribution of positive and negative frictional resistance, combining with the variation law of soil heave with depth, a nonlinear analysis method to calculate internal forces of single piles during water infiltration is proposed. Based on the infiltration stage, the formulas for calculating the bearing capacity of single piles in expansive soil after water infiltration are derived by taking into account the residual displacement of the pile–soil interface caused by soil heave, in the post-infiltration loading stage. The validity of the proposed approaches are confirmed through comparisons with the tests results. It is found that in medium-expansive soil, the relative displacements of pile top and surface increase rapidly with time, and then tend to be stable after about 14 days. Positive and negative frictional resistances occur along the pile shaft during water infiltration. Axial forces are tensile along the pile shaft, and the neutral point is found at one-half of the pile length. The bearing force of single piles in expansive soil after water infiltration is reduced obviously than that before water infiltration.