A novel experimental–numerical approach to quantitatively evaluate open-ended piles in unsaturated ground

The groundwater level (GWL) fluctuates significantly with seasons, which may alter the suction distribution within the ground. Studies have shown that the variation of soil suction can affect the mechanical behavior of the piles. However, few pile load tests have been conducted under controlled suction distribution conditions. Thus, there is a lack of quality data to numerically quantify the influence of suction on the bearing capacity of piles in unsaturated ground. In this study, we propose a novel experimental–numerical approach to quantitatively examine the effects of suction on open-ended single piles in unsaturated ground. A novel model test device was first designed in which the suction distribution of the soil was uniformly controlled using hanging water column technique with a microporous membrane filter. Using this device, a series of load tests were conducted on a model open-ended pile in sandy ground under three specific suction conditions. A soil–water–air coupled finite-element-finite-difference analysis method was used to simulate the model test results. The test and simulation results showed that the suction generated by the changes in GWL increases the Bishop-type skeleton stress and dilatancy of the soil, thereby strengthening the bearing capacity of the pile. Additionally, the numerical method accurately captured the bearing characteristics of the pile in unsaturated ground, making it possible for engineers to efficiently estimate the bearing capacity of the pile in real unsaturated ground, which still remains a puzzle problem and is being avoided constantly till now.