Full-scale experimental study on bearing capacity of uplift piles in wetting expansive soil

In order to study the bearing mechanism of pile foundations in unsaturated expansive soil, a full-scale experimental study on bearing capacity of uplift piles was carried out in the expansive soil area of Nanyang, China. Based on the field test, the evolution law of swelling deformation of foundation and the neutral point (section with zero relative pile-soil displacement) of pile during immersion were analyzed, and the weakening characteristics of the uplift bearing capacity of pile foundation after humidification were revealed by the axial force of pile, the ultimate friction resistance of pile side and the load-displacement curve. By comparing the results of full-scale test and model test, the evolution and the transfer law of pile lateral friction resistance were analyzed, and the calculation of pile lateral friction resistance after immersion was discussed. The results show that the swelling deformation of the expansive soil foundation after immersion mainly occurs in the atmospheric sharp influence layer. In the process of immersion, the neutral point of the pile moves down continuously and finally stabilizes at half of the pile body. Due to the lateral swelling pressure of the pile side induced by the wetting, the pile side friction after immersion is distributed as large at both ends and small in the middle, and increases linearly in the middle along the depth direction. Due to the humidification, the capillary suction stress in expansive soils significantly decreases, which far exceeds the contribution of the lateral swelling pressure to friction resistance, resulting in the significant weakening of pile bearing performance.