Mechanical Behaviors of Cast-In-Place Pile in Loess Area upon Wetting Effect

In order to clarify the change mechanism of bearing properties of bored piles in wetted loess during rainfall infiltration, static load test and infiltration test of bored piles in wetted loess are carried out. The water content, cumulative wetting amount, axial force of the pile body and settlement of the top of the pile in the wetted loess around the piles were monitored in real time. The results show that: With the occurrence of wet subsidence of loess, the axial force distribution of the pile body is roughly in the shape of "D", and the location of neutral point also changes according to the different stages of wet subsidence. The increase of loess wetting deformation around the pile and the change of pile settlement at different stages during the infiltration process change the direction and size of pile-soil relative displacement, which leads to the change of bearing properties of the piles. Based on the principle of unsaturated soil mechanics, the change of matric suction is used as the key parameter to calculate the wet subsidence deformation of the soil around the pile. Considering the change of shear strength at the loess-perforated pile interface, a pile shaft friction load transfer curve model applicable to the loess-perforated pile interface is proposed. Also, the traditional load transfer method is simplified and corrected, so as to calculate the axial force and pile-side resistance change curve of the perforated piles. The experimental values are compared with the calculated values, which are in good agreement. The research results can support the design of bored piles and the evaluation of engineering properties in the region of collapsible loess under complex environmental loads.