Calculation and prediction of the uplift capacity of squeezed branch piles (SBP) are still immature. This study develops a method to predict the load-displacement relationship and ultimate capacity of SBP under pullup load by using a hyperbolic model to describe the nonlinear load transfer between pile-soil and plate-soil. The uplift bearing behaviors of SBP are analyzed through six sets of indoor model tests in homogeneous soils. The results, along with field tests of single-plate piles in layered soils and the indoor tests, confirm the high accuracy of the theoretical prediction method. The effects of three factors, including the pile side soil damage ratio (Rf), the horizontal earth pressure coefficient (k) and the damage angles of the soil under plate (psi), on the prediction results are analyzed. The results show that these factors significantly affect the second half of the loaddisplacement curve of SBP. Furthermore, as the Rf rises, the anticipated ultimate uplift capacity of SBP decreases linearly; as the k rises, it increases linearly; and as the psi rises, it increases nonlinearly.

An analytical framework to analyze the progressive failure behavior of axially loaded single pile embedded in unsaturated soils is presented by means of the load transfer method (LTM) coupling with shear displacement method (SDM). In this study, the proposed DSC-based interface constitutive model and modified small-strain stiffness model undertake the role of load-transfer mechanism for the pile shaft and pile end, respectively, and the shear displacement method is adopted to take the soil deformation surrounding the pile shaft in consideration. This study adopts a stress loading approach in the solution process, differing from traditional strain loading methods, which involves assuming a segment of displacement at the pile end. By successively applying loading increments, the entire load-displacement relationship of the pile is accurately determined, effectively reproducing the authentic stress process of pile foundation, and analyzing the gradual failure processes of friction-dominated piles and end-bearing friction piles under varying suction conditions in unsaturated soil. Customized model piles with smooth, rough and ribbed surfaces and a stress-controlled servo system were developed to conduct static load tests on pile foundations in unsaturated sand-clay mixture and grey clay. Model parameters were calibrated through suction-controlled unsaturated ring shear tests. Finally, the validity of the solutions proposed in this study was verified by comparing the results of static load tests on smooth, rough and ribbed model piles. Subsequently, the effects of suction, interface dilation, and environmental factors on the load-displacement response were analyzed. The research findings of this study can provide a theoretical basis for the design of pile foundations with displacement control in unsaturated soil.