Experimental study on mechanical behavior and working mechanism of unloading pile-sheet retaining walls

The unloading pile-sheet retaining wall is a new type of support/retaining for embankment slopes and has demonstrated excellent performance in engineering applications. However, its mechanical behavior and operational mechanisms are still not fully understood. This study conducted model tests on unloading piles and cantilever piles. Backfilling was conducted in four stages: 30 cm for the first three layers and 10 cm for the final one. The tests focused on the evolution of earth pressure, internal forces, and deformation in both pile types. The results show that: 1) Upon completion of backfilling, the horizontal displacement at the top of the cantilever pile reaches 81.76 mm, which is 5.45 times that of the unloading pile (14.99 mm). The maximum earth pressure on the unloading pile is 10.08 kPa, accounting for 66.40% of the 15.18 kPa recorded on the cantilever pile. The unloading effect alters the distribution pattern and magnitude of earth pressure. 2) The bending moment distributions differ significantly. The cantilever pile exhibits a “fish-belly” pattern with a maximum moment of 115.8 N· m. In contrast, the unloading pile shows an “S-shaped” profile, featuring a pronounced point of contraflexure at the unloading platform and a maximum negative moment of −60.99 N· m. 3) Incorporating an unloading platform effectively reduces earth pressure and enhances the anti-overturning moment. These effects jointly improve sliding resistance and overall structural stability. These findings offer theoretical insights and technical guidance for the practical implementation of unloading pile-sheet retaining walls.