Experimental Investigation of Passive Failure against Retaining Structures under Various Displacement Modes

This study conducted model tests to simulate the passive failure of granular soils under different displacement modes, including the translational and rotation modes concerning different pivot points, to investigate the effect of displacement modes on the failure mechanisms and earth pressure. Experimental results were compared with the finite element limit analysis (FELA) method and theoretical solutions. Test results show that a composite log-spiral shear band formed under the translational mode, whereas a single log-spiral shear band can be observed under the rotation mode around the top. Furthermore, the failure mechanism of the rotation mode around the midpoint involved wedge-type and rotation-type flow zones induced by the combined active unloading and passive loading. Given a lower pivot point, the required wall rotation for the soils reaching the passive limit state increases. Earth pressure distribution varies across displacement modes: in the translational mode, earth pressure increases uniformly with depth, whereas rotational modes show nonlinear distributions. Classical earth pressure theories are only applicable to the translational mode and tend to overestimate passive earth pressure in rotational modes. The experimental results provide a valuable benchmark for validating numerical simulations of passive failure, and charts of passive earth pressure coefficients considering displacement modes are presented for the design of rigid retaining structures.