Effect of Particle Regularity on the Bidirectional Cyclic Shear Behavior of Geogrid-Granular Material Interface

The bidirectional cyclic shear characteristics of geogrid-soil interface is more useful for the analysis of the seismic response of reinforced soil structures. The effects of bidirectional cyclic loading and overall regularity on a geogrid-granular material interface were investigated in this study through cyclic direct shear tests. The interface shear behaviors for different overall regularity under unidirectional and bidirectional cyclic loading were compared. The results showed that the shear strength, vertical displacement, enhancement coefficient, and shear stiffness under bidirectional cyclic loading decreased with an increase in the overall regularity. The increase in shear stress for a regularity of 0.707 was larger than that for a regularity of 0.975 when the initial normal loading and normal cyclic loading amplitudes increased. For variable overall regularity, the relative time shift at the backward half-cycle at different conditions increased from 0.6 s to 5.0 s with an increase in the normal cyclic loading amplitude. The maximum damping ratio correlated positively with the regularity and normal cyclic loading amplitude and correlated negatively with the initial normal loading. The peak shear stress in postcyclic direct shear tests under bidirectional cyclic loading was smaller than that under unidirectional cyclic loading for different regularity.