Effect of Particle Overall Regularity on Macro- and Microscopic Cyclic Shear Behavior of Geogrid–Granular Aggregate Interface

Macro- and micromechanical interactions between the geogrid and granular aggregates considering particle shape effects are essential for the performance of reinforced soil structures under cyclic normal loading (CNL). Crushed limestone and spherical granular media were mixed to obtain samples with different overall regularities (OR = 0.707, 0.774, 0.841, 0.908, and 0.975). Direct shear tests under CNL were conducted at various overall regularities, normal loading frequencies, and waveforms. Consistent with experiment tests, a discrete-element method (DEM) simulation was performed, incorporating authentic particle shapes obtained through three-dimensional (3D) scanning technology. The results showed that the macroscopic interface shear strength and volume change decreased with an increase in the overall regularity and normal loading frequency. The interface shear strength and deformation under the square waveform are bound to be higher than that under other waveforms. The coordination number, porosity, and fabric anisotropy were used to explain the macroscopic interface shear behavior in relation to the overall regularity. A higher coordination number and stronger contact force were observed with a decrease in the overall regularity. As the overall regularity decreased, the interface integrity and stability became stronger, with the result that the reinforced soil structure can withstand a larger principal stress deflection. Through experimental and DEM analyses, the underlying explanation for the effect of particle shape on the mechanical interaction of reinforced soil was revealed.