Particle shape effects on the cyclic shear behaviour of the soil–geogrid interface

Abstract The accurate determination of the interface shear strength is essential in the design of geosynthetic-reinforced soil structures. The particle geometries of three types of soil materials and a spherical granular medium are imaged and quantified using binary image-based methods and described in terms of regularity. Cyclic direct shear tests are conducted to investigate the effects of particle regularity on the interface shear strength, stress–displacement relationship, shear stiffness, and damping ratio. The results reveal that the interface shear strength and deformation strongly depend on particle regularity. The vertical displacement ratio is found to increase with particle regularity under the same cycle number. The interface stiffness is observed to increase with the cycle number for particle regularities of 0.453, 0.565, and 0.672 but decreases with the cycle number for a particle regularity of 0.971. For a given regularity, the trend of damping ratio with the increasing cycle number is contrary to the that of shear stiffness. Finally, it is observed that the cyclic friction angle decreases with increasing particle regularity, the relationship of which is determined using linear regression. Thus, the systematic quantification of particle shape characteristics can lead to a better understanding of soil–geogrid interface behaviour.