In order to study the softening characteristics of gravel-geogrid interface during and after cyclic shearing

a series of displacement controlled monotonic direct shear tests

cyclic direct shear tests with 2 000 cycles and post cyclic direct shear tests were carried out on the gravel-geogrid interface using dynamic direct shear apparatus. The shear strength characteristics

volume change behavior

shear stiffness and damping ratio of the gravel-geogrid interface under four groups of normal stresses of 20

40

60 and 80 kPa were studied. The direct shear characteristics of the gravel-geogrid interface before and after cyclic shear were compared and analyzed. The results show that: in the cyclic direct shear test

the average peak shear stress of gravel-geogrid interface first increases and then decreases

and finally tends to be stable with the increase of number of cycles

and the interface shows shear softening characteristics; the vertical displacement increment of gravel-geogrid interface decreases gradually with the increase of number of cycles; the shear stiffness first increases and then decreases with the increase of number of cycles

and finally tends to be stable; the damping ratio first decreases and then increases with the increase of number of cycles

and finally tends to be stable; under the same normal stress

the peak shear stress increases and the residual shear stress decreases in the cyclic direct shear test compared with the monotonic direct shear test; the cyclic shear makes the interface cohesion increase significantly and the internal friction angle decrease.