Effect of cyclic shear on interface characteristics of geogrid-soil-gravel mixture

In order to study the cyclic shear characteristics of soil-rock mixture-geogrid interface under different gravel contents, monotonic direct shear tests, cyclic direct shear tests and post-cyclic monotonic direct shear tests were carried out under different vertical stresses, shear displacement amplitudes and shear frequencies by using cyclic direct shear apparatus. The effects of five gravel contents (0%, 25%, 50%, 75%, 100%), three shear displacement amplitudes (1, 3, 6 mm) and three shear frequencies (0.2, 1.0, 2.0 Hz) on the peak shear stress and volume change of soil-rock mixture-grid interface were investigated. The test results show that when the gravel content is between 0% and 75%, with the increase of gravel content, the cyclic peak shear stress and maximum shear stiffness of the soil-rock mixture-grid interface increase, and the absolute value of final vertical displacement and the maximum damping ratio decrease. When the gravel content continues to increase to 100%, the maximum peak shear stress and maximum shear stiffness of the soil-rock mixture-grid interface decrease, and the absolute value of fmal vertical displacement and the maximum damping ratio increase. Under the same gravel content, a great shear displacement amplitude and a high shear frequency lead to a high maximum peak shear stress and the absolute value of final vertical displacement of the interface. Compared with the monotonic direct shear test, the internal friction angle and quasi-cohesive force obtained by the monotonic direct shear test after the cycle increase. In the range of 0%-75% gravel content, the interface friction angle and quasi-cohesive force increase linearly with the increase of gravel content. When the gravel content continues to increase to 100%, the interface friction angle and quasi-cohesive force decrease.