Cyclic shear characteristics of granite residual soil-geogrid interface with different water contents

Water content has a great influence on the mechanical properties of granite residual soil reinforced with geogrids. In order to study the cyclic shear characteristics of granite residual soil-geogrid interface under different water contents, a series of cyclic shear tests were carried out by large-scale indoor direct shear apparatus. The shear stress-shear displacement curves, shear strength, shear stiffness and volume of the soil-reinforced interface were analyzed under four values of water content (13%, 19%, 25%, 32%), three values of normal stress (50, 100, 150 kPa), four shear frequencies (0.2, 0.5, 1, 2 Hz) and four shear amplitudes (5, 10, 15, 20 mm). The test results show that: When the soil is saturated with water content of 32%, the peak shear stress and shear stiffness of the interface increase first and then decrease during the cyclic shearing process. The initial increase of the peak shear stress under the normal stress of 50, 100 and 150 kPa is 6.2%, 22.3% and 33.0%, respectively, indicating that the increase of the normal stress is greater than that of the interface at the initial stage. The interface of soil-reinforced unsaturated soil shows shear softening characteristics. Under different normal stresses, the cyclic shear strength of the interface is negatively correlated with the water content. When the water content is 13%, 19%, 25% and 32%, the final shear shrinkage of the interface is 4.6, 7.7, 8.6 and 7.2 mm, respectively, indicating that the shear shrinkage increases first and then decreases with water content. At each water content, the maximum shear stiffness of the interface decreases first and then increases with the increase of shear frequency, and decreases with the increase of shear amplitude. The shear frequency of 0.5 Hz has the strongest weakening effect on the interface shear stiffness of the interface.