To delve into the micromechanical deformation and failure mechanisms of the geogrid-soil interface, a series of direct shear test models for granite residual soil with geotextiles containing different rock contents (50%, 75%, and 100%) under two loading conditions (normal static load and normal cyclic load) were established using the discrete element software PFC3D, based on the results of large-scale indoor direct shear tests. The study analyzed changes in micromechanical shear characteristics such as porosity, coordination number, fabric anisotropy, and particle rotation at the geogrid-soil interface. The results indicated that the change in sample porosity increased with higher rock content and was primarily concentrated near the shear plane, with normal cyclic loading causing a slight increase as well. The coordination number at the interface ranged between 5.19-6.05, 4.74-5.77, and 4.35-5.53 as the rock content increased, indicating a reduction in particle contacts. Under both loading conditions, the principal direction of anisotropy of contact forces between particles shifted, with the normal contact forces under normal static load being greater than those under normal cyclic load. The average rotation angle of particles with 100% rock content was smaller than that with 50% rock content, and normal cyclic loading caused a slight increase. Overall, the rotation angle distribution was normally distributed, with the maximum value located near the shear plane.