Due to the extrusion shear action caused by long-term tectonic movement

fault zones are usually filled with fault gouge

significantly affecting the mechanical behavior of the rock mass and influencing the cementation effect of grouting. This study investigates the compression-shear behavior of grouted and non-grouted rock joints with sandy fillings

based on a tunnel passing through a fault zone in Yunnan Province

China. A series of direct shear tests was conducted on grouted and non-grouted rock joint samples with varying degrees of filling. The test results show that: 1) For both grouted and non-grouted specimens

sandy filling reduces the peak shear strength of joints. The former is because the sand weakens the contact between the joint walls

while the latter is because the sand affects the strength of cement stones and the thickness of the filled layer. 2) Grouting significantly improves the shear strength of rock joints with sandy fillings. The higher the filling degree

the greater the increase in shear strength after reinforcement. 3) Based on the joint roughness coefficient-joint compression strength (JRC-JCS) criterion

shear strength models for grouted and non-grouted rock joints with sandy fillings were established. The predicted values of these models were in good agreement with the test data. It is helpful to further understand the influence of fault gouge on grouting cementation of fractured rock mass.