Abstract
The basic friction angle is one of the important parameters reflecting the friction characteristics of joints, however, water saturation and temperature have great influence on the basic friction angle. In this study, 11 types of rocks were measured by using the tilt test to investigate the effect of water saturation on the basic friction angle. The basic friction angle displays a reduction trend with decreasing water saturation, because the loss of surface moisture will reduce the suction effect. In addition, the basic friction angle is much smaller at a low temperature, because the created ice film promotes the shear slide of blocks. However, the tilt test should not be used at a low temperature, because the adhesive ice film on the sample surface could prevent the slide activation of cylindrical samples. Moreover, the effect of freeze-thaw treatment was also investigated. With increasing freeze-thaw cycles, the surface roughness increases while the basic friction angle decreases, because the bulges are more easily crushed under normal stress after freeze-thaw damage. It is suggested that the direct shear test method under a low normal stress should be adopted to determine the basic friction angle at the low temperature and freeze-thaw condition. This study has provided a better understanding of the changes of basic friction angle and a good choice of suitable measurement method at different temperature conditions.