Comparative analysis of basic friction angles of rock joint based on different experimental methods

The basic friction angle of rock joints is a key parameter for stability assessment in rock mass engineering and determination of slope instability. The reliability of its testing methods directly dictates the representativeness and applicability of this parameter. Focusing on common basic friction angle testing methods such as direct shear tests, tilt tests, push-pull tests, and rebound tests, this study obtained the mechanical properties of rock joints. Using sandstone and granite as test specimens, the test data based on different testing methods were collected and comparatively analyzed. The results show that: In direct shear and push-pull tests, the stress state of structural planes is significantly affected by the sliding distance of specimens; in tilt tests, the stress state is related to the rotation angle and dimensions of specimens. During direct shear tests, normal stress induces strong interlocking and frictional effects on joints, resulting in higher test data than other methods. As normal stress increases, the basic friction angle first decreases and then stabilises. Excessively high normal stress or repeated testing, however, causes damage and fracturing of rock joints, leading to greater data dispersion. In both tilt and push-pull tests, the basic friction angle decreases with an increase in the number of tests. Specifically, the data from push-pull tests are 1°–2° higher than those from tilt tests, with smaller dispersion. Data from rebound tests exhibit significant fluctuations, which are influenced by the surface condition of specimens and impact parameters. This research provides a basis for the theoretical study and engineering application of the basic friction angle of rocks.