Analysis of Rock Friction Coefficient Characteristics Based on Friction Experimental Equipment

Friction coefficient, as a parameter of mechanical state, plays a crucial role in the shear failure of rocks in the field of Earth sciences. This paper investigates the frictional characteristics and anisotropy of rock by analyzing the coefficient of variation of the friction coefficient (f) and the anisotropy index of rock friction coefficients Af. Rotational friction tests were conducted using cylindrical granite against square samples of granite, sandstone, and andesite in three directions to analyze the relationship between the friction coefficient and various drilling parameters. This study reveals the variations in the friction coefficient and notable changes in the friction coefficient’s anisotropy. The results indicate a correlation between the alignment of turning points during the frictional stage and the rock strength. During the experiment, the friction coefficient undergoes cyclic variation before gradually stabilizing. The anisotropy of rotational friction follows the order: granite > andesite > sandstone, suggesting that the higher rock strength corresponds to greater frictional anisotropy. The rotational friction control coefficient C is derived and linked to the rotational friction stage. The duration of effective contact between rock surfaces and directional cutting efficiency are the primary factors contributing to anisotropy. The results offer practical implications for drilling design and seismic risk assessment in anisotropic rock formations.