Surface roughness evolution and mechanical behavior of rock joints under shear

Abstract

Abstract To find out the relationship between topography and mechanical behavior of rock joints, experimental investigations of extension fractures induced in samples of several sandstones have been carried out in the laboratory. Shear tests under uniaxial compression were conducted at three different angles of shearing: 35°, 40° and 45°. Such an arrangement allowed the joint behavior to be investigated under different normal forces. The shear experiments were stopped at various shear displacements so that the damage process of joint surfaces could be examined in reference to the loading history. Laser profilometry was employed for the non-contact asperity measurement. Fracture surfaces of each jointed rock sample were digitized both before and after every stage of mechanical excitation. The scanning results were analyzed according to the fractal theory. The geostatistical method of variogram analysis was employed to determine the fractal dimension (D) and the y-intercept (A) on a log-log plot of variance of rough surface profiles vs lag. Based upon the experimental data, an empirical evolution law of surface damage has been developed to predict the degradation of surface roughness in the process of shearing. The law expresses the roughness parameters (D and A) as functions of the plastic shear work.