Roughness Evaluation for Distinguishing Fresh and Sheared Rock Joint Surfaces with Different Sampling Intervals

Abstract

The subtle alteration of surface geometry from a fresh surface to a sheared surface usually results in a considerable variation in the shear strength of jointed rock mass. Through profiling surfaces of the granite joints before and after the shear tests, an evaluation scheme was newly proposed by determining a desirable characteristic index and sampling interval of surface measurement in order to distinguish fresh and sheared joint surfaces quantitatively. The measured data demonstrated that although the mean Z₂ (root-mean square first derivation) values of all the profile lines were confirmed reasonable for estimating the joint roughness coefficient (JRC) value of the fresh joint surface, it could not completely evaluate the roughness of the sheared joint surfaces. Meanwhile, the distribution of slope angles, as the characteristic parameter, was proved to enable to clearly distinguish the fresh and sheared rock joint surfaces incorporating the small sampling scales (≤0.1 mm). The numerical simulations implemented in a mechanical shear model could confirm the critical effect of a slight change in surface geometry and further prove that the sampling interval of 0.1 mm could sufficiently capture the evolved waviness and unevenness of rock joint surfaces. Overall, it was confirmed that the results of our study provide new clues for evaluating the surface roughness of fresh and sheared rock joints and can be beneficial for understanding the variation of surface geometry during the shear process.