Frictional characteristics of rough granite fractures subjected to various normal loading /unloading rates and shear velocities

Abstract

The shear behavior of rock joints under dynamic disturbances is still not well understood, especially when subjected to irregular stress waveforms, which are common in real-world scenarios. In this study, a series of cyclic normal loading/unloading direct shear tests were conducted on rough granite fractures using a laboratory direct shear apparatus. The effects of different normal loading rates, unloading rates, and shear velocities on shear stress, apparent friction coefficient, normal displacement, and shear work were systematically analyzed. The experimental results indicated that as the normal loading and unloading rates increase and the shear velocity decreases, the peak shear stress and shear work decrease. Compared with quasi-static shear strength, dynamic normal stress disturbance may strengthen the dynamic shear strength or weaken it, and the strengthening/weakening degree is controlled by the normal loading/unloading rates and shear velocity. Furthermore, three distinct shear stress variation patterns (linear decay, nonlinear decay, and peak delay) are observed. These findings provide a theoretical basis for evaluating the stability of jointed rock masses under complex dynamic disturbances such as earthquakes, tidal effects, traffic loads, and blasting activities.

Keywords

rough granite fracture / normal loading/unloading rates / shear velocity / frictional strengthening/weakening

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