Experimental and numerical study of asperity degradation in the direct shear test

• The shearing mechanisms and asperity degradation of rock joints were studied.
• PFC2D was used for numerical simulation of direct shear tests.
• Direct shear tests under different normal stresses were undertaken.
• Three shearing mechanisms of sliding, surface wear and shearing off were observed.
• A good agreement was found between the results of numerical and experimental tests.

In this paper, the shear behaviour and mechanisms of asperity degradation of rock joints under direct shear tests were studied using numerical and experimental approaches. PFC2D was used for numerical simulations, in which the intact material is simulated by a dense packing of circular particles bonded together at their contact points and by breakage of these bonds under loading regimes, the damage process is simulated. The joint interfaces were simulated by a newly developed modified smooth joint model in which micro-scale slip surfaces are applied at contacts between particles of upper and lower blocks of the shear box. In order to study the ability of this numerical approach in reproducing the shearing mechanisms and asperity degradation of rock joints in direct shear tests, a comparative study was carried out against the physical experiments. Experimental and numerical direct shear tests were carried out on saw-tooth triangular joints with the base angles of 20° and 30° under different normal stresses. Three shearing mechanisms of sliding, surface wear and asperity shearing off were observed in these experiments. The comparison of the shear behaviour and mechanisms of asperity degradation of physical and numerical experiments showed that the results of numerical models are in good agreement with physical experiments and this numerical approach can reproduce the shear behaviour of rock joints under different loading conditions.