Study on shear mechanical responses of three-dimensional rough joint surfaces under cyclic dynamic load boundary conditions
Shear tests of three-dimensional rough joint surfaces were conducted under superimposed actions of sinusoidal cyclic normal dynamic loads and sinusoidal cyclic shear displacements.The effects of initial normal static load(Fs),dynamic normal load amplitude(Fa),dynamic normal load frequency(fv)and the number of shear cycles(N)on the shear properties were explored.With an increasing of Fs or Fa,the variation range of the normal load for the joint surfaces gradually increases.Within a shear displacement cycle,the shear load experiences a variation of fluctuating increase→fluctuating decrease→fluctuating increase.The peak shear load in stable states increases by 4.90 times and 65.12％,respectively,with an increasing of Fs and Fa,implying a gradually enhanced shear resistance capacity.However,as f,increases,the progressive accumulation of damage on the joint surfaces results in a gradual reduction in the peak shear load,and the moment when the peak shear load occurs gradually moves forward.The peak shear load in stable states decreases by 17.49％.Within a shear displacement cycle,the normal displacement of joint surfaces shows a variation trend of fluctuating increase→fluctuating decrease→secondary increase→secondary decrease.When the joint surface shears away from the initial position,the continuous"climbing effects"of the surface asperities lead to a gradual increase in the normal displacement.A significant negative correlation between the normal displacement and normal load for the joint surfaces is recognized,and the maximum normal displacement lags behind the maximum shear displacement by a quarter of a normal load period.As N increases,the continuous wear and deterioration of the joint surfaces lead to an exponential decrease in the maximum normal displacement.The maximum normal displacement exhibits change characteristics of gradually decreasing withFs,gradually increasing with Fa,and initially increasing and then decreasing with fv,respectively.The surface roughness coefficients of joints after shearing decrease by 57.79％and 43.26％withFsandFa respectively,while shows a variation of first increasing and then decreasing with fv at 1 Hz as the inflection point.
rock mechanicsrough joint surfacecyclic shearnormal dynamic loadnormal deformationsurface wear
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