Experimental Study On Shear Characteristic Of Rock-like Infilled Discontinuities

Discontinuities are widely distributed in natural rock mass,which plays a dominant role in the mechanical properties and deformation characteristics of rock mass.Infill materials found in natural rock joints may cause a reduction in joint shear strength,influencing rock mass stability.This paper reports a study aimed at shear characteristic of rock-like infilled discontinuities.On the basis of Barton's standard roughness profile,the JRC values of 3,7,15 and 19 has been choose to casted rock-like specimens with concrete,cement mixed with sand and water in a 26:25:10 ratios by weight form a viscous paste that can be moulded readily into our wanted shape,with sands and different water content of the clay used as infill materials.Director shear tests were carried out in the RYL-600 Rock Mechanics Shear Rheometer at normal stress of 0.5,1,1.5 MPa,the shear behavior and the effects of the factors on the shear characteristic of rock-like infilled discontinuities has been discussion.And PFC2 D has been employed to study the infill sands and clay soil how to influence the shear characteristic of roughness discontinuities from microscopic view.The results indicate that:(1)Shear stressdisplacement test curve can be divided into gentl type and hump type,the discontinuities of small JRC value and the filled discontinuities of larger JRC value under low normal stress mainly belong to gentl type;the clean discontinuities and the filled discontinuities of larger JRC value under high normal stress mainly belong to hump type.(2)Peak shear stress increases as JRC value increases.The friction force and climbing resistance of the rock discontinuities increases due to the existence of normal stress.Fill material has a significant weakening effect on the shear strength,clay with different moisture content has more weakening effect than sands,and clay soil has a most obvious weakening effect on the peak shear stress of the discontinuities.(3)The JRC-JCS model is modified by introducing the weakening coefficient ?,the maximum shear stress of filling discontinuities calculated by modified JRC-JCS model and compared with the experimental values has a good linear relationship.(4)Normal displacement increases as JRC values increases,the increase in normal stress was usually associated with a reduction in joint dilation,and the reduction increase as normal stress increase.As for infilled discontinuities,the dilation or shear contraction most depends on the relation between compression of infill and asperity dilatancy,if the compression of infill took over from asperity dilation as the predominant at the shear behavior,overall shown dilation,or shear contraction.(5)The discontinuities dilation pattern can be divided into three modes: pure shear dilation,pure shear contraction and shear dilation-contraction,the infilled discontinuities most belong to shear contraction,and the large roughness infilled discontinuities most belong to shear dilation-contraction.The shear displacement of the peak strength point of the discontinuities is about 0.72 times the maximum shear dilatancy point.(6)Through the numerical simulation of PFC2 D we obtained that the occurrence of micro-cracks in the discontinuities mainly concentrated in the vicinity of the peak shear stress,Micro-cracks are mainly composed of shear cracks,due to the presence of the filler,reducing the micro-cracks in the discontinuities surface,thus reducing the discontinuities damage.