Study On Shear Characteristics Of Rock Joints Based On Wavelet Analysis

In rock engineering,the shear behavior of jointed rocks mainly depends on the surface characteristics of joints.It has been found that rock joint surfaces can be decomposed into a first-order waviness and a second-order unevenness,which play different roles in the shear behavior.In order to quantitatively estimate their influences,wavelet analysis was employed to decompose joint surfaces,and a two-dimensional particle flow code combined with direct shear experimental verification was used to study the micro-scale failure pattern of wavy joints with different undulation angles(4°,8°,12°,16°,20°)and first-order waviness wavelength(15mm,20 mm,25mm)and second-order unevenness wavelength(1mm,2mm,3mm)on the shear strength.The results show that :(1)the wavelength slightly influences the shear strength,while the undulation angle is the dominant factor determining the shear strength,The shear strength and frictional angle of the waveform increase linearly with the increasing undulation angle;(2)In the process of direct shear,the crack propagation process of the two kinds of waveform is also changed due to the change of normal stress,but the tensile crack is still the main crack;(3)The relationship between the undulation Angle and the friction Angle of the first-order waviness is y=0.7727x+12.88,and that between the undulation Angle and the friction Angle of the second-order unevenness is y=0.706x+12.808.To further study the shear characteristics of natural jointed rock,two-dimensional particle flow numerical simulation of composite jointed surface with different combination of undulation angles was carried out.The results showed that:(1)When the waviness undulation angle is small or the waviness undulation angle is large(under high normal stress),the increase of the unevenness undulation angle does not have much effect on the crack direction of the composite joint,but will intensify the crack propagation behavior;(2)When the waviness undulation angle is small and the normal stress is low,the shear crack grows slowly in the shear process,while the tensile crack grows obviously with the increase of the unevenness undulation angle,and the crack also appears earlier.Under the high normal stress,the tensile crack and the shear crack grow obviously with the increase of the shear displacement.When the waviness undulation angle is large,the increase of the unevenness undulation angle has little effect on the shear crack and tensile crack under the low normal stress,but the effect of the unevenness undulation angle under the high normal stress cannot be ignored;(3)When the waviness undulation angle is small,the shear strength increases with the increase of the unevenness undulation angle,and increases with the increase of the normal stress.When the waviness undulation angle is larger,the effect of the unevenness undulation angle on the shear strength is weakened.