Study On Roughness Evaluation Method Of Rock Mass Discontinuities

The rock mass discontinuities refer to the material interface with a certain shape and scale in the rock mass,such as cracks,layers,faults,etc.The shear strength of discontinuities has a great influence on the overall mechanical properties of rock mass.The important purpose of the current research on the roughness of the discontinuities is how to quickly and accurately quantitatively analyze the roughness of the discontinuity,and then combine the surface roughness to estimate the peak shear strength.At present,although the existing methods for characterizing the roughness of discontinuities can better describe the undulating morphology of structural planes,there are still some shortcomings,mainly as follows:the physical meaning of roughness evaluation parameters is not clear,and its peak shear strength is not closely related.In this paper,combined with the shear failure mechanism of structural plane,the completely consistent rock mass discontinuities were selected.Based on the roughness evaluation parameter of structural plane-projection area percentage（PAP）,the main research contents and related results are summarized as follows:（1）Based on the rock discontinuity roughness evaluation parameter PAP,the rock discontinuity profile roughness evaluation parameter PAP_2D is further proposed.PAP_2D refers to the ratio of the projection length of all potential contact line segments of the rock mass discontinuity profile in the plane perpendicular to the shear direction to the horizontal projection length of the rock mass discontinuity profile.Based on PAP_2D,the roughness of 10standard profiles proposed by Barton is evaluated.The results show that there are obvious anisotropy and point spacing effects in the roughness of rock mass discontinuity contour lines based on PAP_2D.In addition,the relationship between PAP_2D and JRC values of 10 standard profiles is fitted by four functions.The results show that PAP_2D has a good correlation with it,and the logarithmic correlation between them is higher than that between Z₂ and JRC.Three groups of artificially simulated rock mass discontinuities R_1,R₂ and R₃ are selected to evaluate the roughness of the contour line by PAP_2D.The results show that for the same structural plane,the PAP_2D evaluation results are close to the PAP_3D evaluation results under the same shear direction and sampling interval.The roughness evaluation results obtained by Grasselli’s method and back-calculation method are compared and analyzed.The calculation results show that PAP_2D has a good correlation with the calculation results of the above two evaluation methods.（2）Research on the evaluation method of structural plane roughness based on PAP^*.In this paper,based on the study of the discontinuity roughness evaluation parameters PAP,based on the Patton’s model and the Grasselli’s model,the discontinuity roughness evaluation parameter PAP^*,which considering the undulating angle distribution characteristics of the potential contact part of the structural surface is proposed.PAP^*further considers the undulating angle distribution characteristics of the potential contact part of the discontinuity on the basis of the rock mass discontinuity roughness evaluation parameter PAP.Based on PAP^*,the roughness of artificially simulated rock mass discontinuity R1,R2 and R3 is evaluated.The results show that PAP^*can characterize the anisotropy and sampling interval effect of rock mass discontinuity roughness.The roughness evaluation results obtained by PAP^*method,Grasselli’s method and back-calculation method are compared and analyzed.The calculation results show that there is a good correlation between PAP^*method and Grasselli’s method and back-calculation method,which also proves the rationality of PAP^*.（3）Engineering example application.For the point cloud data of 11 groups of irregular natural rock mass structural discontinuity,a three-dimensional model of natural rock mass discontinuity is established by MATLAB programming.The roughness of each natural rock mass discontinuity is evaluated by PAP_2D,PAP^*and back-calculation method respectively.The results show that the evaluation results of PAP_2D are close to those of PAP_3D under the same shear direction and sampling interval for the same discontinuity.PAP^*has a good correlation with the results of Grasselli’s method and back-calculation method.Figure[43]table[10]reference[91-]...