A discontinuity roughness parameter combined with shear failure mechanism and its correlation with JRC

Previous studies have noted variations in the effective value of the joint roughness coefficient (JRC) under different normal loads. Also, the apparent dip angle (ADA) distribution is one of the important characteristics of discontinuity morphology. In this study, the parameter PAP* is proposed by simultaneously considering the normal load ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>σ</mml:mi> </mml:math> ) and the ADA distribution parameter ( K ) to correct PAP (the projection area percentage), where PAP is a parameter obtained by calculating the ratio of the projected area of all potential contact parts of a discontinuity on a plane perpendicular to the shear direction to the horizontal projected area of the whole discontinuity. Additionally, the parameters PAP′ and PAP″ are separately proposed by considering only <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>σ</mml:mi> </mml:math> or only K to correct PAP, and their roughness evaluation effects are analysed. The results show the following: (1) the correlation coefficients ( R ) of PAP* with JRC are in the range of 0.924–0.967, which are significantly stronger than those of several other parameters with JRC; (2) the normal load significantly affects the roughness evaluation results, where the results refer to the effective value of JRC of discontinuities; (3) there is a correlation between the parameter K and roughness evaluation results under low normal loads (such as 0.5 or 1 MPa).