Research On The Quantitative Characterization Of Rock Joint Roughness And Peak Shear Strength Criterion

The roughness of rock joints is of great importance and has been discussed and investigated over a long period.There is a close relationship between the peak shear strength of rock joints and surface roughness.Among the approaches of characterization of joints roughness,Grasselli's roughness theory is one of the best methods that can properly describe the anisotropy and three-dimensional characteristics of rock joints.Thereby,it is widely recognized that Grasselli's theory is the new milestone since Barton's theory was acknowledged to be subjective.The main research of this work can be concluded as follows:(1)There are a great number of problems and shortcomings of Grasselli's roughness theory.The famous Maxwell-Boltzmann distribution function of idealized gas was introduced in this paper,in order to reveal the physical meaning of Tatone's roughness index.The results show that under specific conditions,the new roughness index can be transferred into Grasselli's roughness index and Tatone's roughness index.The physical meaning of Tatone's roughness index is: the expectation of apparent dip angle facing the shear direction.It is also found that Grasselli's roughness index is lack of explicit physical meaning.(2)Two new approaches were proposed to improve Grasselli's theory.Firstly,a new roughness index was established by taking the steeper apparent dip angle rather than the gradual angles into consideration.Secondly,using the analogy of Maxwell-Boltzmann distribution function,a new metric with clear physical meaning can be obtained.It was found that the new roughness index had a definite physical meaning.The optical scaner,freescan X3 was used to perform morphological test on4 rock joints named s1,s2,s3,s4,respectively.The corresponding programs used to analysis the roughness of rock joints was obtained,and the point clouds of the surface were digitized to get the Grasselli's roughness metric.(3)The relationship between the two new index and peak shear strength of rock joints were established,respectively.The experimental data based on Grasselli's theory in the last twenty years were collected including the work carried out by Grasselli,2001;Fardin,2008;Cottrell,2009;Yang et al,2011;Xia et al,2014;Yang et al,2016;Tang et al,2016.The first new criterion of peak shear strength of rock joints based on the first new roughness index has a better accuracy in predicting the peak shear strength of joints,when it is compared to another 6 method proposed by Grasselli,Tatone,Xia et al,Yang et al,Tang et al,Tian et al,which indicates that the new method is practical and reasonable.The relationship between the second new roughness index and JRC was built up,thus the classical Barton-Bandis model was revised.Again,the results show that the new model has a good agreement with the experimental results.