Shear Strength Analysis of Rock due to the Effect of Surface Roughness Based on Laboratory Testing and Numerical Modeling

Abstract

The shear strength of rocks was influenced by internal and external factors whose presence can reduce the shear strength of rocks. Therefore, it was important to analyze the shear strength of rock that has joints in carrying out mining planning in excavations. This study was focused on determining the shear stress of rock samples resulting from direct shear tests by considering the joint roughness coefficient (JRC) so the relationship between the two can be determined and validated using numerical modeling. In this case the author uses the finite element method using Phase2 software. Determination of surface roughness using the Z2 coefficient, the sample was grouped into several sets based on the roughness value. Other tests carried out are physical properties test, compressive strength test, and Brazilian test, the results of which were used as rock characteristics in modeling. Numerical modeling requires rock characteristics in the form of compressive strength, Young's modulus, Poisson's ratio, tensile strength, internal friction angle, cohesion, normal joint stiffness, and joint shear stiffness. Laboratory test results analyzed using linear regression showed that at peak conditions, JRC’s influences on shear stress was very strong at each loading (R2 = 0.93 to 0.97). For the residual condition, a very strong influence occurs only at the highest loading of 640 N (R2 = 0.91). The results of the comparison of the weak plane shear test with the modeling results showed the error percentage of 1.4% - 41.7%, this error percentage value was estimated because the analysis used was 2D-based numerical modeling so that the interpretation results only included the cross section of each sample 3D-based laboratory test covering the entire surface of the shear plane.