Numerical Simulation on the Effect of Rock Joint Roughness on the Stress Field

In view of the influence of Joint Roughness Coefficient (JRC), which is for quantitative description of the joint surface roughness, on the stress field of the rock mass, compression test and shear-compression test were simulated on models with different joint roughness. The photoelasticity technique is applied to examine the feasibility of numerical simulation. The results show that numerical simulation results are in agreement with the results of photoelastic experiments. The stress concentration area is distributed near the joint plane. Thus, the joint plane controls the shear strength of the rock. In compression test, the maximum shear stress of the model is proportional to JRC and the normal pressure. In shear-compression test, when the ratio of the axial shear to the normal pressure is small, the maximum shear stress is nonlinearly positively correlated with JRC. When the ratio of the axial shear to the normal pressure is relatively large, the relationship curve between the maximum shear stress and JRC is parabolic. When the JRC is small, as the ratio of the axial shear force to the normal pressure increases, the maximum shear stress changes abruptly, and the maximum shear stress after the mutation decreases significantly. The reason is that the upper and lower parts of the model have slipped, resulting in a redistribution of stress. In addition, when the JRC is 6 to 12, it is more likely to cause stress concentration.

A Novel Discontinuity Roughness Parameter and Its Correlation with Joint Roughness Coefficients

Joint roughness determination is a fundamental issue in many areas of rock engineering, because joint roughness has significant influences on mechanical properties and deformation behavior of rock masses. Available models suggested in the literature neglected combined effects of shear direction, scale of rock discontinuities, inclination angle, and amplitude of asperities during the roughness calculations. The main goals of this paper are to establish a comprehensive parameter that considers the characteristics of the size effect, anisotropy, and point spacing effect of the discontinuity roughness, and to investigate the correlation between the proposed comprehensive parameter and joint roughness coefficients. In this work, the Barton ten standard profiles are digitally represented, then the morphological characteristics of the discontinuity profiles are extracted. A comprehensive parameter that considers the characteristics of the size effect, anisotropy, and point spacing effect of the discontinuity roughness is established, and its correlation with joint roughness coefficients (JRC) is investigated. The correlation between the proposed discontinuity roughness parameter and the joint roughness coefficients can predict the JRC value of the natural discontinuities with high accuracy, which provides tools for comprehensively characterizing the roughness characteristics of rock discontinuities. The roughness index Rvh[−30°,0] reflects the gentle slope characteristics of the rock discontinuity profiles in the shear direction, which ignores the segments with steep slopes greater than 30° on the discontinuity profiles. The influence of steep slope segments greater than 30° should be considered for the roughness anisotropy parameter in the future.

The Effect of Joint Roughness on Shear Behavior of 3D-Printed Samples Containing a Non-Persistent Joint

The goal of this paper is to study the applicability of 3D printing technology to assess the effect of joint roughness on the shear strength of weakness planes with non-persistent discontinuities. Three disc-shaped profiles were generated to make joints with low, intermediate, and high levels of roughness. Powder-based 3D printing technology was applied to provide two types of samples: Type-A samples (joint samples) and Type-B samples (samples with a non-persistent joint). Type-A samples were printed to assess the shear behavior of 3D-printed joints, and Type-B samples were printed to investigate the joint roughness and rock bridge cohesion contributions to the shear strength of partially discontinuous planes. For comparison purposes, several plaster samples containing a non-persistent joint were cast as well. Three series of direct shear experiments were performed on Type-A, Type-B, and plaster samples under constant normal load conditions. The effects of two parameters, namely normal stress and joint roughness, on the shear behavior of the 3D-printed specimens were separately investigated, and the interaction between them was analyzed. The evaluation of the experimental results indicates the existence of two-way interaction between the joint roughness and the applied normal stress of Type-B samples. The experimental results obtained from plaster samples were compared with those obtained from Type-B samples. The comparison reveals that 3D-printed samples properly reflect the effects of joint roughness and normal stress on the shear strength of partially discontinuous planes, although their prepeak and post-peak behaviors are different from those of plaster specimens.

Joint Roughness Profiling using Photogrammetry

We propose an automated camera setup for photogrammetric roughness analysis in the laboratory environment. The developed fast and low-cost automation setup can be very useful for tedious and laborsome manual field logging practices. The photographs are processed in MATLAB to obtain disparity maps. Coding routines for stereo photogrammetry and digital measurements are written in MATLAB. Secondly, 6 effecting factors (projecting an image onto core face, depth of field, brightness, camera-to-object to baseline distance ratio, projected image size and occlusion) influencing noise in roughness depth maps computed by employing stereo photogrammetry are investigated. After deciding the best values that allow the lowest amount of noise, depth maps of 6 core faces are computed. Using the 3D point cloud generated, roughness profile measurements are made. Then, 8 profile measurements are made for each core face, both manually and digitally. The accuracy of the disparity maps has been verified by comparing 48 joint roughness coefficient (JRC) measurements made manually using a profile gauge. It was proved that surface roughness can be measured very fast in millimetric accuracy with an average Root Mean Square Error (RMSE) of 3.50 and Mean Absolute Error (MAE) of 3.02 by the help of the proposed set-up and calibration.