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.

Determination of Joint Surface Roughness Based on 3D Statistical Morphology Characteristic

Roughness significantly affects the shear behavior of rock joints, which are widely encountered in geotechnical engineering. Since the existing calculation methods on the joint roughness coefficient (JRC) fail to obtain a sufficiently accurate value of JRC, a new determination method was proposed in this study, where the 3D laser scanning technique and self-compiled Python code, as well as the statistical parameter methods, were applied. Then, the shear strength of jointed rock was evaluated via Barton's model, and therefore, a comprehensive comparison between the calculating results and experimental results was executed. Ultimately, the influencing factors of roughness profile extraction on the accuracy of JRC value, such as the measuring point interval, profile number, and measuring direction, were investigated. The results show that (1) equipped with the 3D laser scanning technique, the roughness profiles can be accurately extracted via the self-compiled Python code, (2) an excellent consistency of shear strength could be observed between the calculating value and experimental results, verifying the validity and accuracy of the proposed method, and (3) a smaller measuring point interval can produce a more accurate digital profile and more accurate JRC value. To a certain extent, the more the sample numbers of profiles, the smaller the value of JRC.

Neutrosophic Function for Assessing the Scale Effect of the Rock Joint Surface Roughness

A new investigation method is proposed for recording large-sized joint profiles and making statistical analyses of the joint roughness coefficient (JRC) values of the 10–300 cm sized profiles. The mechanical hand profilograph is used for joint roughness measurement due to its advantage of easy operation and high accuracy in recording joint traces. Based on the proposed method, it provides sufficient samples from various positions on the large joint profile, which allows the statistical evaluation of JRC values. A neutrosophic number (NN) is employed for revealing determinate and/or indeterminate information as it consists of determinate and indeterminate parts. Due to the uncertainty of JRC in the real world, NN is chosen to represent the JRC value, which is not only random but also a fuzzy indefinite parameter. The neutrosophic function is used to analyze and express the scale effect of joint surface roughness, and its derivative is used to describe the changing trend of the scale effect. The results show that the JRC value of the joint profile is related to the scale and has a negative effect on the surface roughness of the rock joint. The indeterminate information about the scale effect on joint roughness is described by the neutrosophic functions, and the derivative indicated that the JRC values of small samples are more sensitive than those of large-sized examples. When the length of the sample exceeds the stationarity limit of 80 cm, the roughness appears to be almost scale independent.

Effect of Cement Injection on Shear Behaviour of Jointed Rock based on Mohr-Coulomb Criterion

Common problem in mining activity is instability caused by jointed rock mass. The strength of jointed rock masscan be increased by cement injection. An artificial rock sample made from dental plaster type of moldano tara isused in this study to evaluate the influence of cement injection to the strength of jointed rock sample. The roughnessof joint surface are obtained from the natural rock joints and divided into three groups of Joint RoughnessCoefficient (JRC) values based on Barton criteria. The injection materials are mixture of cement and water withthe ratio of water and cement of 4: 5 and 3: 2. This artificial samples are then subjected to direct shear tests. Thetest results are analyzed by Mohr-Coulomb criterion to obtain the cohesion and internal friction angle. It isrevealed that cohesion and internal friction angle increased for injected rock sample. The strength increase variesby JRC condition. For Sample with JRC value between 8-10, the study find that injection material with water tocement ratio of 4:5 is more effective than cement injection with ratio of 3:2. For JRC value between 12-14, 16-18,and 18-20, it is found that cement injection with ratio of 3:2 is more effective than 4:5.

Study on Shear Properties of Rock Structural Plane by Grouting Reinforcement

In order to study the grouting reinforcement effect of structural plane in cracked rock mass under uniaxial compression test and reveal the essence and mechanisms of grouting reinforcement, the roughness of structural plane in cracked rock mass was measured and studied. The influence of grouting on strength, JRC and stiffness was analyzed through shear tests of structural plane of cracked rock samples around grouting reinforcement. Test results were back-analyzed using JRC－JCS mode. The results showed that the JRC of structural plane in artificial cracked rock of the same rock mass was similar and replicable, the JRC value was about 8-10. Stiffness, roughness, peak shear strength (PSS), residual strength (RS), shear strength parameters (SSP) and slope of upward section (SUS) of structural plane were significantly improved by grouting reinforcement. The theoretical formula of structural plane stiffness was given by theoretical analysis.