Search

Identifying rock mass discontinuities and their plane orientation are crucial factors when determining rock mass characteristics. Rock mass discontinuity mapping is fundamentally dependent on joint trace surveying since traces of them are most often the only visible features in rock outcrops. Traditional methods for joint trace surveying using tape and a geological compass are challenging, time-consuming, and hazardous. Fortunately, non-contact measuring techniques offer the advantage of generating accurate objective records of rock masses and enabling the measurement of discontinuities from digital surface models and 3D point clouds of outcrops without requiring direct access to the rock mass and associated constraints. Herein, an innovative approach for identifying discontinuity planes in rock formations using 3D trace data is presented. We introduce the concept of curved and straight traces, with a curvature index indicating the trace's accuracy by representing its discontinuity plane. In addition, we identified co-planar traces by analyzing intersecting straight traces, thereby further contributing to discontinuity plane determination. The methodology's effectiveness was established through validation using a predefined 3D trace network of discontinuity planes with known orientations on a 3D digital rock outcrop model. The methodology was then applied to trace data collected from an actual rock outcrop. The algorithm successfully matched >66% of traces with their corresponding discontinuity planes. After clustering, 80% of the identified planes aligned with principal joint sets within the rock mass. These identified planes accurately aligned with their expected jointing pattern, thereby validating the robustness of the method. Despite challenges presented by discontinuous and complex trace segments obtained from semi-automatic trace detection techniques, the algorithm effectively processed such traces, thereby enabling a comprehensive understanding of the rock mass's jointing system. This enables swift identification of the main joint orientations. We leveraged stereonet analysis to identify principal joint sets using kernel-based and fuzzy C-means clustering techniques. Our approach represents an important advancement in the characterization of rock mass structural properties. • AI-based semi-automatic 3D trace detection method enhances safety and reliability. • Digital joint mapping yields more objective results in structural geology. • Complex 3D trace data processing identifies joints' orientation, spacing, and length. • Kernel and fuzzy c-means clustering Identifies principal joint sets on stereonet. • Machine learning can improve digital joint mapping to characterize rock mass. [ABSTRACT FROM AUTHOR]

In relation to the shearing of rock joints, the precise and continuous evaluation of asperity interlocking, dilation, and basic friction properties has been the most important task in the modeling of shear strength. In this paper, in order to investigate these controlling factors, two types of limestone joint samples were prepared and CNL direct shear tests were performed on these joints under various shear conditions. One set of samples were travertine and another were onyx marble with slickensided surfaces, surfaces ground to #80, and rough surfaces were tested. Direct shear experiments conducted on slickensided and ground surfaces of limestone indicated that by increasing the applied normal stress, under different shearing rates, the basic friction coefficient decreased. Moreover, in the shear tests under constant normal stress and shearing rate, the basic friction coefficient remained constant for the different contact sizes. The second series of direct shear experiments in this research was conducted on tension joint samples to evaluate the effect of surface roughness on the shear behavior of the rough joints. This paper deals with the dilation and roughness interlocking using a method that characterizes the surface roughness of the joint based on a fundamental combined surface roughness concept. The application of stress-dependent basic friction and quantitative roughness parameters in the continuous modeling of the shear behavior of rock joints is an important aspect of this research. [ABSTRACT FROM AUTHOR]

Among all parameters that affect the friction of rocks, variable normal stress and slip rate are the most important second-order parameters. The shear-rate- and normal-stress-dependent friction behavior of rock discontinuities may significantly influence the dynamic responses of rock mass. In this research, two limestone rock types, which were travertine and onyx marble with slickenside and grinded #80 surfaces, were prepared and CNL direct shear tests were performed on the joints under various shear conditions. The shearing rate varied from 0.1 to 50 mm/min under different normal stresses (from 2 to 30 % of UCS) in both dry and wet conditions. Experiments showed that the friction coefficient of slickensided and ground #80 surfaces of limestone increased with the increasing shear velocity and decreased with the increasing normal stress. Micro-asperity interlocking between ground #80 surfaces showed higher wear and an increase in friction coefficient ( µ) compared to slickensided surfaces. Slickensided samples with moist surfaces showed an increase in the coefficient of friction compared to dry surfaces; however, on ground #80 surfaces, the moisture decreased the coefficient of friction to a smaller value. Slickenside of limestone typically slides stably in a dry condition and by stick-slip on moist surfaces. The observed shear-rate- and normal-stress-dependent friction behavior can be explained by a similar framework to that of the adhesion theory of friction and a friction mechanism that involves the competition between microscopic dilatant slip and surface asperity deformation. The results have important implications for understanding the behavior of basic and residual friction coefficients of limestone rock surfaces. [ABSTRACT FROM AUTHOR]

Determining the residual frictional properties of rock discontinuities in detail is crucial for the design of safe rock structures. In this paper, direct shear experiments were conducted on two types of artificial limestone joint samples (rough standard tensile joints and grinded planar small joints). The primary goal of this study is to compare the shear behavior of the two above-mentioned types of rock joints during the residual state of shear. The result of roughness analysis shows that during the shearing of rough joints, the increase in normal stress resulted from reduction in contact area which is caused by the mismatch between two surfaces in residual state, will lead to the stress concentration, asperity degradation and plastic deformations. Therefore, several CNL direct shear tests under different normal stresses were carried out on planar joint samples having small contact area (10 × 10 mm2) and it was found that when approximately similar normal stress acts on contact areas during residual state, the residual shear strength measured from those ground surfaces show a good accordance with the residual friction of standard rough joint samples. [ABSTRACT FROM AUTHOR]

• This study introduces a new approach utilizing 3DP technology to fabricate bedded rocks, demonstrating its feasibility. • The study meticulously explores both the qualitative and quantitative impacts of bedding planes and flaws on the fracture behavior of soft 3DP bedded rocks. • Accurate determination of strength and strain is achieved through meticulous comparison of stress–strain curves and REVC-strain curves. • The implications of the study's findings for engineering failures are thoroughly discussed. Bedded rocks are a typical geological formation with significant implications for understanding tectonic evolution, rock engineering, and geological hazard mitigation. This study introduces a novel method for fabricating bedded rocks using 3D printing (3DP) technology. By comparing the mechanical anisotropic properties and failure modes of 3DP bedded rocks with natural bedded rocks, we validate the feasibility of this approach. Compression tests are conducted on 3DP bedded rocks containing a single flaw to investigate the coupled effects of bedding planes and flaws on the mechanical properties. Digital image correlation (DIC) is employed for full-field deformation measurement during loading, enabling the study of deformation and crack evolution patterns. The results indicate that bedding planes dominate the brittleness of 3DP bedded rocks containing a single flaw. Significant plastic characteristics and prolonged nonlinear deformation stages are observed when the bedding angle (α) is between 0° and 45°, while brittleness becomes apparent beyond 45°. Both strength and elastic modulus are decided by bedding planes and initial flaws. By comparing stress–strain curves and rate of effective variance change (REVC)-strain curves, crack initiation can be quantitatively identified, revealing a linear correlation between strength and stress values at crack initiation points. The bedding plane also dominates crack propagation and failure modes: when α ≤ 30°, cracks propagate through the bedding, indicating tensile failure; when 45° ≤ α ＜90°, cracks propagate along the bedding, indicating tensile-shear or shear failure; and when α = 90°, cracks propagate along bedding planes, indicating tensile failure. The findings of this study provide insights for explaining and predicting failure modes in engineering projects involving bedded rock formations, such as slopes, tunnels, and coal mines. [ABSTRACT FROM AUTHOR]

3D printing technology allows for precise control of preparing complex geometries and internal defects in printed rock analogs, while in-situ Micro-CT imaging enables real-time observation of crack behavior. The combination of these technologies offers a new research approach for studying rock crack behavior. In this study, 3D-printed rock-like specimens containing a pre-existing flaw were prepared using a gypsum powder-based 3D printer. An advanced in-situ Micro-CT system equipped with a loading device was used to quantitatively and visually investigate the crack behavior in 3D-printed specimens under uniaxial compression testing. 2D CT images obtained from in-situ compression testing at different deformations could be used to reconstruct a 3D model and visually identify the crack patterns of the extracted cracks in 3D-printed specimens. The initiation angle of cracks, volume of the pre-existing flaw, volume of newly formed cracks, and damage value with respect to strains were analyzed to quantitatively investigate crack behavior. The results indicated that within the 3D-printed specimens, tensile cracks were first initiated near the internal flaw, followed by the occurrence of shear cracks or tensile-shear mixed cracks at the flaw tips. Additionally, there was a negative linear correlation between the initiation angle of newly formed cracks and the initial flaw angle. For flaw angles in the range of 0° ≤ α ≤ 45°, a higher number of newly formed cracks were observed in the 3D-printed specimens, and the rates of increase in crack volume and damage values with strain were faster. However, for flaw angles in the range of 45° < α ≤ 90°, the results showed the opposite trend. Furthermore, through comparison with the crack behavior of natural rocks containing a single flaw, it was found that the failure modes and crack behavior of the 3D-printed specimens exhibit certain similarities with natural rocks. [ABSTRACT FROM AUTHOR]