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Three-dimensional (3D) roughness of the rock discontinuity plays a controlling function on the rock mass stability of excavation face during deep buried tunnel construction, which can be predicted based on the discontinuity outcrop from excavation face. However, there exist some disturbing factors such as dust and debris which affect the non-contact measurement accuracy on the outcrop information under construction environment. In this study, a new method to predict three-dimensional roughness of rock discontinuity (JRC 3d) based on the limited outcrop and drilling test information from the rock mass of excavation face is proposed. Two-dimensional roughness of rock discontinuity (JRC 2d) is derived based on different asperity orders firstly. The first-order profile roughness is calculated by combining drilling test result, and the second-order profile roughness is predicted on establishing the statistical relationship between the geometrical parameter of the outcrop and the entire profile. Based on the prediction of JRC 2d , JRC 3d is characterized probabilistically with the improved Bayesian theory where the bootstrap method is used to deal with the difficulty of obtaining μ and σ of the prior distribution because the sample size is limited. A rock tunnel engineering in southwest China is taken as the engineering application, and the relative errors of the predicting JRC 3d are lower than 11 %. Finally, the effect of outcrop width on the predicting JRC 3d results is investigated. For Barton standard profiles, the statistical parameters of the first k climbing angles of the second-order roughness profiles are calculated to estimate the appropriate outcrop width as 16 mm. A rock discontinuity is generated to study the effect of discontinuity size on the predicting JRC 3d , and the relative error of the predicting JRC 3d is lower than 12 %, thereby validating the method applicability across a broad spectrum of discontinuity sizes, ranging from small to large. • A new method of predicting JRC 3d is proposed considering insufficient outcrop information during the tunnel construction. • The second-order roughness is derived by studying the geometrical parameters of the outcrop and entire profile. • JRC 2d and JRC 3d are predicted based on two asperity orders and the improved Bayesian theory respectively. • The sensitivities of the influencing factors which are the outcrop width and discontinuity size are analyzed. [ABSTRACT FROM AUTHOR]

Discontinuity mapping on tunnel faces is crucial for assessing stability and determining the need for additional reinforcement during tunnel construction. The traditional manual mapping approach is time-consuming and error-prone, necessitating a more accurate and efficient approach. This study explores a novel approach using photogrammetry to reconstruct digital 3D models of tunnel faces, enabling comprehensive discontinuity characterization without any time restriction. Despite challenges in image data collection and processing procedures, photogrammetry proves to be a viable alternative to LiDAR scanning for reconstructing precise 3D models of tunnel faces. Additionally, a deep learning technique is proposed to automatically identify rock mass discontinuities departing from massive random fractures on the 3D tunnel face. Since working directly with 3D models in deep learning is still challenging, the 3D tunnel face model is projected into four 2D images (i.e., RGB, depth map, normal vector, and curvature images) encompassing all necessary information of the 3D model. Afterward, a 2D semantic segmentation deep learning model is trained to identify areas of discontinuity based on the projected multi-2D images. Finally, the identified discontinuities are re-projected onto the 3D model to accurately reflect their original 3D context. Our results indicate that the proposed approach not only automatically and accurately quantifies rock discontinuities but also minimizes subjectivity inherent in manual judgment. [ABSTRACT FROM AUTHOR]

Digital photogrammetry is widespread in site investigation of rock discontinuities. However, existing methods often rely on multi-frame synthesis techniques and calibrating references to achieve three-dimensional (3D) modeling and orientation analysis of rock discontinuities, which limits the rapid application of digital photogrammetry techniques onsite. To address this challenge, this paper introduces a hybrid machine learning architecture called OneShot-DisconNet. This method first utilizes deep neural networks trained on the MegaDepth dataset to predict single-layer depth map from monocular images. Subsequently, multi-viewpoint depth fields and textures is reconstructed on the layered depth images (LDIs) using Partial Convolutions (PConv), enabling point cloud modeling of rock surfaces. Additionally, a novel uncertainty-based multi-population genetic algorithm-driven backpropagation (UB-MPGA-BP) neural network is developed based on the MegaDepth dataset to enable true-scale mapping of 3D point clouds without references. Finally, by addressing the limitations of the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm in handling outliers and coplanar point clouds, the robustness of the structural analysis results has been enhanced. Case studies in the Beiyi Section of Shilu Iron Mine and the Rockbench database demonstrate that the proposed method is comparable in performance to Lidar-based digital photogrammetry technology, enabling true-scale mapping and orientation analysis of rock discontinuities in various scenarios. [ABSTRACT FROM AUTHOR]

Discontinuities have huge impact on civil and mining engineering. To understand the spatial features of discontinuities, it is common to group them into different sets based on orientation. In this paper, a new algorithm is introduced for the identification of discontinuity sets. The new algorithm is developed by combined fuzzy C-means algorithm with variable length string genetic algorithm. In the new method, the number of discontinuity sets is not the necessary input parameter any more. This method is robust, global optimal and totally automatic. To verify its validity, the new method was firstly applied to an artificial data as well as a published data. For artificial data set, the assignment error rate is only 7.4%. For published data set, only 2 discontinuities are assigned to wrong sets. The results indicate that the new algorithm is better than fuzzy C-means algorithm and comparable with other common methods. Afterwards, the new method was utilized to analyze the orientation data sampled at an underground storage cavern site. The new method determines that the ideal number of sets is 3. The new method provided satisfactory results, which confirm its effectiveness and convenience. [ABSTRACT FROM AUTHOR]

Research on rock slopes has attracted considerable attention in the fields of infrastructure construction and disaster prevention. The search for an efficient and reliable method for discontinuity collection is an important task for various studies of jointed rock slope. Capturing high-precision and complete rock exposure images based on unmanned aerial vehicle (UAV) multi-angle and nap-of-the-object photogrammetry technology is proposed to realize the construction of a millimeter-level 3D point cloud for the high and steep slope. This study develops a new automatic methodology for discontinuity identification and interpretation. A Delaunay triangulation network is created for connecting adjacent points in the point cloud to calculate normal vectors and search for neighbor points efficiently. Combined with the modified region-growing algorithm, an automatic procedure which identifies discontinuities and acquires geometrical parameters efficiently and accurately is established. The proposed approach is applied to the high-steep rock slope on the northern bank of the Sequ Grand Bridge in the Changdu area of Tibet. Compared with the results from the manual survey, the proposed method is more reliable and exhibits high accuracy for discontinuity identification and interpretation on rock exposure. [ABSTRACT FROM AUTHOR]

Stress relaxation is an important time-dependent behavior of rock mass. To investigate the stress relaxation behavior and the influence of stress history and surface morphology on the stress relaxation of rock discontinuity, iso-stress cyclic relaxation tests and shear stress relaxation tests with loading–unloading stress histories were conducted on artificial rock discontinuity samples and natural rock discontinuity samples. The characteristics of the stress relaxation curve with different stress histories were investigated in detail, and the relationship between the accumulated plastic deformation and relaxation stress was established. Results revealed that the stress history caused the weakening of the stress relaxation ability. The greater the joint roughness coefficient (JRC), the more noticeable is the stress relaxation. Moreover, the stress history presents a greater effect on stress relaxation as the JRC increases. The stress relaxation exhibits a linear relationship with the plastic deformation that occurred before the stress relaxation. It demonstrates that the relaxation stress and plastic deformation are homogenous and that the elastic energy is the power of stress relaxation. The roughness or asperities of rock discontinuity provides the "space" for the stress relaxation. • The greater the joint roughness coefficient (JRC), the more noticeable was the stress relaxation. • The stress history caused the weakening of stress relaxation ability, and the roughness influenced this feature. • The relaxation stress exhibited a linear relationship with plastic deformation occurring before the stress relaxation. • The elastic energy was the power of stress relaxation, and the roughness provided the "space" for stress relaxation. • A speculative result about the limit curve was that it was a straight line. [ABSTRACT FROM AUTHOR]

The shear strength of rock discontinuities is known to be scale dependent, and past research has revealed that both positive and negative scale effects could be observed. It is far from trivial to predict the occurrence of the scale effect and, to date, there is still no consensus on how to satisfactorily predict the shear strength of large discontinuities. A new stochastic approach was proposed and validated at laboratory scale by the authors. The approach consists of (1) using the information available from visible traces to create synthetic surfaces via a random field model and (2) estimating the shear strength of each one of the synthetic surfaces in order to obtain a distribution of shear strength and a mean shear strength. This paper presents the first application of this new approach to a large discontinuity that was surveyed with a resolution of 1 mm and an accuracy in the order of 150–230 µm in the Pilkington reserve of Newcastle, Australia. The paper first confirms that a scale effect does exist for the surface tested, before demonstrating that the new stochastic approach produces a strength envelope that is very close to the deterministic failure criterion of the whole surface. The key conclusion of this research is that there is enough information on visible traces, if surveyed accurately, to obtain an estimate of the shear strength of the discontinuity. [ABSTRACT FROM AUTHOR]

Rock mass characterization is obviously a key element in rock fall hazard analysis. Managing risk and determining the most adapted reinforcement method require a proper understanding of the considered rock mass. Description of discontinuity sets is therefore a crucial first step in the reinforcement work design process. The on-field survey is then followed by a structural modeling in order to extrapolate the data collected at the rock surface to the inner part of the massif. Traditional compass survey and manual observations can be undoubtedly surpassed by dense 3D data such as LiDAR or photogrammetric point clouds. However, although the acquisition phase is quite fast and highly automated, managing, handling and exploiting such great amount of collected data is an arduous task and especially for non specialist users. In this study, we propose a combined approached using both 3D point clouds (from LiDAR or image matching) and 2D digital images, gathered into the concept of ''solid image''. This product is the connection between the advantages of classical true colors 2D digital images, accessibility and interpretability, and the particular strengths of dense 3D point clouds, i.e. geometrical completeness and accuracy. The solid image can be considered as the information support for carrying-out a digital survey at the surface of the outcrop without being affected by traditional deficiencies (lack of data and sampling difficulties due to inaccessible areas, safety risk in steep sectors, etc.). Computational tools presented in this paper have been implemented into one standalone software through a graphical user interface helping operators with the completion of a digital geostructural survey and analysis. 3D coordinates extraction, 3D distances and area measurement, planar best-fit for discontinuity orientation, directional roughness profiles, block size estimation, and other tools have been experimented on a calcareous quarry in the French Alps. [ABSTRACT FROM AUTHOR]

• Dynamic finite element models were proposed to investigate the dynamic responses and damage mechanism of rock under blasting. • The propagation of blasting stress waves was analyzed together with the interaction of discontinuity orientation and confining stress magnitude. • The extension mechanism of the discontinuity was explored from the perspective of stress distribution and dynamic stress intensity factor (DSIF). • Rock discontinuity can weaken the crack-guiding effect of high confining stress, and high confining stress can suppress the development of radial cracks around borehole. The propagation of seismic waves induced by blasting changes significantly at rock discontinuities such as joints and faults, many studies have focused on the mechanism of wave propagation at joints. However, in deep rock masses, high in-situ stress is non-negligible, and the interaction between confining stress and discontinuity under blasting disturbance remains poorly understood. To explore the role of confining stress and discontinuity on the dynamic responses and damage mechanism of rock masses, this paper employed the dynamic finite element method and a series of numerical models were subsequently developed. The Riedel-Hiermaier-Thoma (RHT) model was used to simulate the blast-induced damage of rock. Under blasting disturbance, the propagation of stress waves and damage patterns within the rock at different discontinuity orientations and different confining stress magnitudes were presented. Around the discontinuity, the principal stress distribution and displacements were presented and the dynamic stress intensity factor (DSIF) of the discontinuity tip was obtained to analyze the extension mechanism of the discontinuity. Numerical results show that the discontinuity, the magnitude and direction of confining stress significantly contribute to the damage patterns of rock masses, and the guiding effect of high confining stress on cracking will be weakened due to the existence of discontinuity. [ABSTRACT FROM AUTHOR]

This study proposes a numerical simulation procedure to evaluate the accuracy of geometric parameters of 3-dimensional models reconstructed by photogrammetry based on the Open Graphics Library. As a technical mean to obtain photogrammetric photos and data, this method has achieved the goal of controlling the parameters in the photogrammetric process at will. The proposed method is validated by several physical model experiments using the unmanned aerial vehicle Phantom 4 Real-time kinematic (RTK). Through a series of numerical experiments, this study quantitatively analyzes the error of geometric parameters of discontinuities in rock masses caused by coordinate accuracy of camera positions and shooting distance, and some quantitative findings were obtained. These results conforming to common sense also validate the proposed simulation procedure. This numerical simulation procedure has a broad application prospect in guiding and optimization of photo acquisition of field outcrop balancing the accuracy and efficiency. • A numerical simulation procedure was first developed to evaluate the AGP3MRP. • The procedure was used to evaluate the rock discontinuity geometric parameters. • Physical tests were performed and the results show that the procedure is validated. • The influence law of the photogrammetric parameters on the results was drawn. [ABSTRACT FROM AUTHOR]

Abstract: The point bearing behavior of rock-socketed drilled shafts under axial loading is investigated by numerical analysis and a load transfer approach (q–w). A numerical analysis using the distinct element method (DEM) is carried out to investigate the effects of pile diameter and the elastic modulus, discontinuity spacing and the inclination of rock mass on the point bearing behavior. The emphasis is quantifying the point bearing mechanism by taking rock discontinuity into consideration based on field loading tests performed on 39 instrumented piles. A new hyperbolic q–w function is proposed considering the point bearing resistance influence factors, including rock mass discontinuity. Through comparisons with other field data, the proposed q–w function represents a significant improvement in the prediction of the point bearing load transfer characteristics of jointed rock-socketed drilled shafts. [Copyright &y& Elsevier]

Abstract: The shear strength of rock discontinuities strongly depends on the water content especially when the rocks contain clay materials. To assess the decrease in the mechanical properties of clay-infilled discontinuities due to water saturation, a series of direct shear tests was performed using an advanced shear box that allows the injection of water into the discontinuity. Results show that both the friction coefficient and the cohesion decrease when the discontinuity is saturated. Overall, the shear strength of the discontinuity is considerably reduced to approximately 50% of its original value. This reduction has to be accounted for when conducting stability analyses of rock slopes, dam foundations or underground openings. [Copyright &y& Elsevier]

This paper describes a computer approach that has been developed for estimating three-dimensional fracture orientations from two-dimensional fracture trace information gathered from digital images of exposed rock faces. The approach assumes that the fractures occur in sets, and that each set can be described by a mean orientation and a measure of the scatter about the mean. Mathematical relationships are developed that relate the 3D fracture properties with the trace angles that would be measured on one or more rock faces. These algorithms are used in conjunction with a genetic algorithm to invert the trace angles to estimate 3D joint orientation. A number of case studies have been conducted indicating a great potential for the technique. [Copyright &y& Elsevier]

Discontinuity shear strength plays a critical role in many problems encountered in rock engineering, especially in the design of rock slopes. Since its precise estimation is generally not possible, it is crucial that the errors and uncertainties associated with its estimate be quantified and reflected in the design procedure. In this study, the uncertainties underlying discontinuity shear strength are thoroughly examined and an uncertainty analysis model is developed for the estimation of in situ discontinuity shear strength with a special emphasis on rock slopes. An extensive literature survey on shear behavior of unfilled rock discontinuities has been carried out and the necessary data for the quantification of uncertainties are extracted from this survey. These uncertainties stem from the discrepancies between laboratory-measured and in situ discontinuity shear strength values, as well as from the inherent variability of shear strength within a rock medium. The main causes of discrepancies, namely, scale, anisotropy and water saturation are considered. For each source of discrepancy a correction factor, treated as a random variable, is assigned and guidelines for the quantification of the statistical parameters of these correction factors are presented within the framework of the proposed uncertainty analysis model. The proposed uncertainty model provides an analytical tool for the systematic treatment of uncertainties involved in the estimation of the in situ value of peak friction angle from the laboratory test results. [Copyright &y& Elsevier]

The slip shear failure along rock discontinuities is one of the predominant failure modes of landslides. To simulate impact shear loads during landslide and rockburst, an experimental method is presented to achieve the dynamic shear load in a direct shear testing configuration. The dynamic loading system is derived from the SHPB methodology and can provide high shear velocities around 1–10 m/s. Dynamic direct shear experiments on rough rock discontinuities are conducted by using a dynamic shear apparatus combined with a high-speed digital camera. The effects of shear velocity and normal stress on the slip displacement, slip velocity and slip acceleration of rough rock discontinuities are analyzed using a two-dimensional digital image correlation (DIC) technique. It is observed that the rate of the slip is linearly proportional to the shear velocity and decreases with the increasing normal stress. Using the DIC method, the strain at failing asperities is calculated as a function of the shear velocity and the normal stress. The micro-structural characteristics of the shear zone formed in the slip failure is examined to understand the slip failure mode. Moreover, the dynamic viscous is added to the static Barton's shear strength criterion and the damage evolution occurred at the asperities due to the dynamic loading is introduced by means of a damage control parameter D. Thereafter, a dynamic failure criterion is developed by considering both surface roughness and dynamic loading. The failure model can provide a good prediction of the experimental data, indicating that the proposed models can describe well the dynamic shear process of rock discontinuities under high velocity impact. [ABSTRACT FROM AUTHOR]

• Three-dimensional DEM investigation of the fracture behaviour of thermally degraded rocks. • Consideration of material anisotropy. • Investigation of thermal degradation, fracture complexity, and micro-mechanisms. • Comparison of the findings of the DEM study with laboratory experiments and theoretical analysis. A complete understanding of the fracture behaviour of anisotropic rocks under elevated temperatures is fundamentally important for rock and reservoir engineering applications. This paper shows a three-dimensional numerical investigation of the fracture behaviour of anisotropic sandstone, with consideration of the effects of temperature and material anisotropy. In the study, a 3D semi-circular bend (SCB) model was established by using the Discrete Element Method (DEM). The thermal responses of different minerals and the strength anisotropy of incipient bedding planes were considered in the model. The DEM model was calibrated against a series of laboratory experiments on Midgley Grit sandstone (MGS) that exhibits intrinsic anisotropy. The pure mode I, mode II, and mixed-mode (I+II) fracture characteristics of the MGS were investigated under elevated temperatures (up to 600 °C) using the established DEM model. The thermal degradation (i.e., fracturing) of the rock, the fracture load, the evolution of micro-cracks, and the stress-strain relationship around notch tips were analysed, with emphasis on enlightening the micro-mechanisms underlying the fracture behaviour. The results of the study were discussed and then compared with experimental observations and theoretical predictions. [ABSTRACT FROM AUTHOR]