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The mechanical characteristics of anchor cable (AC) play a vital role in determining the design of prestressed support for roadways in deep coal mines. To investigate the shear mechanical properties of AC, a multifunctional testing device for AC was developed, which can conduct mechanical behavior tests such as anchoring, tensioning, and shearing on full-size AC. The research results showed that under shear stress, the AC presented a Z-shaped or S-shaped morphology, and the failure morphology of the rock surrounding the partial contact area with the AC was consistent with the shape of the AC. The initial tensioning force of the AC and the method used to anchor it greatly influenced the shear force, axial force, and shear deformation experienced by the AC. The analysis of the test results involved examining the shear force and deformation properties of the AC at various stages, and proposing the stress and deformation pattern of the AC when subjected to shear forces. The AC was analyzed to determine its bending deflection, rotation angle, bending moment, and shear force distribution pattern, which provided insights into the composite fracture mechanism involving bending, tensile, and shear stress. Highlights: The multifunctional testing device for anchor rods (cables) was developed, which can achieve mechanical behavior testing such as anchoring, tensioning, and shearing of full-size AC. The AC's shear force–displacement curve can be categorized into five stages, each characterized by distinct shear forces and deformation mechanisms. The influence of the initial pretightening force of the anchor cable and the anchoring method on the shear force, axial force, and shear deformation of the anchor cable is revealed. [ABSTRACT FROM AUTHOR]

The shear mechanical properties are the important factors affecting the failure of rock mass. At present, tests measuring the shear mechanical behavior characteristics of rocks under three-dimensional stress are rare. In particular, the influence of lateral stress on the shear failure mechanism of rock is less often considered. The true triaxial test device was used to conduct direct shear, true triaxial stress shear, and confining shear tests under three-dimensional states of stress. Through the three different types of shear tests, the deformation, failure modes, strength, and surface roughness of sandstone were investigated. Focusing on the acoustic emission (AE) characteristics during the failure of sandstone specimens, the influences of lateral stress on the shear failure mechanism of sandstone under true triaxial stress were studied. The test results show that lateral stress can increase the peak strength and residual strength of sandstone, significantly affecting its lateral deformation. Under high normal stress, the weaker the lateral restraint on the rock, the more severe the lateral deformation failure. The analysis found that lateral stress increased the compressive compactness of the mineral particles inside the sandstone and the occlusal hinge strength of the particles. It also restricts the lateral deformation of the sandstone and the germination of the number of internal cracks. Crack propagation is also accelerated under the combined action of high normal stress and lateral stress. Highlights: Direct shear, true triaxial shear and confining shear tests on sandstone specimens were carried out using true triaxial test device. Through the different types of shear tests, the strength, deformation, JRC and failure modes of sandstone were investigated. Focusing on the AE characteristics, the influences of lateral stress on the shear failure mechanism of sandstone were studied. [ABSTRACT FROM AUTHOR]

Rock joints in faulted zones are usually filled with large amounts of fault gouge, in which clay-rich fillings are very common. Fault water can significantly influence the mechanical parameters of clay-rich fillings and affect the shear mechanical behaviour of rock joints. Based on a tunnelling project passing through a faulted zone in Yunnan Province of China, this paper investigates the mechanical behaviour of rock joints with clay-rich fillings. A series of direct shear tests are conducted on rock joint samples made from rock blocks and fillings collected from a fault zone. The shear stress‒displacement curves and shear failure characteristics of rock joints are obtained, and several key factors of the fillings are considered, such as particle size, mineral composition, clay content, and water content. Furthermore, the peak and residual shear strengths are analysed by considering the influence of the water content and normal loading pressure. The test results show that water content of fillings has a great influence on shear strength of clay-filling rock joints; there is a trend to a negative correlation between the shear strength of rock joints when water content (w) exceeds the plastic limit (wp). Finally, a shear strength model for rock joints with clay-rich fillings is proposed based on the JRC-JCS strength criterion. Influence of water content on the shear strength of rock joints with clay-rich fillings is studied. A series of direct shear tests are conducted on rock joint samples based on a tunnelling project. The shear stress–displacement curves of rock joints with clay-rich filling are obtained. A shear strength weakening model of clay-filled joints is proposed. Highlights: Influence of water content on the shear strength of rock joints with clay-rich fillings is studied. A series of direct shear tests are conducted on rock joint samples based on a tunnelling project. The shear stress-displacement curves of rock joints with clay-rich filling are obtained. A shear strength weakening model of clay-filled joints is proposed. [ABSTRACT FROM AUTHOR]

The large-scale model test bench frame is adopted to carry out shear test on the pre-stressed anchor block containing structural plane, and the characteristics of tensile, bending and shear failure of anchor cable are analyzed. Furthermore, the structural calculation software ABAQUS 2020 is utilized to construct the spiral structure model of composite steel wires and the anchor cable is simplified to be composed of bending inner and outer steel wires and central steel wire, so as to simulate accurately the interaction, failure mode and mechanical mechanism between anchor cable and grouting body, as well as between grouting body and concrete block. The results show that the anti-shearing process of pre-stressed anchor blocks can be divided into the anti-shearing stage of structural plane and the anti-shearing stage of anchor cable. Affected by the anti-shearing and deformation characteristics of the bending inner and outer steel wires, the shear stress of the anchor cable has experienced an alternate change process from strong to weak, then from weak to strong, and finally to weak. The axial force of the anchor cable continuously increases until the fracture of the anchor cable. Anchor cable fracture first appears at plastic hinge position of the inner bending steel wire, and then at the interface between the anchor cable and the structural plane, the central steel wire occurs tensile–shear fracture. Highlights: The interaction, failure mode, and mechanical mechanism of the internal components of anchor block have been simulated accurately. The tension, bend, and shear failure of anchor cable are analyzed based on the large-scale model test bench frame. The failure modes of the tension–bend–shear of the inner steel wires, the tension–shear of the outer steel wires, and tension of a single central steel wire of the anchor cable are significantly different. [ABSTRACT FROM AUTHOR]

The primary objective of this work is to improve our understanding of the scale effect of the joint shear behavior. Attempts are made to combine different proposed methods with the multiscale joint shear test. First, a new type of rock-like material made from a mixture of raw materials is used to simulate rock joints. Then a new sampling method is used with the progressive coverage statistical method for the representative sampling of actual joints, and an inverse controlling technology is designed with an invented series of multiscale molds for the construction of a similar surface model in series scale (100 mm × 100 mm to 1000 mm × 1000 mm). Finally, the independently developed multiscale direct shear tester is used to measure the shear behavior of joint replicas. The quality of results shows the capacity of this experimental technology in investigating the scale effect of the joint shear behavior. [ABSTRACT FROM AUTHOR]

When translating digital roughness profiles of a closed rock joint along the shear direction, the overlapping translational areas can reasonably represent the main potential contact areas in shear tests. By translating Barton's ten typical roughness profiles, a series of statistical parameters, including the overlapping areas (S*), overlapping number (N*), cumulative overlapping projection length (Lsum∗), and the weighted cumulative overlapping projection length (Ssum∗), were utilized to quantify the 2D joint roughness. Based on the dimensional analysis, these parameters were combined to estimate the joint roughness coefficient. The correlation coefficient results show that the parameter combinations of S∗/L and N∗-1 or Ssum∗/STotal allow good estimation of the joint roughness coefficient of Barton's 2D roughness profiles. A conceptual joint model was used to extend the 2D translational overlapping statistical parameters to a 3D condition, revealing the suitability of the 3D translational overlapping volume parameter V∗/SL and the hourglass parameter to estimate the joint roughness coefficient of common rock joints. However, the overlapping number parameter N*−1 becomes unreliable and lacks practical significance for common rock joints because there are so many meaningless weak links among the overlapping volumes. Shear tests were conducted on 25 sandstone joints to verify the applicability of V∗/SL and Vsum∗/VTotal to estimate the joint roughness coefficient. The results indicated that these two parameters show good agreement with the experimentally back-calculated values, allowing the establishment of a new joint roughness coefficient fitting formula. [ABSTRACT FROM AUTHOR]

Conventional tunnelling methods (i.e., the drill and blast tunnelling method or the new Austrian tunnelling method) have been frequently applied for the construction of tunnels/caverns under a high overburden and with a large cross section. Under such adverse conditions, tunnel support materials may yield because of ground pressure and tunnel deformation. As a result, a tunnel may lose its stability due to a reduced effectiveness of the tunnel supports. Rock bolts have been widely used as an essential component of tunnel support, and many studies have been conducted on the performance of rock bolts in strengthening the jointed rock mass. However, there is a lack of understanding on the interface behaviour between the rock bolt and the bond material, especially the crack initiation and propagation inside the bond material. This study aims to investigate the interface behaviour between rock bolts and bond materials using laboratory tests (shear tests) and numerical simulations (Discontinuous deformation analysis). By assessing the impact of the key parameters in the rock bolting system, such as the ribs, rib angle, strength of the bond material and the confining pressure, we are able to better understand the supporting mechanism and the effects of rock bolting. [ABSTRACT FROM AUTHOR]

The peak shear strength of a cement-filled hard rock joint is studied by theoretical analysis and laboratory testing. Based on the concept of the shear resistance angle, by combining the statistical method and fractal theory, three new parameters are proposed to characterize the three-dimensional joint morphology, reflecting the effects of the average roughness, multi-scale asperities and the dispersion degree of the roughness distribution. These factors are independent of the measurement scale, and they reflect the anisotropy of the joint roughness. Compressive shear tests are conducted on cement-filled joints. Because joints without cement can be considered special cement-filled joints in which the filling degree of cement is zero, they are also tested. The cement-filled granite joint fails primarily along the granite-cement interfaces. The filling degree of cement controls the joint failure and affects its mechanical behaviour. With a decrease in the filling degree of cement, the joint cohesion decreases; however, the dilatancy angle and the basic friction angle of the interface increase. As the filling degree approaches zero, the cohesion approaches zero, while the dilatancy angle and the basic friction angle increase to those of the joint without cement. A set of formulas is proposed to evaluate the peak shear strength of the joints with and without cement. The formulas are shown to be reasonable by comparison with the tested peak shear strength, and they reflect the anisotropy of the strength. This research deepens the understanding of cement-filled joints and provides a method to evaluate their peak shear strength. [ABSTRACT FROM AUTHOR]