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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]

During the mining process of impact-prone coal seams, drilling pressure relief can reduce the impact propensity of the coal seam, but it also reduces the integrity and strength of the coal mass at the side of the roadway. Therefore, studying the mechanical properties and energy evolution rules of coal samples containing holes and filled structures has certain practical significance for achieving coordinated control of coal mine rockburst disasters and the stability of roadway surrounding rocks. To achieve this aim, seven types of burst-prone coal samples were prepared and subject to uniaxial compression experiments with the aid of a TAW-3000 electro-hydraulic servo testing machine. Besides, the stress–strain curves, acoustic emission signals, DIC strain fields and other data were collected during the experiments. Furthermore, the failure modes and energy evolutions of samples with varying drilled hole sizes and filling materials were analyzed. The results show that the indexes related to burst propensity of the drilled coal samples decline to some extent compared with those of the intact one, and the decline is positively corelated to the diameter of the drilled hole. After hole filling, the strain concentration degree around the drilled hole is lowered to a certain degree, and polyurethane filling has a more remarkable effect than cement filling. Meanwhile, hole filling can enhance the strength and deformation resistance of coal. Hole drilling can accelerate the release of accumulated elastic strain energy, turning the acoustic emission events from low-frequency and high-energy ones to high-frequency and low-energy ones, whereas hole filling can reduce the intensity of energy release. The experimental results and theoretical derivation demonstrate that hole filling promotes coal deformability and strength mainly by weakening stress concentration surrounding the drilled holes. Moreover, the fillings can achieve a better filling effect if their elastic modulus and Poisson’s ratio are closer to those of the coal body. [ABSTRACT FROM AUTHOR]

Roof management in coal mines is a critical technology challenge to realize safe production. Dynamic disasters can be induced by a sudden collapse of the roof when encountering a thick hard roof above a coal seam. To solve this problem, directional hydraulic fracturing technology was utilized in the coal mine WP with a thick hard limestone roof. To effectively cut artificial transverse grooves in a fracturing hole in rock with a high strength, the KZ54-type transverse grooving bit was developed. Furthermore, the developed small-aperture high-pressure span-type expansion sealer can effectively seal the holes and ensure hydraulic crack expansion. The field observations show that the radii of extension of the hydraulic fractures were 15–20 m and that the rupture pressure at various depths in the holes ranged from 9 to 32 MPa from the orifice to the bottom of the hole. The deeper the fracturing location in the hole, the higher the fracturing pressure was. The principal stresses in front of the working face and the resistance forces of the hydraulic supports at the working face were monitored when the working face advanced. The first weighting of the roof decreased from 38.3 to 26 m, and the periodic weighting decreased from 26 to 13.7 m. Hydraulic fracturing reduced the resistance force of the supports at the working face. [ABSTRACT FROM AUTHOR]

The strength and the related parameters of unsaturated soil are the key issues in unsaturated soil mechanics. The triaxial or direct shear apparatus with suction control is used to measure the related parameters in the strength formulas proposed by Bishop and Fredlund. However, the technique is time-consuming for cohesive soils because it takes a long time to achieve a water–air equilibrium condition under a given suction state. In addition, the feasibility of the technique is also doubted. Lu et al. proposed the concept of suction stress and expressed the unsaturated strength as a function of suction stress which can be determined by the conventional triaxial test. The method can avoid measuring matric suction and is convenient in engineering application. In this paper, conventional triaxial CU tests with different moisture contents were utilized to obtain the effective steady state strength parameters and then the suction stress characteristic curves were obtained. To compare Lu et al.’s strength formula with Bishop’s and Fredlund’s, the soil–water characteristic curve of the same loess sample was also measured by the tensiometer. Theoretically, the three strength theories are different in physical mechanisms, but they can transform to each other mathematically. From the point of view of engineering applications, Lu et al.’s shear strength theory based on suction stress is more convenient to apply in engineering. [ABSTRACT FROM AUTHOR]