The aim of this paper is to determine the influence of heating rate on the dynamic mechanical performance of coal measure rocks after heat treatment. Uniaxial compression tests were conducted using a split Hopkinson pressure bar system on coal measure rocks after heat treatment at 800°C at different heating rates. The results reveal that a high-temperature treatment changed the physical and mechanical properties of the sandstone. When the heating rate was increased, the natural and mechanical properties were reduced gradually. The failure mode of sandstone after heat treatment was tension destruction, and shear fracturing occurred locally only at high heating rates. Original cracks grew inside the sandstone after heat treatment, while the number of defects (including cracks and pores) increased gradually with an increased heating rate, which was the main reason for the change in the sandstone’s macromechanical properties. The energy dissipation during fracturing was correlated closely to the fracture characteristics and increased with increased heating rates. The results of this work can provide references for future engineering projects, such as underground coal gasification and coal-bed methane thermal exploitation.

The seepage action of underground water accelerates the deformation of roadway surrounding rock in deep mines. Therefore, the study of creep characteristics of surrounding rock under seepage action is the basis for the stability control of roadway surrounding rock in deep water-rich areas. In this paper, a seepage-creep coupling test system for complete rock samples was established. Combined with a scanning electron microscopy (SEM) test system, the seepage-creep law of coal measures sandstone and the damage mechanism were revealed. The study results showed that the maximum creep deformation of sandstone under natural and saturation state decreased gradually with the increase of confining pressure, and the maximum creep deformation under saturation state was greater than the corresponding value under natural state when the confining pressure was same. When the confining pressure was constant, the creep deformation, the constant creep deformation rate and the accelerated creep deformation rate of sandstone increased rapidly with the increase of infiltration pressure. With the change of time, the change of permeability parameters went through three cycles; each cycle was divided into two stages, slow change stage and rapid change stage, and the rate of variation increased with the increase of the seepage pressure. Based on the macroscopic and microscopic characteristics of sandstone rupture, the connection between macroscopic and microscopic mechanism on sandstone rupture was established. The results in this paper can provide a theoretical basis for stability control of roadway surrounding rock in water-rich areas.

Dynamic properties of rocks are extremely important in a variety of rock mechanics and rock engineering problems. The split Hopkinson tensile bar (SHTB) system is used in this paper to measure the mechanical properties of sandstone specimens under dynamic direct tension, and the full stress-strain curves of the specimens at different strain rates is obtained. The experimental results indicate that the tensile strength, the tensile modulus and the peak strain of the specimen increase almost linearly with the strain rate. The increases in the tensile strength, the tensile modulus and the peak strain reach 125 %, 37 % and 98 % respectively as the strain rate increases by 252 %. The microscopic structure characteristics of the fracture surfaces after the tensile failure of the specimens are investigated by three-dimensional scanning. The results suggest that the fracture surface roughness of the sandstone under direct tension is significantly sensitive to the strain rate. Both the roughness coefficient and the fractal dimension of the specimen increase with the strain rate. The fracture surface of the specimen changes from a relatively flat two-dimensional state to a three-dimensional state, and its relative area gradually increases. Finally, it is manifested from the aspect of energy consumption that both the energy consumed in the fracture process and the dynamic direct tensile strength enhance with the fracture surface roughness. It is believed that the investigation results can provide an important reference for the research on dynamic properties of rocks involved in experimental research and engineering practice.

The physical and mechanical properties of rocks change significantly after being subjected to high temperatures, which poses safety hazards to underground projects such as coal underground gasification. In order to investigate the effect of temperature on the macroscopic and microscopic properties of rocks, this paper has taken sandstone as the research object and conducted uniaxial compression tests on sandstone specimens at different temperatures (20–1000 °C) and different heating rates (5–30 °C/min). At the same time, the acoustic emission (AE) test system was used to observe the acoustic emission characteristics of the rock damage process, and the microstructural changes after high temperature were analyzed with the help of a scanning electron microscope (SEM). The test results show that the effect of temperature on sandstone is mainly divided into three stages: Stage I (20–500 °C) is the strengthening zone, the evaporation of water and the contraction of primary fissures, and sandstone densification is enhanced. In particular, the compressive strength and elastic modulus increase, the macroscopic damage mode is dominated by shear damage, and the fracture micromorphology is mainly brittle fracture. Stage II (500–600 °C) is the transition zone, 500 °C is the threshold temperature for the compressive strength and modulus of elasticity, and the damage mode changes from shear to cleavage damage, and the sandstone undergoes brittle–ductile transition in this temperature interval. Stage III is the physicochemical deterioration stage. The changes in the physical and chemical properties make the sandstone compressive strength and modulus of elasticity continue to decline, the macroscopic damage mode is mainly dominated by cleavage damage, and the fracture microscopic morphology is of a more toughness fracture. The effect of different heating rates on the mechanical properties of sandstone was further studied, and it was found that the mechanical properties of the rock further deteriorated under higher heating rates.

Understanding the creep behaviours of rocks is essential for the long-term stability of underground excavations in mining engineering. Creep behaviours are more important when the mining depth is greater, which leads to the emergence of weak rock masses and high in situ stresses. In this study, the creep behaviours of argillaceous sandstone (AS) were systematically investigated. For the experimental investigation, creep tests were conducted on AS with different confining pressures (3, 6, 9, 12, 15, and 18 MPa) using an MTS815.02 rock mechanics test system. The mechanical characteristics of AS were analysed. For the numerical study, a nonlinear creep model of AS under equal and different confining pressures was established based on rock creep theory and plastic theory. The results showed that confining pressure could effectively improve the creep failure strength of AS, accelerating its creep deformation rate and process and reducing the final expansion volume. The nonlinear creep model was embedded in the FLAC3D software, and the experimental and numerical results agreed well. The experimental investigation and proposed creep model can provide important guidance in underground mines for safe long-term stability of underground excavations.

The surrounding rock control technology of mining roadways in large inclination seams with a weak structural plane in the roof is one of the most challenging fields in underground roadway support. In view of the serious deformation of the surrounding rock of the transportation roadway in the 1201 working face of a mine, the deformation and failure characteristics and instability mechanism of the surrounding rock of the roadway are analysed. The self-stability mechanical model of the roof block structure of the roadway with a large inclination under the support effect is established, and the support concept of “high pre-stressed asymmetric” and the combined support method of bolts, wire mesh, and cables are proposed. The rationality of the supporting scheme is verified by numerical simulation. The results show that: compared with bolt and wire mesh support, the maximum shear displacement of the roof’s weak layer under the combined support of bolt, wire meshes, and cable before and after mining is reduced by 86.78% and 83%, respectively, and the maximum total displacement of surrounding rock surface is reduced by 49.22% and 37.1%, respectively. The field monitoring results show that the combined support scheme can effectively control the deformation of the surrounding rock.