Bo Ren

The mining environment of thin coal seam working faces is generally harsh, the labor intensity is high, and the production efficiency is low. Previous studies have shown that thin coal seam mining finds it difficult to follow machines, does not have complete sets of equipment, has a low degree of automation, and has difficult system co-control, which easily causes production safety accidents. In order to effectively solve the problems existing in thin coal seam mining, Binhu Coal Mine has established intelligent fully mechanized mining and actively explored automatic coal cutting, automatic support following, and intelligent control. The combination of an SAC electro-hydraulic control system and SAP pumping station control system has been applied in 16,108 intelligent fully mechanized coal mining faces, which realizes the automatic following of underground support and the control of adjacent support, partition support, and group operation; the automatic coal cutting of the shearer is realized by editing the automatic coal-cutting state of the shearer and adjusting the automatic parameters. A centralized control center is set up, which realizes the remote control and one-button start–stop of working face equipment. Through a comparative analysis of 16,108 intelligent fully mechanized mining faces and traditional fully mechanized mining faces, it is found that intelligent fully mechanized mining faces have obvious advantages in terms of equipment maintenance, equipment operation mode, and working face efficiency, which improve the equipment and technical mining level of thin coal seam. The application of intelligent mining in Binhu Coal Mine has a great and far-reaching impact on the development of thin coal seam mining technology in China.

Taking the roadway peripheral rock anchoring unit as the research object, the rock compression test containing the anchor solid was carried out to analyze the influence of the degree of peripheral rock fragmentation and the anchor support method on the mechanical properties of the rock body. The test results showed that the smaller the size of the structural surface, the more a greater number of anchor rods were needed, which in turn provided better support. With the increase in the size of the structural surface, the uniaxial compressive strength and modulus of elasticity of the specimen showed a gradual decrease. Numerical tests of the uniaxial compression of rock containing cohesive units showed that the deformation of the specimen near the anchor bar was significantly reduced, while the main rupture surface was blocked, and an obvious reinforcement zone was formed near the anchor bar. Under the double-anchor condition, the anchor tension stress was more obvious, the reinforcement zone was wider, and the rock rupture surface was strongly blocked, all of which made its reinforcement effect the more obvious. This double-anchor condition showed that the anchoring effect of the anchor rods on the specimens was reflected in two aspects of reinforcement and crack stopping. The denser the anchor rods, the wider the reinforcement zone and hence the more likely that the superposition effect will occur, which allowed the anchor rods to play a greater supporting role in stabilizing the rock. The research results can provide a theoretical basis for the design of anchor support and early warning prediction of destabilization damage in the fractured surrounding rock of coal mine roadways.

In this study, a series of true triaxial loading tests were carried out on coal-measure sandstone after high temperature treatment by using a self-developed true triaxial test system combined with acoustic emission (AE) monitoring, and the mass loss, deformation characteristics and loss failure mode of sandstone before and after heat treatment were systematically studied. It is found that the true triaxial mechanical properties of sandstone after high temperature treatment are closely related to temperature, and the peak strength, maximum principal strain, volume strain, minimum fracture angle and elastic modulus, which all showed bimodal changes, and 800 °C is the threshold temperature of the first four parameters. The transition temperature of the elastic modulus is 400 °C. It is found that the test results of true triaxial high temperature sandstone are in good agreement with the existing true triaxial theory and test results. The failure forms of the samples at different temperatures show inverted “Y” or inverted “N” shapes. Shear failure occurs when the temperature is below 400 °C, and shear-tension failure occurs when the temperature is above 600 °C. At the same time, it is found that the AE signal has four periods, namely the quiet period, growth period, explosion period and decline period. The number of AE events corresponds to the deviatoric stress interval well. Experimental study of the mechanical properties of sandstone under the coupling effect of high temperature and true triaxial stress has guiding significance for the parameter selection and safety evaluation of roof sandstone in underground coal gasification.

Considering the harsh environment of deep, fully mechanized working faces and the acutely imbalanced time distribution among excavation, support and anchoring, this paper designed a new type of highly adaptable advance support for fully mechanized roadways that boasts high adaptability, great support strength and a large working space. Firstly, the structure composition and working principle of the advance support were introduced. The structures and mechanical characteristics were then emphatically discussed. Subsequently, with the geological conditions of the 8224-machine roadway in the XT Coal Mine taken as an example, the loads of the advance support were obtained and then imported into the Ansys software to obtain the stress distribution and displacement distribution of the whole advance support and its parts through calculation. Based on the distribution, the stress and strain of the advance support were analyzed. The simulation results are as follows: Under various working conditions, the maximum displacement of the advance support was 4.5 mm, which is negligible compared to the overall size of the support; the maximum stress was 72.8 MPa, which is lower than the yield strength of the material (235 MPa). Therefore, the designed support can bear the pressure from the surrounding rock in the mine. Moreover, the roof beam, which is a weak link in the support, deserves more attention in subsequent engineering designs. This method conduces to not only parallel operations of excavation, support and anchoring, but also to rapid excavation and the safe production of roadways, providing fresh ideas for the advance support for fully mechanized roadways.

To provide technical support for gas extraction and gas accident prevention technology, the permeability law of gas in coal seams under different ground stress and gas pressure has been explored. The evolution law of coal sample permeability under different confining pressure and gas pressure was deeply studied by using the coal rock mechanics–permeability test system TAWD-2000. The conclusions are as follows. The permeability of coal samples can be divided into three stages in the whole stress–strain process, gradually decreasing stage, tending to be stable and slowly rising stage, and significantly rising stage. When the confining pressure and axial pressure of the coal sample are constant, the permeability of the coal sample decreases gradually with the increase in gas pressure. When the gas pressure and axial pressure of coal samples are constant, the permeability of the coal samples first decreases and then rises with the gradual increase of confining pressure. Under different confining pressures and gas pressures, the change degree and change rate of coal permeability and are different in the whole stress–strain process. The research results can provide necessary data support for subsequent numerical calculations and practical engineering application.

Affected by mining stress, roadways surrounding rock face problems such as serious deformation and failure and difficult support. In this study, with the II2 mining area rise in Taoyuan Coal Mine taken as the engineering background, the evolution laws of stress, deformation and plastic zone area of the mining area rises during the advance process of the working face were explored with the aid of FLAC^3D software. The results suggested that the stress, deformation and plastic zone area of the surrounding rock increase significantly when the distance between the working face and the track rise is less than 20 m. Based on this finding, it was further determined that the stopping line of the II8₂22 working face should be at least 20 m away from the track rise. Furthermore, in accordance with the deformation and failure characteristics of surrounding rock under the influence of mining stress, this paper conducted a simulation on four support schemes of mining area rises, and quantitatively analyzed the mechanical response of a roadway surrounding rock under these support schemes. The simulation results revealed that the support scheme of “bolt-mesh-spray-cable + grouting bolt” can effectively deal with the influence of mining stress on the working face. Meanwhile, an engineering application was carried out. By monitoring the surface displacement of the surrounding rock, it was found that the deformation of the roadway surrounding rock was effectively controlled, and a remarkable support effect was achieved. In short, the proposed support scheme greatly improved the stability and safety of surrounding rock in the mining area rise under the influence of mining stress.

In this study, triaxial compression and seepage tests were conducted on briquette and raw coal samples using a coal rock mechanics-seepage triaxial test system (TAWD-2000) to obtain the complete stress–strain curves of the two samples under certain conditions. On this basis, the different damage forms of the two coal samples and the effect of their deformation and damage on their permeability were analyzed from the perspective of fine-scale damage mechanics. Moreover, the sensitivity of permeability to external variables and the suddenness of coal and gas outbursts were discussed. The results show that the compressive strength of raw coal is 27.1 MPa and the compressive strength of briquette is 17.3 MPa, the complete stress–strain curves of the two coal samples can be divided into four stages and show a good correspondence to the permeability–axial strain curves. Since briquette and raw coal have different structural properties, they present different damage mechanisms under load, thus showing great diversity in the permeability-axial strain curve, especially in the damage stage. The deformation affects the seepage characteristics of briquette mainly in the latter two stages, while it affects raw coal throughout the test. The four stages of the complete stress–strain seepage test of raw coal can well explain the four stages of coal and gas outburst process, i.e., preparation, initiation, development, and termination. Hence, the law of coal permeability to gas variation can be utilized for the coal and gas outburst prediction and forecast. The research results are valuable for exploring the real law of gas migration in coal seams.

In this paper, the fracture zone of the Chunxuan Road Tunnel in Jinan, Shandong Province, China was selected for the engineering background. With reference to the field monitoring data, a finite element model was established based on the strength reduction method. With the aid of this model, the influences of different initial support parameters (including lining, bolt and steel arch) on the tunnel deformation in the fracture zone were analyzed to obtain reasonable initial support parameters. The results show that the tunnel deformation under the original initial support is severe. Among the initial support methods, such as lining, bolt, and steel arch, the parameters of the lining and steel arch significantly influence the tunnel deformation in the fracture zone. Therefore, selecting appropriate initial support parameters can effectively control the tunnel deformation in the fracture zone. After the optimized support scheme is adopted, failure instability no longer occurs in the tunnel and the tunnel deformation is also effectively controlled. The research findings provide a clear reference for deformation control and support scheme optimization of similar projects.

Protective coal seam mining can not only effectively prevent coal and gas outbursts in mines, but also provide stress unloading space for the protected coal seam. The coal body in the protected coal seam might undergo deformation, internal damage and structural damage, which changes its gas seepage characteristics. This study aims to explore the variations of permeability of the coal body in the protected coal seam under axial unloading. With the coal body from the outburst coal seam in the Huaibei mining area as the research object, experiments were conducted to explore the gas seepage characteristics of axially unloaded coal body under different confining pressures and gas pressures, using the TAWD-2000 coal-rock mechanics-seepage experimental system. According to the results, with respect to the gas seepage, the variations of permeabilities of axially unloaded coal samples are closely related to their deformation and damage. As the confining pressure and gas pressure rise, the difference between the permeability at the final failure point and the initial permeability rises at a decreasing rate. The experiments fully demonstrate that the protective coal seam is technically important for the unloaded gas drainage and the coal and gas outburst prevention of the protected coal seam. Under different confining pressures and gas pressures, the permeability of axially unloaded coal varies to different extents and at different rates. The mining scheme for the protective coal seam should be designed in accordance with its confining pressure and gas pressure. This study is of guiding significance for the prevention and control of coal and gas outbursts in coal seam groups.