Underground space utilization of coalmines in China: A review of underground water reservoir construction

Understanding the mechanical properties of coal after gas and coal interaction can better guide the mining technology of gas-bearing coal seams and drainage technology of coalbed methane. In this study, triaxial compression tests of coal mass under different gas adsorption pressures are carried out to evaluate the mechanical properties, impact tendency, and brittleness of coal with different gas adsorption pressures. Results show that due to the adsorption of gas, the mechanical parameters, such as elastic modulus and strength of coal are significantly decreased. In addition to the effect of fluid pressure, the decrease of elastic energy absorbed by coal, the increase of ductile deformation and the change of molecular structure of coal particles caused by gas adsorption also significantly affect the mechanical properties of coal. The influence of gas adsorption pressure on energy input becomes gradually evident when the coal enters the stage of plastic deformation and yield failure. Then the deformation and stress bearing capacity of coal are affected, and the energy accumulation and dissipation process of coal are further affected. The gas adsorption pressure generally develops the energy absorption density and elastic energy density of three characteristic points (initial damage point, volume expansion point and peak stress point), but reduces the dissipation energy density of these points. Gas adsorption reduces the storage of deformation energy of coal, strengthens the energy dissipation, and develops the plastic failure characteristics of coal. It is not prone to appear sudden brittle failure in coal mass. Although high pressure reduces the risk of rock burst, it increases the risk of gas outburst. The chemical effects of pore/fracture fluid caused by the combined action of adsorbed and free gas lead to the further decline in coal brittleness, thus changing the deformation and failure mode of coal. 

https://link.springer.com/content/pdf/10.1007/s40948-022-00439-6.pdf

Experimental investigation of mechanical properties, impact tendency, and brittleness characteristics of coal mass under different gas adsorption pressures

Long-term properties and microstructure change of engineered cementitious composites subjected to high sulfate coal mine water in drying-wetting cycles

To study the weakening mechanism of the shear characteristics of water-bearing rock joints, four types of artificial saw-tooth joints (including tooth inclination angles of 0°, 15°, 30° and 45°) were prepared in sandstone with four moisture content (0%, 1.55%, 3.1% and 4.65%). This work adopted the non-destructive water intrusion, X-ray diffraction (XRD), acoustic emission (AE) and direct shear tests to mainly investigate the water and inclination angle-induced changes in shear mechanical properties, failure modes and AE characteristics of sandstone rock joints. The results show that the sandstone specimens contain quartz (91.04%), kaolinite, illite and montmorillonite, among which the content of quartz decrease while that of kaolinite and illite increase under the action of water, except that montmorillonite is a little controversial. The shear failure modes of the tested rock joints are divided into climbing, climbing-gnawing combined and gnawing. The inclination angle, followed by normal stress, has the greatest effect on the shear failure modes, and the moisture content has the least effect by comparison. The cohesion and internal friction angle have a positive linear relationship with the inclination angle and a negative linear relationship with the moisture content. According to the test results and Mohr–Coulomb model, a shear strength calculation model of rock joints considering the effect of inclination angle and moisture content is established. The intensity of the AE signal released during specimen failure increases with increasing inclination angle and decreases with moisture content.

Experimental study on the shear characteristics and weakening mechanism of water-bearing rock joints

Failure analysis of coal pillars and gateroads in longwall faces under the mining-water invasion coupling effect

Mechanisms of failure in coal samples from underground water reservoir

The invention relates to a supporting and protecting method based on the mining roadway full life circle, and belongs to the technical field of roadway supporting and protecting. The problems that anexisting roadway supporting and protecting method is low in efficiency, complex in operation and high in labor intensity are solved. The supporting and protecting method includes the following steps that during roadway tunneling, on the basis of experiments and field measurement, roadway surrounding rock geomechanics parameters and the surrounding rock broken rock zone range are obtained; by meansof numerical simulation, roadway bearing pressure distribution and magnitudes during tunneling, the plastic zone during tunneling, the advanced pressure influence zone range during mining and the advanced bearing pressure concentration coefficient during mining are obtained; the mining roadway supporting and protecting strength requirement is obtained through theoretical calculation, and the grouting anchor cable construction parameter is determined according to the supporting and protecting strength requirement; grouting anchor cable construction is conducted according to the grouting anchorcable construction parameter, and grouting waits to be conducted; and after mining, grouting is conducted on grouting anchor cables of the advanced supporting and protecting section of a roadway during mining, and supporting and protecting are completed. The supporting and protecting method is high in supporting and protecting efficiency and easy to operate, and the labor intensity is greatly lowered.

Chuanjin Tang

Papers

Mechanisms of failure in coal samples from underground water reservoir

Supporting and protecting method based on mining roadway full life circle