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 grouting anchor cable advanced supporting method, belongs to the field of advanced supporting and aims at solving the problems of insufficient supporting strength and slow supporting speed in the prior art and roof breakage and large worker labor intensity caused by repeated supporting. The advanced supporting method disclosed by the invention comprises the following steps: step 1, determining a mining roadway (1) to be supported on a current working face (3); step 2, determining an advanced supporting distance L according to the advanced supporting pressure distribution law and the engineering geological condition of the mining roadway (1); step 3, adding grouting anchor cable advanced supporting to a roof of the mining roadway (1) to form a roof supporting structure. In a coal mining process, the working face (3) is propelled forwards, the grouting anchor cable advanced supporting is simultaneously and continuously added in the propelling direction, and theadvanced supporting distance is maintained in a safe range. The grouting anchor cable advanced supporting method disclosed by the invention can ensure safe mining and simultaneously improve supporting strength and supporting efficiency and reduce worker labor intensity.

Grouting anchor cable advanced supporting method

The invention relates to a small-section mining roadway mixing type advanced support method and belongs to the technical field of mining roadway supports. The method solves the problems that an existing support method is low in support efficiency, large in labor intensity of workers, high in cost, low in mining efficiency, insufficient in effective construction space and low in operation safety and reliability. The support method comprises the steps that 1, a mining roadway to be supported is determined; 2, a grouting anchor cable and an individual hydraulic prop mixing type advanced support are additionally installed on a top plate of the mining roadway, and a top plate support structure is formed; and 3, in the coal mining process, while the mining working face is propelled forwards, thegrouting anchor cable is additionally installed in the propelling direction constantly, an individual hydraulic prop and a hinge top beam of the working face end are pushed towards the front end of the advanced support constantly, and thus the distance of the advanced support is kept within the safe range. According to the method, the support efficiency and the mining efficiency are improved, thelabor intensity of the workers and the support cost are reduced, the support strength is higher, the support effect is better, and safe and efficiency production is achieved.

Small-section mining roadway mixing type advanced support method

The invention discloses a caving coal mining roadway grouting anchor cable supporting structure and an advanced supporting method thereof. The advanced supporting method of the caving coal mining roadway grouting anchor cable supporting structure includes following steps: step 1, confirming at least one mining roadway to be supported on a current mining face, wherein setting perpetual support on atop plate and two sides of each mining roadway, and using combined anchor-bolt and net support as the perpetual support due to the fact that each mining roadway is dug in advance and the perpetual support is performed in the digging process,; and step 2, performing advanced support on each mining roadway, wherein at the same moment of mining the mining face, constructing anchor cable holes everyother row of anchor bolts in the advancing direction and on the top plate of each mining roadway, mounting grouting anchor cables and anchor trays in the anchor cable holes while constructing the anchor cable holes, and using locksets for pre-tightening. The advanced supporting method of the caving coal mining roadway grouting anchor cable supporting structure and the advanced supporting method thereof have the beneficial technological achievements of 1) greatly improving supporting efficiency on the premise of guaranteeing safe mining; 2) greatly saving the space area of each mining roadway;and 3) being simple in structure, convenient to operate and low in cost.

Caving coal mining roadway grouting anchor cable supporting structure and advanced supporting method thereof

The invention discloses a slurry pressure monitoring device and method for a hollow grouting cable anchor. The monitoring device comprises a pressure gauge, an outgoing line, an elastic piece, an ironball, a strain gauge and a shell. The shell comprises a shell body and a sealing cover. An inflow port and an outflow port are formed in the two sides of the shell body. The iron ball is placed in the shell body. The elastic piece is located in the shell body. The pressure gauge is connected with the strain gauge through the outgoing line. The top of the strain gauge penetrates through the side wall of the shell body and then is connected with the elastic piece. During work, the inflow port is connected with a grouting pump, the outflow port is connected with a grouting opening of the hollowgrouting anchor cable, the iron ball is pushed to move towards the sealing cover under the action of the slurry pressure, slurry passes through the gap between the iron ball and the elastic piece, thedeformation of the elastic piece is monitored, and the borne pressure is monitored and displayed in real time through the pressure gauge. The device is simple in structure, can guarantee one-way flowing of the slurry, the grouting opening can be plugged, and the pressure of the slurry is monitored in real time.

Hui Xindong

Papers

Mechanisms of failure in coal samples from underground water reservoir

Grouting anchor cable advanced supporting method

Small-section mining roadway mixing type advanced support method

Caving coal mining roadway grouting anchor cable supporting structure and advanced supporting method thereof

Slurry pressure monitoring device and method for hollow grouting cable anchor