Search

Under mining conditions, the change of original stress in coal mining face aggravates the desorption of original adsorbed gas and the diffusion and seepage of free gas to varying degrees, which leads to accidents affecting coal mine safety production such as gas overrun. In order to effectively reduce the gas concentration in working face or local area of coal mine, the method of spraying surfactant to specific high concentration gas area is used to inhibit gas desorption. In order to simulate the working condition of inhibiting gas desorption by spraying surfactant solution in coal mine, the effects of mass fraction of surfactant solution and coal particle size on gas desorption under ventilation conditions were studied, and the inhibitory effect of spraying surfactant on gas desorption of coal with different particle sizes under actual coal dust environment was revealed. According to the general situation of working face where gas overrun may exist in underground coal mine, an experimental platform for inhibiting gas desorption by spraying surfactant coal was independently developed. The solution with good wettability was selected by surface tension and settlement experiments. The effects of different mass fractions of surfactant solution and coal particle size on gas desorption were studied. The results showed that when the mass fraction of surfactant solution reached 0.40%, the critical surface tension of octadecyl glucoside APG solution in the five solutions was 26.96 mN/m, and the settling time of coal powder was 18.19 s, indicating that its wettability was the best. When the spray mass fraction is 0. 01% APG - 0. 50% APG solution, the APG solution with different mass fractions has a first-order exponential relationship with the peak gas concentration. When the solution mass fraction reaches a certain degree, the area percentage of oxygen-containing groups tends to be stable with the increase of solution mass fraction. When the spray mass fraction is 0.40% APG solution and the coal particle size is between 2.80 mm and 30.00 mm, the particle size is negatively correlated with the peak gas concentration at the measuring point, but the attenuation rate decreases rapidly, slowly and rapidly with the increase of particle size.

In order to study the dynamic evolution law of the pressure relief gas reservoir in the mining of extra-thick coal seams, the 3DEC numerical simulation software was used to analyze the stress and displacement distribution law of the overburden rock caused by mining, and the evolution characteristics of the pressure relief gas reservoir were studied, and the pressure relief gas was proposed. The method of discriminating the location of the reservoir area, and the practice of gas drainage in high-position boreholes at the test working face. The results show that: after the extra-thick coal seam is mined, the height of the overburden caving zone is 49.5 m, and the height of the fracture zone is 104 m. After the key strata in the pressure relief zone on the working face side loses stability, a pressure relief gas reservoir is formed below it. Pressure relief gas reservoir areas are divided into three categories: ①The key layer is in the bent subsidence zone, and the high-level reservoir is formed below it; ②The key layer is in the fracture zone, and the middle-level reservoir is formed under the masonry beam; ③The key layer is in the fracture zone. In the collapse zone, a low-level storage area is formed under the cantilever beam. The shape and area of ​​the reservoir are closely related to the state of the control key layer above. Before the control key layer is broken, the area continues to increase. The shape of the low-level reservoir is rectangular, and the shape of the middle and high-level reservoir is semi-elliptical, expanding to a three-dimensional shape. It is a rectangular cross-section ring body and an elliptical cross-section semi-ellipsoid body; the area decreases rapidly after breaking, and then changes periodically with the pressure of the overlying rock. The low-level reservoir is trapezoidal, the middle-level reservoir is triangular, and the high-level reservoir is shaped like a trapezoid. The shape is a semi-ellipse, and the three-dimensional shape is expanded to a rectangular cross-section ring, a triangular cross-section ring and an elliptical cross-section semi-ellipsoid. The location of the final hole of the high-level borehole was arranged in the range of the middle reservoir area, and the drainage verification was carried out. The maximum drainage concentration of a single hole was 34.5%, the average drainage concentration was 16.8%, and the upper corner gas concentration after drainage was 0.55%, The gas drainage effect is good, indicating that the arrangement of high-level drilling holes according to this method is reasonable.

In order to study the mechanical damage characteristics and energy evolution law of coal after ultrasonic fracturing, uniaxial compression experiments were carried out on fractured coal with different power by using electronic universal pressure testing machine, acoustic emission system. The mechanical damage parameters of different power ultrasonic fracturing coal were obtained, and the relationship between acoustic emission signal and damage parameters of coal mass with different power fracturing was explored. The fractal characteristics of coal surface cracks were analyzed by box fractal dimension, and the damage degradation mechanism of ultrasonic fracturing coal caused by different ultrasonic power was clarified. The experimental results show that the characteristic strength and elastic modulus of coal gradually decrease with the increase of ultrasonic fracturing power, and the damage parameters of uniaxial compressive strength and elastic modulus of coal are linearly correlated with the fracturing power. During the uniaxial compression process, the acoustic emission ringing count can be divided into three stages, which are quiet period, rising period and fluctuating period. With the increase of ultrasonic power, the incubation period of crack is shorter and the proportion of relative time is smaller. With the increase of crack growth rate, the weakening effect on the strength of coal is gradually enhanced, the sudden increase of acoustic emission signal is obvious., the final failure of coal sample is more broken, and the failure characteristics change from elastic brittleness to ductility-plasticity with the increase of fracturing power. Coal pore fissure extension, and three is a linear positive correlation between the fractal dimension damage parameters of coal surface cracks and the fracturing power. The greater the fractal dimension damage parameter is, the more complex the coal fracture morphology is. Based on the acoustic parameters, the relationship between the damage parameters and the normalized parameters of acoustic emission is analyzed, and it has a good fitting relationship. The above results show that ultrasonic fracturing causes damage to the coal structure, makes the coal seam damage and deformation, and forms a complex coal seam seepage network, thus improving the permeability of coal seam.

To explore the evolution law of overburden strata during the mining of huge thick coal seams, an experimental study on the distribution characteristics of the overburden three zones with large mining height was carried out. Based on the geological conditions and mining methods of the huge thick coal seam, a two-dimensional physical similarity simulation experiment under the condition of huge thick coal seam was carried out. The results showed that the height of the overburden strata of the huge thick coal seam in Liuhuanggou（９－１５） 06 working face was 60 m. The horizontal fracture density of the overburden strata in the gob was distributed as a parabola as the propulsion distance increased. Affected by the distribution of strata in the “horizontal three zones”, Delamination of goaf was characterized by “high on both sides and low in the middle”. By calculating physical quantities such as mining overburden subsidence, fissure density, and layer separation and other physical quantities, the formula for determining the height of overburden “three zones” under huge thick coal seams was derived.