To explore the law of ground deformation from shallow-buried close-distance multi-seam mining, an observation station was built in the Bulianta Coal Mine to measure and record the periodic variation ...of related parameters about ground subsidence and surface cracks with the advancement of working face. From the data observed from the field, it can be found that, when lower seam mining, the ground subsidence above the previously mined area was deeper and steeper than that above the left pillar; besides, the influence scope of the former was larger than that of the latter. In terms of ground cracks, the ground cracks were formed ahead of the working face and developed rapidly during the period of the breakage of the immediate roof. Besides, the average interval of the ground cracks above the previous gob was 14.75 m, and still existed and hardly changed after the advancement of the working face; while that above the left pillar was 27.8 m and most of them were closed. In addition, when the advance rate of the working face was 12.8 m/day, the advance influence distance of the mining surface crack reached the minimum of 13.6 m. This finding is helpful for protecting the surficial environment in mining area during and after mining operations and is also of significance to conduct green mining in other mining areas.
Coal-like material for coal and gas outburst simulation tests Hu, Qianting; Zhang, Shutong; Wen, Guangcai ...
International journal of rock mechanics and mining sciences (Oxford, England : 1997),
February 2015, 2015-02-00, Letnik:
74
Journal Article
Recenzirano
•A method of coal-like material making for coal and gas outburst is proposed.•Relations between effect factors and relevant indexes of material are analyzed.•Uniaxial compressive strengths between ...different size material samples are compared.
Coal and gas outburst disasters affect safe production from coal mines. There has been limited progress in understanding and predicting these outbursts in the past years. Therefore, a novel large ...scale three-dimensional simulation experimental apparatus to study mechanisms of coal and gas outburst was developed. The experimental apparatus has dimensions of 1.5 m × 0.8 m × 0.8 m and can achieve a gas seal of 6 MPa. Its hydraulic sub-system can perform axial (3000 t) and horizontal symmetric (2000 t) loading. The outburst port can be initiated actively and instantaneously, similar to the sudden excitation of an outburst. The apparatus realizes the roadway network simulation of various fluid migration routes, resistance characteristics, and ventilation facilities. Simultaneously, 90 test channels and a sampling frequency of up to 4 Ms/s can be used to monitor the time–space distribution law of multiple parameters in the apparatus and realize the real-time observation of the experimental phenomena. The experimental apparatus can be used to simulate the entire process of the coal and gas outburst, including accumulation, motivation, development, and termination stages as well as systematically study the features and mechanisms of the outburst. A complete simulation experiment of an outburst under a high geo-stress was performed. The distribution and variation of the gas pressure and geo-stress before, during, and after the outburst were analyzed. The distribution of the outburst-pulverized coal and gas concentration rule was obtained, which shows the characteristics of the extrusion type. This experiment validates the capability and reliability of the newly developed coal and gas outburst simulation apparatus.
Coal and gas outburst is one of the main gas hazards in coal mines. However, due to the risks of the coal and gas outburst, the field test is difficult to complete. Therefore, an effective approach ...to studying the mechanism and development of outburst is to conduct the similar physical simulation. However, the similarity criteria and similar materials in outburst are the key factors which restrict the development of physical simulation. To solve those problems, this paper has established similarity criteria base on mechanics model, solid–fluid coupling model and energy model, and presented high similar materials. Combining with three groups of similar number, and considering similar mechanical parameters and deformation and failure regularity, the similarity criteria of outburst is determined on the basis of the energy model. According to those criteria, we put forward a similar material consists of pulverized coal, cement, sand, activated carbon, and water. The similar material has high compressive strength and the accordant characteristics with the raw coal, include density, porosity, adsorption, desorption. The new research is promising for preventing and controlling gas hazards in the future.
The permeability of coal reservoirs prominently determines methane flow in reservoirs. A large amount of coal reservoirs containing methane, however, have low permeability because pores in reservoirs ...are sealed. To solve this issue, we investigated the pore structure and permeability law of coal through contrastive analysis of the microstructure and macrostructure before and after acidizing, using ASAP 2020 and triaxial servo-controlled seepage equipment. An analysis of the experimental data revealed the mechanism and the key parameters of acidizing, such as acid mass fraction and acidizing time. In addition, we hold that the optimal mass fraction for the test specimens is about 12~15%. Furthermore, the acid reaction is divided into three stages according to characteristics of the reaction progress. An analysis of the reaction kinetics of “HCl-HF” states that the significant factors will impact the process of reaction, like the composition of coal, surface area of the acid-coal reaction, mass fraction of acids, and environment of the reaction system. The results provide a new idea and research method for further enhancing permeability and gas extraction.
Based on thermal–fluid–solid coupling law in coal and gas outburst, a multi-physical field numerical analysis model is built for the whole outburst process. The response laws of stress, gas pressure, ...temperature, and seepage in different areas and different time nodes around coal and rock mass in the coal and gas outburst under high stress condition are discussed. Research results show: Firstly, the stress response law of the coal and rock mass around the burst hole is initial vibration–sudden attenuation–late stability. Secondly, the gas pressure response law in different areas is that the gas pressure response rate decreases gradually with the increase of the distance from the outburst. Thirdly, the adsorbed gas contained in the broken coal near the outburst port is desorbed rapidly and expands to do work, and the temperature changes dramatically after outburst occurs. In contrast, with the increase of stress, the proportion of elastic potential in total coal and gas outburst energy increases, and the proportion of elastic potential is positively correlated with stress. The critical gas pressure under the energy condition of coal and gas outburst decreases with the increase of stress. It illustrates that the lower gas pressure can also meet the energy condition of coal and gas outburst under high stress.
Stress-dominated coal and gas outburst disaster has become one of the main safety problems in deep coal mines. Acoustic emission (AE) or microseismic technology has been viewed as a promising method ...that can effectively reflect the stress and stability status of rock mass. The AE activity precursor of coal failure is the theoretical basis of this technology. In this study, AE experiments in failure process of coal specimens with different properties and under different stress conditions were performed in laboratory to explore influence factors and their effect of AE activity, and AE activity pattern classification was proposed based on the failure type of coal. The results indicate that the AE activity of different coals under loading are associated with the failure phase, and the evolution pattern of AE activity depends on the failure type of stressed coal. Both the mechanical property and the external stress condition have an important influential effect on the failure type and AE activity pattern in coal failure process. The internal mechanical property decides the inherent tendency of stressed coals to perform brittle or ductile behavior, and the responded AE activity pattern. The contrast of fissure distribution of specimens suggested that fissure structure in coal significantly affects the fracturing mode of coal in uniaxial compression and the AE activity pattern. The external stress condition has a transition effect on AE event energy distribution and AE activity pattern. Under the effect of external stress condition, the energy distribution of AE events was transforming between relative disperse and relative concentration, the failure type and AE activity evolution pattern of coal could appear the brittle-ductile transition. Based on the view of failure type, the pattern of AE activity of coal failure can be classified into three types, i.e., ductile, brittle, and semi-brittle pattern. It is suggested that the high-level AE activity can be viewed as the precursor of brittle instability of coal, and relative quiet phenomenon of AE activity as the precursor of ductile or semi-brittle instability. The research achievement can provide a theoretical base for the prewarning criteria establishment of coal and rock dynamic disasters at depth and improve the insight of AE activity in the coal failure process.
Particle size and shape distribution can be measured in great detail by dynamic image analysis (DIA). The narrow dispersion of repeated experiment results indicates that the particle size ...distribution can be obtained with high reliability. Particle size distribution can be better fitted to Rosin-Rammler equation than Gaudin-Schuhmann distribution and the lognormal distribution. The spread parameter (m) and the location parameters (d0) of the Rosin-Rammler equation can be calculated precisely. We analyzed the similarities and differences between the different particle shape distributions. The distributions of form factor and circularity are right-skewed distributions, while the distributions of ellipse ratio, irregularity, and aspect ratio obey a normal distribution. By studying the relation between particle size and shape, we find a linear relationship between the ellipse ratio and the Legendre ellipse diameter on the logarithmic scale.
Passive explosion-isolation facilities in underground coal mines, such as explosion-proof water troughs and bags, face challenges aligned with current trends in intelligent and unmanned technologies, ...due to restricted applicability and structural features. Grounded in the propagation laws and disaster mechanisms of gas explosions, the device in this paper enables accurate identification of explosion flames and pressure information. Utilizing a high-speed processor for rapid logical processing enables judgments within 1 ms. Graded activation of the operating mechanism is enabled by the device. The tunnel flame-proof device’s flame-extinguishing agent has a continuous action time of 6075 ms. Experiments on the active flame-proof effect of a 100 m3 gas explosion were conducted using a cross-sectional 7.2 m2 large-tunnel test system. With a dosage of 5.6 kg/m2, the powder flame-extinguishing agent completely extinguished the explosion flame within a 20 m range behind the explosion isolator. Numerical calculations unveiled the gas-phase chemical suppression mechanism of the powder flame-extinguishing agent NH4H2PO4 in suppressing methane explosions. Building upon these findings, application technology for active flame-proofing was developed, offering technical support for intelligent prevention and control of gas explosions in underground coal mines.
Deep mining will increase the likelihood of coal and gas outburst accidents and do harm to the safety of coal mining. In this study, a coal and gas outburst experiment under deep high‐stress ...conditions was carried out and stress–gas pressure–temperature response laws in coal and rock surrounding the burst hole were evaluated. The experimental results showed that the stress response around the burst hole was intense and stress variation decreased as distance from the position to burst port increased. The gas pressure in the coal decreased sharply and oscillated several times during the burst process. The maximum rebound range was 0.05 MPa during this process. The decreasing rate of gas pressure reduced with the increase of the position‐burst port distance. The temperature response near the burst port was stronger than peripheral area. The gas internal energy was still the main energy source of coal and gas outbursts, accounting for 75% of the total energy, and played a key role in the burst process. The contribution of elastic potential energy was 22% under deep high‐stress conditions in this study. Based on the analysis of burst energy, the gas and stress were key factors of an outburst.
1.
A coal and gas outburst experiment under high‐stress condition was carried out.
2.
S–GP–T response laws surrounding the burst hole were evaluated.
3.
The burst coal distribution characteristics were obtained.
PDF
