Coal Mines In China Research Articles

Research on the Development Law of Pre-Mining Microseisms and Risk Assessment of Floor Water Inrush: A Case Study of the Wutongzhuang Coal Mine in China

Coal-mining areas are widely distributed in Northern China, but are under threat from confined water in the mining operation, resulting in a series of floor water- inrush hazards. Therefore, it is significant to effectively evaluate the floor water inrush to ensure safe and efficient coal mining. The 182602 working face of the Wutongzhuang coal mine served as the background for our research. The concept of “pre-mining microseisms” was proposed, and based on this, microseismic monitoring equipment was arranged on site. The correlation between microseismic events and the water abundance of an aquifer was analyzed, and a floor water inrush evaluation method was constructed based on the three elements of an aquifer and pre-mining microseisms. The main results are as follows: first, the microseismic events were excited by artificial disturbances before the mining of the working face including slurry diffusion and neighboring mining, which had the characteristics of sporadicity, clustering, and periodicity. Second, the regional distribution of water abundance was determined by taking the water inflow, water pressure, and grouting volume as the outward performance characteristics of water abundance in the Shanvuqing aquifer. Furthermore, the correlation coefficient between the pre-mining microseisms and the three elements of the aquifer (water inflow, water pressure, and grouting volume) was larger than 0.7. On this basis, an evaluation method associated with the water inrush risk along the strike of the working face was established based on pre-mining microseisms, dividing the working face into dangerous zones, suspected dangerous zones, and safe zones. Furthermore, pre-mining microseisms, water abundance, and structures were introduced as risk-evaluation indices, and the complete weight was calculated using an analytic hierarchy process and entropy-weight technique, before a vulnerability index model of floor water inrush was built. Finally, targeted treatment procedures were efficiently implemented to ensure the safe mining of working face 182602 due to the successful prediction of potential water risk zones. The research results provide scientific and technological support for pre-mining microseisms combined with water abundance as a technical method to prevent floor water inrush.

Effect of Work Values on Miners’ Safety Behavior: The Mediating Role of Psychological Empowerment and the Moderating Role of Safety Climate

Although numerous studies have confirmed the important influence of values on employees’ behavior, less is known about the relationship between work values and miners’ safe behavior. Based on self-verification theory and trait activation theory, this study constructed a structural equation model to explore the effect of work values on miners’ safety behavior, using psychological empowerment as a mediating variable and safety climate as a moderating variable. Data were collected from 207 miners in three coal mines in China. The model was examined using a hierarchical regression analysis and the bootstrapping method. The results showed that three types of work values significantly and positively predicted miners’ safety behavior, and psychological empowerment mediated the relationship between work values and miners’ safety behavior. However, the moderating role of safety climate was not supported. The results enrich the boundary conditions under which work values influence miners’ safety behavior and provide coal managers with intervention measures such as cultivating miners’ work values and psychological empowerment, which can improve miners’ safety behavior.

Study on Mechanism of Pressure Relief and Permeability Enhancement in Soft-hard Composite Coal Seam by Directional Hydraulic Flushing Technology

The soft-hard composite coal seam composed of tectonic and primary structural coal has the problems, such as high gas content, high pressure, poor permeability and difficult extraction, which seriously affect the production safety in the mining. To study the evolution characteristics of pressure relief in soft-hard composite coal seam based on directional hydraulic flushing technology, taking Hudi coal mine in China as the engineering background, and the pressure relief effect of directional hydraulic flushing on 'two soft and one hard' composite coal seam was studied by theoretical analysis and numerical simulation. The stress evolution of the whole coal seam under a single hole and porous interaction of different flushing radii were analyzed. The field test of directional hydraulic flushing in tectonic soft coal seam similar to protective layer mining was conducted. Results show that when the flushing diameter is 3-4 m, the influence range of stress disturbance covers the whole coal seam, and the vertical stress relief of the primary coal seam is the largest, which provides a theoretical basis for coal seam pressure relief and permeability enhancement technology. The average daily gas extraction (ADGE) concentration has doubled, and the ADGE purity has increased from 0.03 m3/d to 1.07m3/d. The target period of gas extraction is shortened from the expected 6 months to 1 month, and the average daily driving speed of coal roadway increases from 2.32 m/d to 5.37 m/d. The gas extraction efficiency is significantly improved, and the risk of gas outburst is effectively reduced, which has important theoretical and practical significance for improving the pressure relief and permeability enhancement efficiency of the soft and low permeability coal seam.

Substantial methane emissions from abandoned coal mines in China

China has shut down and abandoned a substantial number of coal mines since 1999, which have been releasing methane (CH4) for many years. However, the characteristics of China's abandoned mine methane (AMM) emissions are still unclear; this is a concerning knowledge gap because coal mines are the largest contributor to China's anthropogenic CH4 emissions. This study used two methods to estimate China's historical AMM emissions over the past 40 years (1980–2020) and to project its AMM emissions to 2060 which is the target year for China's carbon neutrality goal. The results show that China's AMM emissions increased substantially from 0.11 ± 0.03 million tons per year (Mt/yr) (3.1 ± 0.84 Mt/yr CO2-eq) in 1980 to 4.7 ± 0.94 Mt/yr (131 ± 26 Mt/yr CO2-eq) in 2020. An accelerated growth rate was found during 1998–2005, with AMM emissions rapidly increasing by approximately three times, which was consistent with the high number of mine shutdowns. In 2019, we found that AMM emissions had become the fourth largest anthropogenic source in China, higher than the national anthropogenic CH4 emissions of individual United Nations Framework Convention on Climate Change Annex I countries excluding the United States of America and the Russian Federation. If unabated, China's AMM emissions are projected to peak at 8.7 ± 2.6 Mt/yr in 2040 and reach approximately one-third of China's anthropogenic carbon dioxide emissions in 2060. This study reveals that understanding AMM emissions can help more accurately quantify China's total CH4 emissions and guide their future mitigation.

True 3D geomechanical model test for research on rheological deformation and failure characteristics of deep soft rock roadways

Deep soft rock roadways generally present large deformation characteristics, and a vast number of workers attempt to repair them to no avail. A true 3D model test was performed based on the engineering background of the transportation roadway of the Huafeng coal mine in China. The selected analogous materials have a significant time similarity relationship with the surrounding rock, and a similar bolt-mesh-shotcrete support structure, according to the engineering background, was applied to the roadway. The test results showed that the evolution process of the rheological deformation of the roadway is two sidewalls → floor → vault → full-section convergence of the roadway. The large deformation zones of the surrounding rock are constantly transferred from the surface to the depth, and the bearing capacity of the bolts decreases rapidly after the deformation of the anchorage zones. The mechanical characteristics of the floor determine that the lower surrounding rock always repeats the failure process of the upper rock stratum, and the floor heave does not stop. The test results revealed the full-section convergence rheological deformation laws and migration laws of the internal key deformation locations of the surrounding rock and clarified the reasons for the floor heave. The model test results are verified through field monitoring, and opportunities and suggestions for secondary support are determined. These results could provide a reference for the failure process and control technology of the same type of deep soft rock roadway.

Calibration of Water Inrush Channel and Numerical Simulation of Water Inrush Process in Coal Mine Roof

The surrounding rock of a coal mine roof fractures with the excavation of the underground working face in coal mining. These mining-induced fractures are connected and extended upward to form water inrush channels. A water inrush accident may occur when there is a sufficiently large water source. To elucidate the formation mechanisms of the roof water inrush channel and the characteristics of water inrush in goafs, we performed a case study of No.18401 Panel of Xiqu Coal Mine in China and determined whether the roof water inrush channel is connected by theoretical calculation and microseismic monitoring. The modified mechanical parameters of rock masses were embedded into the numerical model based on microseismic data. Microseismic monitoring and numerical simulation were organically combined to analyze the connection process of the water inrush channel, after which the roof water inrush channel is calibrated on the No.18401 Panel. We established a non-Darcy flow model for water inrush in the water-conducting fractured zone of mines by coupling the Darcy, Forchheimer, and Navier–Stokes equations. Finite element language and its compiler (FELAC) was used to study the water inrush mechanism of non-Darcy seepage. The results show that the pressure, velocity, and porosity in the water-conducting fractured zone are non-uniform in water inrush occurrence and development, and the mixed fluid mainly passes through the “dominant channel.” The development of water inrush is accompanied by the release of the hydrostatic pressure in the aquifer, the sudden increase of the velocity at the water inrush position, and the increase in fluid concentration. Hence, the underground water inrush can be predicted and prevented by monitoring the aforementioned indicators. This research is of great significance for the calibration of the water inrush channel of the roof and the prediction of water inrush disasters.

Research on Ecological Effect Assessment Method of Ecological Restoration of Open-Pit Coal Mines in Alpine Regions.

Open-pit mining is an important form of coal mining in China, and its damage to the ecological environment is particularly obvious in alpine regions. The ecological restoration of alpine open-pit coal mines faces severe challenges, and its restoration effect will directly affect the ecological security of China. Meanwhile, comprehensive and system-oriented evaluation of ecological restoration effects is still insufficient in current research. In this study, we selected different quantities of assessment factors on the two scales of ecological project area and ecological impact area to evaluate the ecological restoration effect of an alpine open-pit coal mine. Then, we formed a multi-scale and multi-dimensional ecological restoration effect assessment model of the alpine open-pit coal mine and used this model to analyze the implementation effect of the ecological restoration project of the Baiyinhua No. 2 Open-pit Mine. The results show that the multi-scale and multi-dimensional ecological restoration effect assessment model of alpine open-pit coal mine proposed in this study can accurately characterize the restoration effect of open-pit coal mines in alpine regions and can also be used as a significant evaluation tool in the future ecological construction of mining areas. This study hopes the multi-scale and multi-dimensional ecological restoration effect assessment model of alpine open-pit coal mine can provide a comprehensive, systematic, and scientific evaluation method for the ecological restoration of alpine open-pit coal mines and provide a scientific basis for the ecological restoration and green development of relevant mining areas.

Dynamics of coalbed methane emission from coal cores under various stress paths and its application in gas extraction in mining-disturbed coal seam

Uncontrolled and excessive gas emission may affect normal production and even result in serious disasters such as gas explosion and coal and gas outburst. To find out the essence of abnormal gas emission under mining induced stress, in this work, we conducted experiments on gas emitting from coal cores under mining-induced stress paths, and systematically discussed the controlling mechanism of stress change on gas emission. The results show that at the initial period, gas emission rate decreases regardless of the stress path. In this period, stress has little effect on gas emission, and it is mainly controlled by the attenuation of gas pressure gradient. In the middle period, the gas emission rate fluctuates with time. The tipping points of the gas emission rate in this stage is mainly caused by expansion of pores, opening of primary fractures and newly exposed surface induced by shear slip of the primary isolated fractures. With the further increase of the stress difference, failure of the coal core may occur, which creates a large amount of new exposure surfaces, and significantly improves the gas emission rate. Comparing with the minimum value before failure, the gas emission rate of PDS coal after failure increases by 82.35%–990.91%, and that of the JZS coal increases by 75.0%–175.0%. To verify the laboratory test results, in a recently completed research project, we implemented the technique of stress-relieved gas re-extraction in Shoushan coal mine in China. The results show that mining activity can affect the gas extraction in coal seams within 50 m from the coal wall of the working face. The average gas concentration of the boreholes drilled in the mining-disturbed zone is above 40%, and the average net gas flowrate of single borehole reaches 30 L/min. The gas extraction amount in the mining-disturbed zone, with borehole number less than 1% of the total, accounts for 55.1% of the total gas extraction amount in the roadway. This practice could be used as a valuable example for other coal mines with similar geological conditions.

Efficient Excavation and Support Cooperation Technology for Surrounding Rock of Deep Buried Long-Distance and Large Section Gob-Side Roadway: A Case Study

The gob-side roadway technology is widely used in coal mining in China, as it can improves the recovery rate of coal resources and alleviate the shortage of mining replacement. However, it is still difficult to control the stability of surrounding rock in gob-side roadway under deeper mining depth and more complex stress environment. With the auxiliary transportation roadway 30207 (ATR 30207) of the Muduchaideng Coal Mine as engineering background, this paper introduces the engineering case of gob-side roadway characterized by deep buried, long-distance, and large section. Through comprehensive methods, we studied and put forward the efficient excavation-support cooperation technology for surrounding rock of gob-side roadway. The research shows that the head-on cutting of gob-side roadway causes the stress to transfer and gradually adjust in the heading face to form a steady-state advanced abutment stress field. The coupling effect of the advanced abutment stress and the lateral abutment stress of goaf are the main reasons for repeated hole collapse of anchor cable drilling in solid coal rib, development and expansion of the roof separation fracture, and the low excavation speed. Supposed that upon the heading face support is completed, the next excavation-support cycle is quickly started during the early stage of stress adjustment, and the time effect can be fully utilized to alleviate the disturbance intensity of the advanced abutment stress in the heading face, as well as reduce the damage of rock mass. This paper puts forward the time-effect collaborative control countermeasures of the roof and rib in gob-side roadway of “hole collapse anchor cable of solid coal rib lag construction and waits for pressure relief and rapid excavation-support cycle in the heading face.” Engineering practice shows that the mine pressure behavior of roadway roof and solid coal rib is effectively controlled, and the roadway forming speed is greatly improved, which can provide reference for the efficient excavation-support design of gob-side roadway under the conditions of deep buried, long-distance, and large section in similar deep mines.

Model Test of the Water and Sand Mixture Inrush in the Mining-Induced Caving Zone

In western China coal mines, the mining-induced caving zone is regarded as a main pathway for water and sand inrush mixture hazards. The paper experimentally studied the flow behavior and the mechanism of water and sand mixture through mining-induced caving zones. Transport experiments are performed by using a laboratory-scale model, and the caving zone is modelled by using different sizes of glass beads. Four different sand sizes are used for the sand layer. The test results reveal that the mass flow rate of sand and water mixture increases with the increase of the initial water head. And an equation is proposed for the mass flow rate of sand and water mixtures that correctly reproduces the data for all the conditions. In addition, the sudden decreases in water head loss is monitored at the commencement of the water and sand flow, which would result in a large number of sand particles that rapidly start up and make the kinetic energy transfer from water to sand.

Analysis of the Characteristics of CH4 Emissions in China’s Coal Mining Industry and Research on Emission Reduction Measures

CH4 is the second-largest greenhouse gas and has a significant impact on global warming. China has the largest amount of anthropogenic coal mine methane (CMM) emissions in the world, with coal mining emissions (or gas emissions) accounting for 90% of total energy industry emissions. The results of CH4 emission inventories from previous studies vary widely, with differences in the spatial and temporal dimensions of gas emission factors of belowground mining being the main points of disagreement. Affected by the policies of “eliminating backward production capacity” and “transferring energy base to the northwest”, China’s coal production layout has changed greatly in the past ten years, but the closely related CH4 emission factors have not been dynamically adjusted. This paper investigated 23 major coal producing provinces in China, obtained CH4 emission data from coal mining, calculated CH4 emission factors in line with current production conditions, and studied the reduction measures of coal mine gas emission. According to the CH4 emission data of China’s coal mines in 2018, 15.8 Tg of methane is released per year in the coal mining industry in China, and 11.8 Tg after deducting recycling. Shanxi Province’s CH4 emissions are much higher than those of other provinces, accounting for 35.5% of the country’s total emissions. The weighted CH4 emission factor of coal mining in China is 6.77 m3/t, of which Chongqing is the highest at approximately 60.9 m3/t. Compared with the predicted value of the IPCC, the growth trend of CCM has slowed significantly, and the CH4 utilization rate has gradually increased. This change may be aided by China’s coal industry’s policy to resolve excess capacity by closing many high-gas and gas outburst coal mines. In addition, the improvement of coal mine gas extraction and utilization technology has also produced a relatively significant effect. This paper determines the distribution of methane emissions and emission sources in China’s coal mining industry, which is useful in formulating CCM emission reduction targets and adopting more efficient measures.

Ground Stress Analysis and Automation of Workface in Continuous Mining Continuous Backfill Operation

The cost, complexity, lack of filling space and time create challenges in the longwall backfill operation, resulting in poor subsidence control and reduced productivity. This paper proposes an automated continuous mining and continuous backfill (CMCB) method by examining its key requirements and investigates the optimum sequence of coal panel (such as drifts) excavation to ensure ground strata control at relatively high productivity. The automated CMCB adopts the highwall mining technique underground, which enables easier automation at the workface. A numerical simulation of the Changxing coal mine in China was undertaken, and five different sequences of coal excavation were investigated, using the automated CMCB excavation parameters (assuming a 4 m width cut, 5 m mining height for a 200 m long coal slice) to determine the optimum sequence of resource excavation. The plastic zones and vertical displacement across the five models were analyzed. Simulation results of the 5 m high coal seam excavation show that the odd-even slice (OES) mining sequence, which has a vertical ground displacement of 74 mm, is the most efficient excavation method, due to its effective stress redistribution and lower induced ground displacement.

Study on the ideal location of a bottom drainage roadway

The bottom drainage roadway plays a crucial role in preventing coal and gas outbursts by using underground gas drainage methods. Therefore, it is essential to select the ideal position of the bottom drainage roadway. In this paper use a combination of geological data and numerical simulation to study the ideal position of the bottom drainage roadway, we taking the gas drainage of the first workface of No. 3 coal seam in the Yuxi coal mine in China as an example. The geological study showed a limestone marker layer at an average vertical distance of 14 m from the first mining face. Using this marker layer, the bottom drainage roadway could be excavated without the risk of accidentally exposing the coal seam, and less crosscutting borehole drilling from the bottom drainage roadway would be required. Based on the needs of gas control, the layout of the bottom drainage roadway was selected as an external stagger type. Combined with the numerical simulation results, when located 20 m outside of the mining workface 'footprint' on the horizontal projection, the bottom drainage roadway was a sufficient distance from the stress concentration area during mining of workface 1301, which facilitated roadway maintenance. Furthermore, the length of the crosscutting boreholes is also relatively short, which reduces the amount and cost of drilling. The results of this study are expected to provide a reference for the selection of an ideal position of the bottom drainage roadway in field engineering.

Research on security technology of tower foundation based on precise control of freezing temperature field

Freezing method is used in the main shaft slotting repair project in Chensilou Coal Mine in China. According to the actual conditions of Chensilou Coal Mine, this paper established a numerical calculation model which included the following influence factors: thermodynamic parameters, borehole layout, original formation temperature, groundwater seepage, hot water circulation protection. The calculation results show that the reasonable brine temperature for the freezing project in Chensilou Coal Mine should be controlled between -30 °C and -25 °C and the reasonable freezing time should be 160 days. When the freezing time extends to 80–120 days, the freezing front has developed to the temperature-control hole. In this case, the hot water circulation of the temperature-control hole needs to be started and the hot water temperature is not lower than 20 °C. The freezing construction was implemented in accordance with the optimized brine temperature and freezing time, and the freezing of tower foundation has been successfully avoided. The measured results show that the tower tilts to the northeast as a whole during formation freezing and the tilt values are all less than the allowable value.

Design and Workspace Analysis of Drilling Arm of Mining Anchor Drilling Robot

Bolt support is the main way of underground roadway support in coal mines in China. At present, there are some problems in domestic coal mines, such as low efficiency and poor safety. In view of the above problems, a structural scheme of omni-directional multi angle automatic roof bolter is designed. Firstly, based on the D-H method, the kinematics model of the drill arm structure of the anchor drilling robot to the roof and side of the working environment is established, and the space analysis of the four drill arms is carried out; At the same time, due to the design of the drill arm of the anchor drilling robot, the left and right drill arms of the equipment extend, rotate and work at the same time. Combined with the MATLAB kinematics model, the experiment is carried out to simulate the spatial position of the end of the drill arm of the anchor drilling robot. At the same time, the research results show that the robot can quickly replace the anchor drilling arm and ensure the quality of all-round anchor drilling, and the robot can meet the requirements of all-round support.

Comprehensive Monitoring Research on the Effect of Roof Cutting and Pressure Release: A Case Study of the Jiulishan Coal Mine in China

The longwall panel of the Jiulishan coal mine is affected by floor-confined water, while the roof rock weighting makes the production management of some longwall panels difficult. This has caused engineering methods of roof cutting and pressure release to be considered. To explore the dynamic effects of roof cutting and pressure release method, the 14141 longwall panel was taken as the test point, and a variety of monitoring methods were used to comprehensively analyze the characteristics of roof rock weighting, front abutment pressure, and floor mining failure. The main results are as follows: first, the weighting interval, the weighting intensity distribution, and the gateway deformation are asymmetrical. Second, the peak point of the front abutment pressure is approximately 6 m away from the coal wall, the peak stress is 7.02 MPa, the concentration coefficient is 1.54, the range of the pressure increasing area is approximately 16.4 m, and the farthest end of the front abutment pressure effect area is 22.4 m away from the coal wall. Furthermore, the maximum depth of the floor failure is at the No.17 measuring point (A117) position under the condition of one electrode distance. The maximum damage depth is 9.8 m, and the horizontal distance between the location of the maximum failure depth and the working face is 4.1~10.3 m. Finally, compared with the formula calculation value without considering the effect of roof cutting and pressure release or the adjacent 14121 longwall panel, the weighting interval and the weighting intensity, the gateway deformation, the degree of coal wall spalling, the influence range of the front abutment pressure, and the degree of floor mining failure are significantly reduced. The research results provide scientific and technological support for roof cutting and pressure release as a technical method to prevent floor water inrush and reduce the roof rock weighting intensity on the longwall panel.

Reform and development of coal mine safety in China: An analysis from government supervision, technical equipment, and miner education

Coal mine safety management has been one of the most successful public governance cases in China in the last 20 years. This paper systematically analyzes the reform measures and experience effects of the Chinese government in coal mine safety governance. It does so from three aspects: government supervision, technical equipment, and miner training. The results show that the number of coal mine accidents in China has fluctuated greatly, which can be divided into five stages. Small and medium-sized coal mines, dominated by township and village coal mines, are the key targets of coal mine safety management in China. Two policies —"shutting down small coal mines” and “integrating resources"—have strengthened the government's safety management of small coal mines. Secondly, the establishment of the State Administration of Coal Mine Safety has solved the supervision conflict caused by the multiple identities of agents and represents a turning point in China's coal mine safety management. Third, coal mine mechanization has a significant negative correlation with the number of accidental deaths and is a crucial measure for improving the intrinsic safety of coal mines. Fourth, the improvement of miners' overall education level has an obvious effect on enhancing coal mine safety. Following long-term safety education and skills training, the number of unsafe actions caused by knowledge deficits and cognitive errors gradually fell. More accidents are caused by the coal mine management giving wrong orders and illegal commands. Finally, this paper discusses the potential deficiencies of coal mine safety management in China at present, and makes some policy suggestions.

Arbuscular mycorrhizal colonization increases plant above-belowground feedback in a northwest Chinese coal mining-degraded soil by increasing photosynthetic carbon assimilation and allocation to maize.

A three-compartment culture system was used to study the mechanism by which the AM fungus Funneliformis mosseae influences host plant growth and soil organic carbon (SOC) content in a northwest China coal mining area. A 13CO2 pulse tracing technique was used to trace the allocation of maize photosynthetic C in shoots, roots, AM fungus, and soil. Carbon accumulation and allocation in mycorrhizal (inoculated with Funneliformis mosseae) and non-mycorrhizal treatments were detected. AM fungal inoculation significantly increased the 13C concentration and content in both above- and below-ground plant parts and also significantly enhanced anti-aging ability by increasing soluble sugars and catalase activity (CAT) in maize leaves while reducing foliar malondialdehyde content (MDA) and leaf temperature and promoted plant growth. AM fungi also increased P uptake to promote maize growth. Soil organic carbon (SOC), glomalin, microbial biomass carbon (MBC), and nitrogen (MBN) contents increased significantly after inoculation. A mutually beneficial system was established involving maize, the AM fungus and the microbiome, and the AM fungus became an important regulator of C flux between the above- and below-ground parts of the system. Inoculation with the AM fungus promoted plant growth, C fixation and allocation belowground to enhance soil quality. A positive above-belowground feedback appeared to be established.

Effect of Clay Mineral Content and Confining Pressure on Energy Dissipation Characteristics of Basalt with Different Overburden Depths

With the deepening of coal mining in China, dynamic disasters occur with the release of energy. In this study, in order to study the difference between shallow rock and deep rock, conventional triaxial compression tests were carried out on basalts with different overburden depths. The mechanical properties and energy evolution characteristics of basalts with different overburden depths were analyzed. The results show that the strength parameters increase with increasing depths, while the deformation parameters exhibit the opposite phenomenon. The strength and peak strain of basalt with the same depth increase with increasing confining pressure. However, the elastic modulus almost remains unchanged. The prepeak total input energy and dissipation energy decrease with increasing depths, and total elastic energy increases with increasing depths which indicates that the deep rock releases more energy than shallow rock when failure occurs. The input energy, elastic energy, and dissipation energy increase with increasing confining pressure. However, elastic energy ratio decreases with increasing confining pressure. The strength parameters and elastic energy increase with increasing density and deformation parameter, while the dissipation energy decreases. This phenomenon has the opposite law when clay mineral content is increased. The conclusions of this study may provide theoretical reference to dynamic disasters induced by energy in deep coal mines.

Height identification of water-permeable fractured zone based on synchronous movement in overlying strata

Height identification of water-permeable fractured zone (WPFZ) is one of the decisive influence factors for mining safety, especially in some specific conditions, such as mining under aquifer. In order to demonstrate the formation process of the WPFZ, the scaling model experiment is carried out. Through the analysis of movement and breaking in overlying strata, the WPFZ height is significantly affected by mining range, movement characteristics of key strata and its follow-up strata. Based on the research findings, a new theoretical method, " overlying strata synchronous movement method " (OSSM) is established to predict the WPFZ height. Taking 3301 mining face of Zhujiamao Coal Mine in China as the engineering background, the WPFZ height is estimated by OSSM. Additionally, the field detection is carried out by the downhole segmented water injection method combined with borehole camera method. By comparing the results of different methods, the accuracy of OSSM is verified and the WPFZ height is determined finally. What´s more, various methods for determining WPFZ height are evaluated.