Deep Underground Coal Mines Research Articles

Effects of Coal Mining Activities on the Changes in Microbial Community and Geochemical Characteristics in Different Functional Zones of a Deep Underground Coal Mine

Effects of Coal Mining Activities on the Changes in Microbial Community and Geochemical Characteristics in Different Functional Zones of a Deep Underground Coal Mine

A Review on the 3D Cartographic and Spatiotemporal GIS Models for Safety of Accidents in Deep Underground Coal Mines

The aim of this study was the safety risk assessment of accidents that occur because of production dynamics in deep coal mining, one of the highly dangerous business class, with spatiotemporal GIS. In this study, accidents that occur at certain times during production in underground mining workplaces are discussed based on evaluations of spatial and temporal dimensions. Accordingly, various analyses have been handled using criminology science tactics and strategies such as 80–20, kernel density, space–time cube, and hot spot, which have been adapted to GIS tools. Implementations have been realized on 3D underground cartographic models covering accident data from deep coal mine workplaces in the Zonguldak-Kozlu basin in Turkey between 2019 and 2021, at an average elevation of – 400 m. Space–time cube, kernel density, and time series analyses suggest that the Annual Bonus Incentives, which are repeated every year and given before the new year, increase the psychosocial risks for employees. It has been determined that this situation can lead to problems such as poor concentration among miners and loss of focus in some shifts. Additionally, significant relationships were found between the number of accidents and monthly production progress rates as a temporal parameter. The results demonstrate that applying a reactive approach with spatiotemporal GIS to accidents in deep coal mines is becoming increasingly important.

Damage evolution and failure characteristics of a cemented gangue backfill considering direct shear and dynamic tests

Backfill mining is an effective technique that can prevent and control the impact of dynamic disasters which can occur in deep underground coal mines. This technique allows to reduce the surface subsidence and achieve a greener mining. The backfill shear mechanical properties under mining disturbances, are of great significance for ensuring the surrounding rock stability in deep mining. Therefore, studying the shear mechanical properties of the cemented gangue backfill body (CGBB) under coupled dynamic and static loads actions in deep coal mining is of great importance. In this paper, shear mechanical tests and the acoustic emission (AE) technology were used to study the shear mechanical response characteristics of CGBB under low-frequency dynamic normal load conditions. The results show that a dynamic normal load with an amplitude of 5 kN improves the shear CGBB strength, while a dynamic load with an amplitude greater than 10 kN will cause a shear strength deterioration, and the degree of deterioration is positively correlated with the load amplitude. Under low-frequency dynamic normal load conditions, the shear CGBB stress-strain curve exhibits classical characteristics. AE indicate that the main CGBB damage changes from a nonlinear deformation to an elastic stage under low-frequency dynamic normal load conditions. During the shear failure process, the cumulative AE counts are positively correlated with the load amplitude. The crack type identification based on RA-AF shows that the low-frequency dynamic normal load affects the CGBB crack type. Under constant normal load (CNL) conditions, tensile or mixed cracks account for 63.95% and are the main fracture mode. Conversely, under low-frequency dynamic normal load conditions, shear cracks account for more than 60% and are the main failure mode. This research provides a reference for the CGBB stability analysis under complex stress conditions for the case of a deep underground coal mining.

Weak current induced by coal deformation and fracture and its response to mine seismicity in a deep underground coal mine

Weak currents can be stimulated from coal and rock materials under a load. To investigate the response characteristics of weak current to coal failure and mine seismicity, both laboratory experiments and field tests on weak current measurement of stressed coals were conducted. The response characteristics of weak current was analyzed, the quantitative relationship between weak current and mechanical behaviors was studied and the precursors of coal failure and mine seismicity based on weak current response were investigated. The results of laboratory experiments show that the weak current increases linearly with stress and strain in the elastic deformation stage and shows an accelerated increasing trend after entering the elastic deformation stage, reaching its peak value when the final failure occurs. A fracture is accompanied by a suddenly increased current (SIC), of which the intensity is proportional to the stress drop. The accelerated increase of weak current accompanied by fluctuations can be used as a precursor of coal failure. The weak current measured in an underground coal mine responds well to mine seismicity that occurs in the increasing process of a SIC. The continuously accelerated increase of weak current can be used as a precursor of mine seismicity, to which the weak current could respond few minutes in advance. It is feasible to use the weak current technique for rockburst prediction in mines and tunnels because of its strong anti-interference ability and early response to mine seismicity and coal/rock failure.

Improving Workplace Environment of a Deep Underground Coal Mine with Multiseam Workings: An Alternative Approach

Improving Workplace Environment of a Deep Underground Coal Mine with Multiseam Workings: An Alternative Approach

Impact of the closure of a coal district on the environmental issue of long-term surface movements

<abstract> <p>The environmental impact of deep underground coal mines using the longwall mining method is diverse, e.g., short- and long-term subsidence, damage to surface infrastructure, disturbance of the hydrogeological conditions, and the quality of groundwater and surface water. The study presented focusses on the long-term surface movements after the closure of an entire coal district. Due to the flooding of the underground infrastructure and rock mass, an upward surface movement or uplift is observed. For a specific site in the Campine coal district, Belgium results are presented of satellite data (radar-interferometry). However, the main aim of the study is to better understand the process of uplift and to determine the various mechanisms that are involved. For this purpose, an analytical framework was developed recently, and it was applied successfully in a relatively easy case. The case study of the paper is more challenging, but the usefulness of the analytical framework is clearly confirmed. The most important conclusions are that (i) the uplift is induced by an increase in water pressure after the closure, i.e., re-establishing the original hydraulic gradient, (ii) the expansion of both the goaf volumes and the volumes of the non-collapsed rock mass must be considered, and (iii) the assumption of a linear decrease of water pressure variation from the top to the bottom of the mined area at the end of the mining phase provides the most realistic results. However, the next step in the analysis should focus on a more advanced hydrogeological model of the complex underground environment.</p> </abstract>

Stability Analysis of Roadway Groups under Multi-Mining Disturbances

The roadway stability has been regarded as the main challenging issue for safety and productivity of deep underground coal mines, particularly where roadways are affected by coal mining activities. This study investigates the −740 m main roadway in the Jining No. 2 Coal Mine to provide a theoretical basis for the stability control of the main deep roadway affected by disturbances of adjacent working activities. Field surveys, theoretical analyses, and numerical simulations are used to reveal mechanisms of the coal mining disturbance. The field survey shows that the deformation of roadway increases when the work face advances near the roadway group. Long working face mining causes the key strata to collapse based on the key strata theory and then disturbs the adjacent roadway group. When the working face is 100 m away from the stop-mining line, the roadway group is affected by the mining face, and the width roadway protection coal pillar is determined to be about 100 m. Flac3D simulations prove the accuracy of the theoretical result. Through reinforcement and support measures for the main roadway, the overall strength of the surrounding rock is enhanced, the stability of the surrounding rock of the roadway is guaranteed, and the safe production of the mine is maintained.

Laboratory Study of Deformation Behaviour of Two New Reinforcing Polymeric TSLs and Their Potential Application in Deep Underground Coal Mine.

Thin spray-on liner (TSL) is a surface protection technology used by spraying a polymer film, which is widely used for mine airtightness and waterproofing. A reinforcing TSL can replace steel mesh, which is a new method for roadway support. This paper reviews the development of a reinforcing TSL. Considering the deterioration of geological conditions in deep underground mining and the demand for reinforcing automation, two kinds of polymeric reinforcing TSL (RPTSL) materials are developed. The mechanical characteristics of the new TSL materials are studied experimentally. Results show that the average compressive strength, tensile strength, cohesion, and internal friction angle of the two TSL materials are 52 and 32 MPa, 12 and 8 MPa, 6.2 and 17.2 MPa, and 33.6° and 25.9°, respectively. The bonding strength between the two materials and coal is greater than the tensile strength of coal itself, and the mechanical properties of the material for comparison are lower than those of both materials. Based on the TSL support mechanism, we examine the application of the two TSL materials to the mining environment and compare the mechanical properties of polymer materials and cement-based materials. The advantages of polymer materials include versatile mechanical properties, good adhesion, and high early strength. This study provides a new support material to replace steel mesh for roadway surface support, which satisfies the needs of different surface support designs under complex geological conditions, and promotes the automation of roadway support.

A combined “ground support-rock modification-destressing” strategy for 1000-m deep roadways in extreme squeezing ground condition

Deep underground coal mines face great challenges of extreme squeezing conditions resulting from high mining-induced stresses caused by a high recovery of the reserves and low to moderate strength coal measures. This is particularly true for deep roadways that suffer side and front abutment pressures. In this study, a case study was conducted in a 1000-m deep coal mine with extreme squeezing ground conditions. A new strategy of “ground support + rock modification + destressing” was proposed for the ground support. A numerical simulation was performed to evaluate the performance of the new support strategy. Field observations suggested that the proposed strategy could successfully mitigate the extreme squeezing of the double-used entry. The proposed support strategy provides an effective measure for ground control in extreme squeezing conditions.

Wireless Paging System for Underground Mines

Underground working in different horizons with intricate haulage and traveling roadways is very complex in nature. Wired communication is presently the most adopted technology in Indian underground mines. Also, the cellular network cannot be used for communication due to the non-availability of the coverage link. So, addressing of key-personnel to pass on the information and assign task becomes a challenge for mine management. Implementation of wireless paging systems with routers and/or repeaters at strategic locations can instruct manpower for the jobs as well as obviate the impending mishap, if any, at remote locations of the mine. This paper presents a design of a wireless paging system for underground mines which consists of a two-way alphanumeric paging system operating on a ZigBee based wireless network and a paging terminal software. This paging system can be used to unicast or broadcast messages to all the pagers working in the RF network. A successful field trial of the same is also conducted to devise a node placement strategy for the routing units with prototype pagers in the shaft and traveling roadways at 400 and 500 m horizon of a deep underground coal mine.

Analysis of Cooperative Control Effect of Pressure Relief and Long Bolt Support for Deep Roadway Under Strong Mining Disturbance of Adjacent Working Face

The stability of mining roadways is pivotal to safe mining in deep underground coal mines. In order to control the stability of mining roadways in deep mines, this paper studies the cooperative control effect of pressure relief and long bolt support for deep roadway under strong mining disturbance of adjacent working face in Wenjiapo Coal Mine in West China. The numerical calculation software FLAC3D was used to simulate the distribution law of the displacement, stress and plastic zone around the roadway under the disturbance of excavation and working face mining with three support schemes: “short bolt + long cable”, “long bolt + short cable”, and “long bolt + short cable + drillholes and cutting grooves pressure relief”. The results show that extending the length of bolt can ensure the supporting effect while reducing the consumption of anchor cables in the roof, and can reduce the roadway floor heave by 5.5%. Moreover, the peak lateral pressure of the roadway is reduced by 12.5%, the peak value is shifted to the depth by 6 m, and the floor heave of the roadway is reduced by 36% when the countermeasures of pressure relief in the ribs and floor are adopted. This indicates that the schemes of pressure relief and long bolt support has a significant beneficial effect on decreasing the high stress environment and controlling the deformation of roadway.

Effects of loading rate on the compound dynamic disaster in deep underground coal mine under true triaxial stress

The compound dynamic disaster is an abrupt and violent energy-releasing process under the combined action of gas and geological tectonic stress in deep underground coal mines. To investigate the occurrence mechanism of compound dynamic disasters, a novel experimental approach was designed and the one free-face true triaxial tests with different loading rates were conducted. Results shown that the compound dynamic disaster can be classified into several stages: initial quiet period, local particles and fragments ejecting, mid-term quiet period, external coal plate bending accompanied by gas-emitting, dynamic disaster occurring process, and the final re-stabilized period. The presence of the gas can significantly facilitate the development of cracks and enhance the kinetic energy, thus increasing the probability of the compound dynamic disasters. Under the one free-face true triaxial engineering stress conditions, the mechanical properties (e.g. deformation and strength) of coal samples are obviously rate-dependent, and the peak stress exhibits an approximate logarithmically increase trend with increasing loading rate. After failure, several tensile-shear fractures approximately parallel to the intermediate principal stress direction and perpendicular to the free face are generated. And an arc-shaped coal-burst pit on the free face of coal sample is observed, and the pit volume increases with the increase of the loading rate. Moreover, the particle ejection kinetic energy increases gradually as the loading rate increased, suggesting a higher loading rate can enhance the intensity of the disaster. The findings may provide guidance for the prevention and control of the compound dynamic disasters in deep underground coal mines.

Failure Mechanisms of Rheological Coal Roadway

The roadway instability in deep underground conditions has attracted constant concerns in recent years, as it seriously affects the efficiency of coal mining and the safety of personnel. The large rheological deformations normally occur in deep roadway with soft coal mass. However, the failure mechanism of such roadways is still not clear. In this study, based on a typical soft coal roadway in the field, the in-situ measurements and rock mass properties were obtained. The rheological deformation of that roadway was revealed. Then a time-dependent 3D numerical model was established and verified. Based on the verified model, the deformation properties and evolutionary failure mechanism of deep coal roadway were investigated in detail. The results showed that the deformation of the soft coal roadway demonstrated rheological behavior and the applied support structures failed completely. After roadway excavation, the maximum and minimum stresses around the roadway deteriorated gradually with the increase of time. The failure zones in soft coal mass expanded increasingly over time, which had a negative effect on roadway stability in the long-term. According to the findings, helpful suggestions were further presented to control the rheological deformation in the roadway. This research systematically reveals the instability mechanism of the deep coal roadway and provides some strategies for maintaining roadway stability, which can significantly promote the sustainability of mining in deep underground coal mines.

Numerical Study of TBM Excavated Coal Mine Roadway Support Design

In TBM excavation projects of Zhangji coal mine which is the first application of TBM at deep underground coal mine, computational modelling was conducted in surrounding rock stability study and support design of coal mine TBM excavated roadway due to lack of experience in similar projects. This paper presents a support design methodology of TBM excavated roadway at deep underground coal mine. A three-dimension finite element model was established, and the non-uniform tectonic stress filed was also been simulated in the model. Stress redistribution, displacement and plastic zone range of surrounding rock under different support patterns were analyzed and support design of the roadway was made on the base of simulation results. During roadway excavation, instrument rock bolts were installed for monitoring stress distribution and roadway convergence. The monitoring results suggest that computational simulation results correspond with in-situ monitoring data, horizontal stress concentrates on the roof and floor of roadway and vertical stress concentrates on lateral sides. The roadway convergence increased significantly after excavation and then slowed down and finally stopped after 40 days.

True Triaxial Experimental Study of Disturbed Compound Dynamic Disaster in Deep Underground Coal Mine

With the increase of coal extracting depth, a considerable number of dynamic disasters display the co-occurrence and coupling effect of rockburst and coal–gas outburst, which is defined as the disturbed compound dynamic disaster. In this study, two loading modes were adopted to investigate disaster characteristics using true triaxial apparatus. The stress states of one freed and the other five stressed faces were introduced to simulate actual stress conditions. Two high-speed cameras were used to capture the disaster process. The mechanical and strength properties, failure modes, and ejection kinetic energy were analyzed. Results showed that the compound dynamic disaster mainly exhibited local grain ejection, fragment spalling, large-scale grain ejection, plate bending, and ultimately failure. The strength of the sample first increased and then decreased slowly with the increase in the intermediate principal stress. After failure, a V-shaped coal-burst pit was formed, which was approximately parallel to the intermediate principal stress and perpendicular to the free face. The grain ejection exhibited obvious characteristics of spatial sorting, and the grain size decreased with the distance from the free face. The kinetic energy showed little change with increase in the intermediate principal stress in the displacement loading mode; whereas, it first increased and then decreased in the stress loading mode. The pressurized gas promotes the development of coal cracks and fully fractures the coal rock. Under the combined actions of the elastic energy stored in coal mass and the internal energy of pressurized gas, compound dynamic disasters may occur. Gas extraction and coal seam elastic softening techniques can effectively reduce and prevent the occurrence probability of compound dynamic disasters.

Stability Control for the Rheological Roadway by a Novel High-Efficiency Jet Grouting Technique in Deep Underground Coal Mines

In maintaining the efficiency of coal mining, the stability of roadway plays a significant role, as it is closely related to the production of coal and the safety of personnel. In deep underground coal mines, the rheological deformation of roadway normally occurs, which affects its service life. To address this problem, in this paper, a novel high-efficiency Jet Grouting (JG) technique was presented, and its control effect on roadway stability was investigated. A creep test of a coal specimen in a laboratory scale was performed, and its creep behavior was revealed. The rheology of the coal mass surrounding the roadway was further analyzed according to the field-monitoring results of roadway deformation. A time-dependent numerical model with a Burger-creep visco-plastic model (CVISC) was established and validated by comparing the calculated displacement with in-situ measurement. The JG technique was tested in the field, and its applicability and practicability were confirmed. According to the validated model and field test results of JG, a numerical model with CVISC by JG support was established to analyze the effect of JG on the roadway. The results showed that the JG support can effectively reduce roadway deformation, optimize stress conditions, and reduce the extent of the plastic zone around the roadway. The rheological properties of the soft coal roadway were constrained and long-term stability was ensured. This pioneering work can guide the application of JG for the stability control of roadways and promote the sustainability of coal mining efficiently.

Experimental and numerical investigation on a novel support system for controlling roadway deformation in underground coal mines

AbstractRoadway stability in extremely soft coal mass is a typical challenge in deep underground mines, as the most widely adopted support structure such as rock bolting, compound support system normally fails. This paper proposed a novel prereinforcement method for coal roadway, that is, jet grouting (JG) technique, to improve the quality of surrounding soft coal mass and form a stable support structure namely jet grouted coalcrete. The field and laboratory tests were conducted for evaluating the applicability of JG and the mechanical parameters of coalcrete. A numerical model was verified by comparing the calculated results with field measurements. According to the confirmed model, three typical JG support schemes were performed to assess the roadway stability after JG. The results showed that the proposed JG schemes can reduce the deformation and failure zone of the roadway and optimize the stress states around the roadway. The mechanism related to these advantages was investigated. This study provides a promising idea for supporting soft coal roadway in deep underground coal mines, which can promote the JG application in the field.

Real-time measuring and warning of surrounding rock dynamic deformation and failure in deep roadway based on machine vision method

Surrounding rock deformation measuring, which reveals the temporal and spatial evolution rules in deep roadway, is an effective method of preventing dynamic disasters in deep underground coal mines. The current roadway deformation measuring methods have deficiencies of long measurement interval, poor continuity and low-level automation. Therefore, in this paper, a real-time monitoring method and system of roadway deformation based on machine vision were established, and the multi-index early warning criterion of roadway deformation and failure was built. The real-time monitoring on the dynamic deformation of roadway was carried out using the deformation amount, speed and acceleration of surrounding rock as dynamic early warning indexes. The rock real-time image was automatically collected by the machine, processed to restore the current state of surrounding rock. According to the study of two cases in underground coal mines, the real-time monitoring method of roadway deformation system was applied and validated in Chang Gou Yu (CGY) and Zhang Shuang Lou (ZSL) Coal Mines for monitoring the surrounding rock dynamic deformation process. The multi-index early warning criterion of roadway deformation and failure was applied to evaluating the state of the surrounding rock and warning the instability of it. The results show that the indexes could reflect the state and development trend of surrounding rock deformation and failure. The dynamic characteristic, which was consistent with the stress concentration, could be used as the precursory information of surrounding rock instability. The machine vision roadway deformation real-time monitoring system could realize regional, continuous and real-time monitoring and early warning of underground roadway deformation.

Permeability enhancement mechanism of sand‐carrying hydraulic fracturing in deep mining: A case study of uncovering coal in cross‐cut

AbstractCoal and gas outburst disasters are prone to occur within rock cross‐cut coal uncovering in deep underground coal mines. To reduce the risk of coal and gas burst under rock cross‐cut coal uncovering, a technique of permeability enhancement using hydraulic fracturing sand‐carrying is proposed. Field test was conducted using HF sand‐carrying approach, and the effect of permeability enhancement was investigated. The results show that the evolution of cracks has been subjected three stages: energy slowly increasing and crack initiation, damage localization of coal seam and gradually failure, and crack instability expansion and formation of a complex fracture network system. In addition, it is found that “water‐sand” type injection of high‐pressure fluid carried sand into HF cracks, which creates a support force on crack surface and prevents crack closure. A fully developed fracture network system with high flow conductivity capacity is created and thus increases gas permeability largely. Furthermore, a clearly increasing trend associated with the HF sand‐carrying is found for the treated coal seam area. The permeability coefficient is about 21.5‐30.5 times higher than that from the raw coal seam. A good prevention effect of coal and gas outburst is achieved using HF sand‐carrying method.

Gateway stability analysis by global-local modeling approach

Longwall mining is the most widely used mining method in underground coal mining. The stability of gateways is crucial for longwall mining as they provide many essential services such as transportation of excavated coal, ventilation of longwall face. High in situ stresses, mining induced stresses due to advancing longwall face, and poor rock mass quality leads to large deformation jeopardizing the stability of the gateway in Guobei coal mine. In this paper, the global-local modeling approach is used for analysing the stability of the gateway in the mine. In this approach, a mine scale 3D global model was constructed to extract the stresses acting on the gateway. The extracted stresses from global model were implemented into 2D local model of the gateway for detailed analysis. The used approach was verified by the field measurements taken from the modeled gateway. In an attempt to deal with large mine induced displacements, a support system composed of rock bolt, cable bolt and shotcrete was proposed. The verified model was used to evaluate the performance of proposed support system. It was concluded that the proposed support system can significantly reduce the displacements. The verified model facilitates the performance evolution of other alternative support systems considered by the mine management. The presented approach can be applicable for other deep underground coal mines, experiencing large gateway convergence.