Coal Pillars Research Articles

Study on the thermal effect of coal oxidation under different stresses

The utilization of coal resources has been improved by using the method of narrow coal pillar mining, but this leads to a stress concentration in the coal pillars, which causes differences in the oxidation of coal pillars. To study the effect of stress on the oxidation and spontaneous combustion of coal samples, programmed heating-gas chromatography coupling experiments were carried out on coal samples under different stresses, analyzing the effect rule of stress on the gas derivatives of coal samples in the process of heating and oxidation. Furthermore, the mechanism of stress influence on thermal effect parameters is explored on the basis of that analysis. The results show that the rate of oxygen consumption, CO, CO2 concentration and heat release intensity of coal samples show a changing trend, initially increasing and then decreasing with increasing stress, and these values within coal are at the maximum when the stress is 9 MPa; and with increasing stress, the activation energy shows a “V” type change and reaches the minimum of 26.89 kJ/mol at 6 MPa, which indicates that low stress promotes coal spontaneous combustion (CSC), while high stress inhibits CSC. The thermal conduction coefficient of coal samples shows a negative correlation with temperature at the low-temperature stage, while the thermal conductivity of coal samples shows a positive correlation with temperature at the high-temperature stage, and the thermal conduction coefficient of coal samples reaches a minimum at temperatures of 70 °C and 0 MPa of stress. The porosity within coal decreases, and the thermal conductivity coefficient within coal increases with increasing stress because the increase in stress makes the macromolecules within coal disassemble into small molecules, the structure becomes more compact, and the thermal conductivity increases. The study provides an important theoretical basis for better understanding the effect mechanism of stress on CSC.

Numerical analysis on the factors affecting post-peak characteristics of coal under uniaxial compression

The post-peak characteristics of coal serve as a direct reflection of its failure process and are essential parameters for evaluating brittleness and bursting liability. Understanding the significant factors that influence post-peak characteristics can offer valuable insights for the prevention of coal bursts. In this study, the Synthetic Rock Mass method is employed to establish a numerical model, and the factors affecting coal post-peak characteristics are analyzed from four perspectives: coal matrix mechanical parameters, structural weak surface properties, height-to-width ratio, and loading rate. The research identifies four significant influencing factors: deformation modulus, density of discrete fracture networks, height-to-width ratio, and loading rate. The response and sensitivity of post-peak characteristics to single-factor and multi-factor interactions are assessed. The result suggested that feasible prevention and control measures for coal bursts can be formulated through four approaches: weakening the mechanical properties of coal pillars, increasing the number of structural weak surfaces in coal pillars, reducing the width of coal pillars, and optimizing mining and excavation speed. The efficacy of measures aimed at weakening the mechanical properties of coal is successfully demonstrated through a case study on coal burst prevention using large-diameter borehole drilling.

Coal pillar destabilization prediction and mining method in residual mining areas under remining disturbances

AbstractTo address the problem of pillar instability in residual mining areas under repeated mining disturbances, the prediction of pillar instability time and mining technology is studied by using numerical simulations, theoretical examinations, and practical experimentation techniques utilizing the remaining facade of the Shenghua Coal Industry 3103. On the basis of the findings, employing a fully mechanized mining technique exerts greater pressure on the coal pillar, increasing the likelihood of plastic failure. However, adopting the segmental filling mining approach can effectively disperse this pressure, consequently mitigating potential damage to the coal pillar. Initially, the coal pillar undergoes a progressive yielding or collapsing process at its periphery, leading to instability once the area of the projectile core of the coal pillar decreases beyond a specific threshold. The dimensions of both the affected roadway and the coal pillar play a pivotal role in determining the coal pillar's load‐bearing capacity. A prediction model for pillar instability is established. If the area of the projectile core is less than 34% during remining, the mining method should be changed or pillar reinforcement should be implemented. The accurate prediction and adaptation of the model's mining approach ensure the secure extraction of coal pillars within the remaining mining region, with successful validation of the model's performance.

Creep characteristics and damage model of coal–rock combinations with different height ratios

Numerous coal pillars are left after the coal mining process. The composite structure comprising a roof and coal pillar has prominent creep characteristics, which threaten safe underground mining. Therefore, the creep characteristics of coal-rock combinations should be studied to ensure the safety of quarry and surface. Uniaxial creep tests under static load axial pressure and different height ratios were performed using a self-designed rock creep disturbance test device to determine the effect of height ratio and axial pressure on the creep characteristics of coal–rock combinations. From the test results, a creep damage model for coal–rock combinations was established by combining the elastomer, fractional Kelvin body, plastic body, Abel dashpot, and modified nonlinear viscoplastic body; introducing damage variables D related to stress, height ratio, and time; and deriving a one-dimensional creep equation. An improved nonlinear least squares method based on pattern search was utilized to invert the creep parameters. The results of the creep equation calculation were fitted with the experimental results with good results. The creep curve with a height ratio of 2:1 was predicted with good results. The research results provide theoretical references for long-term stability analysis of rock engineering.

Dynamic Evolution of Coal Pore-Fracture Structure and Its Fractal Characteristics under the Action of Salty Solution

The instability and failure of coal pillars is one of the important factors leading to the catastrophic consequences of coal mine goaf collapse. Coal mine water has the characteristics of high salinity. Long-term mine water erosion can easily deform the coal pillar structure, eventually leading to instability and damage. This study carried out tests on coal samples soaked in salt solutions with different concentrations, and the nuclear magnetic resonance (NMR) method was used to obtain the dynamic evolution of the pore-fracture structure of coal. On the basis of fractal theory, the changes in fractal dimension of pore structure during the soaking process were discussed. The damage variable based on the pore fractal dimension was defined and the evolution relationship between the damage variable and immersion time was characterized. The findings demonstrated that the porosity change rate has an exponentially increasing relationship with the immersion time, and with the increasement of concentration of salt solution, the porosity change rate also shows increasing trends. The number of seepage pores and total pores increased with the immersion time. While, with the extension of soaking time, the number of adsorption pores first increased and then decreased. The connectivity between pores was enhanced. The relationship between the fractal dimension and the immersion time is linearly decreasing. The damage variable showed an increasing trend with the immersion time. As the concentration of salt solution increased, the damage of coal increased. The research results are of great significance for rationally evaluating the stability of coal pillars and ensuring the safe operation of underground engineering.

An exploration of improving the stability of mining roadways constructed in soft rock by roof cutting and stress transfer: A case study

In the confinement of traditional supports, reinforced supports are often used to control the deformation of roadways constructed in soft rock. Due to the failure to weaken the factors that induce deformation at the source, the roadway remains damaged after the restoration period. To this end, taking inspiration from roof cutting and pressure relief concepts, the protection mechanism of stress transfer in mining roadways constructed in soft rock of longwall remaining coal pillars was studied in the context of a typical coal mine. Unlike the technical scheme of gob-side entry retaining, no components are added in this study. The roof cutting and coal mining progress are consistent to ensure the integrity of the roadway in front of the longwall coal mining face (LCMF). The effect of the roof-cutting parameter on the roadway is studied via numerical simulations, and the optimal parameters are subsequently applied to similar material simulation experiments. It was found that roof cutting relieved the mechanical connection between the gob roof and the roadway roof, and the high-stress area was transferred from the roadway roof to the front of the LCMF. Roof cutting diminished the abutment stress in the surrounding rock in the area of intense dynamic pressure in front of the LCMF (average reduction of 12.57 %), which effectively improved the stability of the roadway. The roof cutting impaired the traction effect of the roadway roof deformation behind the LCMF on the strata ahead and effectively reduced the roadway deformation (27.3 % reduction) and coal pillar deformation (15.7 % reduction). On-site practice has demonstrated the effectiveness of this research, and the results of this research provide a new idea for preventing the destruction of roadways constructed in soft rock.

Experimental study on failure characteristics and rheological properties of pillar-like rock samples with different shapes

The stability of coal pillar is extremely important to the control of rock strata movement and surface subsidence. It is of great significance for mining design to analyze the stability and failure characteristics of coal and rock pillars left after mining and to study the failure characteristics and rheological properties of coal and rock with different shapes. In this paper, based on uniaxial compression and rheological tests on rock samples, the rheological properties of rock samples with different shapes were discussed by using the nonlinear theoretical mechanics and damage theory, and the rheological mechanical characteristics of coarse yellow sandstone samples under the action of different free surface areas and the same loading contact area were investigated by means of experimental research, theoretical analysis and numerical simulation. The following conclusions were drawn: the failure characteristics and dynamic change process of rock samples with different shapes under the same loading contact area are obtained by uniaxial compression test and multi-stage rheological loading. The uniaxial compressive strengths of rock samples with the same loading contact surface area and different free surface areas are inversely proportional to their free surface areas. For the round sample, the stress level in the rheological test is obviously lower than the instantaneous peak uniaxial compression strength, while for the other samples, the stress level in the rheological test is close to the instantaneous peak uniaxial compression strength. For rock all these samples, both the ratio of steady-state rheological time to final failure time and the deformation degree decrease with the increase of free surface area.

Research on reasonable layout parameters of working faces based on the concept of harmonic extraction to reduce the damage of coal seam waiting for upward mining

Based on the idea of harmonic extraction, the problem of reducing the damage of the coal seam waiting for upward mining. Using the theoretical analysis method, a schematic diagram of coordinated mining along the dip direction of coal seam is established, and the calculation method of reasonable layout parameters of coal seam working face early mining is given. Based on the upward mining problem of the No.1 coal seam in the fifth panel of Zaoquan Coal Mine, the influence parameters of the No.2 coal seam, No.6 coal seam and No.7 coal seam mining on the No.1 coal seam were determined by similar simulation test. Then, the layout parameters of working face were determined. The research method of numerical calculation was used to evaluate the degree and uniformity of movement and deformation of the No.1 coal seam, combining five indicators: subsidence, horizontal movement, inclined deformation, curvature deformation, and horizontal deformation. The results indicate that when the working face is arranged using the layout parameters provided in this article, it can promote the further subsidence of the No.1 coal seam at the position of the remaining coal pillar. The movement and deformation indicators of the No.1 coal seam all reach the most uniform degree of the geological mining conditions, which can effectively offset the uneven deformation problem of the No.1 coal seam caused by the influence of the remaining coal pillars, making multiple mining operations a favorable condition for upward mining and achieving the goal of reducing the damage of the No.1 coal seam.

Stability Control Technology for Surrounding Rocks in Gob-Side Entry Driving with Small Coal Pillars under Dynamic Pressure

To address the support difficulties caused by the dynamic pressure from the adjacent working face in gob-side entry driving, this study, taking the 8103 working face of the Jinhuagong Coal Mine in Shanxi Province as an example, adopted methods such as theoretical analysis, physical experiments, numerical simulations, and field practices to explore roof-cutting and pressure-relieving techniques to control the surrounding rocks in gob-side entry driving with small coal pillars under dynamic pressure. Fractures of the lateral roof, stresses on the surrounding rock, and deformations with different cutting-roof parameters were analyzed to determine the reasonable parameters for applications. The following results have been obtained. The longer the lateral cantilever length of the roof, the greater the load borne by the surrounding rock. Therefore, the key to reducing the confining pressure in a roadway is reducing the lateral cantilever length of the roof. After roof cutting, the roof of the gob area collapsed more completely. The stress on both sides of the coal pillar and that on the ribs of the solid coal dropped by 7.72 MPa and 4.16 MPa, respectively. The key roof-cutting parameters were analyzed by the UDEC numerical software, and the reasonable roof-cutting angle and height were determined to be 12° and 14 m. A support scheme combining “steel strip + bolt + anchor cable + roof cutting” was proposed. With the scheme applied, the displacement of both sides of the coal pillar was 61 mm shorter than that in the non-test section, and the duration in which the roadway was affected by mining was 11 days shorter. Therefore, the rationality of the selected roof-cutting and support parameters in this study is verified. The proposed scheme can effectively control the stability of surrounding rocks in gob-side entry driving with small coal pillars under dynamic pressure.

Optimization and Application of Coal Pillar in Fully Mechanized Mining Face based on Energy Analysis

Based on the theory of energy dissipation, a numerical model of goaf excavation was established by FLAC3D based on the backflow channel of Heilong Coal Industry 2202. The dissipative energy distribution characteristics of coal pillars with different widths were studied, and the dissipative energy evolution law of surrounding rock of goaf roadway was analyzed. With the increase of the width of coal pillar, the width of elastic core zone is positively correlated with the bearing capacity. The peak value of dissipated energy density decreases with the increase of the width of coal pillar, and the concentration degree and region of dissipated energy density on the side of coal pillar are greater than that on the side of solid coal pillar. The project is applied to Heilong 2201 working face, and the optimum width of coal pillar and its supporting scheme are given. The practice results show that when the width of coal pillar is 5m, the deformation of surrounding rock can be effectively controlled and the demand for safe and efficient production can be met.

Subsidence Analysis for Old Abandoned Board and Pillar Coal Mines Using ANSYS and Monte Carlo Simulation

Subsidence Analysis for Old Abandoned Board and Pillar Coal Mines Using ANSYS and Monte Carlo Simulation

A New Method for Identifying Coal Pillar Instability Based on Energy and Stress Correlation Characteristics and Its Engineering Application

Accurately distinguishing the stability of the residual coal pillars formed by the room-and-pillar mining method is significant for the safe mining of adjacent coal seams. In this study, the correlation between the rapid decrease in vertical stress and the connectivity of the internal dissipative energy core during the instability of coal pillars is revealed. Then, a new method for distinguishing the stability of coal pillars based on the above correlation is proposed, overcoming the shortcomings of previous studies that only used the plastic zone range to determine the stability of coal pillars. Based on this discriminant index and simulation method, the mechanism of residual coal pillar failure as well as the dynamic instability and expansion characteristics of multi-pillars have been revealed. The engineering method of grouting and filling to enhance the bearing capacity of coal pillars is proposed, and an in-depth study is conducted on the improvement effect of different strength filling materials on the bearing capacity of coal pillars. And the reasonable filling body strength is determined to be greater than 3MPa. The new discrimination method has important guiding significance for the analysis of coal pillar stability and the formulation of safety protection technical measures on engineering scales.

A Fractional-Order Creep Model of Water-Immersed Coal

The long-term stability of a coal pillar dam is a serious concern for coal mine underground reservoirs because of the creep behavior of coal in complex water immersion and mechanical environments. In order to investigate the characteristics of creep deformation of water-immersed coal and develop a proper creep model, this paper implemented a series of creep experiments of coal via multistage loading at various water-immersion times. The experiment data were analyzed, in terms of immersion-induced damage, elasto-plastic performance, creep behavior, etc., suggesting obvious mechanical properties’ degradation of coal by water. The elastic modulus and peak strength of water-immersed coal decrease exponentially with the immersion time, while the creep rate of coal shows an upward tendency with the promoted immersion time. According to the remarked relationships of elastic, viscoelastic, and viscoplastic properties versus the stress levels and water-immersion time, a creep model based on conformable fractional derivatives is proposed, considering the influence of the water-immersion time and variable stress level. The proposed model was verified using the experiment data, showing a good capacity of the creep model for reproducing the creep process of water-immersed coal. This paper provides a fundamental model for further studying the stability of coal pillars and their influence on the safety of underground water reservoirs.

Surrounding Rock Deformation Mechanism and Control Technology for the Roadway in the Fault-Disturbed Zone under Special-Shaped Coal Pillars

In order to explore the impact of residual special-shaped coal pillars and fault disturbances on the lower layered roadway, this study takes the short-distance coal seam mining in Luwa Coal Mine as the engineering background to explore the surrounding rock deformation mechanism along the mining roadway in the fault-disturbed zone under special-shaped coal pillars, it presents the roadway surrounding rock control technology and it conducts on-site industrial test verification. The study shows that the abutment pressures on the floor of special-shaped coal pillars are distributed as “three peaks and two ridges”. The part beneath coal pillars is mainly disturbed by vertical stresses, while the part below the coal pillar edge is co-affected by vertical stresses and shearing stresses, generating a stress concentration coefficient ranging from 1.26 to 1.38 in the lower coal seam. According to the superposed effects of special-shaped coal pillars and fault disturbance on the mining roadway, the mining roadway is divided into the lower section of goaf, the section crossing the coal pillar edge, the lower section of coal pillars, and the section obliquely crossing the coal pillar edge. According to the above sections, the segmental control strategies of “improving stress distribution on surrounding rock + reinforcing support on special sections” are proposed. A joint control technology of large-diameter drilling hole pressure relief and special section anchor cable reinforcement support was adopted to carry out on-site industrial testing and monitoring. Overall, the convergence rate on the roadway surrounding rock is controlled within 5%, and the deformation of roadway surrounding rock is under effective control.

Energy evolution mechanism during rockburst development in structures of surrounding rocks of deep rockburst-prone roadways in coal mines

Influenced by the deep high-stress environment, geological structures, and mining disturbance in coal mines, the frequency of rockburst disasters in roadways is increasing. This research analyzed energy evolution characteristics during rockburst development in the elastic bearing zone and energy conversion in the plastic failure zone. The critical energy criteria for structural instability of roadway surrounding rocks were deduced. Numerical software was also applied to simulate the energy evolution during rockburst development in surrounding rocks of rockburst-prone roadways under conditions of different mining depths and coal pillar widths. The occurrence mechanism of rockburst deep in coal mines was analyzed from the perspective of energy in structures of deep roadway surrounding rock in coal mines. The research results show that the critical energy criteria are closely related to the elastic strain energy stored in deep roadway surrounding rocks and the energy absorbed by support systems. The impact energy in roadways is directly proportional to the square of the stress concentration factor k. Moreover, as the mining depth increases, the location of the peak point of maximum energy density gradually shifts to coal ahead of the working face. The larger the mining depth is, the more significantly the energy density is influenced by advanced abutment pressure of the working face and the wider the affected area is. With the increment of the coal pillar width, the distance from the peak point of energy density to the roadway boundary enlarges abruptly at first and then slowly, and the critical coal pillar width for gentle change in the distance is 30 m. Changes in the peak elastic energy density in coal pillars with the coal pillar width can be divided into four stages: the slow increase stage, abrupt increase stage, abrupt decrease stage, and slow decrease stage. The elastic energy density is distributed asymmetrically in deep roadway surrounding rocks in coal mines. Under the action of structures of roadway surrounding rocks, energy evolution in these structures differs greatly during rockburst development under conditions of different coal pillar widths. This research provides an important theoretical basis for the support of rockburst-prone roadways during deep coal mining.

Application of suitable methodology for control of coal fire according to its magnitude in hot strata blast-holes–an approach

ABSTRACT Coal mine fire is a common phenomenon in Indian coalfields and great concerned on safety of the person engaged in mining operations. In opencast coal mine, particularly where the extraction of previously developed coal pillars has been carried out by opencast mining method, chances of spontaneous fire became more frequent and complicated. In such prevailing situations deep holes charging and blasting operation in hot strata may create every possibility to premature detonation of explosives, which leads to fatalities. Henceforth, it is imperative to use appropriate methodology to combat the fires and make it possible for wining of coal safely. This paper highlighted a methodology adopted for safe and effective management of fire by using two different chemical additives admixed with water to bring down temperature under safe workable limit in short duration of time and also make it suitable for charging and blasting operation in hot deep drill holes. On the basis of the magnitude of fires 0.5 to1.0% concentrations of MgCl2 and CaCl2 mixed with water were applied for cooling of high temperature fire in coal bench, overburden as well as hot blast holes with encouraging results in supressing of the flames and rapid cooling of hot strata.

Influence law and control mechanism of overburden isolated grout injection on methane emission in the working face

Overburden isolated grout injection (OIGI) can well reduce surface subsidence, waste emission, and coal resource waste while preserving the ecological integrity of mining areas, thereby becoming the development direction of green coal mining in the future. However, its influence law and control mechanism on methane emission under coal seam mining remain unclear. In light of this, data including methane emission and surface subsidence during the mining of the 22301 working face in Tunlan Mine was collected by on-site measurements through online methane extraction monitoring systems, leveling instruments, and electronic total stations. The collected data and geological information were subject to numerical simulation and theoretical analysis to explore the methane emission law and its controlling factors after OIGI. The results demonstrate the following: (1) The total methane emission decreases by 46% after the implementation of OIGI, primarily due to reduced methane emission from the adjacent seams into the mining coal seam. (2) After OIGI, the vertical stress on the coal and rock strata in goaf rises, while the stress on the surrounding coal pillars decreases; the stress in the whole stope tends to be distributed more uniformly. (3) A relationship between the overburden stress and permeability was established, which reveals that stress plays a major role in controlling methane emission from adjacent seams into the goaf. After OIGI, the rising stress on the overburden above the goaf reduces the porosity and permeability, narrowing methane migration pathways, consequently reducing the volume of methane emission from surrounding seams into the coal seam. Stress redistribution after mining gives rise to methane rivers and low-permeability walls around the goaf, the volumes of which decrease as the grouting pressure rises. Methane rivers are where methane accumulates, and pre-drainage boreholes from adjacent seams should be directed towards these methane rivers to achieve enhanced methane extraction. The conclusions of this study provide theoretical support for efficient methane extraction under OIGI mining.

Progressive microstructural evolution characteristics and weakening mechanism of coal exposed to acid mine drainage (AMD)

This study aims to analyze the extent of softening structural deterioration of coal pillars over time when exposed to acid mine drainage (AMD) from abandoned pits. The research involves using microscopic recognition techniques on coal samples and hydrochemistry tests in solution to identify changes in mineral compositions and microstructure parameters quantitatively. The study examines the micro-scale changes in microstructural hydro-chemical damage processes in coal samples. Based on the findings, the decrease in pH of the acidic pit effluent leads to degradation in the physical microstructural characteristics of the coal. Specifically, there is a 6.90% increase in the fractal dimension and a 23.33% rise in the area porosity. Similarly, the chemical parameters of the coal also undergo significant changes. The thickness of the aromatic layer in the coal decreases significantly, while the average diameter of the aromatic layer increases by 16.9%. The aromaticity of the coal increases, indicating noticeable deterioration of the matrix layer, particularly fragmentation. Moreover, the solution characteristics reflect the progressive coal deterioration, including increased metal ions in the soaking solution, the transformation of divalent iron to trivalent iron, and a continuous rise in sulfate content. These results have implications for assessing and maintaining load-bearing structures in underground abandoned pits subjected to long-term immersion.

Study on the mechanism of coal pillar instability in coal seam sections containing gangue

The tail entry of the Shanxi Mine No. 10103 working face is a gob-side roadway featuring a 25 m protective coal pillar that contains double-strata gangue. This composition poses a risk of instability and failure, which can endanger personnel safety and mining efficiency. To address this issue, a mechanical model of coal pillars containing gangue was constructed, and a combination of discrete element modeling and engineering monitoring was utilized to reveal the failure mechanism and influencing factors of such coal pillars. The study offers a sound theoretical foundation for the support of coal pillars in gob-side roadways. Through an examination of the friction coefficient (f) of the coal gangue interface in relation to the Barton peak shear strength (τmax), it was determined that coal pillars containing gangue are susceptible to slip instability failure at the coal gangue interface when the normal stress (σR) reaches 20 MPa. The stability of coal pillars containing gangue was further analyzed using discrete element numerical simulation software, which identified key factors such as gangue hardness, thickness, location, and number of strata. Utilizing the outcomes of discrete element simulation, the FLAC-PFC coupling model was formulated to meticulously scrutinize the temporal and spatial progression of the deformation of the surrounding rock, as well as the features of its deformation and failure. As a result of this research, the implementation of the grouting cable + through layer bolt anchoring technique is proposed, wherein the bolt is inclined on both sides to traverse through the coal seam and gangue, thereby stabilizing the interface between the two.

Research on the coupled support technology of a composite rock beam-retained roadway roof under close coal seams

IntroductionThe technology of gob-side entry retaining without coal pillars in close (distance) coal seams is still immature, and the roof control and support technology in this case is not perfect.MethodsIn this paper, the coupled support technology of a composite rock beam roof under close coal seams is systematically studied by using theoretical analysis, numerical simulation and field test.ResultsBoth the floor slip calculation results and numerical simulations indicate that the vertical failure depth in the plastic zone of the #8 coal seam has not penetrated the roof of the #9 coal seam after mining, which is consistent with the field electronic imaging results. A theoretical formula for a composite rock beam model anchored by high-prestressed anchor cables was derived, and a formula for the optimal spacing of anchor cables under noncompressive shear failure of the roof was obtained. Identification of the internal stress hazard region of the rock beam provides a basis for determining the locations of vertical support. Through numerical simulation of different support schemes, including roof cutting, arrangement of high-prestressed anchor cables, and setting up of vertical supports, roof cutting was found to effectively reduce the stress of supporting structure and roof pressure. Setting up of vertical supports can reduce the roof convergence by 25.2%, and coupling with anchor cables can reduce the convergence by more than 49.1%. The feasibility of this support scheme was verified through field tests, with a maximum convergence of 99 mm between the roof and floor.DiscussionThis two-way verification approach, in which the damage degree of the roof of a close coal seam is analyzed through multiple means, targeted support plans are proposed, the support mechanisms are explored, and feedback is conducted through field tests, plays a certain guiding role in solving roof control of the gob-side entry retaining under similar geological conditions.