Transportation Roadway Research Articles

Monitoring of Overburden Failure with a Large Fractured-Height Working Face in a Deep Jurassic Coal Seam Based on the Electric Method

The development height of a water-flowing fractured zone is the key parameter to consider when carrying out mining under water pressure and coal mining with water conservation. In this paper, Jurassic coal seam 3-1 in the Menkeqing Coal Mine was taken as the research target, and a three-dimensional mining geological model was established by using FLAC3D to study the deformation and failure rules of overburden. Three roof boreholes were drilled in the auxiliary transportation roadway of adjacent working faces for dynamic monitoring by the resistivity method, which can better observe the whole process from failure to stability of the overburden. The results show that due to the complex sedimentary environment and large buried depth of coal seams in western China, there is a large deviation between the calculation results of the empirical formula of the fractured zone height under the “Regulations of buildings, water, railway and main well lane leaving coal pillar and press coal mining” (three regulations) and the simulation and on-site measurement. Based on the comprehensive analysis, the influence range of mining advance abutment pressure is approximately 60 m. The height of the water-flowing fractured zone is approximately 106 m, and it is located at the interface between sandy mudstone and mudstone. The height of the caving zone is approximately 22 m, and it is located at the interface between fine sandstone and medium sandstone. The ratio of the fractured height and coal seam thickness (Rf) reached 24.4, which was basically consistent with the test result of the adjacent Yushenfu mining area (which was 26 on average). There is no obvious change in the development height of the caving zone and water-flowing fracture zone from the working face to the drilling borehole position of more than 120 m, which reflects that the height of the overburden failure zone is related to the control of lithological combination.

Based on Flac3D Research and Analysis of the Mining Pressure Development Law in the Top Coal Section of the Roadway Support of the Working Face Transport

Top coal supporting roadway is widely used in the transportation roadway of thick coal seam face, which can not only increase the coal extraction rate but also reduce the driving cost. Based on the engineering geological conditions of the transportation lane of the working face of Zhongma Cun mine, the law of mine pressure development in the roadway of the top coal section is studied and analyzed based on Flac3D and field monitoring methods. The numerical simulation analysis shows that when the working face is pushed to 55m for the first time, the displacement of the area affected by the leading abutment pressure and the surrounding rock on the mining side of the roadway reaches the peak value, and the step distance of the first time is 55m. According to the analysis of stress monitoring data of single pillar and roof anchor cable on site, the first pressure occurs when the working face advances to 51m, which is consistent with the numerical simulation conclusion.

Study on Critical Width of Semi-Coal Rock Roadway of Shallow-Buried Thin Coal Seam Based on Coal Side Self-Stabilization

In the context of a shallow-buried thin coal seam, the surrounding rock deformation in the semi-coal rock roadway is comparatively small, resulting in self-stabilization of the two sides of the roadway without the need for support when the roadway is below a critical width. This study focuses on the transportation roadway of the 2107 working face in the Anzhe Coal Mine, employing a combination of laboratory tests, field tests, theoretical analyses, and numerical simulations. A mechanical model for the layered roof of the semi-coal rock roadway in a shallow-buried thin coal seam is developed, along with a calculation formula for determining the critical width of such roadways. The study also initially examines the correlation between the critical width and factors such as the tensile strength of the roof, the buried depth of the roadway, and the thickness of the immediate roof strata under conditions where the coal sides of the roadway are self-stabilizing. The results showed the following. (1) The calculation formula has good applicability for typical shallow-buried mine roadways in the Niuwu mining area and shallow-buried semi-coal rock roadways with coal thickness below 0.7 m under similar geological conditions. The critical width is related to the tensile strength of the roof, the buried depth of the roadway, and the thickness of the immediate roof strata. The degree of influence is determined by the thickness of the immediate roof strata > the tensile strength of the roof > the buried depth of the roadway. Among these, the tensile strength of the roof, the thickness of the immediate roof strata, and the critical width are basically in a positive exponentially increasing relationship, and the buried depth of the roadway and the critical width are basically in a negative exponentially decreasing relationship. (2) The on-site measurement of the loose circle on both sides of the roadway revealed that the rock mass loose circle had a thickness of 0.2 m, while the coal loose circle had a thickness ranging from 0.6 m to 0.7 m, aligning closely with the results obtained from theoretical calculations. The thickness of the coal loose circle on both sides served as the basis for determining the critical width of the semi-coal rock roadway in the shallow-buried thin coal seam. The calculated critical width of the roadway was 2.9 m, whereas the actual width measured was 2.4 m. Consequently, the two sides of the roadway are deemed capable of self-stabilization in the unsupported state. (3) Following the optimization of the support scheme, engineering analysis indicates that the roof and floor exhibit a maximum convergence of 46.3 mm, while the two sides show a maximum convergence of 18.4 mm. It is observed that the surrounding rock of the roadway satisfies the safety requirements for production. This study can provide theoretical support and a scientific basis for the stability discrimination of two sides and surrounding rock control of semi-coal rock roadways in shallow-buried thin coal seams under similar conditions.

Experimental Study on Gas Drainage Through Long-distance Bedding Directional Borehole

In order to solve the problem of gas exceeding the limit in the No.3 coal seam excavation face of Huoerxinhe coalmine, the gas outburst control measure was adopted to pre-evacuate the gas by the long-distance bedding directional borehole. The results show that after 25 days of gas drainage by long-distance bedding directional borehole, the gas content of test point decreased from 13.81m3/t to 7.81m3/t, and the gas pre-pumping rate was about 43.30%. The driving speed of the main transport roadway was 1.48 times that of the traditional ordinary drilling drainage measures, and the tunneling efficiency indicators had not exceeded the standard. Through the application of this measure, it is confirmed that the long-distance bedding directional borehole can effectively reduce the drilling hole construction amount and increase the gas extraction rate, and effectively eliminate the danger of protruding, and realize the safe and rapid excavation of the coal mine roadway.

Study on the Influence of Mining Stress on the Sustainable Utilization of Floor Roadway in Qinan Coal Mine

Aiming at the problem of large deformations and difficult maintenance of cross-mining floor roadways, taking the track transportation roadway of the cross-mining east wing floor in Qinan Coal Mine as the engineering background, the stress field distribution of mining stress in floor strata and surrounding rock of floor roadway during the cross-mining process of the working face is studied by combining theoretical analysis with numerical simulation. The results show that the influence of mining stress on the vertical stress of floor strata is reflected in the stress-increasing area in front of the coal wall and the stress-decreasing area in the rear of the coal wall. With the increase in the depth of the floor strata, the peak value of the vertical stress gradually decreases, and the distance from the peak value of the vertical stress to the coal wall and the influence range of the vertical stress gradually increases. When the width of the coal pillar is greater than the influence range of advance abutment pressure of the working face, the development speed of the plastic zone is slow. When the roadway is located in the influence range of advance abutment pressure, the plastic zone of the roadway’s surrounding rock develops rapidly. When the working face crosses the floor roadway more than 10 m, the depth of the plastic zone of the surrounding rock of the roadway is no longer increased; the siltstone above the roadway is the key layer of fracturing, and the deformation of the roadway has been effectively improved after hydraulic fracturing. Through the analysis of numerical simulation results, the fracturing scheme has a significant effect on the stability control of the surrounding rock of the cross-mining floor roadway. This study has certain guiding significance for the maintenance and sustainable utilization of floor roadways in the cross-mining process, which is conducive to ensuring the sustainable mining of underground coal and the safety of personnel and equipment and is of great significance to the sustainable development of the coal mining industry.

"Three Zones" Division of Spontaneous Combustion in Goaf of Y-type Ventilation Fully Mechanized Mining Face

The goaf of coal mine is accompanied by residual coal, and the possibility of spontaneous combustion determines whether the mine can work safely. Therefore, the division of "three zones" of spontaneous combustion in goaf under different working conditions is of great significance. This paper takes the 3154 fully mechanized coal face of Longmen Xianan Coal Mine as the research background to explore the "three belts" distribution under the Y-type ventilation mode. Based on the laboratory measured coal related spontaneous combustion characteristic parameters, the division standard of "three zones" is determined. Combined with the daily monitoring of the temperature and gas collection devices deployed on the site and the numerical simulation of the wind speed in the goaf, the comprehensive division of "three zones" in the goaf is realized. The results show that the range of "three zones" divided by temperature is similar to the range of oxygen concentration. The average width of heat dissipation zone and oxidation zone in the transport lane is 34.7m and 48.8m respectively. The asphyxiation zone is located at an average distance of more than 83.4m from the working face; The average width of the heat dissipation zone of the return air lane is 30.6m, the average width of the oxidation zone is 42.7m, and the average distance from the working face is more than 73.3m. In the numerical simulation, the width of the heat dissipation zone of the transport roadway is 35.0m, the width of the oxidation zone is 50m, and the asphyxiation zone is more than 85m from the working face. The width of the heat dissipation zone of the return air lane is 30m, the width of the oxidation zone is 40m, and the asphyxiation zone is more than 75m from the working face. The simulation results are close to the measured range of "three zones" of spontaneous combustion, and the width of "three zones" of return air roadway with Y-type ventilation is obviously different from that of transport roadway.

Study on failure mechanism and control of surrounding rock of inclined strata crossing roadway in deep coal mine

China’s coal mines are mainly underground mines, and a large number of roadways have to be excavated underground. It is of great significance for coal mine production to adopt safe and reasonable roadway support methods. In the process of roadway excavation, the rock stratum is inclined and the roadway pass through the layer. Since the surrounding rock conditions of the roadway passing through the layer are more complicated, it is easy to cause deformation of surrounding rock, failure and floor heave, which makes the support work difficult. In order to solve this problem, the mechanical properties of roadway surrounding rock were tested and the failure of roadway surrounding rock was analyzed using the +260 horizontal centralized transportation roadway in Changcheng No.2 mine. The surrounding rock of the roadway was divided into 8 regions, and the stress analysis of the surrounding rock in different regions was carried out. It is found that the left shoulder pit, the right side and the floor of the roadway are prone to damage. The influence of the lateral pressure coefficient, the rock dip angle and the lithology on the failure of the roadway surrounding rock was analyzed by Mohr-Coulomb failure criterion, and the specific failure range of the roadway surrounding rock was obtained. The support optimization design of the roadway was carried out, and the weak area of the surrounding rock was reinforced. The deformation monitoring of roadway surrounding rock after support optimization was carried out. The field monitoring results show that after the optimized support, the displacement of the roof and floor of the roadway section and the two sides are reduced by 43.6% and 40.8% respectively compared with the original scheme, and the deformation of the surrounding rock also shows a trend of gradual stability, and the surrounding rock of the roadway is effectively controlled. The research can provide a new way for the stress and failure analysis of the surrounding rock of the inclined rock roadway.

Study on roadway layout and surrounding rock control of isolated island panel

During the re-mining of historical residual coal resources, the stress environment is complex, the surrounding rock conditions are bad, the mining roadway is significantly affected by ground pressure, the layout is difficult, and the safety is poor. Taking the recovery of isolated island coal pillar in 4# coal seam as the research background, based on the difference in the distribution morphology of the goaf on both sides of the isolated island coal pillar, the stress and failure law of the isolated island panel boundary are studied by numerical simulation method. (1) The peak stress difference of multiple goaf boundaries on both sides of the isolated island coal pillar is between 0.18 and 4.51 MPa. The peak stress is affected by the change of the length of the roof “cantilever beam” at the stopping line of the goaf, so that the peak stress of the goaf boundary is periodic. (2) The high stress is mainly concentrated in the center of the pillar. The peak stress at the end of each pillar is 35–40 MPa. The coal pillar bears high stress, and the stress zone of the original rock moves to the end of the coal pillar. (3) There is a plastic zone of 8–20 m at the corner of the end of each coal pillar. On the basis of the stress zone and failure zone distribution of the goaf boundary on both sides of the isolated island panel, the roadway layout of the isolated island panel is determined, that is, the air-return roadway of the isolated island panel is arranged at random, and the width of the isolated island coal pillar d1 is selected as 10 m. The transport roadway is arranged straight, and the transport roadway of the isolated island panel is in the width section area of the goaf X4103. The width d1 of the isolated island coal pillar is selected to be 8 m, and the length d5–d7 of the mining roadway layout in the width of the coal pillar is 24 m. The roadway of isolated island panel is divided into 4 areas for support control, and the drilling pressure relief technology is proposed for high stress roadway. Through the field monitoring data, it can be seen that the mining roadway can meet the requirements of isolated island coal pillar recovery, which provides reference for the layout and control of abandoned coal roadway in this mine and other mines.

Investigation of the Time-Dependent Stability of a Coal Roadway under the Deep High-Stress Condition Based on the Cvisc Creep Model

Creep is a fundamental property that naturally exists in some types of rock, which is significant for the long-term stability of roadways during the mining process. In this paper, the long-term strength of coal and rock were determined via laboratory experiments, and a Cvisc elasto-viscoplastic model was adopted and introduced in FLAC3D, based on the 31101 transport roadway in the Hongqinghe Coal Mine, to investigate the influence of creep on the stability of a deep high-stress roadway. The test results show that the long-term strength of 3-1 coal and sandy mudstone was 18.65 MPa and 39.95 MPa, respectively. The plastic zone, the deformation, and the damage of the roadway’s surrounding rock displayed an obvious increase after being excavated for 720 d as the creep model was chosen. The plastic zone failure was modeled with shear-p (1090.7 m3), shear-n (381.7 m3), tension-n (98.4 m3), and tension-p (30.8 m3). The damage value had an obvious increment of 21.2% (0.053), and the deformation increased in the order of the two sidewalls (1978 mm), the roof (907 mm), and the floor (101 mm). The creep of the roadway can be divided into three stages: the accelerating stage, the decaying stage, and the stable stage. The creep speed of each stage is greatly affected by the presence or absence of anchor spray support: the creep speed of the bare roadway roof, sidewalls, and floor stability was 1.01, 1.02, and 0.12 mm/d, respectively. After anchor spray support, the creep velocity, correspondingly, decreased to 0.69, 0.37, and 0.12 mm/d, and the amount of surrounding rock damage decreased from 0.302 to 0.243. This indicates that the anchor spray support can significantly reduce the creep effect of the roadway. The Cvisc creep model was verified to be reliable and can provide guidance for deep high-stress coal roadway support.

Characteristics of the spatial and temporal evolution of the environmental parameters for belt fire in underground coal mine roadway

The high temperature and toxic gases produced by burning belt in mine are a serious threat to the miners’ safety. A full-scale fire experiment was conducted in an exercise roadway, as a basis for which a physical model was established. The spatial and temporal evolution of the environmental parameters was obtained in the U-shaped working face, and the effect of wind speed on the fire parameters was studied. It was found that the smoke concentration and temperature from large to small are the downwind side of the transport roadway, working face and return airway. The structure of smoke layer near the working face is disorganized, which is related to the local turning structure of the roadway. The smoke reverse occurs later than the spread of smoke downstream of the fire area. The thickness and maximum temperature of counterflow layer decreases linearly with the increase of ventilation speed. Increasing the critical ventilation speed can control the smoke reserve and increase the risk downstream of the fire area. The harmfulness of wind speed to smoke reserve and spread in single roadway and complex network is then discussed. In addition, the influencing factors of fire evolution in confined space are put forward.

Failure mechanism and stability control of surrounding rock in mining roadway with gentle slope and close distance

In this study, theoretical analysis, numerical simulation and field measurement were adopted to analyze the difficult problem of controlling the stability of surrounding rock in gently inclined and close-distance coal seam mining roadways. The results showed that: (1) According to the properties and stress environment of the roadway roof, to determine the specific spatial range of the original roof stage, transition stage and regeneration roof stage of the roadway, and corresponding to the distribution of plastic zones in the spatial stages, was an important basis for analyzing the deformation mechanism of the roadway and proposing a phased collaborative control plan. (2) Under the influence of mining, the plastic zone of the transportation roadway expanded violently by about 10 m ahead of the working face. Within the range of roadway passing the overlying goaf, the plastic zone of the surrounding rock between the layers runed through, especially extending to the roof and two shoulder corners of the roadway. The roof and two shoulder corners of the roadway became the key parts for the stability control of the surrounding rock. (3) The mechanical mechanism of asymmetric expansion of the plastic zone was obtained as follows: the range was determined by the magnitude of the deviatoric stress and the orientation was dominated by the direction of the principal stress. The combined effect of the magnitude of deviatoric stress and the angle of principal stress caused asymmetric expansion of the plastic zone. (4) A phased collaborative control scheme was proposed, and numerical simulation and industrial verification were carried out on the proposed scheme. The deformation of the surrounding rock of the roadway at the engineering site was less than 150 mm, and the control effect of the surrounding rock was good, ensuring the safe and efficient recovery of the fully mechanized mining face. The present study revealed the mechanical mechanism of failure and instability of the surrounding rock of the gently inclined close distance coal seam mining roadway and proposed a phased collaborative control scheme, which could provide valuable information for mining research.

Research and application of self-powered induction spray dust removal system for long-distance belt conveying in underground coal mines

A self-powered induction spray dust removal system for long-distance belt conveying in underground coal mines was developed. In the system, the kinetic energy of the conveyor belt can be converted into the electrical energy required by the infrared sensing atomization spray device. When the rotational speed of the roller reaches 230 r/min, 12.33 V electricity can be steadily generated. Further proposed to install multiple sets of dust reduction systems with an optimal spacing of 240 m. The effectiveness of this installation method was verified by turning systems on one by one in the 25211 transportation roadway of the Hongliulin coal mine. The total dust concentration was reduced from 11.78 mg/m3 to 3.88 mg/m3, and the respirable dust concentration was reduced from 6.33 mg/m3 to 2.48 mg/m3. The results show that the developed self-powered induction spray dust removal system can dramatically improve the long-distance belt conveying environment in coal mines.

Study on the dust migration law and a spray dust suppression scheme in transportation roadway

To solve the problem of excessive dust concentration in the belt transportation roadway of the mine. Numerical simulations were used to study the dust migration in the belt transportation roadway under 1.5m/s ventilation conditions. The simulation results show the process of dust ejection from the inflow chute to contamination of the whole belt transportation roadway, and the spatial distribution of dust velocity. A comprehensive dust reduction scheme of "central suppression and bilateral splitting" was designed according to the dust distribution, with simultaneous control of the infeed chute and the roadway. In practical application, pneumatic spraying greatly reduces the amount of dust in the guide chute. The misting screen has a significant effect on dust collection and segregation. The solution effectively controls the dust in the space of 20m on both sides of the transfer point, and the dust removal efficiency reaches more than 90%.

Study on Stability Control Mechanism of Deep Soft Rock Roadway and Active Support Technology of Bolt-Grouting Flexible Bolt

In order to study the stability control mechanism of deep soft rock roadway and the active support technology of the anchor-grouting flexible bolt, this paper takes the west wing transportation roadway of Yuandian No. 2 Coal Mine of Huaibei Mining Co., Ltd., Huaibei, China as the research background. By analyzing the occurrence conditions and failure characteristics of the surrounding rock of the west wing transportation roadway and the structural characteristics and mechanical properties of the anchor-grouting flexible bolt, combined with the elastic–plastic and superimposed arch theory analysis, the superposition community theoretical model and the superposition joint support scheme of “bolt (cable) + anchor net + anchor-grouting flexible bolt + shotcrete support” are proposed. The reliability of the combined support scheme is analyzed by FLAC 3D numerical simulation software and field experiment. The results show that the maximum roof-to-floor convergence and two-side convergence of the west wing transportation roadway are only 30.7 mm and 27.1 mm after adopting the combined support scheme, and the deep displacement variation is within 7 mm, which can effectively maintain the stability of the roadway. The combined support scheme has a certain reference value for other similar roadways.

Spatial-temporal evolution of roadway layout system from a space syntax perspective

Human activities and public organizations at different scales are affected by spatial forms and relationships. Using the roadway layout system (RLS) of an underground mine as an example, this paper discusses the potential application of space syntax theories and techniques in the construction and development of the mine underground space (MUS). We quantitatively analysed the spatial–temporal evolution characteristics of the RLS from 2013 to 2020 by combining space syntax theories with multi-scale thinking. The results showed that the core of the degree of integration each year had a strong correlation with the main transport roadway network, the development of the mining edge area being relatively backward. The MUS under consideration was in its development stage from 2013 to 2017, when a basic framework was built outside the mining area and the ore was mined within it. After 2017, the basic framework had been perfected, fully entering the production stage. We used space syntax to analyse and resolve the spatial–temporal evolution of the built MUS, combining the characteristics of the MUS itself, which revealed the development law of the MUS and RLS during the construction process and verified the feasibility of auxiliary decision-making in the process of space planning and construction. The study also showed that space syntax could provide scientific support and useful references for the orderly expansion, rational layout, safe construction, and sustainable development of the MUS.

Research on Stability Control Technology of Mining Roadway Based on Energy Transformation

The process of roadway surrounding rock deformation and instability is always accompanied by energy changes, and the energy transformation of surrounding rock directly drives its deformation and failure. In order to realize the stability control of mining roadway, the distribution of elastic strain energy and plastic strain energy of surrounding rock was analyzed by using FLAC3D numerical simulation software on the basis of the energy transformation law of sandstone under different confining pressures revealed by indoor triaxial compression test. Based on this, combined with the energy transformation, the principle of roadway surrounding rock stability control technology is proposed. One is to reduce the elastic strain energy of surrounding rock, that is, by increasing the extension of support body, part of the roadway energy is transferred to the support body, so as to improve the energy release of surrounding rock, or by optimizing the layout of roadway to reduce the energy accumulation of surrounding rock. The second is to increase the plastic strain energy of surrounding rock, that is, to increase the energy dissipation of surrounding rock by setting weak structure. The above research results are applied to the surrounding rock control of the right second transport roadway in the 91st coal of Xinjian coal mine. After the optimization of support measures, the roadway surface displacement and its increase rate decreased significantly, roof subsidence decreased from 247 mm to 62 mm, floor heave decreased from 120 mm to 26 mm, and the right rib shrinkage decreased from 292 mm to 94 mm, that is, the floor heave control effect was particularly obvious. The deformation of surrounding rock gradually stabilized after 45 days.

Unsafe Mining Behavior Identification Method Based on an Improved ST-GCN

Aiming to solve the problems of large environmental interference and complex types of personnel behavior that are difficult to identify in the current identification of unsafe behavior in mining areas, an improved spatial temporal graph convolutional network (ST-GCN) for miners’ unsafe behavior identification network in a transportation roadway (NP-AGCN) was proposed. First, the skeleton spatial-temporal map constructed using multi-frame human key points was used for behavior recognition to reduce the interference caused by the complex environment of the coal mine. Second, aiming to solve the problem that the original graph structure cannot learn the association relationship between the non-naturally connected nodes, which leads to the low recognition rate of climbing belts, fighting and other behaviors, the graph structure was reconstructed and the original partitioning strategy was changed to improve the recognition ability of the model for multi-joint interaction behaviors. Finally, in order to alleviate the problem that the graph convolution network has difficulty learning global information due to the small receptive field, multiple self-attention mechanisms were introduced into the graph convolution to improve the recognition ability of the model for unsafe behaviors. In order to verify the detection ability of the model regarding identifying unsafe behaviors of personnel in a coal mine belt area, our model was tested on the public datasets NTU-RGB + D and the self-built datasets of unsafe behaviors in a coal mine belt area. The recognition accuracies of the proposed model in the above datasets were 94.7% and 94.1%, respectively, which were 6.4% and 7.4% higher than the original model, which verified that the proposed model had excellent recognition accuracies.

Mechanism of Rock Burst and Its Dynamic Control Measures in Extra-Thick Coal Seam Mining from below the Residual Coal Seam to below the Gob

Abstract In this paper, aiming at the mechanism and regulation of overburden breakage induced by mining from the residual coal seam to the mined-out area, taking Kuangou Coal Mine as the background, the mechanism of rock burst from the residual coal seam to the mined-out area was revealed through the laws of overburden breakage and its structural evolution, ground pressure appearance, and energy release. The impact risk area is determined by the comprehensive evaluation results of multimethod face impact risk. A roof pressure relief and impact prevention control method using large-diameter empty hole combined with advanced deep hole blasting was formed, and the field verification was completed. The research results show that an obvious inverted trapezoid structure is formed when the residual coal seam of the W1123 working face is mined to the working face under the gob, which is related to the energy release caused by the occurrence of periodic pressure and the rupture of the critical layer. The shock ground pressure of the working face predicted by the neural network is mainly weak shock and medium shock risk; the numerical simulation analysis shows that the shock hazard area of the W1123 face below the solid coal is mainly located in the lower part of the working face near the transportation roadway and the shock below the W1145 gob. The dangerous area is about 32~72 m away from the return air alley. Through the plastic zone distribution and the orthogonal test, the optimal pressure relief scheme for large-diameter holes is 12 m in depth, 300 mm in diameter, and 2 m in spacing. When the blasting angle is consistent with the overlying rock fracture angle obtained from the simulation experiment, a better pressure relief can be achieved. When the bursting angle is consistent with the simulated overburden rupture angle, it has a better pressure relief effect. The pressure relief and anti-scour control method of large-diameter holes combined with advanced deep hole blasting reduce the daily average vibration frequency, energy, incoming pressure, and step distance of working face mining. The safe and efficient mining has a certain reference effect.

Analysis of Roof Stability of Coal Roadway Heading Face

One of the challenges that urgently needs to be addressed, both in current times and in the future, is to improve the heading speed of coal roadways. The roof instability of the heading face is the main factor restricting the rapid heading of coal roadways. Based on the theory of thin plate, a mechanical model of the roof in the heading face is established, the distribution law of deflection, stress, and internal force is discussed, and the supporting principle of the roof is clarified. Through a Flac3D numerical simulation, the main influencing factors of roof stability in the heading face are analyzed, including ground stress, surrounding rock strength, roadway section, unsupported distance, etc., and the regression analysis of each factor is carried out by evaluating the amount of roof subsidence. The results show that the maximum tensile stress and the corresponding bending moment of the roof appear at the fixed supported edge, and the maximum compressive stress and the maximum value of the corresponding bending moment appear at the center of the roof slightly close to the simply supported edge. In the on-site construction process, the position close to the fixed supported edge needs to be supported first. The roof subsidence has a positive exponential relationship with the stress level, a negative exponential relationship with the surrounding rock strength, a quadratic functional relationship with the roadway section, and a logarithmic relationship with the unsupported distance. In fractional support, the initial partial support can timely reduce the roof span and partially recover the confining pressure. Under certain geological and production conditions, the use of fractional support can not only effectively maintain the stability of the roadway but also speed up the heading speed. According to the research results, it is determined that in the auxiliary transportation roadway of the Caojiatan Coal Mine, the 122,110 working face adopts the fractional support model, the maximum roof subsidence is 18 mm, the roof is stable, and the monthly progress is more than 1000 m, which significantly improves the roadway heading speed.

Rockburst mechanism and the law of energy accumulation and release in mining roadway: a case study

The rockburst dynamic disasters in the process of deep coal mining become more and more serious. Taking the rockburst occurred in the 23130 working face of Yuejin Coal Mine as the engineering background, we study the characteristics of mining stress field around roadway, the plastic failure morphological characteristics of surrounding rock and the accumulation/release law of elastic energy before and after burst. An analysis model quantitatively describing the physical process of rockburst in the mining roadway is established, and the calculation method of dynamic release of elastic energy in the physical process of rockburst is educed. The mechanism of rockburst in mining roadway is revealed. The results show that an “L-shaped” stress concentration zone is formed within 100 m of the 23130 working face, and the principal stress ratio of the surrounding rock of the transportation roadway is 2.59–4.26. The change of the direction of the maximum principal stress has a significant effect on the burst appearance characteristics. The failure strength of different sections of the mining roadway is characterized by the elastic energy release value. With the increase of the working face distance, the elastic energy released by burst failure and the expansion variation of failure boundary radius show a nonlinear variation law that tends to decrease steadily after sharp fluctuation. The closer to the working face, the higher the burst risk. At a distance of 10 m from the working surface, the maximum principal stress reaches its maximum value. The butterfly-shaped failure system generated by the surrounding rock of the roadway has energy self-sustainability, and the elastic energy released by the sudden expansion of the butterfly leaf is enough to cause a burst damage of 1.9 magnitude. This work could provide theoretical support for the prediction and prevention of rockburst.