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Land subsidence has become a widespread engineering geological problem, which can quickly induce many derived disasters. Over-exploitation of groundwater is one of the main factors of urban land subsidence. There is severe land subsidence in Jining, mainly induced by groundwater over-extraction. Therefore, the numerical simulation method is used in this paper to analyze and predict the law of land subsidence in Jining. Combined with the engineering geological and hydrogeological conditions of Jining City, a three-dimensional fluid–solid coupling model of land subsidence was established by using COMSOL software. The numerical results were verified using site monitoring data. The article predicts the land subsidence in the study area in 2030. In 2030, the maximum land subsidence is 224 mm. And this paper analyzes the land subsidence pattern under different groundwater extraction amounts. The results show that the land subsidence in the study area is effectively alleviated under the condition of reducing water extraction by 30%. It provides a basis for preventing and controlling land subsidence in Jining city. It is proved that land subsidence caused by groundwater extraction positively correlates with the pumping time and amount of water pumped. [ABSTRACT FROM AUTHOR]

Assessment of mining impact on groundwater is one of critical considerations for longwall extension and sustainability, however usually constrained by limited data availability, hydrogeological variation, and the complex coupled hydro-mechanical behaviour. This paper aims to determine the factors and mechanism of groundwater depressurisation and identify knowledge gaps and methodological limitations for improving groundwater impact assessment. Analysis of dewatering cases in Australian, Chinese, and US coalfields demonstrates that piezometric drawdown can further lead to surface hydrology degradation, while the hydraulic responses vary with longwall parameters and geological conditions. Statistical interpretation of 422 height of fracturing datasets indicates that the groundwater impact positively correlates to panel geometry and depth of cover, and more pronounced in panel interaction and top coal caving cases. In situ stress, rock competency, clay mineral infillings, fault, valley topography, and surface–subsurface water interaction are geological and hydrogeological factors influencing groundwater hydraulics and long-term recovery. The dewatering mechanism involves permeability enhancement and extensive flow through fracture networks, where interconnected fractures provide steep hydraulic gradients and smooth flow pathways draining the overlying water to goaf of lower heads. Future research should improve fracture network identification and interconnectivity quantification, accompanied by description of fluid flow dynamics in the high fracture frequency and large fracture aperture context. The paper recommends a research framework to address the knowledge gaps with continuous data collection and field-scale numerical modelling as key technical support. The paper consolidates the understanding of longwall mining impacting mine hydrology and provides viewpoints that facilitate an improved assessment of groundwater depressurisation. [ABSTRACT FROM AUTHOR]

The roof water inrush disaster induced by coal mining is becoming a vital bottleneck restricting mine safety. To accurately predict the water inrush position of the coal seam roof sandstone aquifer and accurately prevent and control it, this paper takes Lilou Coal Mine in Juye Coalfield as an example. Based on the comprehensive analysis of hydrogeological data, drilling data, and geophysiological data, this paper examines the water richness of the roof aquifer, the water insulation and geological structure, and the fracture development characteristics of the roof aquifer. Starting from the general side, nine factors, including fault strength index, tectonic intersection point, tip extinguishing point, development height of water conduction crack zone, roof sandstone aquifer thickness, aquifer drilling unit inrush, geophysical prospecting water-rich anomaly area, roof key layer thickness, roof aquifer thickness, brittle plastic rock thickness ratio, etc., form the roof plate roof. The main control factors for water inrush are deeply discussed. Through the spatial analysis function of GIS, unique drawings of different evaluation indicators are drawn, and the data are normalized. Combined with the AHP hierarchical analysis method, the corresponding weight is determined. Finally, a comprehensive water inrush risk assessment map of the roof of coal seam 3 in Lilou Coal Mine is obtained. Through the verification of the coal mine water inrush survey ledger over the years, it has been found that the evaluation results of the coal seam roof water inrush model are consistent with the actual situation. The evaluation results are reasonable and accurate, which can provide a reference basis for coal seam mining and water damage prevention and control in the future. [ABSTRACT FROM AUTHOR]

In the late stage of underground brine mining in salt lakes, the method of injecting fresh water is often used to extract the salt from the brine storage medium. This method of freshwater displacement breaks the original water–rock equilibrium and changes the evolution process of the original underground brine. To explore the mechanism of salt release in saline water-bearing media under conditions of relatively fresh lake water dissolution, this paper analyzes the changes in the chemical parameters of brine from 168 sampling points in the Mahai salt lake in the Qaidam Basin at three stages (before exploitation, during exploitation, and late exploitation) by correlation analysis, ion ratio analysis, and other methods and investigate the variations in porosity and the evolution laws of brine. The results show that the changes in the main ion content and brine mineralization during the exploitation process are small. The changes in Ca2+ content are significant due to the low solubility of calcium minerals, the precipitation of gypsum during the mixing process, and the adsorption of cations by alternating with Ca2+. Primary intergranular pore skeletons are easily corroded to form secondary pores, which increase the geological porosity. Na+ and Cl- are the dominant ions in the brine in the study area, but the concentration of Ca2 + decreased significantly under the influence of mining, by 41.7% in the middle period and 24.5% in the late period. The correlation between Ca2+ and salinity changes significantly in different mining stages, and the reason for the decrease of Ca2+ may be due to the influence of mineral dissolution, mixing, and anion-cation exchange. The porosity of the layer in the study area showed the opposite trend of Ca2+, and the porosity increased first and then decreased. The innovation of this paper lies in analyzing the reasons and mechanisms of the disturbance of artificial dissolution mining on stratum structure by comparing the hydrochemical characteristics and porosity of underground brine storage media in three different mining stages. The research in this paper provides a theoretical basis for the calculation of brine resource reserves and the sustainable development of underground brine in salt lake areas. [ABSTRACT FROM AUTHOR]

Close-distance coal seams (CDCS) are widely distributed, and the layout of the upper and lower panels can be divided into "=" type and "+" type. The "+" superposition of upper and lower coal pillars in CDCS caused strong mine pressure, but there are few studies on the panel crossing residual coal pillars (RCP) when the upper and lower coal seams are "+" type layout. In view of the special spatial position ("+" type layout), this paper takes the typical panel 4-301 of a particular mine as the project indagation background and studies mining and crossing the overlying coal pillars by dint of field measurement, numerical simulation, indoor test, and engineering application. Compared with vertical stress or horizontal stress alone, the indexes of deviatoric stress and plastic zone can reflect the failure evolution of surrounding rock more comprehensively. Hence, this paper analyzes the expansion form of the plastic zone and the variation law of deviatoric stress before and after mining influence in the underlying mining roadway. The research results show that: (1) There is a sub-peak zone of deviatoric stress under the RCP. The deviatoric stress is bimodal in the range of 9 m below. After the peak value decays to 7.4 MPa, it changes to a single peak located in the area directly below the middle of the RCP. (2) The maximum plastic zones of the roof and two ribs of the roadway below the RCP are 3.4 m and 5 m, respectively. The crest value of deviatoric stress reaches 10 MPa. As the distance between the panel and the RCP decreases, the shape of the high deviatoric stress area presents the evolution law from the "ellipse" of the roof → the "crescent" of two ribs → the "cochlea" of the tips of the ribs. (3) When the mining of the underlying panel is 10 m, 0 m, or − 10 m away from the RCP (without passing through the RCP). The crest value of deviatoric stress within 5–10 m in advance of the roadway increases in turn. However, the peak value is significantly reduced when it is − 20 m away from the RCP (through the RCP). The crest value of deviatoric stress of two ribs decreases in turn along the panel rib → section coal pillar rib → solid coal rib. Based on this, the underlying 45 m of the RCP is divided into area I (10 m), area II (overlapping area 20 m), and area III (15 m) based on the degree of disturbance. And propose the technical scheme of asymmetric combined control in different zones by using asymmetric channel steel truss anchor cable for the top-ribs of areas I and III, and top-ribs asymmetric channel steel truss anchor cable + door-type support in area II. On-site project practice shows that the partitioned control technology successfully resisted the roadway instability and failure caused by the dynamic-static superimposed stress disturbance under the RCP and realized the primary support of the sectional coal roadway. The conclusion provides technical support and scheme design for the partitioning support of roadways under similar "+" type cross‐panels. [ABSTRACT FROM AUTHOR]

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Under the condition that the working face was directly covered with hard roof, the abrupt breaking of hard roof release significant amount of energy, thus prone to triggering dynamic disasters such as roadway instability or rockburst. This paper based on the engineering background of the Xieqiao Coal Mine's 11,618 working face, a numerical simulation method was put forward to study the dynamic response of roadway under the disturbance of hard roof breaking and proposed an evaluation index IC for roadway stability. Research indicates that the elastic energy released during the periodic weighting of the hard roof is higher than that released during the first weighting. Under the dynamic disturbance caused by hard roof breaking, the peak stresses of the roadway was slight decreased, accompanied by a significant increase in the range of stress concentration and plastic zone expansion. Roadway deformation patterns are significantly influenced by hard roof breaking, with noticeable increases in deformation on the roof and right side. During the period of hard roof breaking, the possibility of instability of the roadway increase significantly due to the disturbance caused by the dynamic load. The research results reveal the instability mechanism of roadway under the condition of hard roof, and provide a more reliable basis for evaluating the stability of roadway. [ABSTRACT FROM AUTHOR]

Intelligent computing is transforming safety inspection methods and response strategies in coal mines. Due to the significant safety hazards associated with mining excavation, this study proposes a multi-source data based predictive model for assessing gas risk and implementing countermeasures. By examining the patterns of gas dispersion at the longwall face, utilizing both temporal and spatial correlation, a predictive model is crafted that incorporates safety thresholds for gas concentrations, four-level early warning method and response strategy are devised by integrating weighted predictive confidence with these correlations. Initially tested using a public dataset from Poland, this method was later verified in coal mine in China. This paper discusses the validity and correlation of multi-source monitoring data in temporal and spatial correlation and proposes a risk warning mechanism based on it, which can be applied not only for safety warning but also for regulatory management. [ABSTRACT FROM AUTHOR]

The no-pillar longwall mining method (NPLM) by roof cutting technology (RCT) is an innovative longwall mining method proposed in China. Its essential technology is the employment of RCT to replace the chain pillar to safeguard the roadway. In this paper, a novel physical model test method is designed to investigate the protective mechanism of RCT for roadways in greater detail. Furthermore, the physical model test of RCT is conducted in consideration of the effect of broken roof rock bulking. Combined with numerical simulation, the results indicate that RCT can increase the degree of gangue bulking in goaf, hence providing effective support to the overlying strata and maintaining their integrity. Moreover, RCT can significantly reduce the abutment stress of the roadway roof and solid coal side, thereby ensuring the stability of roadway surrounding rock. This paper proposes three protection mechanisms of RCT for roadway based on the findings of the conducted research: I. Reducing the dimensions of roadway roof; II. Utilizing bulking gangue to support the overlying strata; III. Eliminating the cavities in the goaf adjacent to the roadway. The in situ application provides evidence that RCT is effective in controlling roadway deformation. This paper can serve as a reference for no-pillar mining and analogous geotechnical engineering physical model tests. Highlights: A novel two-dimensional physical model test method is developed that can achieve bulking after failure. Three protection mechanisms of roof cutting technology for the gob-side roadway are elucidated. The effect of roof cutting technology on the bulking of broken roof rock is analyzed by experiment. In conjunction with the in-situ application, the key to no-pillar longwall mining by roof cutting technology is proposed. [ABSTRACT FROM AUTHOR]

To solve the problems of high ore resources loss and natural pillar splitting failure in multi-stope mining of gently inclined thin orebody by traditional room-and-pillar method, the overburden stability control technology by replacing natural pillars with pre-stressed expandable pillars (PEP) is developed in this paper. By means of numerical simulation and physical experimental methods, the distribution characteristics of stress, displacement, and failure zone of surrounding rock in multi-stope mining with and without PEP support were studied. The results demonstrate that the PEP supporting effect can improve the stress environment of surrounding rock compared with the unsupported condition, divide the stress reduction zone of the stope roof, and avoid the overburden failure induced by tensile stress penetration in the shallow-buried stope. Moreover, the PEP support can effectively limit the crack propagation depth and damage degree of the surrounding rock. Deriving from the physical test, compared to the unsupported scenario, the vertical deformation of the stope roof is reduced by about 44% on average with the PEP support, thus preventing overburden collapse caused by large deformation. Besides, the greater the mining depth of the stope, the greater the increase in the bearing capacity of the PEP support. Field industrial test shows that the stope and PEP supports are visually safe and stable after mining. The overburden stability control technology with PEP support proposed in this study can offer a key reference for improving ore resource recovery in multi-stope mining of gently inclined orebody. [ABSTRACT FROM AUTHOR]

In order to study the evolutionary law of roof migration on Gob-Side Entry Retaining, this paper takes the gob-side entry retaining in the comprehensive mining face of the Ningtiaota coal mine as the engineering background, and analyzes the evolutionary law of the overlying rock layer on the roof at different locations during the roadway stay and the stress distribution around the roadway through numerical simulation software, which shows that there is a concentration of stress inside the Flexible formwork concrete wall, and therefore the maximum settlement of the roof on the side of Flexible formwork concrete wall is 35.35 mm, due to the existence of "arch-shaped" decompression area from the working face. Therefore, the maximum settlement of the roof slab on the side of flexible formwork concrete wall was 35.35 mm. Due to the existence of "arch-shaped" decompression area on the roof and floor of roadway, the settlement of the roof slab on both sides of the roadway gradually increased when it was from − 20 to 10 m away from the working face, and the central position had the following pattern of firstly decreasing and then gradually increasing, and then exceeding the top of the roadway. After decreasing and then gradually increasing, after 10 m ahead of the working face, the two sides of the roadway roof subsidence law and the central part of the roadway to maintain the same; the use of cutting the top of the flexible mold concrete wall support technology as a means of controlling the top of the roof along the empty roadway subsidence, the analysis shows that the roof after roof cutting of the amount of subsidence have been reduced, the maximum difference in the rate of change of the displacement is 0.011%, and the maximum difference in the amount of subsidence of 4.98 mm; through the field monitoring data analysis of the pressure of mining The peak value of the influence curve of the working face is located at 19 m of the working face, 9 m of the lagging working face and 19 m of the roadway outside the working face are less affected by the additional mining stress field, comparing the fracture brokenness of the roadway roof before and after the roof cutting, the fracture area in the uncut section is much larger than that in the section of the roof cutting. [ABSTRACT FROM AUTHOR]

Based on the 7618 working face in Yaoqiao coal mine of Datun mining area, the activation mechanism of water-rich faults and the development characteristics of water-conducting fractures in overlying strata under the influence of faults are studied by theoretical analysis, numerical simulation and field measurement in this paper. The research results show that Anderson model and Mohr–Coulomb strength criterion are combined to establish the fault failure mechanical model, and the fault activation criterion under the influence of mining is obtained. FLAC3D numerical simulation results show that with the advance of the working face, the fault begins to be affected by the mining effect of the working face at the distance of 20 ~ 30 m from the fault. Meanwhile, with the advance of the working face, the overburden shear failure range also expands, and the fault fracture gradually expands from top to bottom. The failure zone of the working face roof is connected with the fault fracture zone. Then the fault is "activated" and causes the fault to become a water gushing channel, and finally the water gushing disaster occurs. Through numerical simulation and comparative analysis, the development height of water-conducting fracture is 73.2 m in the absence of fault, and 73.7 m in the presence of fault, indicating that the fault has little influence on the maximum development height of water-conducting fracture. The actual development height of the water-conducting fracture zone in the 7618 working face is 73.97 m and the fracture production ratio is 13.7. The research results can provide theoretical reference for the safe mining of similar working faces across faults. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the internal dislocation law of coal seam working face under coal pillars with different widths and evaluate the safety of using the combined mining of close-distance coal seams under different layer spacing. Based on elastic–plastic mechanics and mine pressure theory, theoretical calculation and numerical simulation were implemented to establish a numerical model consistent with the actual production. Based on the theoretical and simulation results, the abutment stress distribution of surrounding rock in coal seam stope was analyzed and the stress transfer law of coal pillar floor under the influence of different coal pillar width and floor depth was studied. Finally, this paper analyzed the limit span of goaf under two different beam structures. The results indicate that with the same coal seam distance, the interior dislocation distance increases linearly with the increase of coal pillar width. With the increase of floor depth, the vertical stress under the coal pillar decreases, but the influence area increases slightly. Finally, the ultimate spans of two different beam structures were calculated. In summary, this paper explored the strata behavior, i.e., the deformation and failure mechanism of surrounding rock in coal seam mining. The research results demonstrated the feasibility of using the combined mining method in close-distance coal seams. The methodology proposed in this paper could be implied in similar working environments, and this study provides new insights into the mining technology in lower coal seams. [ABSTRACT FROM AUTHOR]

Cropland is the foundation of food security. Coal is the guarantee of energy security. As China's demand for coal and grain continues to increase, so does the overlap area of their production bases. Unrestrained underground mining can cause serious damage to cropland, leading to increasing conflicts between coal mining and food production. Thus, this paper used a partial backfilling mining technology to control surface subsidence and thus protect cropland. The key to successfully implementing the technology is how to design the panel size. However, the design efficiency of the conventional enumeration method is low. Therefore, this paper proposed a design approach based on improved particle swarm optimization. The results indicated that the approach could quickly find the optimal size of the panel compared with the enumeration method and particle swarm optimization. Moreover, if the longwall panel is mined according to the size designed by the approach, the cropland will be protected, and the cost will be reduced. This study can provide technical support for the cooperative development of cropland protection and coal mining in a coal-cropland overlapping area. [ABSTRACT FROM AUTHOR]

In order to solve the water and gas discharge hazard caused by gob water and harmful gases (such as CO), the method of grouting overburden fractures is adopted to achieve the purpose of safe and efficient mining production in coal mines. This paper carries out the experimental research on the permeability reduction effect of grouting in fractured rock mass, expounds the relationship between gas flow rate and pressure gradient, seepage pressure and permeability, confining pressure and permeability, and analyzes the permeability change law of fractured rock mass before and after grouting. Besides, the grouting migration and permeability reduction model of fractured fine-grained sandstone is constructed by combining grouting test and numerical simulation, which reveals the dynamic evolution law of rock mass permeability in the grouting process. The results show that the permeability of the grouting rock sample decreases from 700–13,000 to 15–300 mD than that of the ungrouting rock sample, and the decrease is more than 95%, which indicates that the sealing performance of grouting slurry is better. Besides, numerical simulations show that the initial permeability of rock samples is 971.9 mD, and the permeability decreases to 45.79 mD after 1800s, and the permeability decreases to 95.3%, which is basically consistent with the experimental results after grouting. The greater the grouting pressure is, the better the grouting effect is. With the increase of the grouting pressure, the increase of the grouting effect is no longer obvious. [ABSTRACT FROM AUTHOR]

Accidents such as roof caving, water permeation, and instability of supporting structures often occur in the roadway in the fault fracture zone of the Beizhan iron mine after excavation because of the coupling effects of high ground stress, surrounding rock breakage, freeze–thaw damage of rock, and intense mining. It brings construction difficulties and safety problems to the tunneling of the roadway. This paper analyzed and summarized the roadway instability mechanism of the fault fracture zone in the Beizhan iron mine. Corresponding support schemes and technologies were formulated according to different engineering geological conditions of the roadway. On this basis, FLAC3D was used to simulate the stability evolution of surrounding rock under different support modes in the fault fracture zone. According to the simulation results, the combined support method of bolt + anchor mesh + shotcrete was adopted to carry out the field test in the no.17 approach of section 3392 in the fault fracture zone. The results of surrounding rock deformation monitoring and borehole exploration show that the maximum displacement deformation of the monitored cross sections in the X, Y, and Z directions of the no.17 approach are only 4, 3, and 6 mm, and the surrounding rock fissures do not expand further, which proves that the roadway deformation is controlled. Conclusions and suggestions of this paper might help provide a reference for other similar projects. [ABSTRACT FROM AUTHOR]

Most of the published research on goaf-hole failures are performed using 2D numerical analyses. However, 2D analyses of the goaf-hole failure mechanism, which is truly a 3D problem, often do not provide a full picture of strata movement and stress change effect. In particular such 2D models completely fail to capture the longitudinal deformation and associated shear component yielding a false sense of goaf-hole stability. This paper uses advanced 3D numerical modelling to understand the fundamentals of goaf-hole shear failure mechanism and conceptualize the transverse, longitudinal and total shears developments during longwall extraction. A mine specific geotechnical model has been developed to compare the conceptualized goaf-hole failure mechanism with the simplified representative model. The effect of geo-mechanical properties and panel widths on shear development has also been investigated. The analysis is based on a case study; however, it is expected that the results presented in this paper will be applicable to other mines with similar geological environment or will at least highlight the need for a 3D modelling to capture the true three-dimensional strata deformation behaviour and goaf-hole shearing mechanism enabling safe and stable vertical drainage hole design. In the modelled scenario, the shear increased as the face advanced, and large shears would be experienced behind 50–100 m of the face. The longitudinal shear was dominant towards the centre of the panel and the transverse shear was dominant towards the panel edges. The layered seam appeared to generate lesser shear compared to the solid seam; this could be attributed to the dissipation of shear in the layer strata of the material. [ABSTRACT FROM AUTHOR]

Shenfu Dongsheng coal field is a cross-century energy base which is developed and constructed in China. In recent years, some mines have successively entered to the coal seam of the second layer. Due to the reasons of early mining, many coal pillars are left in the coal seam of the first layer, resulting in the phenomenon of strong ore pressure in the mining range before and after the coal pillar in the lower coal seam and even causing the buckling accident. In order to solve such safety problems, this paper takes the 22,307 working face in Bulianta coal mine as the research object, adopts physical similarity simulation experiment and theoretical analysis to systematically study the overlying rock characteristics and abnormal ore pressure manifestation mechanism of shallow and close coal seam in different working stages. The results show that the roof overburden of the key layer in the lower group bends and sinks when the coal pillar is mined, resulting in the activation and instability of the "masonry beam" structure formed by the roof of the upper coal seam. When the coal pillar is discharged, the residual concentrated coal pillar and the room type coal pillar are unstable under the action of high supporting stress, resulting in shear failure of the inter-layer rock in the upper part of 22,307 working face, causing the strong dynamic pressure of the working face to appear and then leading to the buckling accident. The working resistance of the support in each stage is obtained by establishing the structure diagram of the overlying rock under each stage and the corresponding mechanical structure model. Finally, the working resistance required by the support in the mining stage under the goaf is 16,692.6 kN, the working resistance required by the support in the coal pillar stage is 19,692.6 kN, the working resistance required by the support in the mining stage under the concentrated coal pillar is 13,150.6 kN, and the working resistance required by the support in the coal pillar stage is 19,215.6 kN. [ABSTRACT FROM AUTHOR]

In the N00 coal mining method, one of the most critical issues is ensuring the safety of the entry behind the working face. To address this challenge, various roof control techniques, such as precise directional roof-cutting technology (PDRCT), constant-resistance cable supporting technology (CRCST), and dynamic pressure-bearing supporting technology (DPBST), have been developed. However, the design method for these technologies has not been clearly defined, resulting in a lack of theoretical basis for parameter selection. This paper seeks to address this gap by further studying the mechanisms of PDRCT, DPBST, and CRCST in the N00 coal mining method, and proposing corresponding mechanical calculation models, design ideas, and calculation methods for these technologies. The results reveal that the primary function of PDRCT is to expand the height range of the caved rock mass in the mined area, thus reducing the subsidence space of the high-level roof and mitigating the dynamic pressure effect of the entry surrounding rock. The height of the roof cutting is crucial to the design, and its theoretical value must satisfy the condition that the broken expansion volume of the caved rock mass is equal to the volume that is mined. DPBST is essential for protecting the entry immediate roof and preventing internal damage during the movement of the upper roof. The dynamic pressure-bearing support strength should be appropriately designed to prevent the short cantilever roof structure from breaking within the entry's width during the movement of the high-level roof. Similarly, CRCST's most critical function is to maintain the long-term stability of the entry immediate roof by relying on the cable support forces and the stability properties of the high-level roof strata while it is not moving. The anchor cable support strength should be reasonably designed to prevent the short cantilever roof structure from collapsing under its own gravity. The proposed design method was applied to the Ningtiaota coal mine, leading to a 15.6% reduction in maximum roof deformation and a 12.0% decrease in average deformation, demonstrating the favorable impact of the approach. Highlights: The mechanisms of precise directional roof cutting technology (PDRCT), constant-resistance cable supporting technology (CRCST), and dynamic pressure-bearing supporting technology (DPBST) in the N00 coal mining method were revealed. Corresponding mechanical calculation models, design ideas, and calculation methods for the key parameters of PDRCT, DPBST, and CRCST were obtained. [ABSTRACT FROM AUTHOR]

Hard roof's 3D breaking characteristics is vital for mining pressure control. However, the research concerning a longwall face that employs an innovative roof-cutting technology via a chainsaw arm machine (RCTCAM) is scant. To address this gap, this paper thoroughly analyzes RCTCAM's core equipment and roof-cutting procedures. Firstly, the thin elastic plate theory and the superposition principle were applied to establish the first and periodic break mechanical models of hard roofs using the RCTCAM. These mechanical models elucidated the distribution laws of the first and third principal bending moments in a hard roof. Following this, based on tensile failure criteria and crack expansion criteria, the study uncovered that the hard roof's first break transitioned from an 'O–X' shape to a 'U–Y' shape, while its periodic break morphed from a 'C–ン' shape to an 'L–ノ' shape. This transformation led to a unique phenomenon. The rotation of arc-shaped triangular plates formed during the 'O–X' and 'C–ン' -shaped breaks resulted in severe damage to a gob-side roadway. However, a longwall face employing the RCTCAM did not produce such plates, effectively avoiding the associated damage. By implementing the RCTCAM in Workface 8311 of the Yanya Mine in China, the stress peaks of the coal pillars were reduced on average by 22.8%, and the deformation of the roadway decreased by 27.8%. These findings underline the success of the RCTCAM in achieving pressure relief for a gob-side roadway. Highlights: It was given that the theoretical calculation method for deflection, bending moment, and stress of a hard roof with the RCTCAM under the first and periodic breaks. When with the RCTCAM, hard roof's first break exhibits a transition from an 'O-X' shape to an 'U-Y' shape, while its periodic break changes from a 'C-ン' shape to an 'L-ノ' shape. Due to rotation of arc-shaped triangular plates formed in the 'O-X' and 'C-ン'-shaped breaks, a gob-side roadway bear severe damage. However, a longwall face with the RCTCAM has no such plates, thus avoiding damage. With the RCTCAM in Workface 8311 of the Yanya Mine, China, the stress peaks of a gob-side roadway's coal pillars dropped averagely by 22.8%, indicating that the RCTCAM achieve pressure relief for a gob-side roadway. [ABSTRACT FROM AUTHOR]

Coal mine water outburst under fluid-solid coupling is a hot topic in coal geology. In this paper, the FLAC 3D simulation method is used to systematically study the water outburst problem of fluid coupling with coal mine floor. The results show that the vertical stress of the floor in the goaf has an obvious downward trend after coal seam excavation. Under the joint influence of mine pressure and bearing water pressure, the working face before the old roof pressure can be affected by two stages: the first stage is the advance pressure compression section on both sides of the working face, and the other stage is the pressure relief expansion section under the goaf. Before the old roof is pressed, the shear stress near the roof and floor is also affected to some extent. The front and rear displacement value of the goaf is negative, which is the result of the advance supporting pressure. The effective thickness of the floor waterproof layer decreases gradually with the advance of the working face. When the working face continues to advance, there will be a risk of water outburst. With the increasing width of the working face, the height of the guide belt increases. Therefore, in the process of mining activities, a variety of factors should be considered comprehensively, and a reasonable width of the working face should be selected to ensure the safety of mining. [ABSTRACT FROM AUTHOR]

The grand-scale suspended roofs overlying the goaf are commonly developed under thick-hard rock strata (THRS) during the mining process of the deep coal seam. As a result, strong mine seismicities triggered constantly by deep mining have impeded severely the safety and efficient operation of deep mines. The working-face deep-hole blasting technology has been utilized to weaken the roof for releasing the mine pressure, thereby reducing the risk of violent dynamic hazards. In this paper, Dongtan deep coal mine is taken as an example, the radius of rock failure regions induced by blasting is calculated based on the expansion theory of cylindrical charges. LS-DYNA and UDEC7.0 softwares are employed to simulate the rock pre-splitting and overburden migration under the working-face deep-hole blasting, and the roof pre-splitting and pressure relief mechanism of the working-face deep-hole blasting are revealed. According to the micro-seismic, support working resistance and real-time stress monitoring results, the working-face deep-hole blasting technology could actively break the integrity of the roof. Using the blasting, high-energy mining-induced seisms are decreased dramatically or disappeared fully. The advanced abutment pressure of the coal seam decreases with the increase of the working-face deep-hole blasting time, which indirectly indicates that the weakening degree of the thick-hard roof gradually increases under the action of multiple blasting. The working-face deep-hole blasting technology has achieved the desired effect in the pressure relief in hard suspended roofs for preventing and controlling strong mining-induced seismicity. Highlights: The distribution of mining-induced seismicities before and after the working-face deep-hole blasting is revealed by the micro-seismic system. The rock pre-splitting and overburden migration influenced by the working-face deep-hole blasting are numerically simulated. The effectiveness of strong seismicity prevention and control is systematically evaluated by a series of monitoring technology. The working-face deep-hole blasting technology could achieve the desired effect in the pressure relief of roofs. [ABSTRACT FROM AUTHOR]

Automatic roadway formation by roof cutting is a sustainable nonpillar mining method that has the potential to increase coal recovery, reduce roadway excavation and improve mining safety. In this method, roof cutting is the key process for stress relief, which significantly affects the stability of the formed roadway. This paper presents a directionally single cracking (DSC) technique for roof cutting with considerations of rock properties. The mechanism of the DSC technique was investigated by explicit finite element analyses. The DSC technique and roof cutting parameters were evaluated by discrete element simulation and field experiment. On this basis, the optimized DSC technique was tested in the field. The results indicate that the DSC technique could effectively control the blast-induced stress distribution and crack propagation in the roof rock, thus, achieve directionally single cracking on the roadway roof. The DSC technique for roof cutting with optimized parameters could effectively reduce the deformation and improve the stability of the formed roadway. Field engineering application verified the feasibility and effectiveness of the evaluated DSC technique for roof cutting. Highlights: A directionally single cracking (DSC) technique for roof cutting in automatic roadway formation of the non-pillar mining method is proposed. The mechanism of the DSC technique to achieve single cracking relies on effective control of the blast-induced stress. DEM simulation and field experiments are effective methods to evaluate the DSC and roof cutting parameters to improve the stability of the roadway surroundings. [ABSTRACT FROM AUTHOR]

Under double-seam mining, the main roadway surrounding rock is affected by the superposition of the advanced stress of the two-seam coal working faces. The stress superposition mode and degree are of great significance to the width calculation of the protective coal pillar and the determination of the critical control direction of the surrounding rock. This paper uses theoretical analysis, numerical simulation, and site engineering practice to carry out targeted research. The conclusions are as follows: Under different lateral pressure coefficients, the superposition evolution law of maximum principal stress direction of two coal seams with different offsets; Two developmental trends and three types of evolution models of J2 peak zone (the critical area of the stress increase and deflection changes) under different superimposed loading modes are summarized. Based on the typical asymmetric evolution model of the J2 peak zone, an asymmetric truss-cable co-anchoring method is proposed aimed at the J2 critical zone. The field monitoring results show that the main roadway surrounding rock is stable after support when the upper coal seam protective coal pillar is left 80 m, and the lower one is 60 m wide. It is of great reference importance for similar engineering practices. [ABSTRACT FROM AUTHOR]

Emulsion pump station is widely used to provide power for full-mechanized coal mining face equipment. With the development of the mining technique of longwall face and the extensive use of large mining height and high working resistance of the hydraulic support, the fluid supply pressure is more unstable and the pressure impact is increasingly intensified. The intelligent control of the emulsion pump station is the key to the development of the stable fluid supply technology at the working face. This paper develops a new on-line adaptive learning technique to improve the response speed of pumping station based on the optimal control algorithm of adaptive dynamic programming (ADP). The state space model of the working face fluid supply system in the process of no-load column lifting of hydraulic support is first established using the flow relationship, and the effectiveness of the proposed control algorithm is then verified by simulation validation. Moreover, combined with a certain fluid supply system of a fully mechanized caving face in Shandong Energy Xinwen Group XinJulong Co., Ltd, a technical scheme of adaptive stable fluid supply is verified in engineering practice. The results indicate that the fluid supply system using the proposed control algorithm has a favorable tracking effect on the ideal trajectory, and the tracking error can converge to near zero. The output pressure of the fluid supply system using the stable fluid supply technology is more stable, and the practical effect is good, which meets the demand of stable fluid supply in the mining face. [ABSTRACT FROM AUTHOR]

Underground mining of minerals is accompanied by a change in the rock mass geomechanical situation. This leads to the redistribution of stresses in it and the occurrence of unexpected displacements and deformations of the earth's surface. A significant part of the civil and industrial infrastructure facilities are located within the mine sites, where mining and tunneling operations are constantly conducted. Irrational planning of mining operations can lead to loss of stability and destruction of undermined facilities. Therefore, it is important to study the earth's surface deformation processes during mining operations, which ensures safe and sustainable operating conditions. The research objective of this paper is to analyse the behaviour of a natural gas pipeline under the influence of underground mining activities, with a particular focus on understanding the effects of horizontal surface deformations and their potential impact on pipeline safety and structural integrity. Its performance and safety are determined on the basis of the found parameters of the earth's surface horizontal deformations and their comparison with permissible parameters characterizing the conditions for laying pipelines, depending on the mining-geological conditions and the degree of their undermining. Based on determined conditions for the safe undermining of the natural gas pipeline, it has been revealed that in its section between the PK212+40 and PK213+80 (140 m) pickets, the estimated parameters of the earth's surface horizontal deformations exceed their permissible values. This can cause deformation and damage to the pipeline. For the safe operation of the pipeline during the period of its undermining, in order to eliminate the hazardous impact of mining the longwall face, additional protection measures must be applied. It is therefore recommended that the gas pipeline between the PK212 and PK214+20 pickets be opened prior to the displacement process (200 m from the stoping face), thus reducing the density of the gas pipeline-soil system. Recommendations for controlling the earth's surface deformations within the natural gas pipeline route are also proposed, which will ensure premature detection of the negative impact of mining operations. [ABSTRACT FROM AUTHOR]

The causes of ground fissure formation are closely related to the change in the stress state in a loose layer, but many researchers often ignore the dynamic processes of mining when studying mining-induced damage mechanisms. The study of stress evolution in a loose layer during mining can help to reveal the causes of surface damage and its self-healing mechanism. This paper establishes a numerical model to study a loose layer’s stress evolution and its causes during mining. The discriminative conditions of the potential dynamic fissure formation cycles and self-healing are given. The vertical and horizontal stresses in the loose layer at the mining boundary increase and then decrease under the mining disturbance, and the vertical stresses in the loose layer above the comprehensive mining surface undergo two increasing and decreasing stages, while the horizontal stresses increase and decrease and then increase again. The permanent fissures at the mining boundary form because of the decompression- and compression-related damage caused by horizontal unloading, while the dynamic fissures in the loose layer at the mining surface form due to the first horizontal unloading effect; the shear damage is caused by the second increase in vertical stress. Additionally, the soil Mohr‒Coulomb strength criterion and the linear elastic stress‒strain relationship are used to discriminate the single- and double-cycle development patterns of the dynamic fissures on the ground surface. [ABSTRACT FROM AUTHOR]

The primary key stratum (PKS) is an important research object in ground control, and all strata up to the surface are controlled by it. However, the geological conditions of coal mining are complex, and coal mining under different geological conditions will cause different degrees of impact on PKS. This paper takes the Meihuajing coal mine as an example, theoretical analysis, numerical simulation and geological condition analysis are comprehensively applied to study the subsidence mechanisms of PKS under the influence of different factors. The results show that subsidence of the PKS is directly proportional to the coal thickness (M) and buried depth (D), and inversely proportional to the distance between the coal seam and the primary key stratum (H). The order of the disturbance degree with each factor on the maximum subsidence of the PKS is M > D > H. It is demonstrated that the disturbance impact of coal seam mining on the PKS in an area with thick coal seams needs to be paid more attention. The research results guided adjusting and reducing the disturbance impact of mining on the PKS. [ABSTRACT FROM AUTHOR]

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Shearer is an essential equipment in mechanized coal mining process. Roof cutting often turns up for shearer during working process, leading to extra vibration on shearer and reducing its service life. Coal and rock interface recognition is a fundamental technical way for shearer to avoid continuous roof cutting. In this paper, an effective method for coal and rock interface is proposed and it is mainly based on the cutting loads on shearer drum in three different kinds of working states. The constitutions of cutting force on shearer drum are analyzed under conditions of different proportions of rock thickness in the cutting range and then model for calculation of cutting force in the coal–rock mixed seam are proposed which is a function of rock proportion in the cutting range. To verify the model, hard roof with different material strengths and different interfaces are established with the numerical method and rock proportions in the cutting range are derived based on the mentioned method. In terms of the situations where rock material properties are close to coal and the results are obtained with lower accuracy, enlarging the difference of rock proportions in the second and third states is proposed and the relations between the recognition accuracy and the differences of rock proportions in different states are explored as well. The results show that the estimation method works well with qualititative analysis of coal and roof interface even if coal and rock material properties are various and not able to be known in advance. In addition, the adjustment height of shearer drum is the important factors highly related with the estimation accuracy and it would be helpful for accuracy improvement in conditions where the material properties of coal and roof are closer to each other or larger roof cutting thickness happens in coal mining. The method provides the possibility for qualititative analysis of coal and roof interface with easy accessibility and wide adaptability. [ABSTRACT FROM AUTHOR]

The method of filling mining can solve the problem of surface subsidence caused by coal mining. Among them, it is crucial to study the mechanism of filler strength improvement timeliness and filler mining to control rock movement for filler mining. In this paper, by combining theoretical analysis and similar simulation experiments, compressive strength is used as the research parameter to conduct proportioning test research on paste filling similar materials such as coal gangue, fly ash, and cement. The results prove that the strengths of the test ratios can meet the strength design criteria and lay the foundation for the requirements of similar simulation experiments. In order to study the characteristics of overburden failure, stress and displacement in the process of filling mining, the key technical parameters of overburden movement are determined. Similar simulation experiments were conducted to study the movement and deformation of overburden rock and the displacement and stress distribution law of overburden rock in the coal mine under different filling rates and filling steps conditions. The results show that the filling rate and filling step are the keys to preventing the overlying rock from rupture and collapse, and the larger the filling rate is, the smaller the stress and displacement of the overburden; the larger the filling step is, the larger the displacement and stress change of the overburden, and vice versa. In addition, the displacement curve along the strike is basically an "arch" type distribution, and the stress variation trend is "large-small-large" with a "Z" type distribution. The research results are of great significance to guide the practice of filling mining and can provide the theoretical basis for its further promotion. [ABSTRACT FROM AUTHOR]

The deformation and failure of mining slopes in layered rocks predominantly result from shear landslides. However, the instability process of the Pusa rock avalanche in Guizhou, China, revealed a unique damage phenomenon: prominent breaking and toppling of rock blocks occurred in the central section of the mountain, with a lack of commonly observed shear landslide features. This paper aims to investigate the underlying reasons behind this distinctive damage pattern. The study employs various methods including geological survey, UAV aerial survey, physical simulation, and discrete element numerical simulation. The findings indicate that the geological conditions, characterized by a hard upper layer and a soft lower layer along with underground mining activities, play a significant role in triggering the landslide. Furthermore, the presence of a columnar structured rock mass emerges as the primary factor influencing the instability of the Pusa rock avalanche. To elucidate the mining failure mechanism of the rock mass with vertical joints, we propose a "subsidence-buckling" failure model. Following the subsidence and collapse of the roof rock mass in the goaf, the columnar rock mass in the upper and middle portions of the slope undergoes deflection and deformation, forming a three-hinged arch structure. This structural configuration converts the pressure exerted by the overlying rock mass into both vertical pressure and lateral thrust. Under the influence of external loads, the slope experiences buckling failure, ultimately leading to instability upon fragmentation. By shedding light on these findings, this study contributes to a better understanding of the spatiotemporal evolution of mining slope fractures and their impact on slope stability. [ABSTRACT FROM AUTHOR]

To build a digital twin model of intelligent longwall coal mining, this paper presents a new full-parameter position and attitude digital twin model of hydraulic supports. A full-parameter matrix describing the position and attitude of a support is established first. Then, the position and attitude digital twin model of a support based on this matrix is built. Afterward, a position and attitude digital twin model of the hydraulic support system in the workface is established using the Unity3D software and the Runge–Kutta algorithm as a motion calculation method. Finally, a simulation experiment is conducted based on the digital twin model of hydraulic supports, and results show its effectiveness. This digital twin model has the potential to control the hydraulic support system in future intelligent coal mining. [ABSTRACT FROM AUTHOR]

The emission of gas from the coal seams is one of the most important issues during the underground coal mining operation. Each year, coal gas emission from the underground stopes leads to the death of a large number of miners and is one of the biggest threats to workplace safety. In addition, ventilating and releasing coal gas outside of the mine is too expensive and, in most cases, might be impossible. Therefore, it is necessary to increase gas emissions and improve the efficiency of methane drainage for securing the mining workplace. The main aim of this paper is to investigate the capacity of the drainage system in the Parvadeh Tabas Coal Mine, Iran. For this purpose, the effect of the specification of the drilling pattern such as the length and drilling direction of the drilled boreholes on the methane gas concentration was investigated. The results of this study show that, with the change in the length of the borehole and the angle of the boreholes according to the axis of the tailgates, the volume of the methane drainage changes, significantly. The boreholes with lengths between 60 and 80 m drilled in lines with 16-degree division from a line perpendicular to the tailgate have the highest methane concentration. [ABSTRACT FROM AUTHOR]

To explore the stability control mechanism of surrounding rock during coal seam mining, the rock mechanical properties under the mining stress path were studied in this paper. The study begins by summarizing the mining roof and floor triaxial stress (MRTS and MFTS) paths through numerical simulations. The MRTS path is characterized by axial loading and confining unloading, while the MFTS path involves axial loading and confining loading. Subsequently, triaxial tests were conducted on rocks subjected to the mining stress path. The results indicated that compared to the standard triaxial stress (STS) path, the peak strength, peak axial strain, elastic modulus, and Poisson's ratio under the MRTS path were lower, whereas those under the MFTS path were higher. The MRTS path exhibited a more forward dilation deformation, rendering it more susceptible to damage, whereas the MFTS path displayed a more stable and backward dilation deformation. Tensile failure was primarily observed under the MRTS path, whereas the MFTS path resulted in shear failure. Furthermore, the study analyzed the variation of rock permeability with axial and volumetric strain. The relationship between permeability and axial strain follows a √ shape, initially decreasing and subsequently increasing. The relationship between permeability and volumetric strain is found to be complex. Before the dilation onset point, the permeability decreases under both the STS and MFTS paths, while it decreases and increases slowly under the MRTS path. After the dilation onset point, the permeability increases under the STS and MRTS paths but initially decreases and then increases under the MFTS path. The research findings provide valuable theoretical guidance for mining strata control and water conservation mining practices. [ABSTRACT FROM AUTHOR]

For underground deep mines, mining activities often cause mining disasters such as rock burst, roof fall and water inrush. Especially for underwater mines in the fault zone, surrounding rock instability and water inrush are the main threats to mining safely and efficiently. This paper briefly reviews the research progress and development trend of deformation law and failure mechanism of jointed rock mass specimens, multi-field coupling numerical simulation method of rock mass with faults, prevention of water inrush. Geological tectonic movement and rock mass excavation destroy the integrity and continuity of rock, break the in-situ stress field of rock mass, and lead to weak structural planes such as joints, cracks, and faults. The stress and strain properties of rock mass reflects the mechanical effects of rock mass and joints comprehensively. The physical, chemical, and stress environments of rock masses in deep mines are more complex. The mechanism of rock failure and water inrush disaster under the coupling effect of THMC multiple fields is worth further research. By combining CT scanning technology, digital core construction, and 3D printing technology, a digital core model and repeatable rock specimens can be constructed to study the mechanical properties and permeability evolution mechanism of jointed rock masses. According to the development of 5G technology and artificial intelligence technology, 5G technology is integrated into the monitoring, early warning, and emergency disposal of water inrush disaster. [ABSTRACT FROM AUTHOR]

A novel fluid–solid coupling simulation method in coal weakening considering moisture content, immersion time, coal anisotropy, stress and plastic state was proposed in this paper. Based on this, the stability of the residual coal pillar (RCP) in the underground water reservoirs during longwall mining and water storage was studied by numerical simulation and field measurement. The results indicated that the RCP stress continually increased during adjacent longwall face mining, enhancing the development of the plastic zone of the RCP. However, in the following longwall face mining, there was minimal effect on the RCP. The fluid solid coupling analysis indicated that the plastic zone can develop further into the RCP until it breaks through it due to the instability of the RCP. Therefore, it is necessary to consider the effect of the instability of the RCP on the stability of the underground water reservoir. [ABSTRACT FROM AUTHOR]

The interaction of mining and the surface water or aquifer system in varying overburden strata conditions is one of the most critical aspects of sustainable mining practices, that can lead to water loss or water inrush into openings. This paper examined this phenomenon in a complex strata condition via a case study, and proposed a new mining design to minimize the impact of longwall mining on the overlaying aquifer. A range of factors have been identified contributing to the potential disturbance of the aquifer, including the extent of the water-rich area, the characteristics of overburden rock units, and the development height of the water-conducting fracture zone. In this study, the transient electromagnetic method and the high-density three-dimensional electrical method were used to identify two areas prone to water inrush danger in the working face. The vertical range of the water-rich abnormal area 1 is 45–60 m away from the roof, with an area of 3334 m2. The vertical range of the water-rich abnormal area 2 is 30–60 m away from the roof, with an area of approximately 2913 m2. The bedrock drilling method was used to determine that the thinnest part of the bedrock, with a thickness of approximately 60 m, and the thickest part, with a thickness of approximately 180 m. The maximum mining-induced height of the fracture zone was 42.64 m using empirical method, theoretical prediction based on the rock stratum group, field monitoring. In summary, the high risk area was determined, and the analysis shows that the size of the water prevention) pillar was 52.6 m, which was smaller than the safe water prevention pillar actually set in the mining range. The research conclusion provides important safety guidance significance for the mining of similar mines. [ABSTRACT FROM AUTHOR]

This paper constructs a geophysical model of hidden disaster-causing anomalies in coal rock for simulation experiments based on the structural design of coal rock seams at the mine working face to study the geophysical response characteristics of geological anomalies in coal rock seams. The material ratio and petrophysical parameters of the coal seam, roof, floor, collapse column, and fault in a mining area in Shanxi were tested using homogeneous and orthogonal test methods, and their petrophysical parameters, such as Vs,Vp, resistivity, permeability, and dielectric constant, were obtained. The coal dust and sand–cement contents are the main factors affecting the wave velocity, whereas the dielectric constant and resistivity are highly influenced by the water content of the material. The response characteristics of the petrophysical parameters of various types of geological structures measured via experiments are consistent with the corresponding geophysical responses of actual geophysical exploration methods. The experimental data were comparatively analyzed with the original coal rock samples and field in-situ probing results, and the best construction ratios of each geological structural unit were as follows: coal seam ratios of 61.11%, 11.11%, and 27.78% were selected for coal dust, sand, and cement content, respectively; sand–cement and gypsum–cement ratios of 2:1 and 2:8, respectively, were selected for the roof; and sand–cement and gypsum–cement ratios of 3:1 and 4:6, respectively, were selected for the floor. The optimal ratios of 75% sand, 10% gypsum, and 15% cement were chosen for the fault; those for the collapse column were 66.7% sand, 6.67% gypsum, and 26.6% cement. This study focuses on the ratios of various geotectonic physical models and their physical properties, it provides data support for subsequent model construction and a good experimental platform for the demonstration of various geophysical exploration methods and techniques. [ABSTRACT FROM AUTHOR]

The severe deformation of surrounding rock and the easy failure of the anchoring structure of roadway under large dynamic pressure influence in the short distance are the urgent issues to be paid more attention. Based on this problem, this paper is a case study on the instability mechanism and control technology of surrounding rock in the deep roadway under dynamic mining loading in the Gubei Coal Mine of China. The vertical distance from the − 575 m roadway of 11–2 mining area and mining working face is only 68 m. Firstly, the main factors influencing the surrounding rock's severe deformation are determined by the analysis of site investigation, surrounding rock composition and structure, overlying strata failure measurement, and borehole camera detection. The stress distribution, displacement distribution, plastic zone, and lining stress distribution of roadway of three reinforcement schemes, including nine working conditions, were calculated by numerical simulation for ordinary bolt support, bolt-support + grouting of roof and two sides, and bolt-support + full section grouting. Then the combined support technology system of "36 U-shaped steel + bolt + anchor cable + grouting" was proposed. The field monitoring results showed that the deformation of two sides and roof were only 20 mm and 16 mm, respectively, during the 65 day monitoring period. Furthermore, the cracks in the surrounding rock are almost filled with grouting materials, and the overall stability of roadway surrounding rock was completely achieved. This successful case study demonstrated that the optimized supporting structure is reasonable and the deformation of surrounding rock has been effectively controlled. [ABSTRACT FROM AUTHOR]

Aquicludes may become unstable during mining under loose pressurized aquifers, resulting in water inrush and sand burst at the working face. To deal with this problem, we established a mechanical model for a composite clay-overlying strata aquiclude during mining under a loose pressurized aquifer. We used the principles of the minimum potential energy and force equilibrium to deduce a deflection function coefficient for each plate. Drawing an isoline between the stress component and the function showed that the plate can easily stretch and undergo shear failure at the midpoint of the long side along the advancing direction of the working face. We then used the Griffith yield and Mohr–Coulomb yield criteria to obtain an equation for the critical hydraulic pressure when the composite aquiclude fractures and becomes unstable. We used this equation to analyze example in the 312 working face of the qinan mine, the results showing that the maximum hydraulic pressure measured on site was 3.16 MPa, and it's lower than the computed hydraulic pressure 3.87 MPa, so there is no risk of water inrush when advancing on the working face. Finally, the dynamic apparent resistivity test method was used to verify the correctness of the theoretical results derived in this paper. [ABSTRACT FROM AUTHOR]

Longwall mining operation is mainly accompanied by the roof fall phenomenon and out of seam dilution (OSD). These occurrences are strongly dependent on the quality of the face's roof and floor. Therefore, the existence of discontinuities in the floor and roof reduces their quality, increasing the intensity of roof fall and OSD. This paper suggests a synthetic rock mass (SRM) model which is able to simulate roof behavior by initiating and tracking of fractures in cave mining, in order to predict the roof fall and OSD and to evaluate their event risk. For this purpose, longwall mining, including excavation of coal, installation of powered support, and caving the roof, has been successfully established in this numerical model using the PFC2D approach. The risk analysis in a panel of Tabas mine using the matrix risk model indicated that the risk level of roof fall is moderate and the risk level of OSD is high. The results of SRM modeling are consistent with previous studies and field observations at the Tabas coal mine, indicating that the SRM model is a powerful technique for studying the behavior of discontinuities in mining. [ABSTRACT FROM AUTHOR]

Since the western region of China, which is typical of extraordinary resource endowments, has gradually emerged as the major mining zone in China, the mining of thick coal seams and roadways with coal-rock composite roof have become more and more common in this region. However, it is extremely difficult to realize safe and effective maintenance and control of such roadways due to the differences in natural endowments of coal-rock masses. With the roadway with coal-rock composite roof of Hulusu Coal Mine in western China as the engineering background, experiment research on large-scale similarity model was conducted through comprehensive measures such as the pneumatic loading system, the surrounding rock stress monitoring system, the roadway deformation monitoring system, the bolt load monitoring system, and the displacement field monitoring system in this paper. According to the results of the experiment, the control effects of the three support systems on the roadway with coal-rock composite roof were significantly different. When the single support of short anchor bolts was applied, the comparatively low initial anchor-hold failed to constrain the initial micro deformation of the roof. Consequently, wide-range fractures of the roof were triggered at a loading pressure of 0.8 MPa. In the meanwhile, the deep surrounding rocks witnessed a downward inflection point in stress, accompanied by the possibility of the collapse of the thin-layer anchorage zone at any time. As for the support combining both short anchor bolts and long anchor cables, though a reinforced effect on the bolt anchorage zone could be achieved with the help of the cables, the active reinforcement capacity of the bolt was limited. The bolt anchorage zone was the first to be damaged at a loading pressure of 0.9 MPa, which would subsequently affect the effective bearing capacity of the deep surrounding rocks. In the application of the single support of high-strength long anchor bolts, the long bolts with high pre-tightening force were able to lock multiple groups of coal-rock strata to form a thick-layer anchorage bearing structure capable of withstanding a load as high as 1.0 MPa. The crash and collapse of the coal wall eventually caused the subsidence of the roof. Based on the intense dynamic load experiment and the feedbacks of engineering application outcomes in the field, it was concluded that the high-pretension thick-layer (HPTL) anchoring technology can effectively constrain the deformation of roadways with coal-rock composite roof with favorable application outcomes. [ABSTRACT FROM AUTHOR]

Excessive strain energy accumulation in the coal seam is one of the essential conditions for rockbursts to occur. It is imperative to understand the parameters that affect the strain energy accumulation in retreating longwall mining to optimise the design and minimise rockbursts occurrences. In this paper, new analytical models were developed to calculate the strain energy accumulation considering the current state-of-the-art longwall machinery being used in the industry. Seven parameters, i.e., mining depth, length of the cantilever roof, coal seam thickness, thickness of the immediate roof, Young's modulus of coal and the roof, and Poisson's ratio of the coal seam, were identified as the parameters affecting the strain energy accumulation. A detailed statistical analysis of the parameters was conducted using the orthogonal testing method, which revealed that mining depth, Young's modulus of coal and the coal seam thickness significantly influence the strain energy accumulation within a 99% confidence interval. Highlights: An analytical model to calculate strain energy accumulation in longwall mining panels. Excellent agreement between analytical and numerical models. Parametric dominance was determined using the orthogonal testing method. Easy to use equations to calculate rockburst risk in longwall mining panels. [ABSTRACT FROM AUTHOR]

A theoretical basis for evaluating safety and stability of underground engineering is to study changes in rock strength and failure. In the process of coal mining, the failure mechanical properties in coal present a complex change principle that, under various in situ stresses and in a hydrological environment, results in material failure because of its unstable state being driven by energy. Therefore, by establishing a relationship between energy change and deformation process of coal failure, it would contribute to reflecting the essential characteristics relating to coal strength and failure. In order to explore the mechanics and energy evolution characteristics of water-bearing coal under the triaxial compression process, triaxial compression mechanical experiments of coal under different water contents and confining pressures have been conducted in this paper, whose effects relating to different confining pressures, including water content on changes in total strain energy, elastic strain energy, and the dissipation energy of coal have been analysed. As coal is a porous medium containing a pore and fissure structure, the volume change law relating to coal during the deformation and failure process is characterised by porosity, consequently, a damage constitutive model for coal was established from the perspective of energy dissipation based on statistical damage theory. It is believed that this model could better reflect the deformation behaviour of coal under triaxial compression, in which the relationship between damage evolution characteristics and energy dissipation changes has been reflected in the model. Further, the methods of determining the model's parameters have been proposed to verify the rationality of the established model. Finally, the influence of confining pressure and water content on the brittleness in coal has been discussed from the position of energy evolution. Highlights: Triaxial compression experiments were conducted on coal specimens to investigate the effects of water content and confining pressure on energy evolution. Based on statistical damage theory, the constitutive model that combined energy dissipation and coal failure was established. The effects of water content and confining pressure on the coal brittleness were discussed from the aspect of energy evolution. [ABSTRACT FROM AUTHOR]

Development and selection of fuzzy variable weight vector and its application on fuzzy comprehensive decision-making (FCDM) are studied in detail in this paper. Firstly, a parameter contained variable weight vector is developed based on the definition of variable weight vector, and then further extended to obtain the fuzzy variable weight vector. Its capability on weights changing can be adjusted by changing the parameter. In order to make the fuzzy variable weight vector for different changes of states to be selected and applied easily, the concept of fuzzy dispersion degree, which can be used to measure the balance of decision factors' states, is proposed; And then the concept of fuzzy average relative adjustment degree, which can be used to measure the capability of fuzzy variable weight vector on weight changing, is also proposed. Based on the concepts of fuzzy dispersion degree and fuzzy average relative adjustment degree, relationship between the weight changing capability of the developed fuzzy variable weight vector and the parameters it contains is analyzed. With consideration of keeping balance among states, steps on selecting fuzzy variable weight vector with its corresponding capability on weight changing are presented. Based on the fuzzy combined weighting method, a FCDM model with fuzzy variable weight is developed. The fuzzy structured element is used to express fuzzy numbers and fuzzy operations in the model. An analytical algorithm of the FCDM model based on the fuzzy structured element is presented. The developed model was then applied on evaluating and predicting for coal and gas outburst of coal mining panels. The research finding provides an alternative way for fuzzy operations and determination of weights in other fuzzy analysis models. [ABSTRACT FROM AUTHOR]

In the process of coal mining, the residual goaf will destroy the stress balance state of the overlying strata, which will result in a large number of fractures. The development of overburden fractures not only affects the movement of strata and the subsidence of surface, but also determines the dominant channel of gas, groundwater and other fluid migration. Therefore, this paper uses 3DEC software to simulate the temporal and spatial evolution of fractures in overlying strata during the mining of coal seam #15 in Pingshu Coal Mine, Qinshui Coalfield, and studies the fractal characteristics of mining overburden fissure development, then we use the drilling hole backwater method to verify the development height of mining-induced fractures. The results show that the overlying strata bend and collapse obviously with the advance of the working face. The development of overburden fractures shows very regular fractal characteristics, and the fractal dimension can be divided into four stages in time and two stages in space. The research results have guiding significance for mastering the law of overburden movement, accurately identifying groundwater and gas enrichment areas, and strengthening the prevention and control of mine water hazards and the effect of gas drainage. [ABSTRACT FROM AUTHOR]

Impoundments of tailings and active surface subsidence zones induced by ore mining were the major environmental problems. The aim of this study was to investigate the technical feasibility of impoundment of tailings using active surface subsidence zones. The self-designed scaled physical model was conducted to investigate the movement laws of tailings under different heights of granular media and tailings, and then drawing ore in these experiments was performed to simulate the mining process. The experimental results showed that the isolated extraction zone and stoping sequence had a primary influence on the doping process of tailings. Besides, when the height of granular media was more than that of the isolated movement zone, the uniform mode of drawing ore could be decreased the amounts of tailings drawn from drawpoints. Meanwhile, the doping process was not impacted by continuously emission of tailings to active surface subsidence zones. Thus, the field test was employed in the Dabeishan Iron Mine and the mining schemes were put forward based on the experimental data. The results showed that the recovery ratio and dilution ratio were 80.9% and 24.3% respectively, and that the scheme established in this paper could be used in practice. [ABSTRACT FROM AUTHOR]

Urban rail transit is widely used in major cities worldwide due to its high efficiency, safety, and environmental friendliness. Shield construction has a fast excavation speed and a negligible impact on ground transportation; thus, it is the preferred construction method for urban rail transit tunnels. Mudstone is a widely distributed soft rock characterized by large deformation, low strength, and significant rheological differences in different areas. Mudstone causes problems in the design and construction of subways. This paper uses finite element analysis to establish a three-dimensional numerical model of a double-line tunnel in a weathered mudstone area and analyze the influence of the stratum, design, and construction parameters on surface settlement and deformation during asynchronous and simultaneous shield construction. The research results show that the lateral surface settlement curve obtained from the simulation is consistent with the measured data, demonstrating the reliability and feasibility of the three-dimensional numerical model. The surface settlement is affected by the deformation modulus, cohesion, and the angle of internal friction, and the deformation modulus has the most significant impact. The surface settlement decreases as the buried depth of the tunnel or the distance between the two center lines of the two tunnels increases. As the buried depth of the double-lane tunnel decreases or the distance between the two center lines of the two tunnels increases to a certain value, the lateral surface settlement curve exhibits two peaks. The surface settlement shows a decreasing trend with an increase in the thrust of the shield machine and an improvement in the grouting quality. However, excess grouting pressure causes surface uplift and a subsequent increase in surface subsidence. [ABSTRACT FROM AUTHOR]

Combined mining is when two working faces separated by a certain distance simultaneously advance in the same direction, which commonly results in stress concentration and rockburst. This paper investigates the rockburst mechanism due to inclined coal seam combined mining under complex geological conditions in the Da'anshan Coal Mine, China. Based on the experimental analysis, there is an impact tendency of the No.10 coal seam. A theoretical model is established to evaluate rockburst risk due to combined mining. In addition, a 3D multifactor numerical model of inclined coal seam combined mining is established. The novel "PyFlac-Exc" calculation code and the "PyFlac-Eng" elastic strain energy calculation script are compiled. The evolution of elastic strain energy is obtained during combined mining. Theoretical and numerical results show that a rockburst occurs in the western fourth working face of the No. 10 coal seam, which is consistent with the on-site rockburst accident. In addition, the kernel density estimation method is proposed to reduce stress concentration by changing the coal pillar widths and misalignment distances. Numerical results show that the elastic strain energy levels are low for the same coal pillar width, and the misalignment distance is arranged from 50 to 80 m. With the same misalignment distance, a coal pillar width greater than 45 m can effectively reduce the rockburst risk. [ABSTRACT FROM AUTHOR]