Current Issue

  • Experimental study on mechanical characteristics and damage degradation mechanism of conglomerate under drying-wetting cycles

    CHEN Shaojie;XUE Shouzhen;YIN Dawei;WANG Yabo;QU Xiao;MA Hongfa;State Key Laboratory of Mine Disaster Prevention and Control, Shandong University of Science and Technology;

    To study the mechanical characteristics and damage degradation mechanism of conglomerate samples under drying-wetting cycles, uniaxial compression tests were carried out under different drying-wetting cycles(0～4 times, drying-wetting cycles period of 10 d). The strength, deformation and failure characteristics of samples were analyzed, and the deterioration effect of the mechanical properties of the conglomerate samples was explored. The damage degradation model of conglomerate samples during drying-wetting cycles and before and after drying-wetting cycles was established, and the damage degradation mechanism of conglomerate samples under drying-wetting cycles was analyzed from the aspects of meso-structure and component changes. The results show that(1) the mechanical properties of conglomerate samples decrease with the increase of drying-wetting cycles, and the uniaxial compression stress-strain curve changes from steep decline to ductile decline modes in the post-peak stage. Also, the plastic failure degree of conglomerate samples increases, and the failure mode of samples changes from tensile failure to shear ejection failure.(2) With the increase of the number of dryingwetting cycles, the formation time of deformation localization zone of conglomerate samples is advanced and the number of localization zones increases, and the ringing count of acoustic emission of samples increases sharply.The decrease of elastic energy density in the pre-peak stage leads to the decrease of peak stress of samples, and the increase of energy density in the post-peak stage causes the increase of crushing degree of samples.(3) In the process of drying-wetting cycles, kaolinite, illite and other minerals are dissolved, and the internal defects of the conglomerate samples continued to expand and shrink. Compared with the the XH–0d group samples, the average porosity at the fracture surface increased respectively by 6.96%, 14.41%, 24.00% and 48.10%. With the increase of the number of drying-wetting cycles, the damage of the conglomerate samples increases, and the effective bearing structure area decreases, which ultimately contributes to the deterioration of its mechanical properties.The research results can provide some reference for ensuring the safe mining of coal seams.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 4051K]

  • The influence of abrupt changes of coal dip angle on coal and gas outburst and impact evolution characteristics

    TANG Jupeng;HUANG Lei;PAN Yishan;ZHANG Xin;REN Lingran;ZHANG Zhonghua;School of Mechanics and Engineering, Liaoning Technical University;School of Environmental, Shenyang University;Institute of Disaster Rock Mechanics, Liaoning University;

    To investigate the influence of abrupt changes in coal dip angles within deep and complex geological structures on the evolution characteristics of coal and gas outburst and impact evolution characteristics, an interface with an abrupt change in dip angle is established by taking into account the practical situation of coal and gas outbursts. The upper side of the interface consists of virgin coal, while the lower side consists of briquetted coal, which are utilized to simulate the virgin and the tectonic coal, respectively. With monitoring units, such as impact force testers, acoustic emission detectors, and data acquisition systems, coal and gas outburst simulation experiments under three-dimensional stress conditions are conducted considering different conditions of abrupt dip angle(the initial angle of coal dip angle mutation θ_I, the mutation angle θ_M) changes. The influence of coal dip angle mutation on outburst intensity and impact parameters(peak impact force, maximum negative pressure, and duration of sharp change) are analyzed. The research results show that within the range of 10°<θ_I≤20° and 10°≤θ_M≤20°, a critical value of coal dip angle mutation θ_T exists. When both θ_I and θ_M are greater than or equal to θ_T, low-index outbursts are prone to occur. Given a constant θ_I, the critical gas pressure exhibits a negative correlation with θ_M, while the outburst intensity per unit shows a positive correlation with θ_M. The evolution process of impact force in the simulated roadway can be divided into rapid change stage, fluctuation change stage and stable change stage. The number and density of high-frequency pulse A in the positive pressure stage and high-frequency pulse B in the negative pressure stage are closely related to θ_M. With the increase of θ_M,the fluctuation of the impact force in rapid change stage becomes more complex, and the high-frequency pulses A and B gradually show a highly concentrated trend in this stage. The peak impact force and the maximum value of negative pressure stage have a negative linear relationship with the gas concentration factor I_θ, while the duration of the rapid change stage has a positive linear relationship with the gas concentration factor. The peak velocity of impact airflow and the cumulative AE energy show basically the same trend. Both of them have a negative linear relationship with the gas concentration factor, and exhibit more significant changes when θ_M is greater than or equal to θ_T.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 4231K]

  • Research on mechanism and parameters of reaming anchorage for grouted anchor cable in roadway floor

    LIU Shaowei;ZHANG Runze;HOU Jianjun;YAO Bing'ao;FU Mengxiong;HE Deyin;School of Energy Science and Engineering, Henan Polytechnic University;Collaborative Innovation Center of Coal Work Safety and Clean High Efficiency Utilization;Xinzheng Coal Electricity Co., Ltd.,Zhengzhou Coal Industry Group;

    For design of reaming parameters of grouted anchor cables borehole in coal mine roadway of weak floor, the influence of reaming parameters, such as reaming diameter, length, number of segments and spacing, on the anchoring performance was investigated by conducting theoretical analysis, numerical simulation and laboratory tests, and the optimal reaming parameters for floor anchor cables borehole was ultimately determinated. The results show that the anchorage force of floor reamed anchor cables is positively correlated with both reaming diameter and segment length. The growth rate of anchorage force initially accelerates and then gradually slows down with the increase of reaming diameter, while it exhibits an almost linear increase with the segment length. Multi-segment reaming outperforms single-segment reaming, but beyond three segments, the improvement becomes negligible. The anchoring force of floor reamed anchor cables increases first and then decreases with the increase of reaming spacing, achieving the peak at 50 mm in space. By orthogonal simulations and pull-out test validation, the optimal reaming parameters were determined as a reaming diameter of 90 mm, a segment length of 100 mm, two reaming segments, and a spacing of 50 mm. The research results can advance the application of reamed anchorage technology in floor strata control of coal mine roadway.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 2422K]

  • Damage characteristics and energy evolution mechanism of heterogeneous granite under true triaxial dynamic and static loading

    GONG Hangli;WANG Mingyang;LUO Yi;QIU Yanyu;LIU Tingting;LI Xinping;School of Civil Engineering and Architecture, Wuhan University of Technology;State Key Laboratory of Explosion and Impact and Disaster Prevention and Mitigation, Army Engineering University of PLA;

    To investigate the dynamic mechanical properties and energy evolution behavior of heterogeneous granite under triaxial stress condition, combined dynamic-static loading cyclic tests were conducted on muscovite and vein-type granites using a true triaxial Hopkinson apparatus. Using the couploed FLAC3D-PFC3D coupling modeling, the effects of triaxial stress constraints and high strain rates on the dynamic crack propagation and energy evolution mechanisms of heterogeneous granite were investigated. The results show that during the cyclic dynamic loading process, the connectivity of the internal crack network in granite gradually increases, ultimately forming a highly dense macroscopic shear fracture network parallel to the direction of the minimum principal stress, with the dike specimens showing significantly lower impact resistance. Increasing axial stress raises the proportion of intergranular tensile cracks. This in turn reduces the crack initiation stress ratio(σ_(ci)/σ_d) and the damage threshold stress ratio(σ_(cd)/σ_d), achieving crack initiation stress and damage stress threshold earlier, and significantly weakening the dynamic strength of the samples. Lateral stress confinement increases the dynamic damage stress threshold of the samples, delays the timing of its occurrence, suppresses the frictional sliding of particles, reduces the release of destructive kinetic energy, and shows a strengthening effect on the dynamic strength of the samples. Under the true triaxial stress confinement, the impact loading mainly contributes to the dissipation of sliding friction energy, while the kinetic energy remains at relatively low levels throughout the process.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 5447K]

  • Study on mechanical properties of fractured sandstone under stress-seepage coupling conditions

    ZENG Bo;FENG Jiangrong;QIN Ken;XU Ersi;WANG Lu;LI Ruigen;LIU Jianfeng;Shale Gas Research Institute, Petro China Southwest Oil & Gasfield Company;PipeChina Energy Storage Technology Co.,Ltd.;School of Architecture and Civil Engineering, Xihua University;College of Water Resource and Hydropower, Sichuan University;

    With the increase of mining depth of resources, the influence of high stress, high pore pressure and engineering disturbance on the mechanical behavior of rocks is more pronounced. This is particularly true in fractured rock formed under complex conditions, affecting the engineering safety. Focusing on fracture-developed aquifer sandstone commonly encountered in deep resource extraction, laboratory tests were conducted to simulate the stress process of fracture formation. Fractured sandstone specimens replicating the in-situ fracture-forming stress environment were prepared. Stress-seepage coupling tests were then performed on these specimens to investigate their deformation, strength, and permeability characteristics. The results show that both the deformation and strength of the fractured sandstone exhibit significant confining pressure strengthening effects and water pressure weakening effects. Under the low seepage pressure, the shear strength of fractured sandstone is determined by cohesion c and internal friction coefficient f, while with the increase of the seepage pressure, the shear strength is mainly determined by the internal friction coefficient f only. The permeability decreases with the increase of the confining pressure and increases exponentially with the increase of the seepage pressure.Considering the influence of confining pressure and seepage pressure, a prediction model of elastic modulus of the fractured sandstone is proposed under the conditions of σ_3≤16 MPa and P_w≤15 MPa.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 2232K]

  • Dynamic evolution and damage fracture characteristics of coal mass during confining pressure unloading

    LEI Guorong;LI Chunyuan;CUI Chunyang;WANG Jiamin;LI Xiangshang;YUAN Honghui;LIU Huaguang;Deep Mining and Rock Burst Research Institute, Chinese Institute of Coal Science;CCTEG Coal Mining Research Institute;

    To study the dynamic fracture evolution and damage characteristics of coal during confining pressure unloading, the mechanical experiment was carried out on coal samples using an in-situ loading and unloading CT scanning system. The stress-strain curves of coal samples during the process of confining pressure loading were obtained, and the dynamic evolution of geometric characteristics, such as ratio, volume, fractal dimension,quantity, length and angle of cracks in two-dimensional plane and three-dimensional space was statistically analyzed. The correlation among three-dimensional crack volume, fractal dimension, and unloading amount was analyzed, and the relationship between crack volume and damage degree of coal sample was established. The dynamic evolution characteristics of shear and tensile fracture damage during confining pressure unloading and its influence mechanism on final failure of coal samples were explored. The results show that the axial strain of coal increases continuously with the increase of unloading stress, and the fracture rate increases with the increase of unloading amount, showing a sudden increase trend. In addition, the three-dimensional crack volume, fractal dimension and overall damage variable show a nonlinear exponential growth trend with the increase of unloading amount. It can be concluded that the confining pressure unloading can simultaneously induce shear and tensile fractures of coal samples and the damage degree of the two significantly influences the final failure mode of the coal.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 2241K]

  • Intelligent identification of water inrush path of floor with fault based on A-Star algorithm in deep coal seam mining

    SUN Wenbin;SUN Zhihui;LIU Hongqiang;CHU Yixin;College of Energy and Mining Engineering, Shandong University of Science and Technology;Department of Energy and Mineral Engineering, The Pennsylvania State University;

    To predict the water inrush risk of floor in deep coal seam mining, theoretical analysis, similar physical modeling and other research methods are used to conduct the intelligent identification of floor water inrush path.The prediction contour of floor water inrush is obtained based on the water pressure-stress monitoring data during the advance of mining face. According to the water pressure and stress data of each monitoring station, the probability index of water inrush at each position is quantitatively calculated. It is found that the greater this probility index, the higher the risk of water inrush. Taking the spatial distribution of water inrush probability index as the constraint condition, the A-Star path planning algorithm is used for the effective identification of the spatial path of water-conducting fracture, and an intelligent identification system of water inrush path is developed. Finally, similar material simulation was conducted for validation purpose. It is found that the path characteristics planned by the proposed method are highly consistent with the actual water-conducting fracture evolution trajectory of the model, and are highly consistent with the electrical monitoring results, verifying the effectiveness of the A-Star algorithm in water inrush path identification. The research results provide a new technical approach for real-time monitoring and early warning of floor water inrush disaster and guarantee safety of intelligent mine under deep mining conditions.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 2736K]

  • Fracture characteristics and deformation evolution of sandstone in groutreinforced holes

    SU Haijian;ZHANG Luqing;WU Chen;CHEN Guofei;ZHANG Boyang;School of Mechanics and Civil Engineering, China University of Mining and Technology;School of Civil Engineering, Henan Polytechnic University;

    Research on the fracture behavior and coalesence of defective rocks is of great theoretical and practical significance for rock engineering in mines, tunnels and underground chambers. Here, the notched semi-circular bending specimens containing holes of different sizes were filled and reinforced, respectively, and the effect of filling size on the fracture behavior of sandstone under three-point bending loading was investigated. The results show that the proportion of grout significantly affects the mechanical properties and damage process of sandstone specimens. Compared with the intact specimens, the fracture toughness and fracture energy of the specimens decrease by 82.18% and 84.30%, respectively, when the filling diameter reaches 16 mm. During the loading process, internal cracks first appear at the upper end of the straight-cut groove, but with the increase of the filling diameter, the cracks gradually turn to expand along the interface perpendicular to the loading end, and finally overshot failure occurs. In addition, the horizontal displacement of the upper end of the straight-cut groove generally shows mutation behavior, and the mutation area is significantly enlarged with the increase of filling diameter, accompanied by more active acoustic emission behavior. Finally, the effect of water-cement ratio on the mechanical behavior of the filling-reinforced specimens is briefly discussed. With the increase of water-cement ratio, the failure angle of the upper end of the notch increases significantly, the crack tends to develop along the interface, and the overall mechanical properties of the specimens are further weakened.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 2961K]

  • Thermo-hydro-mechanical-chemical characteristics of mining-integrated geothermal systems

    WEI Xi;ZHU Meng;ZHANG Yuzhong;RUAN Zhuen;WANG Yong;YANG Xingguo;LU Gongda;State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University;College of Water Resource and Hydropower, Sichuan University;China International Engineering Consulting Corporation;Zhejiang Geology and Mineral Technology Co., Ltd.;School of Civil and Resources Engineering, University of Science and Technology Beijing;

    With continuous increase of mining depth, the deep high-temperature strata with geothermal gradients provides significant opportunities for developing high-grade geothermal resources. To explore the feasibility of closed-loop geothermal extraction using abandoned mines, a multi-field coupling model for time-dependent cemented backfill was established based on Biot's porothermoelastic theory, where a non-isothermal pipe-flow module based on the Navier-Stokes equations was implemented. A new simulation system for co-mining of coal and geothermal energy with backfill was developed. The multi-physical field response of backfill and outlet water temperature development under different mining methods and geothermal conditions, and the evolution patterns of thermal efficiency and structural stability during system operation were analyzed. The results show that backfill hydration heat is the core early-stage thermal source, contributing 47.1% of energy within 90 d under calculated conditions. Geothermal extraction enhances system stability. Under conditions of backfill/fluid temperature at 15 ℃ and surrounding rock temperature at 35 ℃, peak pore water pressure and total stress decreased by 40.6% and 22.1%, respectively, when compared to non-geothermal-extraction scenarios. The cooling effect of heat-exchange fluid causes confined contraction of pore water and reduces backfill water pressure, thereby improving system stability.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 1809K]

  • Research on the characteristics of overlying rock fracturing in roadway maintained by roof cutting and connecting adjacent goaf and its application

    LIN Haifei;LIU Sibo;LI Shugang;SHUANG Haiqing;TIAN Yu;LUO Rongwei;CHEN Zhiheng;GOU Rui;College of Safety Science and Engineering, Xi'an University of Science and Technology;Western Coal Mine Gas Disaster Prevention and Control Key Laboratory of Colleges and Universities in Shaanxi Province;Western Engineering Research Center of Mine Gas Intelligent Drainage for Coal Industry;

    To investigate the fracture evolution characteristics of the overlying strata in a roof cutting and roadway retaining(RCRR) mining face, physical similarity simulation was employed to analyze the development height of mining-induced fractures, bed separation, and strain distribution. The evolution characteristics of the roof structure and the asymmetric fracture pattern of the overlying strata in RCRR mining were systematically explored. Based on the virtual work principle and plastic hinge theory, calculation formulas for the broken block size of the roof at different stages of RCRR mining were derived. The results show that tIn the first mining face,fractures are more developed within the caved zone on the roof-cutting side, while fractures within the fractured zone are more prevalent on the non-roof-cutting side. After the non-first mining face of the roof-cut retaining roadway penetrates the adjacent goaf, the overlying rock fracture and the separation volume curve are asymmetrically distributed. The fracture on non-roof-cut side is compacted and closed, while fractures on the roofcut side are stable. The bedding separation is reduced by 0.46～8.50 mm, along with the reduction of fracture development degree. The initial fracture morphology of lower-level rock strata in the first mining face of the roof cutting roadway is ''U + Y'', and the fracture line on the roof cutting side is parallel to the roof cutting direction.The lower-level rock strata of the non-first mining face is broken in a "rectangle" pattern, and the higher-level rock strata is broken in an asymmetric ''O + X'' shape for the first time. The periodic breaking is in a combined''U + Y'' shape, and the fracture trace biased towards the non-cut side. In non-first mining faces, the breaking step of high-level rock strata increases, producing the larger sizes of fractured blocks with a decrease in the number of fractures per unit volume. Consequently, the upward migration of methane becomes more difficult. Based on this,it is proposed that for methane pressure relief management in non-first mining faces with top-cutting and gob-side entry retaining technology, the height of methane drainage boreholes should be appropriately reduced. By considering fracture characteristics, the position of key strata and air leakage effects, an efficient methane drainage area for working faces with roof cutting and roadway retaining is determined. Field tests on methane drainage from boreholes have verified the accuracy of the zoning.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 1835K]

  • Study on roadway layout optimization and coal pillar stability under the influence of denudation area

    XIE Panshi;ZHANG Bo;HUANG Baofa;ZHANG Hao;LU Bei;LEI Erhui;WANG Xi;LIU Xin;Key Laboratory of Western Mine Exploitation and Hazard Prevention Ministry of Education, Xi'an University of Science and Technology;College of Energy Science and Engineering, Xi'an University of Science and Technology;Shenmu Coal Mine Safety Law Enforcement Brigade;Shenmu Yaoqu Coal Industry Co., Ltd;

    For the optimization of roadway layout and coal pillar stability under the influence of denudation areas in shallow buried coal seams, the air-return roadway in the western mining area of Yaoqu Coal Mine was selected as the research object. Through a combination of theoretical analysis, numerical simulation and field engineering verification, the deformation and failure characteristics, as well as the energy evolution law of the roadway under the influence of the denudation area, were thoroughly examined. Additionally, the failure behavior of coal pillars of varying widths was analyzed based on the partial stress yield criterion and energy criterion. Ultimately, the optimal coal pillar size was determined following the optimization of the roadway layout. The results indicate that the presence of a denudation area significantly increases the stress in the surrounding rock and leads to the accumulation of strain energy, thereby exacerbating the deformation and failure of the roadway's surrounding rock. When the hard rock strata are disturbed, the change in strain energy is relatively minor. However, this disturbance does not impede the transfer of energy. In contrast, the soft coal rock mass exhibits a substantial change in strain energy. Following the optimization of the roadway layout, the deviatoric stress and strain energy within the coal pillar initially increase, then stabilize, and ultimately decrease during the excavation process.When the width of coal pillar between roadways is less than 9 m, both the deviatoric stress and energy curves within the coal pillar exhibit a "bell-shaped" distribution, with values exceeding the threshold for yield failure.When the width of coal pillar is between 10 and 13 m, the deviatoric stress and energy curves transform into a "saddle-shaped" distribution. During this period, the area within the coal pillar where the stress is below the yield limit gradually expands, and the bearing capacity correspondingly increases. Conversely, when the coal pillar width exceeds 13 m, the air-return roadway becomes too close to the denudation area. The coal body becomes unstable due to the superposition of dual stress and energy influences from both the denudation area and the airreturn roadway. Accrodingly, the optimal width range for the coal pillar is determined to be 10 to 12 m.Considering both the stability of coal pillar and the minimization of the denudation area's impact, a coal pillar width of 10 m is selected for engineering implementation. Further monitoring demonstrates that the overall deformation of the roadway is minimal, and the deformation of surrounding rock is effectively controlled.

    2025 03 v.7;No.30 [Abstract][OnlineView][Download 2280K]