Search Results (648)

The retreating roadway is a critical passage for the safe and efficient retreat of equipment from a fully mechanized longwall face. Its roof stability directly affects the transportation safety of large equipment such as hydraulic supports and the shearer. However, the structural evolution of the overlying strata of the retreating roadway and the roof stability under monorail crane loading have not been systematically investigated. Therefore, taking the retreating roadway of the 1093 fully mechanized longwall face in a coal mine in Anhui Province as the engineering background, this study combined physical similarity simulation, digital image correlation (DIC), and theoretical analysis to investigate the evolution of overlying strata fracture, caving, displacement, and stress fields during face extraction and retreating roadway formation. An analytical model was established to calculate bed separation between the immediate roof and the main roof under an equivalent static concentrated monorail crane load. The results indicate that the vertical displacement field of the overlying strata exhibits an overall trapezoidal distribution and continuously extends toward the higher overlying strata as the longwall face advances. In the physical model, no further propagation of fractures or bed separation toward the retreating roadway was observed after either roof-cutting operation. The withdrawal of hydraulic supports caused no significant changes in the stress or displacement of the overlying strata of the retreating roadway, indicating that the integrity of the overlying strata structure was well maintained. The model predicted a maximum bed separation of 6.39 mm between the immediate roof and the main roof at the gob-side end. The model can assist in identifying critical roof locations susceptible to bed separation and in prioritizing roof monitoring and support optimization during monorail-assisted equipment withdrawal. Full article

The dynamic load generated by the fracture of a hard roof significantly disturbed the stability of the surrounding rock in the lower roadway of the study site. This study established a dynamic transmission model of hydraulic fracture mesh and analyzed the influence of the hydraulic fracture mesh parameter on dynamic load attenuation from the perspectives of energy distribution and stress wave attenuation. The SHPB numerical model was established and calibrated based on PFC2D, and the findings were as follows: the hydraulic fracture mesh changes the rock into a discontinuous structure, which hinders the propagation of dynamic load and changes the medium of dynamic load propagation, resulting in part of the dynamic load being reflected and accumulating in the mesh area, causing the rock in the mesh area to break up or making the rock on the side of the hydraulic mesh to slip, which reduces the energy of the dynamic load. Finally, an industrial experiment was conducted on the 10107 working face of Huayuan Coal Mine. Monitoring results showed that the deformation of the roadway sides and roof was reduced by 833 mm and 861 mm, respectively, and the stability of the surrounding rocks of the roadway was effectively improved. Full article

Aiming at the engineering problems of composite roll, pitch, and yaw pose errors of the roadheader body induced by floor undulation and geological variation, as well as insufficient anchoring accuracy caused by the incapability of traditional 1–3-degree-of-freedom (DOF) drilling–anchoring arms in dynamic error compensation during coal mine roadway excavation and bolting, this paper proposes an inverse kinematics solving method for a 5-DOF drilling–anchoring arm based on an improved Deep Deterministic Policy Gradient (DDPG) algorithm. Firstly, the modified Denavit–Hartenberg (MDH) approach is adopted to establish a full-link kinematic model incorporating body pose errors, where the drill rod length, mounting offset, and world coordinate transformation are fully considered. Secondly, an Actor–Critic dual-network architecture tailored for drilling and anchoring tasks is constructed with an 11-dimensional state space and a 5-dimensional action space. The coupling optimization between body pose errors and joint adjustments is realized by designing a hierarchical gradient reward function, a dynamic noise decay exploration strategy, and an optimal state restart mechanism. Finally, 1000 episodes of training and verification are carried out on a Python 3.10 simulation platform. The simulation results reveal that the average end-effector position error of the improved algorithm reaches 0.71 mm, and the deflection angle toward the roof is less than 1°, which outperforms the specified industrial standard. The proposed method realizes real-time compensation for dynamic body pose errors and provides crucial technical support for intelligent excavation and anchoring in underground coal mines. Full article

To address the engineering challenges of asymmetric large surrounding rock deformation and roadway support failure of deep gob-side entry retaining (GER) in the top-coal roadway, the progressive surrounding rock instability mechanism and fracture spatiotemporal evolution characteristics are revealed via theoretical analysis and universal distinct element code (UDEC) Trigon discrete element simulation. Results show that the top coal first undergoes bed separation and tensile failure, followed by backfill corner crushing and bearing capacity loss, which ultimately induces roadway support failure. Using UDEC simulation and mechanical tests, the influences of top-coal thickness, key block B length, backfill performance, and roadway support mode on roadway support stability are systematically clarified. Results indicate that keeping full top coal within the reinforcement zone, reducing key block B length, adopting a backfill width-to-height ratio of 0.45–0.8, a water–cement ratio of 1.5:1, and combining synergistic anchoring with delayed reinforced support can reduce the risk of roadway support failure. An optimized support scheme for the entry is proposed and field-implemented. Monitoring shows that the backfill has a smooth surface; reinforcement ladder beams and steel mesh have no fracture; coal pillar peak stress reaches 5.95 MPa; coal rib bolt load (178 kN) is significantly higher than that in the backfill section (115 kN); and the backfill adapts well to roof rotation and subsidence. The results support the feasibility of the proposed control scheme under the studied geological and engineering conditions and may provide a useful reference for similar GER projects. Full article

To reveal the stress transfer mechanism of overlying coal pillar loads in hard–soft composite floor strata during close-distance coal seam mining, this study comprehensively employed theoretical analysis, similar material simulation, and numerical simulation to systematically investigate the floor stress distribution characteristics under different pillar widths and rock combinations. This study focuses on the instantaneous elastic response of hard–soft composite floor strata under static coal pillar loading, providing a theoretical foundation for pillar design and roadway layout in multi-seam mining. The limitations and future research directions are also discussed. First, based on the elastic layered half-space theory, mechanical models for stress transfer in the floor under narrow coal pillars (unimodal load) and wide coal pillars (bimodal load) were established. Analytical expressions of stress at any point in the floor were derived, and the influence laws of key parameters, including Poisson’s ratio, interlayer spacing ratio, and shear modulus ratio, were clarified. Second, two typical physical models, namely “hard–soft–hard” and “soft–hard–soft”, were constructed. Experimental results revealed that the weak interlayer exhibits a significant “barrier effect” in the hard–soft–hard combination, causing the stress contours to contract in a “bulb-like” shape; whereas the hard rock layer plays a “bearing effect” in the soft–hard–soft combination, leading to stress contours diffusing in a “gourd-like” shape. Furthermore, numerical simulation revealed the controlling mechanisms of rock combination and thickness ratio: the hard rock layer dominates stress concentration, with the peak stress zone evolving from an “inverted water droplet” shape to a “platform” shape as the thickness increases; the soft rock layer governs stress diffusion and buffering. The depth of the plastic zone significantly decreases with increasing hard rock thickness ratio, achieving a reduction of 44.4%. Full article

Severe air leakage in the goaf of gob-side entry retaining panels can intensify oxygen supply to residual coal and consequently increase the probability of coal spontaneous combustion. Taking the 3451S working face of a coal mine in Hebei Province as the engineering case, this study integrated in situ beam-tube monitoring with Fluent-based numerical simulation to characterize the evolution of the spontaneous-combustion three zones and to optimize prevention and control measures. The results demonstrate that the oxidation zone is characterized by an inclined, continuous band-like distribution penetrating the goaf. The simulated oxygen distribution is consistent with the field measurements, demonstrating the reliability of the established numerical model. The ventilation pattern markedly affects the air-leakage flow field and oxygen concentration distribution, and the Y-type ventilation mode exhibits a higher spontaneous-combustion risk. When the air-volume ratio between the 3451S haulage roadway and the gob-side retained entry is adjusted to 3:1, the oxidation-zone area decreases by approximately 11%. A combined control strategy involving cement-blanket and polymer-spraying leakage sealing, together with precise nitrogen injection, is then proposed to improve the goaf oxygen environment. At a nitrogen-injection rate of 600 m³/h, the oxidation-zone area is reduced by 11,160 m² and the CO concentration remains stable at approximately 4.9 ppm, providing field evidence for improved fire-prevention performance. These results support the design of targeted spontaneous-combustion control strategies for gob-side entry retaining goafs. Full article

To improve the stability of gob-side entry in the mining of extra-thick coal seams, we examined the field practice of reserving a narrow coal pillar with a width of 8 m in a 17 m thick coal seam. A combination of roof directional hydraulic fracturing and pouring concrete to consolidate the coal pillars was proposed and applied to reduce the deformation of the gob entry. First, roof directional hydraulic fracturing inhibits the vertical stress transmission to the key roof strata, and it transfers more vertical stress to the gob and reduces the lateral abutment stress in the roof. Subsequently, the narrow coal pillar is strengthened with a reinforced concrete wall, forming a strong–weak coupled bearing structure capable of bearing the overburden load, and the higher stiffness of the reinforced concrete wall effectively resists the lateral deformation of the coal pillar into the roadway. Additionally, the feasibility of this application was verified by comparing the results with the roadway convergence for a 43 m coal pillar on site. The results show that the maximum convergence, stability time, and advanced influence range were all significantly decreased by the proposed method, and the gob-side entry stability was improved. The proposed method and the results obtained provide a valuable reference for mining in similar conditions. Full article

To overcome the deformation and failure of surrounding rock in bottom-driven roadways within thick coal seams, this paper proposes a cooperative support theory for the sides and roof of such roadways in deep thick coal seams, based on existing support theories and technologies. The haulage roadway of the 2201 working face in the Yingpanhao Coal Mine is taken as the engineering prototype. Using the proposed theory, three optimized support schemes are developed. Numerical simulations are conducted to compare the deformation and failure behavior of roadway surrounding rock under the original support scheme and the three optimized schemes. The optimal scheme identified by simulation is then implemented in field engineering. The results show that, relative to the original scheme, roof subsidence is reduced by 51.99 mm, 43.83 mm, and 21.41 mm for Optimized Schemes 1, 2, and 3, respectively, corresponding to reductions of approximately 39.71%, 33.48%, and 16.35%. Under the three optimized schemes, the convergence of the two sidewalls decreases from 480.21 mm to 157.73 mm, 250.84 mm, and 424.24 mm, i.e., reductions of about 67.15%, 47.76%, and 11.66%, respectively. Under the original support scheme, the vertical stress concentration zone is located approximately 5.4 m from the roadway side. Under the three optimized schemes, this distance is reduced to 3.6 m, 3.8 m, and 4.8 m, respectively. The extent of the plastic zone is also smaller under the optimized schemes than under the original scheme, with Scheme 1 exhibiting the greatest reduction. Based on a comprehensive comparison, Optimized Scheme 1 is selected as the optimal support scheme. In addition, Scheme 1 improves deformation asymmetry, with the left–right sidewall asymmetry index decreasing from 3.34% to 0.06% and the sidewall–roof imbalance index decreasing from 3.67 to 2.00. Field application further confirms that this scheme substantially reduces roof–floor convergence and sidewall convergence, verifying the feasibility of the proposed cooperative support theory and technology for the sides and roof in deep bottom-driven roadways of thick coal seams. Full article

Coal has abundant bedding and joint structures, and most of it exhibits obvious brittle characteristics, which leads to its easy cracking and failure under mining stress. This easily leads to slab cracking and roof collapse in coal mining faces, as well as large deformations in roadways. On-site grouting of fractured coal bodies can effectively prevent these disasters. To reveal this mechanism, this study has first developed a modified ultra-fine cement grouting material and high-pressure continuous grouting system, and then conducted grouting and uniaxial compression tests on post-peak coal samples. Test results indicate that the post-peak residual bearing capacity of grouted coal specimens can recover to 65~85% of the peak strength of intact raw coal. The pre-peak plastic deformation becomes significant, and the post-peak stage exhibits stable strain softening. Grouting is considered to serve to improve the internal stress state of coal samples, act as a ductile grid skeleton, coordinate their internal deformation, and enhance their post-peak bearing capacity. Full article

To address severe stress concentration, excessive convergence, and instability of the roadside backfill body (RBB) in gob-side entry retaining (GER) under thick and hard roof conditions, this study investigates the control mechanism of main roof fracture position on surrounding rock stability, using the 3⁻¹01 working face of Huoluowan Coal Mine as a case study. A combined approach integrating theoretical analysis, numerical simulation, and field investigation is adopted. A statically indeterminate mechanical model based on masonry beam theory is established to characterize the lateral roof fracture behavior. The deflection and bending moment distributions are derived, and a criterion for fracture position determination is developed based on the maximum bending moment condition. The theoretical results indicate that the natural fracture position is located approximately 9.4–11.2 m inside the gob boundary. Numerical simulations using UDEC Trigon under different fracture positions (−2 m, 1 m, 5 m, and 9 m) show that fracture location significantly affects the mechanical response of GER. Fractures occurring above the roadway or RBB induce large deformation levels and more extensive plastic zones, while gob-side fracture conditions correspond to relatively lower disturbance levels and improved structural stability. The RBB exhibits shear-dominated failure characteristics, and the displacement distribution is non-uniform along height, with larger deformation in the middle-to-upper region. To improve stability, a coordinated control strategy combining anchor cable reinforcement and directional long-distance hydraulic fracturing (HF) is proposed to regulate the main roof fracture position through the formation of artificial weak planes. Field monitoring results show that the maximum displacements of the roof, floor, and ribs are 558 mm, 233.5 mm, and 71.3 mm, respectively, with a convergence ratio of 19.8%. Borehole imaging confirms the development of hydraulic fractures within the designed roof stratum, supporting the effectiveness of the proposed control approach. These results demonstrate that the fracture position of the main roof plays a key role in controlling GER stability, and its regulation provides an effective means for improving roadway performance under complex geological conditions. Full article

The severe deformation and failure of reused roadways due to repeated mining disturbances pose considerable challenges to roadway maintenance. In this study, field measurements were taken at the 13092 reused roadway of Zhaozhuang Coal Mine to determine the deformation characteristics of its surrounding rock. Based on the equation for the plastic zone boundary of a circular roadway under a non-uniform stress field, the distribution characteristics of the plastic zone of the reused roadway under different stress conditions were analyzed, and their associated risk levels were assessed. Furthermore, the distribution characteristics of the plastic zone at different locations under primary and secondary mining, the non-uniform evolution of the mining-induced stress field, and the deformation behavior of the surrounding rock under repeated mining disturbances were investigated using FLAC3D 7.0 numerical simulations. The following conclusions were reached: Repeated mining is the primary cause of severe deformation and instability of the surrounding rock in the reused roadway, and there are marked spatial differences in severe deformation between different locations. Under a non-uniform stress field, the distribution of the plastic zone in the surrounding rock varies markedly with the ratio of the maximum principal stress to the minimum principal stress (λ). Specifically, as the ratio λ grows, the shape of the plastic zone evolves from circular to elliptical and ultimately to a butterfly shape. Once the plastic zone becomes butterfly-shaped, further increases in λ cause rapid expansion of the plastic zone. Under repeated mining disturbances, the plastic zone of the surrounding rock can be regarded as a superposition of plastic zones induced by multiple mining activities. The stress distribution of the surrounding rock is markedly different at different locations. The ratio λ, which is the dominant factor responsible for the distinct deformation and failure modes observed in different regions, also varies spatially. Based on these findings, a grouting reinforcement control technique was proposed. The grouting timing, grouting pressure, and grouting radius were determined to formulate a practical grouting control scheme for field application. Field tests demonstrate that the proposed grouting control method effectively covers the deformation range of the surrounding rock and achieves satisfactory control performance. The results of this study are expected to provide a valuable reference for grouting reinforcement control in similar mining scenarios. Full article

This study investigates the fracture development and caving mechanisms in longwall coal mining using powered roof supports (PRSs), simulated with the Finite–Discrete Element Method (FDEM) in Geomechanica’s Irazu platform. It is presented as an application study demonstrating the ability of this established FDEM platform to simulate fracture evolution and caving in a longwall environment, rather than as the development of a new model, criterion, or algorithm. A numerical model of a longwall face, including canopy, shield, and base components, was constructed in SolidWorks and imported for simulation. Fractured and intact coal zones were defined, and boundary conditions were applied to represent the mining advance sequence. Stress redistribution, fracture initiation, and subsequent caving behind supports were analyzed both with Irazu’s native tools and through advanced visualization in ParaView. Results revealed that fracture initiation occurs at the roof–canopy interface, propagating towards the gob and floor, eventually forming an elliptical caving pattern. Stress analysis highlighted critical loading at both canopy–roof and base–floor contacts, consistent with patterns reported in field and theoretical studies. Energy maps reveal elastic energy buildup prior to first break and its stepwise release during fracture propagation and caving. This application demonstrates the potential of FDEM to capture both the mechanical response of supports and the evolution of coal fractures, offering valuable insights for optimizing support design and ensuring roadway stability. These findings contribute to improved prediction and management of strata behavior in underground coal mining, bridging numerical modeling with practical engineering applications. Full article

The synergistic utilization of post-mining spaces and geothermal energy through underground seasonal thermal energy storage (USTES) provides a promising pathway for sustainable heating and the low-carbon redevelopment of mining regions. To advance the thermal management and reveal the thermo-hydraulic evolution patterns within these repurposed environments, this study proposes an integrated approach that utilizes post-mining roadways as heat storage reservoirs, within the scope of a single idealized case study. A comprehensive USTES heating system model was established to systematically evaluate operational characteristics and environmental impacts under diverse conditions assuming homogeneous rock properties and idealized thermal boundaries. Results demonstrate that the surrounding ground temperature and the low thermal conductivity of the rock mass contribute to limiting heat dissipation and maintaining stable seasonal storage performance. For a roadway with a 20,000 m³ water storage capacity and an optimal 3900 m² solar collector area, the system successfully satisfies the thermal demand of 30,000 m² of building area. The configuration achieves 1239 MWh of cumulative heat storage over a 245-day cycle, maintaining a direct heating-to-heat-pump-upgraded heating ratio of 1.02. Furthermore, the implementation of variable-frequency thermal management strategies demonstrates remarkable economic and environmental superiority, yielding a 35.8% cost reduction compared to coal-fired heating, an overall energy saving rate of 77.5% relative to electric heating systems and a 13.5% decrease in CO₂ emissions relative to gas-fired systems. This research provides fundamental design parameters for the synergistic exploitation of mineral and geothermal resources, advancing the development of green heating and the sustainable utilization of post-mining spaces. Full article

Accurate modeling of underground mine ventilation requires reliable estimates of roadway aerodynamic resistance. Conventional methods, based on geometric surveys or barometric pressure measurements, have notable limitations, including neglect of local losses, high time requirements, and sensitivity to environmental disturbances. This paper introduces a two-point flow-based method for determining roadway resistance directly from in situ measurements. Using basic instruments (anemometer, differential manometer, thermometer, and hygrometer), measurements are taken at two points along a straight airway. The pressure drop is calculated via the Bernoulli equation, allowing resistance to be determined without relying on geometric data or friction assumptions. This method captures both frictional and local losses inherently. Field testing in five roadway sections of a coal mine in Vietnam yielded resistance values 10–15 times higher than theoretical friction-only estimates, highlighting the importance of local losses. The equivalent cross-sectional areas back-calculated from the measured resistance using literature-based friction factors showed consistency with geometric survey data (typical deviation 3–6%), indicating internal coherence of the measurements. Full validation against independent barometric or CFD methods remains a subject of ongoing research. The method is simple, fast, minimally disruptive, and compatible with ventilation modeling tools. It provides a practical and accurate alternative for resistance estimation under real operating conditions. Full article

Underground gas control is a critical link in coal mine safety production, and drilling robots serve as the core equipment for gas extraction drilling operations. However, the autonomous locomotion technology of coal mine drilling robots has long been constrained by the unstructured underground environment and the limitations of existing navigation schemes, which restrict their intelligent application. To address this bottleneck, this paper conducts systematic research on key autonomous navigation technologies for coal mine drilling robots operating in narrow underground working faces, focusing on their practical operational requirements. First, a hardware scheme complying with coal mine safety standards is selected, the hardware structure and sensor layout are optimized via digital modeling, and the software interface and data interface format of the navigation system are designed. Second, an innovative 3D point cloud-based offline obstacle avoidance algorithm is proposed, which integrates a terrain analysis module, a local path planning method with maximum arrival probability, a Bézier curve-based trajectory library generation strategy, and a trajectory index construction method. Finally, simulation experiments, ground-simulated roadway field tests, and underground coal mine field experiments are performed to validate the proposed system. Experimental results demonstrate that the constructed autonomous navigation system enables smooth and safe autonomous locomotion and fixed-point parking of drilling robots, with an average parking error lower than 0.17 m, and can effectively avoid obstacles in complex environments. This research provides crucial technical support for the intelligent advancement of coal mine drilling robots. Full article