Search Results (606)

To enhance the understanding of dust diffusion laws in tunnel blasting operations of metal mines and determine optimal ventilation dust removal times, a scaled physical model of a metal mine tunneling face under the China Zijin Mining Group was established based on field measurements. Numerical simulation was employed to investigate airflow movement and dust migration in the tunneling roadway, and the fundamental features of airflow field and dust diffusion laws after tunnel blasting operations in the fully mechanized excavation face were revealed. The effects of three main factors included airflow rate (Q), ventilation distance (S), and tunnel length (L) on the dust removal time after tunnel blasting operations were investigated based on the orthogonal design method. Results indicated that reducing the dust concentration in the roadway to 10 mg/m³ required 53 min. The primary factors influencing dust removal time, in order of significance, were determined to be L, Q, and S. The lowest dust concentration occurs when the ventilation distance was 25 m. A predictive model for dust removal time after tunnel blasting operations was developed, establishing the relationship between dust removal time and the three factors as T = 20.7Q^−0.73S^0.19L^0.86. Subsequent on-site validation confirmed the high accuracy of the predictive model, demonstrating its efficacy for practical applications. This study contributes a novel integration of orthogonal experimental design and validated CFD modeling to predict ventilation dust removal time, offering a practical and theoretically grounded approach for tunnel ventilation optimization. Full article

Roadway deformation failure is often related to the presence of weak structural planes (WSPs) in the surrounding rock mass. Especially in coastal mining environments, WSP-induced deformation can create pathways that connect faults with seawater, accelerating groundwater seepage and inrush hazards. This study employs an optimized Finite–Discrete Element Method (Y-Mat) to simulate WSP-driven fracture evolution, introducing an elastoplastic failure criterion and enhanced contact force calculations. The results show that the farther the WSP is from the roadway, the lower its influence; its existence alters the shape of the plastic zone by lengthening the failure zone along the fault direction, while its angle changes the shape and location of the failure zone and deflects fracture directions, with the surrounding rock between the roadway and WSP suffering the most severe failure. The deformation failure of roadway surrounding rock is influenced by WSPs. Excavation unloading reduces the normal stress and shear strength in the weak structural plane of surrounding rock, resulting in slip and deformation. Additionally, WSP-induced fractures act as groundwater influx conduits, especially in fault-proximal roadways or where crack angles align with hydraulic gradients, so mitigation in water-rich mining environments should prioritize sealing these pathways. The results provide a theoretical basis for roadway excavation and support engineering under the influence of WSPs. Full article

Addressing the stability control challenges of roadways with composite roofs in the No. 34 coal seam of Donghai Mine under high-strength mining conditions, this study employed integrated methodologies including laboratory experiments, numerical modeling, and field trials. It investigated the mechanical response characteristics of the composite roof and developed a synergistic control system, validated through industrial application. Key findings indicate significant differences in mechanical behavior and failure mechanisms between individual rock specimens and composite rock masses. A theoretical “elastic-plastic-fractured” zoning model for the composite roof was established based on the theory of surrounding rock deterioration, elucidating the mechanical mechanism where the cohesive strength of hard rock governs the load-bearing capacity of the outer shell, while the cohesive strength of soft rock controls plastic flow. The influence of in situ stress and support resistance on the evolution of the surrounding rock zone radii was quantitatively determined. The FLAC^3D strain-softening model accurately simulated the post-peak behavior of the surrounding rock. Analysis demonstrated specific inherent patterns in the magnitude, ratio, and orientation of principal stresses within the composite roof under mining influence. A high differential stress zone (σ₁/σ₃ = 6–7) formed within 20 m of the working face, accompanied by a deflection of the maximum principal stress direction by 53, triggering the expansion of a butterfly-shaped plastic zone. Based on these insights, we proposed and implemented a synergistic control system integrating high-pressure grouting, pre-stressed cables, and energy-absorbing bolts. Field tests demonstrated significant improvements: roof-to-floor convergence reduced by 48.4%, rib-to-rib convergence decreased by 39.3%, microseismic events declined by 61%, and the self-stabilization period of the surrounding rock shortened by 11%. Consequently, this research establishes a holistic “theoretical modeling-evolution diagnosis-synergistic control” solution chain, providing a validated theoretical foundation and engineering paradigm for composite roof support design. Full article

To address the limitations of traditional hardened concrete road surfaces in coal mine tunnels, which are prone to damage and entail high maintenance costs, this study proposes using modular concrete blocks composed of fly ash and coal gangue as an alternative to conventional materials. These blocks offer advantages including ease of construction and rapid, straightforward maintenance, while also facilitating the reuse of substantial quantities of solid waste, thereby mitigating resource wastage and environmental pollution. Initially, the mineral composition of the raw materials was analyzed, confirming that although the physical and chemical properties of Liangshui Well coal gangue are slightly inferior to those of natural crushed stone, they still meet the criteria for use as concrete aggregate. For concrete blocks incorporating 20% fly ash, the steam curing process was optimized with a recommended static curing period of 16–24 h, a temperature ramp-up rate of 20 °C/h, and a constant temperature of 50 °C maintained for 24 h to ensure optimal performance. Orthogonal experimental analysis revealed that fly ash content exerted the greatest influence on the compressive strength of concrete, followed by the additional water content, whereas the aggregate particle size had a comparatively minor effect. The optimal mix proportion was identified as 20% fly ash content, a maximum aggregate size of 20 mm, and an additional water content of 70%. Performance testing indicated that the fabricated blocks exhibited a compressive strength of 32.1 MPa and a tensile strength of 2.93 MPa, with strong resistance to hydrolysis and sulfate attack, rendering them suitable for deployment in weakly alkaline underground environments. Considering the site-specific conditions of the Liangshuijing coal mine, ANSYS 2020 was employed to simulate and analyze the mechanical behavior of the blocks under varying loads, thicknesses, and dynamic conditions. The findings suggest that hexagonal coal gangue blocks with a side length of 20 cm and a thickness of 16 cm meet the structural requirements of most underground mine tunnels, offering a reference model for cost-effective paving and efficient roadway maintenance in coal mines. Full article

Under deep, high-intensity mining conditions, a high mineral pressure develops at the working face, which can easily cause floor heave deformation of the roadway. In this paper, with the geological conditions of Buertai coal mine as the background, through on-site monitoring and numerical simulation, the mechanism of strong dynamic pressure roadway floor heave is clarified and a cooperative control method for roadway floor heave deformation is proposed. The main conclusions are as follows: (1) The overall strength of the floor of this strong dynamic pressure roadway is low, which can easily cause roadway floor heave, and on-site multivariate monitoring of the mine pressure is carried out, which clarifies the evolution law of the mine pressure of the mining roadway and along-the-airway roadway. (2) Combined with FLAC3D numerical simulation software, we analyze the influence of coal seam depth and floor lithology on the stability of the roadway floor and find that both have a significant influence on the stability of the roadway. Under the condition of high-intensity mining, the floor will deteriorate gradually, forming a wide range of floor heave areas. (3) Based on the deformation and damage mechanism of the roadway floor, a synergistic control method of “roof cutting and pressure relief + floor anchor injection” is proposed and various technical parameters are designed. An optimized design scheme is designed for the control of floor heave in Buertai coal mine. Full article

Roof water inrush accidents in coal mine driving roadways occur frequently in China, accounting for a high proportion of major coal mine water hazard accidents and causing serious losses. Aiming at the lack of research on the mechanism of roof water inrush in driving roadways and the difficulty of predicting water inrush accidents, this paper constructs a local damage criterion for coal–rock mass and a seepage–fracture coupling model based on peridynamics (PD) bond theory. It identifies three zones of water-conducting channels in roadway surrounding rock, the water fracture zone, the driving fracture zone, and the water-resisting zone, revealing that the damage degree of the water-resisting zone dominates the transformation mechanism between delayed and instantaneous water inrush. A discriminant function for the effectiveness of water-conducting channels is established, and a single-index prediction and evaluation system based on damage critical values is proposed. A “geometry damage” dual-control water inrush prediction model within the PD framework is constructed, along with a non-local action mechanism model and quantitative prediction method for water inrush. Case studies verify the threshold for delayed water inrush and criteria for instantaneous water inrush. The research results provide theoretical tools for roadway water exploration design and water hazard prevention and control. Full article

In order to examine the fracture development law of overlying strata in goafs and to reasonably lay out a high gas-drainage roadway under gob-side entry retaining with roadside filling, the 91–105 working face of the Wangzhuang Coal Mine was selected as the engineering case study. The failure laws and fracture development characteristics of the overlying strata in both the strike and dip directions using gob-side entry retaining and roadside filling were studied through rock mechanic tests and PFC numerical simulations. The optimal layout of the high gas-drainage roadway was determined through theoretical analysis and coupled Fluent–PFC numerical simulations, and on-site monitoring was conducted to evaluate the extraction effects. The results indicate that the first weighting interval of the 91–105 working face was 40 m, while the periodic weighting interval was approximately 14 m. The height of the falling zone was 14.4 m, and the height of the gas-conducting fracture zone was 40.7 m. In the dip direction, compared with coal pillar retaining, gob-side entry retaining with roadside filling formed an inverted trapezoid secondary breaking zone above the retaining roadway. Using this method, the span of the separation zone increased to 30 m, and the collapse angle decreased to 52°, resulting in a shift in the separation zone—the primary space for gas migration—toward the goaf. It was determined that the optimal location of the high gas-drainage roadway was 28 m above the coal roof and 30 m horizontally from the return air roadway. Compared with the 8105 working face, this position was 10 m closer toward the goaf. On-site gas extraction monitoring data indicate that, at this optimized position, the gas concentration in the high gas-drainage roadway increased by 22%, and the net gas flow increased by 18%. Full article

To elucidate evolutionary characteristics of the surrounding rock failure mechanism in a double-roadway layout, this work is grounded on in the research context of the Jinjitan Coal Mine, focusing on the deformation and failure mechanisms of double roadways. This paper addresses the issue of resource wastage resulting from the excessive dimensions of coal pillars in prior periods by employing a research methodology that integrates theoretical analysis, numerical simulation, and field monitoring to systematically examine the movement characteristics of overlying rock in the working face. On that basis, the size of coal pillar is optimized. The advance’s stress transfer law and deformation distribution characteristics of the return air roadway and transport roadway are studied. The cause of the asymmetric deformation of roadway retention is explained. A differentiated design is conducted on the support parameters of double-roadway bolts and cables under strong dynamic pressure conditions. The study indicates that a 16 m coal pillar results in an 8 m elastic zone at its center, balancing stability with optimal resource extraction. In the basic top-sloping double-block conjugate masonry beam structure, the differing stress levels between the top working face’s transport roadway and the lower working face’s return air roadway are primarily due to the varied placements of key blocks. In the return air roadway, floor heave deformation is managed using locking anchor rods, while roof subsidence is controlled with a constant group of large deformation anchor cables. The displacement of surrounding rock increases under the influence of both leading and lagging pressures from the previous working face, although the change is minimal. There is a significant correlation between roadway deformation and support parameters and coal pillar size. With a 16 m coal pillar, differential support of the double roadway lowers the return air roadway deformation by 30%, which improves the mining rate and effectively controls the deformation of the roadway. Full article

A narrow coal pillar in double-roadway excavation can solve the problem of working face connection and improve the resource recovery rate, but narrow coal pillars are affected by the full mining stress. Taking the 2109 double-roadway excavation of Qingwa Coal Mine as the engineering background, the roof mechanical structure model of a narrow coal pillar in a double-roadway excavation layout was established, and the bearing characteristics of different coal pillar widths under the influence of full dynamic pressure were studied. The narrow coal pillar retention width was obtained and tested through field industrial experiments. The main research results were as follows: (1) The relationship between the coal pillar bearing load and the immediate roof length was deduced, and the bearing stress of the coal pillar was divided into the steep decline stage, the transition stage, and the stabilization stage. The coal pillar within the width of the stabilization stage has a certain strength surplus capacity. (2) Under the influence of full dynamic pressure, the 5~7 m coal pillar yielded to failure, and the coal pillar of 8 m and above had a certain residual bearing capacity, compared with the first mining. After the second mining, the elastic zone in the coal pillar of each width was significantly reduced; there was no elastic grid in the coal pillar of 5 m and 6 m in width, and the grid area and proportion of the elastic zone of the coal pillars with widths of 7 m and above were very low. The optimal retention width of the narrow coal pillar was determined to be 8 m. (3) Under the influence of repeated mining, the impact of first mining on the roadway displacement of the roof and floor plate was greater, followed by the solid coal side, which had less impact on the coal pillar side. The secondary mining had a greater impact on the floor, followed by the coal pillar side and the solid coal side, which had little impact on the roadway roof. This paper also provides a significant reference for the retention of narrow coal pillars in double-roadway excavation. Full article

To investigate the degradation mechanisms of the surrounding rock in abandoned mine roadways used for oil storage, this study combined uniaxial compression tests with digital image correlation (DIC), scanning electron microscopy (SEM), and other techniques to analyze the evolution of the rock mechanical properties under the coupled effects of oil–water soaking and initial damage. The results indicate that oil–water soaking induces the loss of silicon elements and the deterioration of microstructure, leading to surface peeling, crack propagation, and increased porosity of the sample. The compressive strength decreases linearly with the soaking time. Acoustic emission (AE) monitoring showed that after 24 h of soaking, the maximum ringing count rate and cumulative count decreased by 81.7% and 80.4%, respectively, compared to the dry state. As the liquid saturation increases, the failure mode transitions from tension dominated to shear failure. The synergistic effect of initial damage and oil–water erosion weakens the rock’s energy storage capacity, with the energy storage limit decreasing by 45.6%, leading to reduced resistance to external forces. Full article

It has been found in engineering practice that the degree of rockburst risk increases when roadway excavation occurs near the stratigraphical boundary of different lithologies. This study uses the 1276 m deep-buried roadway of a lead–zinc mine in Yunnan, China, as its engineering background. Based on a numerical analysis of this case, it investigates the mechanical behavior of surrounding rocks in different lithological formations and explores the causes of excavation-induced rockburst. Additionally, by changing the excavation strategy in a numerical simulation, the influence of the direction of roadway excavation on the degree of rockburst risk in the construction of different lithological formations is assessed. The results are summarized as follows: (1) When the tunnel passes from the C₁b stratum (limestone) to the D₃zg stratum (dolomite), an abnormal stress zone forms in the roof rock strata of the D₃zg stratum (the lower plate of the stratum boundary). The rockburst risk level was evaluated by introducing the numerical rockburst index in this abnormal stress zone, which aligns closely with on-site rockburst investigation results. The rockburst risk is the greatest in the abnormal stress zone, which provides an external energy storage environment for the development of rockburst disasters. (2) Near the stratum boundary, the rockburst risk level when excavating from the D₃zg stratum to the C₁b stratum is greater than that when excavating from the C₁b stratum to the D₃zg stratum. The direction of tunnel excavation significantly affects the rockburst risk level during construction that crosses different lithological strata. These findings can provide a theoretical basis for the construction design of similar underground projects. Full article

The escalating disasters caused by the movement of shallow buried strata in China’s western mining areas are increasingly threatening operational safety. A critical issue in ensuring secure mining practices in these areas is the creep failure of weakly cemented soft rock under low-stress conditions. The unique particle contact mechanisms in weakly cemented mudstone, combined with the persistence of the cemented materials and the particulate matter they form, lead to mechanical responses that differ significantly from those of typical soft rocks during loading. Building on an existing multivariate linear regression equation for new similar materials, this study developed qualified weakly cemented medium similar materials, offering appropriate materials for long-term creep tests of weakly cemented formations. This was accomplished by employing orthogonal proportioning tests. The principal findings of our investigation are as follows: The new, similar material exhibits low strength and prominent creep characteristics, accurately simulating weakly cemented materials in western mining areas. The concentration of rosin–alcohol solution has a measurable impact on key parameters, such as σ_c, E, and γ in the weakly cemented similar material specimens. Furthermore, the creep characteristics of the specimens diminish progressively with an increase in the proportion of iron powder (I) and barite powder (B). The material was applied to a similar indoor model test simulating the weakly cemented material surrounding the auxiliary haulage roadway in Panel 20314 of the Gaojialiang Coal Mine, with speckle analysis employed for detailed examination. The experimental findings suggest that both the conventional mechanical properties and long-term creep characteristics of the material align with the required specifications, offering robust support for achieving optimal outcomes in the similar model test. Full article

With the increasing depth of mining operations, the geological conditions of deep roadways have become increasingly complex. Among these complexities, the issues of fractured zones and groundwater are particularly critical, significantly contributing to the reduced stability of the surrounding rock. This study focuses on the challenging support problem associated with water-bearing fractured surrounding rock in the Y1# belt conveyor roadway of the Wengfu phosphate mine. Through theoretical calculation, laboratory testing, numerical simulation, and field monitoring, the range and displacement of the broken zone in the broken surrounding rock roadway are studied and analyzed. The results show that the physical and mechanical properties of the broken surrounding rock mass are weakened by water, and the range and deformation of the broken zone of the surrounding rock of the water-bearing roadway increase. In response to the failure characteristics of the water-bearing fractured surrounding rock in the Y1# belt conveyor roadway, an optimized support scheme was developed. A combined support system of steel arch frames and localized grouting was proposed to enhance the control of the surrounding rock. Field monitoring data confirmed that the optimized support scheme achieved satisfactory control effectiveness, effectively addressing the stability challenges posed by water-bearing fractured rock masses. Full article

As a part of the mining-induced stress redistribution process during coal mining, the repeated loading and unloading process with increasing peak stresses will cause more severe deformation and damage to mining roadways, which is different from the findings in other underground engineering practices. Consequently, cyclic triaxial compression tests with increasing amplitudes were carried out to investigate the mechanical behavior, acoustic emission (AE) characteristics, and damage evolution of coal materials. It is found that peak deviatoric stress and axial residual strain at the failure of coal specimens increase with increasing confining pressures, while the changes in circumferential strain are not obvious. Moreover, the failure patterns of coal specimens exhibit shear failure due to the constraint of confining pressures while some local tensile cracks occur near the shear bands at both ends of the specimens. After that, the damage evolution of coal specimens was analyzed against the regularity of AE counts and energies to develop a damage evolution model. It is concluded that the damage evolution model can not only quantify the deformation and failure process of the coal specimens under cyclic loads with increasing amplitudes but also takes into account both the initial damage due to natural defects and the induced damage by the cyclic loads in previous cycles. Full article

This study focuses on how rocks respond mechanically and how to keep them stable when soft rock roadways are under deep tectonic stress. It does this through a combination of theoretical analysis, numerical simulations, and field applications. We created a mechanical model of roof strata to calculate how much they would bend under both horizontal tectonic stress and their weight. This modeling helped us determine the critical yield limits. A systematic study of the angle θ between the direction of tectonic stress and the axis of the roadway showed that the concentration of horizontal stress on the roof gets stronger as θ increases, while the vertical stress on the sidewalls slowly gets weaker. The main sign of surrounding rock failure is shear damage that is most severe at the roof, floor, and shoulder angles. The maximum plastic zone depth occurs at θ = 90°. Studies that looked at both gob-side and along-roadway stages found that the two types of failure were very different, characterized by severe roof damage during roadway advancement and pronounced coal pillar instability in gob-side conditions. Based on these results, targeted support strategies were successfully used in field engineering to control deformations and provide both theoretical foundations and practical solutions for stabilizing deep soft rock roadways under tectonic stress. Full article