Search Results (122)

Spacing design for group cable bolt systems remains largely empirical and rarely considers stress interaction and displacement overlap together. This study develops a dual-index interaction framework for two representative cable bolt configurations in deep stope roofs. Mindlin’s semi-infinite body solution and Kelvin’s infinite body solution were combined with a non-uniform interfacial shear stress distribution to model shallow fully grouted and deep end-anchored systems, respectively. The analytical trends were examined using FLAC3D, and the field applicability of the selected spacing scheme was assessed through an industrial test at the Fankou Lead–Zinc Mine. The results show that the fully grouted configuration is strongly affected by the free surface and full-length load transfer, whereas interaction in the end-anchored configuration is concentrated around the deep bonded section. The stress interaction coefficient η provides the primary screening measure for a reference lower spacing bound, while the displacement interaction coefficient α identifies residual displacement overlap. Both are local field interaction indices rather than measures of individual cable capacity or global system stiffness. Using η_ref = 0.9 as an engineering tolerance, stress interaction becomes limited at approximately s/D = 30 for the end-anchored configuration, whereas the fully grouted configuration enters a relatively stable interaction–attenuation stage at approximately s/D = 40. Considering both configurations, s/D ≈ 40 is adopted as a reference lower bound, corresponding to 1.6 m for a 40 mm borehole. The field scheme used a spacing of 1.8 m (s/D ≈ 45) and produced a maximum measured roof displacement of 27.6 mm, with no evident roof fall, cable breakage, or anchorage pull-out. Because characteristic rock mass heterogeneity is not explicitly represented and only one field spacing was tested, the proposed spacing ratio should be regarded as condition-specific rather than universal. Full article

On 22 August 2025, a partially erected section of the Jianzha Yellow River Super Bridge collapsed during cable-tensioning operations, causing 13 fatalities and leaving 3 persons missing. The bridge was being designed as a 366 m main-span continuous steel truss arch, which was erected via cantilever construction supported by a temporary cable-supported fastening system. This document-based forensic engineering synthesis uses the published official investigation report and independently accessed design and technical literature. No independent site inspection, component examination, raw data review, original video review, or validated nonlinear collapse reconstruction was undertaken; the exact instant and progressive development of splice failure are not visible in the report-reproduced chronology and remain unresolved. The official investigation identified bolt-group shear failure and separation at a tower-top distribution beam splice as the initiating physical event following second-stage tensioning of the No. 4 tie cable. These accident-specific findings are not redetermined in the present study; its original contribution is the evidence-status separation and engineering synthesis of the reported evidence through construction-stage load-path reconstruction, connection mechanics assessment, quantitative consistency checks, robustness interpretation, and safety barrier analysis. The reported bolt deficiencies are examined through a limited author-derived normalization combining the material-strength and threaded shear-plane effects at the individual-fastener level; this indicator is used only as a consistency check and is not interpreted as bolt-group or complete splice capacity. Enlarged and irregular holes, missing fasteners, and unauthorized field modifications are interpreted as further impairing bolt-group load sharing. The evidence-constrained load-path assessment indicates that the officially identified splice separation would have interrupted a primary temporary support path while the permanent arch action had not yet developed. Visible cantilever descent was followed by cable rupture, arch-rib fracture, and extensive collapse within approximately 10 s. A qualitative fault-tree and bow-tie analysis organizes the reported procurement, fabrication, design, installation, inspection, monitoring, and governance deficiencies and identifies high-leverage preventive, verification, and consequence-limiting barrier pathways. The findings support consequence-based classification, independent verification, formal hold points, robustness assessment, and personnel exclusion for safety-critical temporary works. Full article

Targeting the rock burst hazard induced by the hard roof key stratum during deep mining at the Mengcun Coal Mine in the Binchang mining area, this study takes the No. 403109 working face as the engineering background and systematically investigates the rockburst prevention mechanism and effectiveness of ground hydraulic fracturing through theoretical analysis, UDEC numerical simulation, and surface microseismic monitoring. The results indicate that fracturing pre-weakens the overlying key stratum, transforming its load-bearing mode from a long-beam rigid support to a segmented flexible support. This significantly reduces the cantilever length, lowers the accumulation of elastic strain energy, and enables flexible load transfer and stress redistribution in the overburden. Numerical simulations reveal that after fracturing, the breakage timing of the key stratum advances, the fragmentation size decreases, and the over-burden movement shifts from stepwise fracturing to sequential caving, with the stress concentration zone substantially narrowed. In the field, a total of 44 fracturing stages were implemented in wells MC-05L and MC-06L, creating a fracture network with an average fracture length of 317 m and an average fracture height of 55 m, achieving an effective stimulated volume ratio of 86.7%. During the mining period, microseismic events exhibited a median energy of only 868.14 J, characterized by high frequency and low energy. The average weighting interval was 13.69 m, the peak coal stress was controlled within 5.0–6.7 MPa, and the loads on roadway bolts and cables remained within safe limits. This study validates the source-control effect of ground hydraulic fracturing on working faces with strong rock burst risks in deep mining, providing a theoretical basis and engineering reference for mines with analogous conditions. Full article

The underground powerhouse of a hydropower station in Northwest China features a large height-to-span ratio and complex geological conditions, posing critical challenges for surrounding rock stability. This study employs a systematic framework of “parameter inversion–stability analysis–support optimization”. The main contributions are: (1) A forward-backward analysis method integrating monitoring data, numerical calculation, and parameter optimization was used to invert the physical and mechanical parameters of the surrounding rock, establishing a practice-consistent numerical model. (2) Considering complex geological conditions from a prior collapse, systematic analyses of deformation characteristics, stress distribution, and overall stability during subsequent bench excavation were conducted, revealing evolutionary patterns of deformation, reproducing the collapse mechanism, and evaluating rock mass safety. (3) An optimized reinforcement scheme was proposed, involving additional anchor cables at arch shoulders and two anchor bolts on each sidewall (Sidewalls 2), with comparative analysis confirming its feasibility. Key findings: (i) Based on the inversion of monitoring data, the obtained physical and mechanical parameters of the surrounding rock can effectively reflect the actual characteristics of the rock mass and align with monitoring trends. (ii) Stability analysis of subsequent layered excavation, accounting for prior collapse impacts, shows that while deformation at key points continued to increase, it remained below critical thresholds, maintaining overall stability—prestressed anchor cables significantly controlled deformation. (iii) The optimized support scheme yields comparatively favorable outcomes with respect to the containment of surrounding rock displacement and the internal forces within the supporting. These outcomes provide valuable references for the design and construction of similar underground powerhouses. Full article

With deep coal mining in China, high in situ stress frequently causes severe floor deformation, bolt-cable support failure, and excessive floor heave, which critically threaten mine safety. In this study, we use physical experiments, numerical simulation, and theoretical analysis to explore how hydraulic fractures with different azimuth angles affect stress transfer in roadways under floor dynamic pressure. Prefabricated fractures simulate weak planes induced by hydraulic fracturing. Uniaxial compression tests and PFC2D fluid–solid coupling simulations analyze mechanical properties, failure modes, acoustic emission behavior, and stress distribution. Results show that fracture azimuth significantly controls rock damage and failure modes. As the angle increases from 0° to 90°, failure changes from gradual degradation to sudden instability. Peak strength first decreases then increases, reaching the minimum at 22.5°, while roadway damage is minimal at 45°. Small-angle fractures lead to shear failure with clear precursors, and large-angle fractures cause sudden tensile failure. Hydraulic fractures form directional stress-relief zones and enable effective stress transfer and pressure relief. The results support parameter optimization of hydraulic fracturing and stability control for deep roadways under floor dynamic pressure. Full article

To determine a rational, narrow coal-pillar width and support scheme for gob-side entry driving in thick coal seams, the 4904 return airway of the No. 9 coal seam at Zhongshui Coal Mine was investigated using limit-equilibrium analysis, FLAC3D numerical simulation, and field monitoring. The theoretical pillar width was calculated as 6.73–7.90 m, and sensitivity analysis showed that the selected 7 m pillar remained within the reasonable range under variations in key empirical and mechanical parameters. Numerical results indicated that a 7 m pillar could form a relatively complete central load-bearing core and effectively control surrounding-rock deformation, whereas further increasing the pillar width provided limited additional deformation reduction but caused greater coal loss. Compared with the 7 m pillar, the 9 m and 11 m schemes would cause additional coal losses of approximately 9.09 × 10³ t and 1.82 × 10⁴ t, respectively. A hierarchical synergistic support scheme consisting of high-strength bolts, long and short roof cables, and pillar-rib reinforcement cables was proposed. Compared with the equal-length roof-cable-plus-bolt scheme, the proposed scheme provided better control of roof subsidence and rib convergence. Field monitoring showed that roadway deformation gradually stabilized after support installation and remained within a controllable range under the monitored engineering conditions. Full article

To address the large deformation and instability of gob-side entry roofs in soft, thick coal seams induced by residual cavities left by hydraulic flushing, the 1609 working face of Jiulishan Coal Mine was selected as the engineering background. Field investigation, numerical simulation, and industrial field testing were combined to investigate the deformation and failure characteristics of surrounding rock and the corresponding control technology for gob-side entries with cavity-bearing roofs. The results indicate that residual cavities created by hydraulic flushing disrupt the stress transfer path within the roof, causing stress field distortion and expansion of tensile stress zones, thereby significantly weakening the roof load-bearing capacity. As the cavity size increases, the surrounding rock deformation and plastic zone continuously expand. When the cavity size exceeds 1.0 m, roof subsidence exhibits a nonlinear increase, and the fractured zone around the cavity connects with the roof plastic zone, forming a continuous failure band that serves as the key factor leading to surrounding rock instability. Based on the deformation characteristics of the cavity-bearing roof, namely shallow fragmentation, deep-seated separation, and structural instability, a collaborative control technology consisting of multi-level cable bolts, steel-beam reinforcement, and grouting through injection pipes was proposed. By establishing a shallow–intermediate–deep hierarchical load-bearing structure and reinforcing the fractured cavity zone through grouting, the technology reconstructs the surrounding rock load-bearing system and optimizes the stress environment. Field application results show that, for a roof containing a 1.5 m cavity, the maximum roof subsidence and separation were controlled within 102 mm and 55 mm, respectively, and the roadway maintained a stable condition throughout the monitoring period. The findings provide both a theoretical basis and engineering guidance for surrounding rock control of gob-side entries with cavity-bearing roofs in soft, thick coal seams. Full article

This study addresses asymmetric large surrounding rock deformation induced by narrow coal pillar instability in a gentle-dipping coal seam gob-side coal roadway (GSCR) under water-immersed and high-humidity conditions. The corresponding instability mechanism and control technology are systematically studied via integrated laboratory, theoretical, numerical and field methods. From constant temperature–humidity rock deterioration tests, SEM and XRD analysis, it is revealed that hydration of hydrophilic minerals (kaolinite, chlorite) in immediate roof mudstone intrinsically drives its macro–micro structural disintegration and mechanical degradation, and the catastrophic chain mechanism of water-induced mudstone weakening–force transmission medium failure of coal pillars and overlying strata–sliding instability of key voussoir beam blocks–linked large surrounding rock deformation is clarified. A mechanical model of the overlying voussoir beam structure for the target roadway is established considering both mudstone weakening and excavation-induced load transfer effects. The sliding criterion of key overlying blocks is derived, which quantitatively confirms that higher mudstone weakening and excavation-induced stress concentration elevate the sliding instability risk of the voussoir beam structure. Based on the findings and field conditions, a combined near-field and low-position field support scheme is proposed, including near-field reinforcement (shotcreting sealing, bolt–cable cascade reinforcement, deep grouting modification) and low-position field pressure relief via liquid CO₂ phase transition long–short boreholes roof cutting. Field application verifies that the maximum roadway deformation is controlled within 172 mm, with excellent surrounding rock control performance. Full article

Coal roadway support design still relies heavily on engineering analogy and simplified analytical rules, which limits transferability across sites with different geological and geometric conditions. This study develops a theory-constrained machine learning workflow for roof bolt-cable support design and evaluates the generated scheme through FLAC3D simulation. A hybrid dataset containing 80 samples, including 30 real engineering cases and 50 constrained augmented samples, was established. Twelve geological and roadway descriptors were used to predict eight roof-support parameters with weighted single-target models based on random forest, XGBoost, support vector regression, and Gaussian process regression. The optimal regressor differed among targets, confirming strong parameter heterogeneity. The 11104 return-air roadway of Jingu Mine was selected as the main validation case, and the Sanxia 1008 material roadway of Fucun Mine was used as an external consistency case. For the 11104 return-air roadway, the workflow predominantly recommended increasing the roof bolt length from 2.00 m to 2.64 m. FLAC3D results showed reduced roof subsidence and slightly lower local stress peaks, but no improvement in rib convergence. The proposed workflow is therefore better interpreted as a roof-priority optimization tool that integrates data-driven prediction, theoretical correction, and numerical verification. Full article

The maintenance of gate roadways after longwall retreat is a critical geomechanical and technological problem in underground coal mining, particularly under conditions of increasing mining depth and complex geological settings. This study investigates the influence of support elements on the stress state of surrounding rocks and the stability of gate roadways intended for repeated use in coal mines of Ukraine and Kazakhstan. The research combines numerical modeling and analysis of field experience from Dniprovska Mine of PJSC “DTEK Pavlogradugol”, Kostenco Mine, and PJSC “Mine Administration Pokrovske”. Elastoplastic deformation of the rock mass was simulated using the finite element method within a stationary formulation, with the Mohr–Coulomb criterion applied to describe rock failure. Different support schemes were analyzed, including steel arch frames, protective structures, rock bolts, and cable bolts. The geomechanical response was evaluated using the parameters Q* and P*, which characterize the heterogeneity of the stress field and the degree of stress relief, respectively, as well as the extent of inelastic deformation zones. The results showed that protective structures significantly improve the condition of surrounding rocks at relatively shallow depths by reducing stress heterogeneity and limiting the development of inelastic deformation. Rock bolting promotes the formation of a reinforced rock–bolt arch in the roof, increasing roadway stability after longwall passage. However, under deep mining conditions, protective structures alone are insufficient, and reinforcement with cable bolts becomes necessary to maintain the integrity of the reinforced roof zone and reduce the load on individual bolts. Field observations from operating mines confirmed the practical efficiency of the proposed support approaches. The study demonstrates the role of each support element in forming a stable reinforced structure around the roadway and provides a basis for selecting rational support systems for gate roadways reused for ventilation or repeated use. Full article

To address the technical challenges of difficult deduction, limited field measurement, and ambiguous instability determination of roof separation critical values in mining roadways within the weakly cemented coal-bearing strata of Xinjiang, this paper proposes a discrete element method that integrates the fracture of anchor bolt and anchor cable support materials with the damage degree of the surrounding rock. Taking a specific mine in the Hosh Tolgay coalfield as the research object, a systematic study was conducted. The research process was as follows. (1) Model parameter calibration was performed. Intact rock parameters were obtained through laboratory basic mechanical tests, and rock mass parameters were corrected based on reduction empirical formulas and the Hoek–Brown criterion. Numerical model verification showed that the errors between the simulated and theoretical values of the elastic modulus, compressive strength, and tensile strength of the rock mass were all less than 10%, indicating that the corrected parameters are reasonable. (2) The critical damage values of the rock mass considering a non-constant confining pressure environment were proposed. Through triaxial compression simulations, the differential evolution patterns of rapid damage increase in sandy mudstone under low confining pressure and stable damage accumulation in coal were revealed, thereby clarifying the damage thresholds for rock mass instability under different confining pressures. (3) A large-scale model was established to analyze the evolution laws of the fracture field, support field, and displacement field of the roadway surrounding rock. A comprehensive determination method for the instability of the roof anchored bearing structure was proposed. By comparing the damage thresholds of the scaled rock mass and the roadway surrounding rock and analyzing the fracture conditions of the roadway support system, a dual-criterion consisting of surrounding rock damage and support material fracture was constructed. Based on this criterion theory, the critical values for deep and shallow separation were obtained. The research results indicate that the evolution patterns of damage in coal and sandy mudstone differ with confining pressure. The sandy mudstone layers in the shallow part of the roof are more sensitive to mining-induced unloading disturbances. Consequently, the surrounding rock damage and support fracture of the mine roof exhibit distinct distribution characteristics: the dominant failure of the roadway is shear failure, with wide-range coalescence of shallow fractures and gradual development of deep fractures, alongside the concentrated failure of shallow anchor bolts and partial failure of deep anchor cables. Based on the instability state of the roof monitoring zones, the critical value for shallow separation was determined to be 90.7 mm, and the critical value for deep separation was 129.03 mm. These results are very close to the field measured values, verifying the engineering applicability of the method. This paper reveals the damage characteristics of the rock mass and surrounding rock in weakly cemented strata, as well as the mechanism of roof separation initiation and evolution. The proposed method for determining critical values provides a scientific and feasible practical reference for the support optimization and monitoring and early warning of roadway roofs in weakly cemented strata, possessing significant engineering value for ensuring safe and efficient mine production. Full article

To address severe mine pressure disasters induced by the coupling of mining-induced dynamic stress and impact disturbance during close-distance coal seam mining, this paper takes the No. 8 and No. 9 close-distance coal seams in the 119 mining area of a coal mine in Ningxia, China, as the engineering background. Theoretical analysis and FLAC^3D numerical simulation methods were adopted to systematically study the evolution of overburden structure, the manifestation law of mine pressure caused by mining disturbance, and the dynamic response mechanism of roadway surrounding rock under impact load. The findings demonstrate: ① Based on key block theory and elasticity mechanics theory, the stress transfer mechanism of the complete bearing type overburden rock in close-range coal seams was clarified. The calculation model of floor plastic zone depth and additional stress was derived, and the influence mechanism of the bearing state of interlayer rock strata on the stability of underlying coal seam roadways was revealed. ② Comparative numerical simulations of mining schemes revealed that both schemes formed a “goaf pressure relief-workface-coal pillar” load-bearing configuration with “upward subsidence and downward bulging” basin-shaped settlement. Scheme A exhibited significantly increased stress peaks and interlayer plastic zones due to repeated mining-induced stress, substantially elevating the risk of strong mine pressure manifestation and surrounding rock instability. ③ Under 8 MPa cosine impact load with a vibration frequency of 50 Hz (peak particle vibration velocity of 9.57 m/s), compared with the unsupported roadway, the bolt–cable collaborative support system reduced the peak displacement of surrounding rock by over 35% and decreased the shock wave propagation velocity by more than 40%, effectively suppressing the expansion of plastic zones and the transfer of impact energy, while significantly enhancing the impact resistance of the roadway. This study not only provides a systematic theoretical basis for close-distance coal seam mining and rock burst prevention but also offers scientific guidance and technical reference for surrounding rock control and dynamic disaster prevention of roadways in similar close-distance coal seam mining projects, which is of important engineering value for ensuring the safe and efficient mining of underground coal resources. Full article

Coal is the primary energy source in China and has long dominated energy consumption, serving as both the cornerstone for safeguarding national energy security and the backbone of stable energy supply. Despite the gradual improvement in the level of fully mechanized and intelligent mining in recent years, as well as the remarkable progress achieved in safe and efficient mining technologies, significant challenges are still encountered in the horizontal slicing mining of steeply inclined coal seams. This study was conducted against the engineering backdrop of the steeply inclined extra-thick coal seam in the Yimen Coal Mine, Sichuan Province. A combination of theoretical analysis, FLAC3D numerical simulation, and on-site monitoring was employed to investigate the support technology for mining roadways. Considering the geological occurrence conditions, roadway dimensions, and service life, the bolt (cable) + steel strip + metal mesh system was selected as the basic support method, with shed supports supplemented for reinforcement in areas with special geological structures or fractured surrounding rock. A non-uniform roadway support technology for horizontal slicing mining of steeply inclined extra-thick coal seams was proposed. The optimal support parameters of the roadways were determined through numerical simulation, and favorable support effects were verified by field measurements. Full article

To address the pronounced asymmetric deformation of roadway-surrounding rock under deep multi-dynamic pressure, the N8003 tailgate of the Wuyang Mine was adopted as the engineering background, and the deformation–failure characteristics of the roadway sidewalls and the evolution of deviatoric stress under dynamic loading were analyzed. Based on numerical simulation, the maximum principal deviatoric stress S₁ was employed as the core indicator for evaluating pressure-relief effectiveness, upon which a three–dimensional Pressure Relief Efficiency Index (PREI) considering strength, range, and position was developed. The key parameters of large-diameter hydraulic cavitation pressure–relief boreholes were optimized, and the evolution patterns of deviatoric stress under static and dynamic conditions were further revealed. To overcome the limitations of conventional high-strength bolt–cable combined support in controlling large deformation, a layered support–relief collaborative control technology featuring “external reinforcement fixation (ERF), near-surface modification and grouting (NSMG), and deep targeted destressing (DTD)” was proposed. Field tests demonstrated that this technology can significantly suppress sidewall deformation, maintain support system stability, and exhibit strong adaptability and application potential in deep roadways influenced by multi-dynamic pressure. Full article

This study addresses the challenges posed by weakly cemented strata in mine tunnels, where surrounding rock softens and deforms upon water exposure, which promotes the development of seepage pathways, and exhibits insufficient stability in bolt (cable) support systems. This study conducts laboratory grouting tests using silica sol on typical weakly cemented sandstone from Xinjiang mining areas. The mineral composition and pore structure were characterized using XRD, SEM, and mercury porosimetry. The injectable mixing ratio parameters for silica sol and the catalyst were determined through viscosity-time evolution tests. Grouting was performed using a custom-built constant-pressure grouting apparatus. After curing, unconfined compressive strength (UCS) and porosity-permeability tests were conducted to evaluate the micro-mechanism of grouting effects on the mechanical and permeability properties of weakly cemented sandstone. The results indicate: (1) The sandstone exhibits a high clay mineral content of 39.8%, dominated by illite. Its pores are primarily small-scale (10–100 nm), accounting for 79.31% of the total pore volume. This scale matches that of silica sol nanoparticles (approximately 9–20 nm), facilitating slurry penetration into micro-pores; (2) microscopic analyses reveal that silica sol effectively reconstructs pore structures through permeation filling and surface coating. Compared to KCl-induced gelation (with approximately 8% gel coverage), NaCl-induced gelation forms a more continuous gel film with more complete pore filling, achieving coverage of around 22%. Furthermore, the larger surface area of the gel aggregates indicates a more thorough filling of micro- and nano-pores, effectively enhancing rock mass compactness. (3) Permeability decreased from 6.91 mD to 3.55 mD, a reduction of 48.6%, while porosity decreased from 16.94% to 13.55%, showing a phased reduction during the grouting process; (4) following pressure grouting stabilization, the uniaxial compressive strength of sandstone increased appropriately by approximately 7–14%, while the elastic modulus rose by about 18–28%. The failure mechanism shifted from shear brittleness to a shear-tension composite state, with enhanced post-peak bearing capacity. These findings provide support for optimizing silica sol grouting parameters in weakly cemented strata tunnels and for the synergistic reinforcement of rock mass permeability and strength. Full article