Search Results (709)

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

The stability of retained roadways in closely spaced coal seams beneath a goaf is strongly affected by complex stress redistribution and the deterioration of roof structures under downward mining conditions. To address this issue, a combined approach involving theoretical analysis, numerical simulation, and field monitoring was adopted to investigate the deformation characteristics and stability control of gob-side retained roadways in short-distance coal seam groups. The movement characteristics of the roof and the deformation law of surrounding rock of the retained roadway under downward mining were revealed. An embedded short-arm beam structural model for a roof cutting retained roadway was established, and a calculation method for determining the required support resistance of the retained roadway was proposed. Based on this model, design criteria for the passive support system of the retained roadway were developed. A surrounding rock control technology with hollow grouting anchor cable support and low-disturbance directional roof cutting as the core was proposed, and the support resistance of a one-beam–four-column support system was determined to effectively limit roof subsidence. Field application results show that the surrounding rock displacement was controlled within 350 mm, and the roadway section shrinkage rate was maintained at 16.4%, indicating good stability of the retained roadway and satisfying the requirements of ventilation and transportation. This study provides a mechanical basis and practical guidance for stability control and support design of roof cutting retained roadways in closely spaced coal seams beneath goaf. Full article

With the increasing depth of mining operations, accurate identification and assessment of rock mass instability risks are crucial for ensuring mine safety. This study proposes an integrated framework combining the Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN), fuzzy comprehensive evaluation (FCE) and kernel density estimation (KDE) for the identification and dynamic assessment of high-risk zones in deep mining. Using microseismic monitoring data from a lead–zinc mine in Northwest China (January–June 2023), the HDBSCAN algorithm adaptively identified 86 high-density clusters from 11,638 events. The weights of five evaluation indicators (moment magnitude, apparent stress, stress drop, peak ground acceleration, and ringing count) were determined objectively using the Euclidean distance method. FCE was then applied to classify cluster risk levels, revealing that 70.9% of the clusters were rated as high-risk (Level IV). KDE further illustrated the spatiotemporal migration of high-risk zones, showing a systematic shift from northeast to southwest along stopes and roadways, driven by mining unloading and geological structures. The integrated HDBSCAN-FCE-KDE framework demonstrates strong applicability and reliability in identifying and predicting rock mass instability risks, providing a scientific basis for proactive risk management in deep mining environments. 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 investigate the dominant factors and instability mechanism of surrounding rock deformation in cross-mining roadways, a systematic study was conducted using theoretical analysis, numerical simulation, and response surface methodology to examine the influence of various factors on surrounding rock stability. First, the theoretical model was refined by introducing a lithology coefficient of the load-transfer layer, thereby improving its engineering applicability. Subsequently, numerical simulations and response surface experiments were employed to analyze the effects of key factors, including the vertical distance between the working face and the roadway, the horizontal distance between the working face and the roadway, the burial depth of the roadway, the mining height of the working face, and the lithology of the load-transfer layer. The analysis results indicate that the vertical distance, horizontal distance, and lithology of the load-transfer layer are negatively correlated with roadway roof displacement, whereas the burial depth and mining height are positively correlated. The p-values for all factors were less than 0.0001. The order of significance of the influencing factors is as follows: vertical distance > horizontal distance > burial depth > mining height > lithology of the load-transfer layer. Among these, the vertical distance has the most significant effect on roadway deformation and exhibits notable interaction effects with burial depth and horizontal distance. Based on these findings, given that construction conditions cannot be altered, modifying the lithology of the load-transfer layer was selected as the control measure. Directional long-hole hydraulic fracturing for roof cutting and pressure relief was implemented in the roof of the return airway in the No. 6 mining district. Field monitoring results show that hydraulic fracturing effectively interrupted the stress transmission path induced by mining activities, transferring roof pressure to deeper strata. Consequently, the deformation of the surrounding rock was significantly reduced, the dynamic pressure effect was markedly alleviated, and the stability of the roadway was effectively controlled. The research results provide a theoretical basis for the design and control of cross-mining roadways under similar engineering conditions. Full article

In order to ensure the smooth and safe advancement of mining faces through abandoned roadways (ARs), this study investigates the backfilling process in a mining operation in western China, where abandoned roadways continuously appear ahead of newly arranged mining faces. A theoretical analysis of the immediate roof of the roadway is conducted, leading to the conclusion that the optimal spacing between backfilling bodies is 8 m. Numerical simulation software is used to examine the effects of different backfilling body lengths—6 m, 8 m, and 10 m—on the stress state, deformation characteristics, and stress distribution of the surrounding rock during mining. Based on the simulation results, appropriate backfilling body lengths are selected: 8 m for ARs perpendicular to the mining face and 10 m for ARs parallel to the mining face. The proposed backfilling process is validated through industrial tests, demonstrating its effectiveness in ensuring mining safety and improving economic efficiency. 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

Deformation monitoring of roadway surrounding rock is the key link to ensure the safety production of the coal mine. The traditional monitoring method can only obtain the displacement information of discrete measuring points, and it is difficult to fully reflect the spatial distribution characteristics and evolution law of surrounding rock deformation. Based on the engineering background of the extra-thick coal seam roadway in the Yushupo Coal Mine, Shanxi Province, China, this study proposes a set of full-space deformation monitoring methods for roadway surrounding rock based on explosion-proof mobile 3D laser scanning technology. Firstly, a hierarchical denoising method based on improved statistical filtering is established. The quality of point cloud data is effectively improved by region clipping, a connectivity analysis guided by multi-dimensional geometric features and adaptive density threshold three-level processing strategy. Secondly, a hierarchical point cloud registration method combining physical anchor geometric constraints and deep learning patch guided matching is proposed to reduce the registration error to millimeter level. Finally, the deformation evaluation of surrounding rock is carried out by combining the overall deformation identification with the quantitative analysis of local section slices. The engineering application results show that the deformation of the roadway floor is the most significant during the monitoring period, the maximum deformation is 90.0 mm, and the average deformation is 46.9 mm. The maximum deformation of the roof is 35.0 mm, and the convergence of both sides is asymmetric. Compared with the total station, the results show that the maximum displacement error in each direction does not exceed 5 mm, and the standard deviation is within 1.3 mm, which meets the engineering accuracy requirements of coal mine roadway deformation monitoring. This study provides a complete technical scheme for panoramic and high-precision monitoring of surrounding rock deformation in coal mine roadway. Full article

To address the engineering challenges of frequent flexural deformation and instability of composite roadway roofs and the difficulty in accurately controlling the support strength range during deep coal mining, this study takes the soft–hard interbedded composite roof of the working face in the West No. 1 Mining Area of Shuangyang Coal Mine in Shuangyashan as the engineering background. Typical fine sandstone (hard rock) and tuff (soft rock) from the on-site roof were selected to prepare layered composite specimens, and indoor four-point bending tests were conducted. Combined with theoretical calculations, strain monitoring, and acoustic emission (AE) real-time localization technology, the regulatory mechanisms of three key factors—lithological combination, loading rate, and span—on the flexural mechanical properties, deformation and failure modes, and fracture evolution laws of layered composite rock masses were systematically investigated. The research results show the following: (1) The flexural performance of layered composite rock masses is dominated by the interlayer interface effect. Their flexural strength is 46.7% and 41.1% lower than that of single hard rock and soft rock specimens, respectively, and the competitive mechanism between interface slip and delamination fracture is the core inducement of strength deterioration. (2) The strength and deformation characteristics of layered composite rock masses exhibit a significant loading rate effect. When the loading rate increases from 0.002 mm/s to 0.02 mm/s, the flexural strength decreases by 51.8% and the mid-span deformation deflection reduces by 50.1%. High loading rates will exacerbate the deformation mismatch between soft and hard rock layers, trigger premature failure of interface bonding, and inhibit the full development of structural plastic deformation. (3) Increasing the span significantly optimizes the flexural bearing performance of layered composite rock masses. When the span increases from 170 mm to 190 mm, the flexural strength increases by 65.7% and the mid-span deformation deflection synchronously increases by 65.7%. A large span can extend the flexural deformation path, promote the coordinated deformation of rock layers, and suppress local stress concentration. (4) The flexural failure of layered composite rock masses is dominated by Mode II shear cracks, while single-lithology specimens are mainly dominated by Mode I tensile cracks. Loading rate and span significantly change the crack propagation mode and energy release law. This study establishes a calculation method for the equivalent flexural stiffness of layered composite rock masses and reveals the mesoscopic mechanism of flexural failure of heterogeneous layered rock masses. The research results can provide a theoretical basis and experimental support for the optimization of support schemes and the prevention and control of roof collapse hazards for composite roofs of deep coal mine roadways. Full article

Deep underground coal mines are severely threatened by dynamic coal rock disasters such as mine pressure bumps and coal and gas outbursts, and coal seam pressure relief technology is widely recognized as the key measure for mitigating these hazards. To investigate the pressure relief effect of coal seam slot cutting using a diamond beaded wire saw, a combined strategy integrating physical similarity simulation and numerical simulation was applied. The stress distribution characteristics of the coal and rock mass during the wire saw cutting procedure were evaluated, and the influence of beaded wire saw diameter on pressure relief efficiency was further examined. (1) Wire saw cutting can substantially decrease the vertical stress within the coal seam; the average pressure relief rate above the slot can reach as high as 61.70%, and the pressure relief effect is clearly stronger than that below the slot. (2) After slot cutting along the roadway, the fully pressure-relieved zone displays an annular spatial pattern; the pressure relief effect at both ends of the slot and around the roadway is particularly evident, whereas the pressure relief degree in the middle part is comparatively low because of the closure effect. (3) Slot closure causes notable changes in the pressure relief state. Before closure, the pressure relief effect above the slot remains satisfactory; after closure, stress recovery appears in the middle part, but the overall pressure relief rate still stays above 10%, and the pressure relief rate at both ends of the slot and near the roadway exceeds 50%, with the fully pressure-relieved zone still maintaining an annular distribution. (4) A positive correlation exists between the wire saw diameter and the height of the fully pressure-relieved zone. For every 0.5 cm increase in diameter, the height of the fully pressure-relieved zone rises by an average of 0.6 m. When the wire saw diameter reaches 3 cm, the full-thickness and adequate pressure relief of a 3 m thick coal seam can be realized. Full article

Large deformation and difficult support are common in soft-rock roadways under deep high-stress conditions. The 1232(3) gob-side roadway of Dingji Mine was taken as the engineering background. A combined approach was used. It included theoretical analysis, numerical simulation, field measurements, and underground tests. The catastrophe mechanisms of surrounding rock and the corresponding stability control technologies were investigated for high-stress soft-rock roadways. The results showed a strong Rp–Rw effect. When the variation coefficient of the maximum horizontal principal stress satisfied Rp > 0.8, the influence on the variation coefficient of roof buckling deflection (Rw) became pronounced. Under this condition, roof deformation increased markedly. As roadway drivage changed from solid-coal-side driving to gob-side driving, the surrounding-rock stress became progressively asymmetric. The peak stress on the coal-pillar side decreased from 25.3 MPa to 21.5 MPa. The plastic zone expanded continuously. Its dominant development also shifted from the roof and floor toward the two ribs. After entering the gob-side condition, plastic-zone development on the coal-pillar side generally exceeded 2.5 m. The original support bolts could no longer remain effective. Different stress states and failure characteristics were observed on the solid-coal side and the gob side. Based on these differences, an asymmetric coupled support and surrounding-rock control system was established. The system integrated “time effectiveness + regional zoning + targeted reinforcement.” A field trial was conducted in the 1232(3) haulage roadway. Surrounding-rock deformation was effectively controlled, and favorable engineering performance was achieved. Full article

Thick oil shale roofs in the Zichang mining area frequently suffer from delamination and sudden brittle fracture, compromising support stability. Using the 50117 return-air roadway as a case study, this paper integrates microstructural characterization (SEM-EDS/XRD), mechanical testing, theoretical interpretation, and FLAC3D simulation to elucidate the instability mechanism. Results indicate that the preferred orientation of clay minerals along bedding yields a “weak friction” signature, facilitating delamination. Simultaneously, the rigid quartz framework enables rapid energy storage, yet constrained bending dissipation triggers instantaneous fracture. This “weak friction-strong cementation” property drives the “delamination-brittle fracture” mechanism. Notably, the roof exhibits low principal stress concentration but extreme sensitivity to deviatoric stress, typifying a “low-stress environment and weak structural damage” behavior. Accordingly, a synergistic control technology featuring “high-prestress normal clamping and dowel shear resistance” was proposed. Field application confirmed its effectiveness in suppressing delamination and reducing rib convergence, thereby ensuring long-term roadway stability. Full article

Large deformations in deep soft rock roadways primarily stem from low rock strength under high in situ stress and intense mining disturbance. This renders stability control a critical challenge in tunneling support engineering. Utilizing Xinhe Coal Mine’s deep soft rock tunnel as a representative case, this study integrates field monitoring, laboratory experimentation, and numerical simulation to investigate how excavation and grouted rock bolting influence surrounding rock stability. Building upon field-observed deformation mechanisms and support failure patterns, constitutive models for FLAC^3D’s embedded cable and beam elements were modified to achieve high-fidelity simulation of grouted support systems. Numerical models simulating diverse support schemes were established to analyze roadway displacement fields, plastic failure development, and structural behavior of support components, ultimately identifying the optimal rehabilitation solution. The research results indicate that the numerical simulation outcomes of the original support scheme exhibit good agreement with field observations in terms of roadway deformation patterns, deformation magnitudes, and occurrences of bolt/cable fractures. This demonstrates that the adopted refined numerical simulation methodology and parameters are reasonable and exhibit high reliability. Considering both surrounding rock stability and cost control, Roadway Rehabilitation Scheme S1 was identified as the optimal support solution. Its specific parameters are pre-grouting + full-section rock bolts (diameter 22 mm, length 2.4 m, spacing 0.8 m, row spacing 1.6 m) + full-section grouted cables (diameter 22 mm, length 6.2 m, spacing 1.0 m, row spacing 1.6 m). Full article

Advance hydraulic supports are widely applied in deep coal mine roadways; however, inappropriate initial support force often leads to either insufficient roof control or over-support, weakening the effectiveness of bolt–cable systems. To clarify the interaction mechanism between advance passive support and active bolt–cable reinforcement, an advance roadway support model was developed using FLAC3D based on the geological conditions of the 1432 working face in the Dongtan Coal Mine. Numerical simulations were conducted by varying the initial support force from 0 to 14 MPa, and the corresponding roof displacement, bolt stress, and cable axial force responses were systematically analyzed. The results indicate that roof subsidence decreases nonlinearly with increasing support force, exhibiting a rapid suppression stage (0–10 MPa) and a stable coordination stage (10–12 MPa). Within this optimal range, load transfer from the roof to the passive support is significantly enhanced, leading to effective stress relief and homogenization in the bolt–cable system. When the support force exceeds 12 MPa, further deformation control becomes marginal, indicating a transition from cooperative load sharing to over-support. These findings reveal the staged interaction mechanism between advance passive support and active reinforcement systems, providing a quantitative basis for selecting appropriate initial support force in deep roadway engineering. Full article

This article addresses the problem of floor heave in preparatory mine workings of the Karaganda Coal Basin and proposes technological solutions based on rock mass anchoring systems. Long-term field observations, supported by analytical interpretation and numerical modeling, made it possible to identify the principal factors controlling deformation processes around mine roadways, including floor rock fracturing, stress redistribution during longwall mining, and the interaction between adjacent workings. Special attention is given to the performance of different types of anchors installed in the floor and to their optimal arrangement depending on the width and geometry of the excavation cross-section. Empirical relationships are proposed for estimating the magnitude of floor heave and determining the required anchor length, and their applicability is supported by numerical simulations performed using RS2 software v. 11.027. Based on the results obtained, technological schemes aimed at reducing the intensity of floor heave and improving the stability of the surrounding rock mass were developed for mining in inclined and gently dipping coal seams. Field experiments conducted in the Kazakhstanskaya, Saranskaya, and Abayskaya mines of the Karaganda Coal Basin confirmed the effectiveness of steel–polymer anchors in stabilizing excavation contours. Full article