Search Results (163)

This study is the first to systematically integrate supervised machine learning (decision tree) and association rule mining techniques to analyze accident data from the Taipei Metro system, conducting a large-scale data-driven investigation into both passenger injury and train malfunction events. The research demonstrates strong novelty and practical contributions. In the passenger injury analysis, a dataset of 3331 cases was examined, from which two highly explanatory rules were extracted: (i) elderly passengers (aged > 61) involved in station incidents are more likely to suffer moderate to severe injuries; and (ii) younger passengers (aged ≤ 61) involved in escalator incidents during off-peak hours are also at higher risk of severe injury. This is the first study to quantitatively reveal the interactive effect of age and time of use on injury severity. In the train malfunction analysis, 1157 incidents with delays exceeding five minutes were analyzed. The study identified high-risk condition combinations—such as those involving rolling stock, power supply, communication, and signaling systems—associated with specific seasons and time periods (e.g., a lift value of 4.0 for power system failures during clear mornings from 06:00–12:00, and 3.27 for communication failures during summer evenings from 18:00–24:00). These findings were further cross-validated with maintenance records to uncover underlying causes, including brake system failures, cable aging, and automatic train operation (ATO) module malfunctions. Targeted preventive maintenance recommendations were proposed. Additionally, the study highlighted existing gaps in the completeness and consistency of maintenance records, recommending improvements in documentation standards and data auditing mechanisms. Overall, this research presents a new paradigm for intelligent metro system maintenance and safety prediction, offering substantial potential for broader adoption and practical application. Full article

Corrosion-related failures have emerged as a critical driver of premature support bolt failures in underground mines, emphasizing the urgency of understanding the phenomenon with respect to enhancing safety in underground environments. This study investigated key factors influencing bolt degradation through extensive experimental evaluation of cable bolts in simulated underground bolt environments. Multi-stranded cable specimens were exposed to saturated clay, coal, mine water, and grout/cement environments. Water samples were collected weekly from critical packing sections and analyzed for pH, electrical conductivity, and dissolved oxygen. The mineralogy and atmospheric conditions were identified as principal corrosion factors, and clay-rich and coal matrices accelerated corrosion, linked to high ion mobility and oxygen diffusion. Secondary factors correlated context-dependently: pH was negatively associated with corrosion in mineral-packed environments, while conductivity was correlated with non-mineral matrices. Notably, multi-stranded cables exhibited higher localized galvanic corrosion in inter-strand zones, highlighting design vulnerabilities. This work provides pioneering evidence that geological conditions are primary drivers for corrosion-related failures, offering actionable guidance for corrosion mitigation strategies in mining infrastructure. 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 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

Unplanned dilution is a critical challenge in underground mining, directly affecting operating costs, resource recovery, stope stability and operational safety. This study presents an empirical–statistical framework that integrates the Mathews–Potvin stability graph, the Equivalent Linear Overbreak/Slough (ELOS) metric, and a site-specific linear calibration to improve dilution prediction in sublevel stoping operations. A database of more than 65 stopes from a Brazilian underground zinc mine was analyzed and classified as cable-bolted, non-cable-bolted, or self-supported. Planned dilution derived from the Potvin graph was compared with actual ELOS measured by cavity-monitoring surveys. Results show a strong correlation between cable-bolted/supported stopes (r = 0.918), whereas non-cabled/unsupported and self-supported stopes display lower correlations (r = 0.755 and 0.767). Applying a site-specific linear calibration lowered the mean absolute dilution error from 0.126 m to 0.101 m (≈20%), with the largest improvement (≈29%) occurring in self-supported stopes where the unadjusted graph is least reliable. Because the equation can be embedded in routine stability calculations, mines can obtain more realistic forecasts without abandoning established empirical workflows. Beyond geotechnical accuracy, the calibrated forecasts improve grade-control decisions, reduce unnecessary waste haulage, and extend resource life—thereby enhancing both the efficiency and the accessibility of mineral resources. This research delivers the first Brazilian case study that couples Potvin analysis with ELOS back-analysis to generate an operational calibration tool, offering a practical pathway for other sites to refine dilution estimates while retaining the simplicity of empirical design. Full article

Pillarless mining technology is of great significance for improving coal recovery rates, but the intense mining-induced stress disturbances on gob-side entries often lead to surrounding rock instability. In this study, we focused on the ground control challenges in the headgate of Panel 81308 at Huayang Mine No. 2. Comprehensive monitoring of roof–floor convergence, rib deformation, and support resistance revealed the gob-side entry retaining deformation mechanisms with roof-cutting pressure relief; the results show that this retaining deformation exhibits the following three phases of characteristics: the rapid, decelerated, and stable stages. The average roof–floor convergence (607 mm) was significantly greater than the average rib deformation (170 mm), with floor heave accounting for 72.6% of total convergence. The coal pillar side showed dominant deformation in rib movements. The mining influence zones can be divided, based on their distances behind the working face, into strong disturbance zones (0–88 m), weak disturbance zones (88–142 m), and stabilized zones (>178 m). The cable bolt support system demonstrated advanced response characteristics. Compared with conventional gob-side entry retaining, the roof-cutting pressure relief technique altered stress transmission paths, significantly reduced roof load transfer efficiency, and effectively controlled roadway convergence, providing technical guidance for safe production in both this panel and mines with similar geological conditions. Full article

To address the issues of severe surrounding-rock failure and ground support component failure in advancing working-face driving roadways (AWFDRs) in ultra-close coal seams, this study used the 5202 air-return roadway in Huaye Coal Mine as a case study and for engineering background. Numerical simulation, theoretical analysis, and industrial application methods were adopted to analyze the laws of the dynamic evolution of vertical stress in such roadways. The mine pressure behaviors of AWFDRs in ultra-close coal seams were also clarified, thereby enabling the proposal of a solution; namely, zoned support technology. The results show that the 5202 air-return roadway, as an AWFDR in an ultra-close coal seam, exhibits five different characteristic behaviors of mine pressure zones during excavation. Zone 1 is influenced by the adjacent working-face mining under goaf; Zone 2 is influenced by the adjacent goaf lateral abutment stress under goaf; Zone 3 is influenced by the stress of the overlying solid coal; Zone 4 is influenced by the adjacent goaf lateral abutment stress under the overlying solid coal; and Zone 5 is influenced by stabilized stress under the overlying solid coal. The mine pressure behaviors of these zones were ranked, from most intense to weakest, as follows: Zone 3 > Zone 1 > Zone 4 > Zone 2 > Zone 5. Based on this, a basic support scheme was proposed, which involves using bolt–mesh–beam supports combined with shed supports under the goaf and bolt–mesh–beam supports combined with roof anchor cables under the overlying solid coal. Additionally, in Zones 1 and 3, roof anchor cables or rib anchor cables were supplemented as reinforcing supports, which were combined with the basic support scheme described above to form a zoned support scheme for the AWFDR. The analysis of mine pressure behavior and implementation of a zoned support scheme for AWFDRs in ultra-close coal seams provides technical and engineering references for roadway supports under similar mining conditions. Full article

As the rock fracture in the roof anchorage blind zone of coal roadway develops, it not only brings about serious deformation, but also results in barrier effect on anchorage stress, restricting the efficiency of the bolt support. In this paper, the existence and formation mechanism of the anchorage blind zone in the roadway roof supported by prestress bolt are found. Through field research, theoretical analysis, and numerical simulation, the main control influencing factors of the anchorage blind zone are studied. Results show that stress of rock mass in the anchorage blind zone increases with stronger bolt prestress and decreases with longer bolts (free-segment length); the length of the free segment is the main control factor that affects the range of the anchorage blind zone. Moreover, the corresponding control countermeasures are put forward that properly increasing the bolt prestress and shortening the free segment can effectively increase the stress value of the rock mass in the anchorage blind zone and reduce the scope of the zone. Under the condition of high prestress of the anchor bolt, how to reasonably select the thickness of the anchor layer so as to control rock mass deformation not only in the anchorage blind zone but also in the whole anchorage area at the same time is the key. Based on the surrounding mining conditions of the test roadway, the working method is proposed that uses a high-prestress cable to construct the roof thick anchor layer as well as a short bolt to strengthen the shallow rock mass of the roof so as to improve the bearing performance of the rock mass in the free segment, especially in the anchorage blind zone. Field validation demonstrated that the proposed strategy not only suppresses the “net pocket” phenomenon but also enhances resource efficiency by optimizing material usage (e.g., reduced bolt length and targeted prestress allocation). This approach contributes to sustainable mining practices by extending roadway service life and minimizing frequent maintenance, thereby reducing long-term environmental impacts associated with roof failures. Full article

To study the response relationship between drilling signal and rock mass geomechanical parameters, accurately and quickly perceive and predict the strength of coal and rock mass, guide the optimization of drilling control parameters and the design of the support scheme, and improve the efficiency of roadway excavation, the prediction of rock uniaxial compressive strength based on drilling signal was carried out. Based on the 112,206 return air chute in the Xiaobaodang No.1 Coal Mine as the engineering background, through the drilling data obtained from the roof anchor cable support, data processing, and feature selection, this paper establishes a coal and rock mass strength prediction model based on the AdaBoost integrated algorithm, optimizes the hyperparameter of the model, and analyzes and evaluates the prediction results. The results show that in the AdaBoost integration model, the R² of SVM is the highest, 0.972, and the values of RMSE, MAE, MAPE, and other error indicators are the lowest. The prediction accuracies of the SVM model, tree model, and linear model are 98.8%, 85.4%, and 75.6%, respectively. The experimental results show that the AdaBoost integrated algorithm using a based learning machine has higher prediction accuracy. At the same time, compared with the current advanced model, it further verifies the effectiveness of the model in the coal mine. Full article

This study investigates the surrounding rock failure caused by the fracture line of the main roof above the gob-side roadway during fully mechanized top-coal caving mining in a 19 m thick coal seam. As mining progresses, stress concentration occurs in the roadway roof. Furthermore, the fracture line of the main roof above the roadway poses a significant threat to the structural stability of the gob-side roadway, leading to the localized failure of the roof structure, which consequently affects the safe and efficient production of the mine. This study investigates the shear failure mechanism of the roadway top coal and analyzes the failure characteristics and stress evolution law of the surrounding rock when the main roof fracture line (MRFL) is located above the roadway through three integrated approaches: theoretical analysis, numerical simulation, and physical similarity modeling. To effectively mitigate damage to the top coal, it is proposed to implement a five-hole tray coupled with high-strength prestressed anchor cables for reinforcing the surrounding rock, while compact wooden piles in combination with single pillars are employed to strengthen the roadway support control measures. It is verified by field tests that these control methods significantly improve the stability of coal above the entry and greatly mitigate the likelihood of surrounding rock failure. Full article

In response to the difficulty of controlling the layered composite roof of large-section coal roadways and the problem of slow excavation speed caused by unreasonable support parameter values, a dynamic staged control principle for surrounding rock based on “high-strength passive temporary support near the excavation face, combined with active support of rear bolts and anchor cables” is proposed by analyzing the evolution law of rock release stress under the spatial effect of excavation face. Based on the geological conditions of the 1211 (1) transportation roadway in Guqiao Coal Mine, a similar physical simulation test model was constructed to conduct experimental research on the bearing capacity and deformation instability mechanism of the surrounding rock of the layered-composite-roof coal roadway. The law of influence of staged support on the deformation and failure evolution of the surrounding rock was obtained. The research results show the following: (1) After loading above the model, the vertical stress on the roof increases rapidly in a “stepped” manner. After unloading the roadway excavation, due to the release of constraints on the roof above the roadway, the vertical stress on the roof rapidly decreases, especially in the temporary support area where the reduction in vertical stress on the roof is most significant. (2) As the vertical load increases, the displacement curve of the roof gradually evolves into a “V” shape. The farther away from the center of the roadway, the smaller the subsidence of the roof. When loaded to 54.45 kN, the subsidence of the roof increases, indicating that the development of roof delamination cracks is faster, and delamination occurs between 12 cm and 22 cm above the roof. (3) With the continuous increase of axial load, cracks first appear around the roof and slightly sink. Then, the cracks gradually expand and penetrate, causing instability and failure of the roadway roof. When the mining stress reaches 54.45 kN, the middle part of the roadway roof in the axial direction breaks, and the cracks penetrate, resulting in overall collapse. Full article

In China’s northwest mining areas, shallow buried coal seams commonly feature double soft composite roof structures of mudstone and clay, resulting in poor roadway stabilization and proving challenging for effective roadway-surrounding rock (RSR) control. A mudstone–clay composite roof is particularly difficult to maintain due to the complex interactions between the soft rock layers and their sensitivity to moisture changes. Previous studies have investigated the properties of these soft rocks individually, but there is limited research on the behavior and control of double soft composite roofs. This study investigated the hydrophilic mineral composition and microstructure of mudstone and clay through X-ray diffraction (XRD) and scanning electron microscopy (SEM) experiments. Through an orthogonal experimental design, the influence of the clay layer thickness, number of layers, layer position, and relative moisture content on the stability of a mudstone–clay composite roof was studied. The results revealed the following: (1) Kaolinite, the primary hydrophilic component, constitutes a high proportion of clay, while both mudstone and clay exhibit abundant pores and cracks under SEM observation; (2) The relative moisture content emerged as the most significant factor affecting roadway deformation; and (3) A combined support of bolts, a short anchor cable, and a long anchor cable effectively controls RSR deformation in the case of a double soft composite roof. The methodology combining comprehensive material characterization and systematic parametric analysis can be extended to the study of other complex soft rock engineering problems, particularly those involving moisture-sensitive composite roof structures. Full article

This study investigates the traditional coal pillar support methods employed in double-roadway excavation of high-mining-height longwall faces, specifically those with widths ranging from 20 m to 30 m. It highlights that these methods not only result in substantial coal pillar loss and low recovery rates but also create conditions for stress concentration due to inadequate dimensions, thereby increasing the risk of accidents. Based on the engineering context of the Jinjitan Coal Mine’s 113 and 111 working faces, this paper optimizes coal pillar dimensions through theoretical calculations and Flac3D numerical simulations, with the results indicating that the optimal coal pillar width is 12 m. Analysis of a 12 m inter-roadway coal pillar focuses on the bearing characteristics of auxiliary transport roadways and coal transportation roadways. Five different reinforcement schemes are examined, including (no support, conventional anchor reinforcement, presser anchor cable through reinforcement, constant-resistance large-deformation anchor cable through reinforcement, and a combination of presser with negative Poisson’s ratio (NPR) constant-resistance large-deformation anchor cable support). The findings reveal that in the investigation of the reinforcement mechanism for the 12 m wide coal pillar, employing NPR constant-resistance large-deformation anchor cables alongside presser anchor cables effectively mitigates the compression deformation caused by dynamic loading disturbances from the overlying rock layers. This approach not only dissipates energy but also transforms the coal pillar from a biaxial stress state to a triaxial stress state. The reinforcement scheme successfully reduces the peak stress of the coal pillar from 68.5 MPa to 35.3 MPa, significantly enhancing both the peak strength and residual strength of the coal pillar, thereby ensuring the stability of the inter-roadway coal pillar and the safe recovery of the working face. Full article

Leaky feeders provide seamless and uniform signal coverage in confined spaces like tunnels, mines, and buildings. Their easy scalability and integration with modern systems, like Multiple Input Multiple Output (MIMO), make them ideal for environments requiring reliable and consistent connectivity. However, using optical fiber as a radiating cable has never been investigated before. This may seem infeasible at first sight. However, our experimental study shows otherwise. We measured light leaking from a bent optical fiber transmitter. We also derived closed-form formulas to describe the amount of leakage energy and found that this energy exponentially varies with the square of the curvature radius. This allows us to design an Optical Leaky Feeder (OLF) transmission system for the first time. Then, we analytically show that a slotted optical fiber can be used as a MIMO receiver. The proposed system can ensure reliable, high-quality signal distribution even in challenging environments like tunnels, industrial settings, and dense urban areas. Full article

Prediction of the spatial configuration of the umbilical cable during deep-sea mining in-situ tests is of great significance because dynamic change may cause the umbilical cable to touch the ground or overturn the mining vehicle. In the present paper, a real-time prediction method for the dynamic spatial configuration of the umbilical cable during the deep-sea mining process is proposed. At first, the environmental information, position and motion of the vessel–umbilical cable–mining system were collected by sensors arranged at different locations. Then, the data were converted and transformed to the local vessel coordinate system. After that, the commercial software OrcaFlex was employed to conduct real-time simulation, in which the spatial configuration of the umbilical cable was predicted by the lumped mass method. Furthermore, the proposed real-time simulation method was employed in a sea trial test of deep-sea mining in an area with a water depth of 1100 m. Comparing the prediction results with the trajectory of the USBL beacon obtained from the monitoring data, the maximum distance of some specific points was close to 5 m, and most of them were less than 3 m. Meanwhile, it could also give the dynamic responses of the deep-sea mining system. For example, the maximum top tension of the umbilical cable was less than 15 kN, which could be used to evaluate the health condition of the system. During the sea trial test, the proposed method played an important role in ensuring the safety of the umbilical cable during wide-range movement of the mining vehicle. With characteristics of good real-time performance, accurate prediction, high reliability and stability, the proposed method could enhance the confidence of engineers for on-site operation as a powerful digital tool for visualization of the subsea working state. Full article