Search Results (2,195)

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

This study examines the evolving patterns and zoning characteristics of gas migration and storage zones during coal seam mining, taking the 215 fully mechanized longwall face at Huangling No. 2 Coal Mine as the engineering background. By integrating theoretical analysis, physical similarity simulation experiments, and field measurements, the research systematically explores the zonal linkage evolution mechanism of mining-induced depressurization gas migration and storage zones, together with the associated depressurization gas extraction technology. A flow regime determination equation, driven by the fracture expansion coefficient and permeability, is established on the basis of the fluid Reynolds number criterion. According to differences in gas flow states and medium morphology, the mining-induced fracture field is divided into five distinct zones: a high-permeability zone dominated by turbulent transport, a medium-to-high permeability zone with transitional flow as the secondary dominant region, a low-permeability zone featuring linear laminar flow with micro-permeability, an extremely low-permeability zone characterized by linear laminar flow in a locked state, and a zone of abrupt permeability change associated with gas enrichment. The dynamic evolution of depressurization gas migration and storage zones and their regional linkage mechanisms are clarified. On the basis of these findings, a dynamic targeted layout strategy for high-level boreholes is proposed that is consistent with the spatiotemporal evolution of the overburden permeability field. Field engineering practice shows that the optimized high-level borehole layout maintains the overall gas extraction rate at the drilling site stably above 70%, with a peak value of 93.7%, thereby ensuring safe and efficient mining of the working face. Full article

CO₂/N₂-enhanced coalbed methane recovery (ECBM) offers a potential route to improve coalbed methane production, reduce CH₄ emissions, and couple gas drainage with low-carbon coal development. However, the relative roles of adsorption-controlled replacement and pressure-driven displacement under deep stress conditions remain insufficiently resolved. Here, CO₂ and N₂ injection experiments were conducted under different vertical stresses to quantify the evolution of gas flow, breakthrough time, increase in coal gas content, replacement–displacement ratios, and injection efficiency. Increasing stress compressed the pore–fracture network, reduced gas transport capacity, and delayed breakthrough of the injected gas. CO₂, because of its strong adsorption affinity, remained dominated by replacement throughout the injection process. Higher stress enhanced CO₂ retention in coal and therefore its potential storage capacity, but it also weakened sustained CH₄ recovery by restricting transport. In contrast, N₂, which adsorbs weakly, rapidly shifted to displacement-dominated recovery after breakthrough. Although high stress delayed the formation of connected displacement pathways, N₂ maintained high injection efficiency. These results show that stress controls the dominant ECBM mechanism by regulating adsorption retention, seepage transport, and displacement outflow. The findings provide a mechanistic basis for selecting injection gases and designing low-carbon ECBM strategies in deep coal seams. Full article

In modern farm management, accurate detection of estrus behavior in dairy cows is essential for improving reproductive efficiency and enabling intelligent decision-making. Although fisheye lenses offer a wider field of view, they often introduce image distortion. This leads to geometric and scale deformation of cow mounting behavior features, which reduces detection accuracy. To address this issue, a lightweight model called Boundary-Enhanced Frequency-Domain Feature Pyramid Network YOLO (BFFPN-YOLO) was developed. It is designed for detecting dairy cow mounting behavior under fisheye imaging, incorporating boundary enhancement and frequency-domain compensation. Initially, the backbone network was equipped with the multi-scale dilated fusion structure SPPELAN. This structure expands the receptive field and preserves detailed information, thereby enhancing boundary modeling for targets with scale variations. Subsequently, a boundary-enhanced frequency-domain feature pyramid network (BFFPN) module was designed for reconstructing the top-down transmission path in the Neck. The module is composed of the frequency-domain detail compensation FreqFusion and the spatial attention enhancement SEAM. By strengthening boundary responses, compensating for high-frequency details, and replacing the traditional upsampling and concatenation operations, it effectively mitigates blurred target boundaries in images of dairy cow mounting behavior. The improved algorithm demonstrates strong detection performance, achieving a Precision of 88%, a Recall of 84.5%, and an mAP@0.5 of 92.7%. Compared with the original YOLOv11, these metrics were increased by 3.8, 2.3, and 4.6 percentage points, respectively. The model parameter count was reduced by 1.10 × 10⁶. In complex scenarios, edge features and high-frequency details of dairy cow mounting behavior are more accurately captured by the improved model. These improvements provide a reliable technical basis for the intelligent detection of estrus behavior. Full article

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

Hard roofs in longwall mining may form large, suspended strata, which induce strong abutment stress redistribution. Therefore, a rational face support design is essential for ground control. This study develops an analytical numerical framework to evaluate support roof interaction under hard roof conditions. A segmented beam foundation model is established for the support roof system, and an equivalent variable foundation modulus is introduced to represent the reduced bearing capacity of yielded coal ahead of the working face. The analytical results are checked against a Particle Flow Code (PFC) and Fast Lagrangian Analysis of Continua (FLAC) coupled model, showing good agreement in the magnitude and location of the peak abutment stress. Parametric analyses are then conducted to examine the effects of support intensity and support distance on roof deflection, rotation, bending moment, shear force, strain energy density, and abutment stress. The results show that increasing support capacity reduces roof deformation and coal wall stress, while redistributing the same capacity over a longer support distance more effectively lowers roof strain energy concentration and inclined fracture development. However, the longer distance, lower density arrangement may transfer stress deeper into the coal seam and increase peak stress fluctuation during face advance. The proposed study provides a practical method for comparing face support schemes under low position hard roof conditions. Full article

The curing quality of epoxy resin at wind turbine blade joint seams critically affects blade integrity and service reliability, yet conventional metallic heating systems often suffer from poor temperature uniformity, limited flexibility, and slow thermal response. In this study, a flexible and lightweight heating blanket based on carbon nanotube (CNT) electrothermal film was developed for blade reinforcement and in situ curing applications. The device employs a multilayer composite architecture consisting of a CNT heating layer, a nano-aerogel thermal insulation layer, a thermoplastic polyurethane electrical insulation layer, and a silicone-coated glass fiber protective layer, together with an intelligent temperature control system. The resulting blanket, with a total thickness of 3.85 mm, exhibited rapid and stable heating performance, increasing from 25 to 120 °C within 8 min. Under resin-curing conditions, it achieved an initial heating rate of 7.2 °C min⁻¹ and a temperature uniformity of ±2.6 °C, markedly outperforming a conventional Ni@Cr alloy heating blanket. Accelerated aging tests further demonstrated stable electrothermal performance under the tested condition. Those results indicate that the proposed CNT-based heating blanket provides an efficient and reliable thermal management strategy for large curved composite structures. Full article

Goaf gas drainage and residual-coal spontaneous-combustion prevention are often designed independently, even though both are controlled by the same leakage-flow, oxygen-transport and heat-release fields in a longwall goaf. This decoupled design may reduce methane accumulation while unintentionally enlarging the oxidation zone. Taking the No. 1217 fully mechanized working face of Zhongxing Coal Mine, Shanxi Province, China, as an engineering prototype, this study develops an integrated laboratory-field numerical framework to quantify the drainage-induced evolution of the three zones of spontaneous combustion. Programmed temperature-rise experiments on the No. 2 coal seam were used to determine the oxygen-consumption rate, heat-release intensity and apparent activation energy under oxygen concentrations of 3–21%, yielding a critical oxygen concentration of 5.9%. Bundle-tube monitoring and distributed optical-fiber temperature sensing delineated the in situ three-zone boundaries, and a three-dimensional CFD model coupling porous-media seepage, species transport and Arrhenius-type heat generation was validated against the field data, with most relative errors below 5%. Parametric simulations for buried-pipe depths of 20, 30 and 50 m and negative pressures of 15 and 20 kPa reveal a pronounced asymmetric response: drainage compresses and advances the return-side oxidation zone toward the working face, but drives the inlet-side oxidation zone deeper into the goaf by enhancing oxygen-bearing leakage. Within the investigated parameter space, a buried depth of 30 m and a negative pressure of 20 kPa provide the best compromise, reducing the return-side oxidation-zone width from 32 to 21 m and the upper-corner methane concentration from 6.80% to 0.58%. The results demonstrate that drainage design should be constrained simultaneously by methane dilution and oxidation-zone control, and provide a quantitative basis for coordinating gas extraction with fire prevention in gas-rich, oxidation-prone longwall panels. Full article

To address the rockburst hazard caused by overhanging hard roofs and difficult caving during the initial mining period of thick coal seam fully mechanized working faces, this study takes the N4202 fully mechanized top coal caving working face of the Santunzi Coal Mine as the field engineering background. The mined No. 4-1 coal seam has an average thickness of 9.46 m, and its overlying hard roof is composed of medium sandstone and siltstone. A total of 39 hydraulic fracturing boreholes, including type A, type B, type C1/C2, and fan-shaped holes, were deployed, with a designed fracturing depth of 19 m. Three testing means, including a CXK12(B) borehole imaging instrument, a KJ1222 microseismic monitoring system, and on-site roof caving observations, were adopted to comprehensively evaluate the field performance of roof hydraulic fracturing, and the rockburst prevention mechanism was analyzed. The field test results indicate that dense and well-connected fractures are formed after fracturing, with more than 8 fractures per single borehole and a fracture aperture of 0.8–2.2 mm, and the connectivity rate between adjacent fracturing boreholes reaches 92.3%. The initial mining top caving step distance of the working face is reduced to 13.2 m, while the theoretical calculated values are 10 m for the immediate roof and 15.6 m for the main roof. The roof gradually collapses, and the mining pressure is alleviated. During fracturing, the frequency and energy of microseismic events increase by 285% and 230%, respectively, compared to the state before fracturing. In the subsequent mining process, the maximum microseismic energy is only 4.56 kJ, which is far lower than the rockburst critical energy threshold (20 kJ) of this mine. Therefore, no rockburst hazard occurs in the working face. These research findings can provide a practical technical reference for rockburst prevention using hard roof hydraulic fracturing in similar thick coal seam fully mechanized mining faces. Full article

Hot-water bottles are widely used domestic heat sources, but seam and neck failures can cause scald injuries, and quantitative evidence supporting replacement guidance remains limited. This study compared the tensile behaviour of unused, dry-stored hot-water bottles manufactured in 2022 and 2024, focusing on vulcanised rubber and plasticised PVC constructions. ISO 37 Type 1 dumb-bell specimens were excised from body panels and seam regions and tested in uniaxial tension at 23 ± 2 °C and 50 ± 5% RH using a grip-separation rate of 500 mm min⁻¹. Stress–strain curves were analysed to determine maximum stress, failure strain, toughness and tangent modulus, with seam and face specimens compared within each material year cohort. PVC specimens were consistently stiffer and stronger than rubber specimens but failed at lower strain. Manufacturing year-associated differences were material-dependent: PVC-2022 generally showed higher maximum stress and toughness than PVC-2024, whereas Rubber-2022 underperformed Rubber-2024 at large strain. Seam–face ordering also depended on material and year, with PVC faces outperforming seams, while rubber showed cohort-specific behaviour. These findings indicate that hot-water bottle durability is influenced by both material system and joint region, supporting the need to consider seam performance alongside bulk material properties in safety assessment and replacement guidance. Full article

Accurate identification of acid-producing layers is key to controlling acid mine drainage (AMD) in abandoned coal mines. This study collected 337 core samples from 34 boreholes in the Modigou mining area, Shanxi, China, and established a combined static–mineralogical–kinetic approach to evaluate the acid-generating and neutralization potentials of sulfur-bearing rocks. Three-stage net acid generation (NAG) tests identified the pyrite-bearing layer of the Benxi Formation and the No. 10 coal seam of the Taiyuan Formation as the main acid producers, with NAG values of 360.41 and 97.87 kg H₂SO₄/t, respectively, while the Taiyuan limestone showed a high neutralization capacity (ANC = 490 kg H₂SO₄/t). NAG pH was strongly negatively correlated with sulfur content (Pearson r = −0.75, p < 0.01). Sulfide oxidation acid production showed staged attenuation, with average decreases of 64.81% and 47.65% in the second and third stages. Humidity cell experiments demonstrated continuous acid production over 63 days under dry–wet cycles, with increased acid generation rates at higher flow velocities (Darcy flux: 3.54 × 10⁻³ cm/s for accelerated vs. 8.84 × 10⁻⁴ cm/s for standard conditions). Multi-dimensional flow-through simulations confirmed the AMD formation mechanism of “acid supply, buffer, and fracture conduction”. The identified acid-producing layers matched well with field discharge points. This multi-method coupling system provides a theoretical basis for source control of AMD in abandoned high-sulfur coal mines in the Yellow River Basin. This study did not account for microbial catalysis, which is a key limitation of the static chemical oxidation method used. Full article

The connection between dissimilar materials, Ti and steel, has been a focal point for global scholars. Establishing a high-strength bond between Ti alloy and stainless steel offers the potential to harness their respective advantages and reduce production costs, holding significant applications and far-reaching implications. Currently, non-transition welding methods for Ti/steel, primarily diffusion welding and vacuum brazing, have been pivotal in the early stages of development. Despite their simplicity and convenience, effectively avoiding the formation of brittle Ti–iron compounds in the weld seam, these methods face challenges such as unwelded defects, posing a risk to the reliability of welded structures under service conditions. This limitation restricts their application in products requiring high reliability. The evolving transition welding process, progressing from a single metal interface layer to a multi-metal interface layer, addresses some of the shortcomings of traditional Ti and steel connections, offering promising application prospects. This article delves into the core issue of selecting interface-layer elements and welding methods. Through an analysis of the metallurgical properties of transition metals in conjunction with Ti and steel, the study investigates the impact of single- or bimetallic elements, such as Cu, V, Nb, and Ni, on preparing interface-layer transition metals. A comprehensive review of existing research on Ti and steel welding is presented, with an emphasis on the metallurgical characteristics of their connection. The influence of element selection and welding processes on the metallurgical features and relevant mechanical properties of the weld metal is systematically analyzed and summarized. Full article

CO₂-enhanced coalbed methane recovery and storage (CO₂-ECBM) is a promising approach for improving methane recovery and increasing CO₂ storage in low-permeability coal seams. However, limited injectivity and insufficient criteria for injection parameter optimization remain major constraints. Taking the No. 11-2 coal seam of the Zhangji Coal Mine in the Huainan mining area as the study object, this study established a thermo–hydro–mechanical coupled model that considers CO₂/CH₄ competitive adsorption, matrix diffusion, fracture seepage, gas–water two-phase flow, coal deformation, and porosity–permeability evolution. A 10-year numerical simulation was conducted to evaluate the effects of initial porosity, initial permeability, elastic modulus, CO₂ injection pressure, and injection scheme on CO₂-ECBM performance. The comprehensive sensitivity results show that initial porosity, CO₂ injection pressure, and initial permeability are the dominant controlling factors, whereas elastic modulus has a relatively weak influence. Initial porosity mainly determines reservoir storage space and CO₂ sequestration potential; permeability controls pressure propagation and gas migration; and injection pressure directly affects CH₄ displacement intensity, CO₂ storage capacity, and reservoir safety margin. Multi-objective evaluation indicates that the injection pressure should be controlled within 8.0–9.0 MPa, with 8.0–8.5 MPa recommended for long-term stable operation. When the engineering objective prioritizes CO₂ storage or CH₄ recovery and sufficient safety margin is confirmed, the injection pressure may be increased to approximately 9.0 MPa. Continuous constant-pressure injection favors cumulative CH₄ production and CO₂ storage, whereas stepwise pressurization reduces early pressure disturbance and improves later-stage injectivity. Therefore, an injection strategy combining early-stage stepwise pressurization with middle- and late-stage constant-pressure injection is recommended. These results provide a reference for injection parameter optimization in similar low-permeability coal reservoirs. Full article

“Interbedded water in thin coal seams” is characterized by its high degree of concealment and complex hydraulic connections. However, due to the confined space of underground mine tunnels and severe electromagnetic interference from metal structures, traditional geophysical methods struggle to accurately delineate the boundaries of water accumulation, making this a major and challenging water hazard in coal mines. Taking the Qinhua Coal Mine in Xinjiang, China, as the engineering context, this paper investigates the detection of water accumulation in interbedded coal seams within goaf areas using the cross-hole resistivity method. It proposes a cross-hole resistivity tomography scanning approach characterized by “progressive depth penetration and layer-by-layer traversal,” and employs an inversion method based on inequality constraints to obtain relatively detailed and reliable imaging results. Through resistivity imaging analysis, low-resistivity water accumulation anomalies were successfully delineated, and water accumulation dead zones were identified. Based on the detection results, effective drainage was carried out beneath the water-filled zones. Subsequent follow-up surveys confirmed the disappearance of the low-resistivity anomalies, thereby validating the reliability and engineering practicality of the cross-hole resistivity tomography method for precisely detecting water body boundaries under complex geological conditions in coal seams. Full article

This study investigates the mechanical performance of a pulsed laser butt-welded IN792 DS joint and its relationship to its microstructure by means of grid nanoindentation. A new ISE-free (rate-derived) hardness parameter (H_R) has been introduced to account for the local bulk elastoplastic behavior of the material in combination with the stable contribution of residual stress, thus overcoming the limitations of the current standard codes. It allows performance comparability between different welding experiments, materials, and joint configurations. It offers an alternate means to mechanically determine the HAZ width when microscopic and metallurgical methods fail to detect it. Moreover, the spectra of two independent indentation parameters have been utilized as an input within an iterative statistical deconvolution scheme to estimate the composition of the relevant phases present within the fused zone. While one parameter spectrum acted as a predictor in the first stage, the second one served as a corrector for the final estimation of the four detected phases, thereby self-validating the iteration procedure with 5% tolerance. The validity of phase estimation was first determined over the entire FZ and then at three levels of the weald seam (top, neck and bottom) for further validation. The results indicate that the γ-matrix and ultrafine fine/hard second phases in the fused zone amounted to 54% and 43% volume fractions, respectively. The associated deconvoluted mechanical performance, expressed in terms of E_IT, H_IT, and H_R, corresponded to approximately 209 ± 4.5, 6.3 ± 0.2, 4.4 ± 0.1 and 224 ± 7.0, 6.7 ± 0.1, and 4.6 ± 0.1 GPa, respectively. A correlation between the estimated phases and the local mechanical performance via the conventional indentation parameter (H_IT and E_IT) and the new H_R parameter in the three relevant regions of the fused zone was discussed while discerning the effect of cooling rate on precipitate size, heterogeneity, porosity, residual stresses, and grain orientation. Further validation studies on different sample geometries, materials and joint configurations are needed to confirm the generality of the proposed methodology. Full article