Search Results (1,696)

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

Bolting height is a key genetic trait that affects the stress tolerance, environmental adaptation, and winter survival of Brassica napus winter rapeseed. It is particularly important for enhancing winter survival in the arid–frigid regions. This study aimed to elucidate the genetic relationship between bolting height and cold stress tolerance, thereby supporting breeding for enhanced cold tolerance. Ninety-five winter rapeseed accessions were used in this study. Through both spring and autumn sowing trials, the dynamic changes in bolting height under different environments were systematically analyzed, and the genetic stability of bolting height as well as its correlation with cold tolerance were clarified. Bolting height showed consistent variation trends between spring and autumn sowing trials, exhibiting high genetic stability. It displayed an extremely significant negative correlation with cold tolerance: genotypes with lower bolting height possessed stronger cold tolerance. The regulatory mechanism underlying low bolting and cold tolerance was revealed at cellular and molecular levels. Low bolting accessions exhibited flat and broad shoot apical meristems, with small and compact cells, a high nucleoplasmic ratio, and indistinct vacuoles. The gibberellin synthesis gene BnaA06g24070D was downregulated, while the key cold-tolerant gene BnCBF5 was upregulated. Exogenous hormone treatment preliminarily verified the causal regulatory effect of bolting height on cold tolerance. In both spring and autumn sowing trials, bolting height at the initial flowering stage showed an extremely significant positive correlation with vernalization index, with correlation coefficients of 0.80 and 0.78, respectively. Lower bolting height corresponded to a smaller vernalization index and stronger temperature sensitivity. Moreover, bolting height at the initial flowering stage showed an extremely significant negative correlation with comprehensive cold tolerance scores, with correlation coefficients of −0.77 and −0.80, respectively. Low-bolt materials had significantly higher overwintering rates and comprehensive cold tolerance scores, as well as a markedly lower semi-lethal temperature (LT₅₀), compared with high-bolt accessions. Low-bolt accessions presented significantly prolonged bolting stage, bud stage, initial flowering stage, and whole growth durations, and their agronomic trait stability across years was significantly superior to that of high-bolt accessions. This study confirmed that low bolting height is a crucial breeding trait for the cold tolerance of winter rapeseed, and thus an important selection indicator for the cold tolerance improvement of winter rapeseed in arid–frigid regions in northern China. Full article

Ensuring the stability of the excavation face is essential for tunnel excavation. Existing limit equilibrium models mainly adopt two-dimensional wedge mechanisms to estimate the minimum support force for tunnels, which cannot accurately represent the failure characteristics of practical tunnels. To address this limitation, a three-dimensional logarithmic spiral sliding model is developed based on the limit equilibrium method and strength reduction technique. The model introduces an equivalent area approach to represent heterologous sections and establishes the global moment equilibrium equation using the slice method. Taking the Huashansong tunnel as a case study, a parametric analysis is conducted on the reinforcement performance of end-anchored and fully bonded rock bolts. The results indicate that the diameter, strength, and density of bolts affect the stability of the excavation face, and the No. 11 end-anchored bolt and No. 37 fully bonded bolt are recommended. Furthermore, numerical simulation shows that the maximum extrusion deformation of the excavation face decreases from 11.57 mm without bolts to 9.13 mm and 8.46 mm for the No. 11 end-anchored bolt and No.37 fully bonded bolt, while tunnel convergence deformation decreases from 4.06 mm to 3.42 mm and 3.23 mm, respectively. The application of the No. 37 fully bonded bolt in the Huashansong tunnel controls the extrusion deformation and convergence deformation within 9.25 mm and 4.47 mm, ensuring the stability and economy of the tunnel excavation. Full article

This study aims to enhance the damage controllability and overall seismic resilience of assembled underground structures under earthquake actions. To achieve this, three types of prefabricated roof–sidewall composite joints are proposed based on the design concepts of cogging for force transfer and local strengthening. These include the high-strength bolt–cogging–grouting sleeve joint (HCG), the prestressed steel strand–cogging–grouting sleeve joint (PCG), and the UHPC–cogging–grouting sleeve joint (UCG). Following the principle of positioning joints in regions of low structural stress, four 1/4-scale reinforced concrete (RC) specimens were designed and fabricated, including one cast-in-place (CIP) reference specimen and three precast RC specimens. Quasi-static tests were carried out to systematically evaluate the seismic behavior and internal force distribution of each specimen. Numerical validation was also performed using ABAQUS. The results show that both UHPC and a reasonable application of prestressing can effectively inhibit crack initiation and damage propagation at the joint seams. When the composite joints are positioned outside the plastic hinge region, they provide a reliable load transfer path for the reinforcement. The HCG and UCG joints significantly enhance the load-bearing capacity and energy dissipation capacity of the specimens. Their ductility and energy dissipation both achieve a seismic performance equivalent to that of the CIP specimen. Furthermore, damage in these specimens is predominantly confined to the designated plastic hinge region of the roof. This effectively mitigates shear damage in the roof–sidewall connection zone (RSC). Although the PCG joint improves the initial stiffness of the specimen, its energy dissipation capacity and ductility are reduced. It also causes damage to be transferred to the RSC. This leads to increased shear deformation and premature shear failure in this zone. Consequently, both UHPC and a reasonable application of prestressing can be used for the prefabrication of underground structures. Positioning the joints outside the roof plastic hinge zone can effectively achieve the seismic design goal of “strong joint, weak component”. Full article

Predicting the concrete breakout strength of an expansion anchor embedded in short carbon fiber-reinforced concrete (SCFRC) is challenging due to the nonlinear and heterogeneous nature of fiber–matrix interaction. This study develops an Artificial Neural Network (ANN) model to estimate the breakout capacity of a single expansion anchor installed in SCFRC. Experimental data from 48 cases covering variations in compressive strength, tensile strength, fiber volume fraction, and fiber length were used to train and validate multiple ANN architectures in MATLAB’s Regression Learner. A 4-4-1 trilayered ANN with Rectified Linear Unit (ReLU) activation and 5-fold cross-validation achieved the most reliable performance, yielding R² values of 0.6726 (validation) and 0.9376 (test), with correspondingly low RMSE, MAE, and scatter index (SI < 0.1). SHAP-based sensitivity analysis identified tensile strength as the dominant predictor, contributing 70.78% to model output influence. ANN predictions were compared with the Concrete Capacity Design (CCD) model adopted by ACI and the National Structural Code of the Philippines (NSCP) and a multiple linear regression (MLR) model, showing that while the ANN is not the most precise model, it provides acceptable accuracy and captures nonlinear concrete breakout behavior more effectively than linear approaches. Results demonstrate that the ANN framework offers a viable data-driven tool for estimating concrete breakout strength in SCFRC anchorage systems. Full article

To solve the problems of easy fracture of reaming cutter arms and mechanical jamming leading to equipment damage when mechanical reaming equipment is used for anchor hole reaming in soft rock roadways, this study proposes the development of a high-efficiency reaming device with a simple structure. This study combines theoretical analysis, numerical simulation, and laboratory experiments to systematically investigate the key parameters of high-pressure water jet reaming equipment. The results show that under the same conditions, the maximum velocity of the high-pressure water jet decreases with an increase in the number of nozzles and the nozzle spacing. Although the correlation between the maximum jet velocity and nozzle angle is weak, the jet velocity acting on the anchor hole wall reaches its peak at a nozzle angle of 60°. Based on the simulation results, a 1:1 scale nozzle model was manufactured using 3D printing technology, and high-pressure water jet reaming experiments and bolt pull-out tests were carried out at a pressure of 20 MPa. The experimental results demonstrate that the optimal reaming effect is achieved with a nozzle configuration of 3 nozzles, 10 mm spacing, and a nozzle angle range of 45–60°. Specifically, after reaming with the nozzle at a 60° angle and 10 mm spacing, the bolt anchoring force reaches 51.99 kN, representing a 41.16% increase in anchoring strength compared with conventional anchoring. This research provides technical support for the engineering application of anchor hole reaming technology in soft rock roadways and is of great significance for improving the support effect of soft rock roadways. Full article

Transmission towers are typically composed of angle steel members connected by ordinary bolts to form spatial truss systems, in which joint slip under axial loading can significantly influence structural performance. In subsidence areas, corrective lifting of tilted towers may cause internal force redistribution, transforming some compression members into tension members and resulting in joints subjected to both compressive and tensile forces. To investigate the slip deformation behavior of angle steel bolted connections under bidirectional axial loading, a series of experiments was conducted on specimens with different angle sizes and bolt numbers, complemented by finite element analysis. The results show that the load–slip relationship exhibits distinct staged characteristics, which can be divided into an initial linear stage, a slip stage, and a hole-bearing stage. The initial slip displacement is generally less than 1 mm, while the slip load and ultimate capacity increase significantly with bolt number, with the ultimate capacity under tension increasing by up to approximately 160% as the number of bolts increases from one to three. Although the slip evolution under compression and tension is generally similar, pronounced differences appear near the ultimate state, indicating a clear directional asymmetry. Based on these findings, a three-stage piecewise mechanical model is established, and a simplified bidirectional slip model is proposed by introducing asymmetric ultimate displacement and capacity parameters. Finite element simulations reproduce the failure modes and load–slip responses with good agreement, confirming the validity of the proposed model. The findings provide a useful reference for the design and performance evaluation of angle steel bolted connections in transmission tower structures. Full article

To support low-cost, non-destructive crop growth monitoring, this study systematically compared different vegetation indices, voxel sizes, and camera angles using a point cloud voxelization approach combined with a vegetation index weighted canopy volume index (CVM_VI) to assess aboveground biomass (AGB) in winter oilseed rape (Brassica napus L.). Field experiments were conducted from 2021 to 2024 at the Yangma Experimental Base of the Chengdu Academy of Agricultural and Forestry Sciences. Red, green, blue (RGB) imagery of oilseed rape was acquired using an unmanned aerial vehicle (UAV) during the following five key growth stages: seedling, bolting, flowering, podding, and maturity. Collected images were processed to generate point clouds, which were subsequently voxelized at four resolutions (0.03, 0.05, 0.07, and 0.1 m). CVM_VI was constructed by integrating vegetation indices (VIs) derived from the RGB data and the voxelized canopy structural information. Regression models were established between the CVM_VI values and field-measured AGB to estimate biomass. Model performance was evaluated using the coefficient of determination (R²), root mean square error (RMSE), and relative error (RE). There were strong correlations (r > 0.80) between the estimated and measured AGB across all voxelization treatments throughout the growth period. Among the 20 VIs tested, regression methods based on the blue green ratio index (BGI), color intensity index, blue red ratio index, vegetative index, and green red ratio index consistently showed superior estimation performance across three consecutive years, demonstrating their good applicability for estimating AGB in oilseed rape under varying agronomic conditions (different varieties, densities, and sowing dates). The cubic regression model CVM_BGI performed best under a 45° UAV camera angle, with the highest R² and lowest RMSE and RE (2021–2022: R² = 0.864, RMSE = 2414.18 kg/ha, RE = 14.8%; 2022–2023: R² = 0.754, RMSE = 2550.53 kg/ha, RE = 14.9%; 2023–2024: R² = 0.863, RMSE = 1953.61 kg/ha, RE = 22.9%). Since the estimation performance showed negligible differences among voxel sizes, and the 0.1–m voxel offered the smallest data volume and shortest analysis time, the CVM_BGI model with a 0.1–m voxel was selected as the preferred approach, providing a practical balance between estimation performance and processing demand. These findings highlight the application potential of point cloud voxelization technology for crop biomass estimation. This study proposes a novel, non-destructive, and efficient framework for estimating field crop AGB using low-cost UAV RGB imagery, facilitating the wider adoption of UAV technology in practical agricultural production. Full article

As mining operations progressively advance to greater depths to meet increasing mineral demand, there is a growing need to develop new or improved rockbolts capable of effectively dissipating energy under dynamic loading conditions. Impact laboratory tests provide valuable insights into the dynamic performance of rockbolts; however, such tests require considerable time and cost associated with specimen preparation and experimental validation. Numerical modeling represents a robust alternative which, when properly calibrated with laboratory results, can accurately simulate the deformation process and energy dissipation mechanisms of support elements. This paper presents the implementation and results of a numerical model developed to simulate the dynamic behavior of a threadbar subjected to impact loading. The model explicitly represents all components of a full-scale impact test configuration, including the impact mass, reaction frame, threadbar geometry, grout, and steel tube. The numerical model enables real-time analysis of the dynamic response and interaction among the test components (steel tube, grout, and bolt). The implemented numerical codes were calibrated and validated against published laboratory results of threadbar dynamic behavior. Subsequently, a comprehensive parametric analysis was conducted to evaluate the response of each component in terms of load, displacement, and dissipated energy. The results allowed identification of the primary factors governing the dynamic response of the rockbolt system. The proposed methodology can be extended to other reinforcement systems and provides relevant insights into the design of bolts under dynamic loading conditions. 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

The combined arch theory provides an effective means for designing support parameters in roadways within loose and fractured surrounding rock. A clear understanding of the internal stress evolution during the load-bearing process of the combined arch is of guiding significance for optimizing roadway support. Taking the 11308 return airway of a mine in Inner Mongolia as the engineering background, this study adopts a combined research approach of theoretical calculation, numerical simulation and laboratory testing. It systematically investigates the internal stress evolution of the anchored combined arch load-bearing structure in roadways with loose and fractured surrounding rock. The load-bearing capacity and failure characteristics of the anchored combined arch under different roof support schemes are explored and analyzed. An optimized support scheme for the loose and fractured roof is proposed and applied in the field, and the monitoring results verify its effectiveness. The results indicate that bolt density is a key factor affecting the load-bearing performance of the combined arch. As bolt spacing decreases, the vertical stress concentration in the anchored structure increases, and its deformation resistance is enhanced. During the stage from load-bearing to failure of the combined arch, the changes in vertical and horizontal stresses within the arch become more stable, and the load-bearing capacity is significantly improved. Comparison between the model test results and theoretical calculations shows good agreement, verifying the rationality of the theoretical calculations. Pressure sensors were pre-installed in the laboratory model to monitor the vertical stress changes in the anchored structure throughout the loading process, and numerical simulations confirmed the stress concentration effect of the combined arch. It was also found that the instability of the anchored structure is controlled by the shear plane at the arch feet. Finally, the bolt spacing in the 11308 return airway of the Inner Mongolia mine was optimized to 0.7 m, and field monitoring was introduced. The maximum roof surface settlement displacement was 15 mm, and the maximum roof separation was 3 mm, confirming that these parameters can meet the roadway stability requirements. Full article

TC4DT (ELI) is a damage-tolerant titanium alloy characterized by high fracture toughness and slow crack propagation rates, and is, therefore, considered one of the standard materials for model fasteners in modern equipment. However, its high yield strength leads to excessive tool wear and forming defects. This paper presents a complete FE simulation framework to investigate the thread-rolling process of TC4DT(ELI) bolts M16 × 1.5. Using the actual geometries of the workpiece and rollers, an elasto-plastic three-dimensional finite element model was built in ABAQUS/Explicit to perform verification simulations, with the theoretical blank diameter and forming force as the reference benchmarks. The simulation results agreed well with the actual industrial data. This study carried out single-factor analyses of the effect of three important process parameters—the roll speed, friction coefficient, and initial temperature—on the resulting stress–strain distribution, forming force, and thread formation depth. A modal analysis was performed in ANSYS Workbench to check the structural integrity and avoid resonance while operating. According to the results, the optimized parameters decreased the maximum forming force by 14.8% and improved thread filling. Compared with experimental data, the simulation error in the blank diameter was controlled within 1.2%. The present work, a reliable numerical underpinning for replacing expensive and time-consuming trial-and-error processes, forms a basis for high-performance titanium alloy fasteners and assists in the wider application of such fasteners in modern equipment and any advanced manufacturing industries. Full article

Accurate prediction and optimization of assembly accuracy are critical to ensuring assembly quality and efficiency for multistage connected aero-engine rotors. To mitigate the effects of residual alignment errors induced by repeated component measurements and to avoid the formation of bowed rotors caused by conventional stacking strategies that only minimize parallel misalignment, a harmonic decomposition-based registration method is proposed to unify inconsistent measurement datums among multiple setups. Meanwhile, key assembly process parameters are considered simultaneously, including front-and-rear support concentricity, front-and-rear bearing mounting face end-face runout, rotor blade-tip runout, and rotor unbalance. Taking the discrete assembly phase angles of each rotor stage as independent variables, a multi-objective genetic algorithm is adopted to realize the assembly accuracy prediction and optimization of multistage flange-bolted rotors. The proposed method is validated using a four-stage simulated rotor assembly. Experimental results show that the harmonic decomposition-based registration method improves the average geometric prediction accuracy of rotor assembly by 1.2 percentage points, with the prediction error of geometric assembly parameters for each stage not exceeding 8.4% and the unbalance prediction error not exceeding 29.0%. Compared with random assembly, four-objective comprehensive optimization achieves significant reductions in all objectives: front-and-rear support concentricity is reduced by 66.2%, front-and-rear support shoulder end-face runout by 63.9%, blade-tip runout by 16.7%, and unbalance by 33.8%. The residual alignment error compensation method and stacking optimization strategy proposed in this study provide valuable engineering guidance for improving rotor assembly prediction accuracy and enhancing assembly reliability. Full article

High-strength bolts are critical structural components that are highly susceptible to corrosion in complex environments, posing significant threats to structural safety and reliability. Although acoustic emission (AE) technology has been widely applied in structural health monitoring, existing studies mainly focus on damage mode identification or source localization, while the identification of corrosion evolution stages based on AE signals remains insufficient. This study develops an intelligent corrosion diagnosis framework for high-strength bolts by integrating multimodal feature fusion and optimized machine learning. AE signals are first collected from the near-end and far-end of bolts using a wireless sensor network and then transformed into time–frequency representations via continuous wavelet transform (CWT). The resulting time–frequency images are fed into a modified ResNet-18 network to extract deep features, while statistical features are simultaneously extracted from the raw signals to preserve global information. These heterogeneous features are subsequently fused to form a comprehensive representation of corrosion characteristics. Furthermore, an artificial protozoa optimizer (APO) is introduced to adaptively optimize the hyperparameters of the XGBoost model. The results demonstrate that AE signals generated by hammering bolts with different corrosion levels can be successfully distinguished. The proposed method achieves high accuracy in corrosion stage classification and outperforms conventional approaches. Even when evaluated on an additional M30 bolt dataset, the proposed method maintains robust performance, demonstrating excellent generalization capability across different bolt sizes. These results demonstrate the practical potential of the proposed method for intelligent bolt corrosion diagnosis. Full article

Assembled H-shaped steel strut (AHSS) has been widely applied in deep excavation projects. In this study, the collapse failure of AHSS C1 in a deep excavation project in China was investigated. The collapse of C1 was directly attributed to the settlement of its supporting columns in the mid-span, which was triggered by a nearby pit bottom leakage through an exploration borehole. Then the implementation of the emergency measures and reconstruction works were introduced. Theoretical and numerical pre-assessments confirmed that the reconstructed C1 exhibited adequate safety for strength, in-plane stability and out-of-plane stability, with all steel components and bolts within their safe limits. The good working performance of reconstructed C1 was finally verified through the monitoring results (i.e., strut axial force, soil horizontal displacement, column vertical displacement, road settlement and building settlement) of the foundation pit during the subsequent soil excavation and basement construction. This study is believed to provide references for future excavation projects using AHSS with similar risks. Full article