Search Results (397)

Blasting is one of the most widely used and cost-effective techniques for rock excavation and fragmentation in open-pit mining, particularly for large-scale operations. However, repeated or poorly controlled blasting can generate excessive ground vibrations that threaten slope stability by causing structural damage, fracturing of the rock mass, and potential failure. Evaluating the effects of blast-induced vibrations is essential to ensure safe and sustainable mining operations. This study investigates the impact of blasting-induced vibrations on slope stability at the Saindak Copper-Gold Open-Pit Mine in Pakistan. A comprehensive dataset was compiled, including field-monitored ground vibration measurements—specifically peak particle velocity (PPV) and key blast design parameters such as spacing (S), burden (B), stemming length (SL), maximum charge per delay (MCPD), and distance from the blast point (D). Geomechanical properties of slope-forming rock units were validated through laboratory testing. Slope stability was analyzed using pseudo-static limit equilibrium methods (LEMs) based on the Mohr–Coulomb failure criterion, employing four approaches: Fellenius, Janbu, Bishop, and Spencer. Pearson and Spearman correlation analyses quantified the influence of blasting parameters on slope behavior, and sensitivity analysis determined the cumulative distribution of slope failure and dynamic response under increasing seismic loads. FoS values were calculated for both east and west pit slopes under static and dynamic conditions. Among all methods, Spencer consistently yielded the highest FoS values. Under static conditions, FoS was 1.502 for the east slope and 1.254 for the west. Under dynamic loading, FoS declined to 1.308 and 1.102, reductions of 12.9% and 11.3%, respectively, as calculated using the Spencer method. The east slope exhibited greater stability due to its gentler angle. Correlation analysis revealed that burden had a significant negative impact (r = −0.81) on stability. Sensitivity analysis showed that stability deteriorates notably when PPV exceeds 10.9 mm/s. Although daily blasting did not critically compromise stability, the west slope showed greater vulnerability, underscoring the need for stricter control of blasting energy to mitigate vibration-induced instability and promote long-term operational sustainability. Full article

In the industrial practice of metal forming, the consistent and reasonable characterization of the material behavior under the coupling effect of strain, strain rate, and temperature on the material flow stress is very important for the design and optimization of process parameters. The purpose of this work was to establish an appropriate constitutive model to characterize the rheological behavior of a hot-formed steel plate (22MnB5 steel) produced through the TSCR (Thin Slab Casting and Rolling) process under practical deformation temperatures (150–250 °C) and strain rates (0.001–3000 s⁻¹). Subsequently, the material flow behavior was modeled and predicted using the Johnson–Cook flow stress constitutive model. In this study, uniaxial tensile tests were conducted on 22MnB5 steel at room temperature under varying strain rates, along with elevated-temperature tensile tests at different strain rates, to obtain the engineering stress–strain curves and analyze the mechanical properties under various conditions. The results show that during room-temperature tensile testing within the strain rate range of 10⁻³ to 300 s⁻¹, the 22MnB5 steel exhibited overall yield strength and tensile strength of approximately 1500 MPa, and uniform elongation and fracture elongation of about 7% and 12%, respectively. When the strain rate reached 1000–3000 s⁻¹, the yield strength and tensile strength were approximately 2000 MPa, while the uniform elongation and fracture elongation were about 6% and 10%, respectively. Based on the experimental results, a modified Johnson–Cook constitutive model was developed and calibrated. Compared with the original model, the modified Johnson–Cook model exhibited a higher coefficient of determination (R²), indicating improved fitting accuracy. In addition, to predict the material’s damage behavior, three distinct specimen geometries were designed for quasi-static strain rate uniaxial tensile testing at ambient temperature. The Johnson–Cook failure criterion was implemented, with its constitutive parameters calibrated through integrated finite element analysis to establish the damage model. The determined damage parameters from this investigation can be effectively implemented in metal forming simulations, providing valuable predictive capabilities regarding workpiece material performance. Full article

The accurate description of plasticity and fracture behavior is essential in numerically investigating the mechanical responses of high-strength bolts under tension, shear and coupling loads. However, based on the von Mises criterion, inputting the constitutive relation and damage model from the tensile coupon test into the finite element method cannot properly predict the shear behavior of high-strength bolts. Cylindrical tensile coupons and shear specimens of common and weathering high-strength bolts are tested to obtain the complete tensile and shear responses. The combined S-V model and the modified shear constitutive model are collaboratively used to calibrate and describe the tensile and shear constitutive relations of high-strength bolts, and then the Bao–Wierzbicki model is used to predict the tensile and shear fracture behaviors. Furthermore, the collaborating method is used to discuss the applicable range of tensile and shear constitutive models for high-strength bolts under a tensile–shear coupling load, based on numerical analysis against available experimental data in the literature. The loading angle of 30° along the bolt rod is defined as the cut-off to differentiate high-strength bolts under a tensile- or shear-dominated state, and the corresponding mechanical responses of high-strength bolts can be predicted well based on the tensile and shear constitutive models, respectively. Full article

Roof water inrush accidents in coal mine driving roadways occur frequently in China, accounting for a high proportion of major coal mine water hazard accidents and causing serious losses. Aiming at the lack of research on the mechanism of roof water inrush in driving roadways and the difficulty of predicting water inrush accidents, this paper constructs a local damage criterion for coal–rock mass and a seepage–fracture coupling model based on peridynamics (PD) bond theory. It identifies three zones of water-conducting channels in roadway surrounding rock, the water fracture zone, the driving fracture zone, and the water-resisting zone, revealing that the damage degree of the water-resisting zone dominates the transformation mechanism between delayed and instantaneous water inrush. A discriminant function for the effectiveness of water-conducting channels is established, and a single-index prediction and evaluation system based on damage critical values is proposed. A “geometry damage” dual-control water inrush prediction model within the PD framework is constructed, along with a non-local action mechanism model and quantitative prediction method for water inrush. Case studies verify the threshold for delayed water inrush and criteria for instantaneous water inrush. The research results provide theoretical tools for roadway water exploration design and water hazard prevention and control. Full article

The aim of this work was to study the influence of temperature and strain rate on the formability and structure of C22 steel. This study was based on tensile and compression tests. In the case of the compression test, the study of the influence that the process parameters (temperature and strain rate) have on the nonuniformity of the deformation was taken into account. This work presents an experimental analysis of the effects of temperature and strain rate on the mechanical and structural properties of C22 mild steel. Uniaxial tension and compression testing at high temperatures (800 °C, 900 °C, 1000 °C, and 1100 °C) and strain rates 0.001 1/s, 0.012 1/s, and 0.089 1/s for tension and 6.35 1/s, 5.72 1/s, 4.67 1/s and, respectively, 0.106 1/s for the compression hammer and hydraulic press served as the foundation for the studies. Analysis was carried out on how temperature and strain rate affected yield stress, strain to fracture, hardness, and structural evolution. Additionally, the nonuniformity of the deformations obtained at various temperature and strain rate values was examined. The fracture behavior of C22 steel can be enhanced by raising the deformation temperature and lowering the strain rate. In the tensile tests, the study of stress and strain distribution and the variation in the normalized Latham–Cockroft failure criterion was performed by numerical simulation using FORGE^® NxT 4.1 software. Full article

Granite is the main rock type in hot dry rock reservoirs, and hydraulic fracturing is always required during the process of geothermal production. It is necessary to understand the strength parameters and failure criterion of granite after high-temperature and water-cooling treatment. In this paper, laboratory uniaxial and triaxial compression experiments are carried out on granite samples after high-temperature and water-cooling treatment. Combined with some experimental data collected from pre-existing studies, the variation behaviors of cohesion (c), the internal friction angle ($\phi$) and tensile strength $\left({\sigma }_{\mathrm{t}}\right)$ are systematically studied considering the heating and cooling treatment. It is found that c and $\phi$ generally show two different types of variation behaviors with the increasing heating temperature. Tensile strength decreases in a similar way for the different granite samples with the increasing treatment temperature. Empirical equations are provided to describe these strength parameters. Finally, a modified Mohr–Coulomb failure criterion with a “tension cut-off” is established for the granite samples, considering the effects of high-temperature and water-cooling treatment. This study should be helpful for understanding the mechanical behavior of hot dry rock during hydraulic fracturing in geothermal production, and the proposed failure criterion can be applied for the numerical modeling of reservoirs. Full article

In cold regions, the rock mass of open-pit mine slopes is continuously exposed to freeze–thaw (FT) environments, during which the fracture structures and their infilling materials undergo significant degradation, severely affecting slope stability and the assessment of service life. Conventional laboratory FT tests are typically based on uniform temperature settings, which fail to reflect the actual thermal variations at different burial depths, thereby limiting the accuracy of mechanical parameter acquisition. Taking the Wushan open-pit mine as the engineering background, this study establishes a temperature–depth relationship, defines multiple thermal intervals, and conducts direct shear tests on structural plane filling materials under various FT conditions to characterize the evolution of cohesion and internal friction angle. Results from rock mass testing and numerical simulation demonstrate that shear strength parameters exhibit an exponential decline with increasing FT cycles and decreasing burial depth, with the filling material playing a dominant role in the initial stage of degradation. Furthermore, a two-dimensional fracture network model of the rock mass was constructed, and the representative elementary volume (REV) was determined through the evolution of equivalent plastic strain. Based on this, spatial assignment of slope strength was performed, followed by stability analysis. Based on regression fitting using 0–25 FT cycles, regression model predictions indicate that when the number of FT cycles exceeds 42, the slope safety factor drops below 1.0, entering a critical instability state. This research successfully establishes a spatial field of mechanical parameters and evaluates slope stability, providing a theoretical foundation and parameter support for the long-term service evaluation and stability assessment of cold-region open-pit mine slopes. Full article

Magnesium (Mg) alloys are gaining widespread use in the automotive and construction industries for their potential to enhance performance and lower manufacturing costs, making them ideal for lightweight structural applications. However, despite these advantages, extruding Mg alloys remains technically challenging due to their inherently limited formability and the strong crystallographic textures that form during deformation. This study aimed to comprehensively characterize the ductile fracture behavior of ZM51M Mg alloy round bars under various stress states and to improve the reliability of ductile failure predictions through the application and calibration of multiple uncoupled damage criteria. Tensile and compressive tests were conducted on specimens of varying geometries (dogbone, notched R5, shear, uniaxial compression, and plane strain compression specimens) and dimensions, meticulously cut along the extrusion direction of the round bar. These tests encompassed a wide spectrum of stress–strain responses and fracture characteristics, including uniaxial tension, uniaxial compression, and shear-dominated states. An inverse analysis approach, involving iterative numerical simulation coupled with experimental data, was employed to precisely determine fracture strains from the test results. The plastic deformation behavior was accurately modeled using the combined Swift–Voce hardening law. Subsequently, three prominent uncoupled ductile fracture criteria—Rice–Tracey, DF2014, and DF2016—were calibrated against the experimental data. The DF2016 criterion demonstrated superior predictive accuracy, consistently yielding the most accurate fracture strain predictions and significantly outperforming the Rice–Tracey and DF2014 criteria across the tested stress states. The findings of this work provide significant insights for improving the assessment of formability and fracture prediction in Mg alloys. This research directly contributes to overcoming the challenges associated with their inherent formability limitations and complex deformation textures, thereby facilitating more reliable design and broader adoption of Mg alloys in advanced lightweight structural solutions. Full article

This study considers the impact and penetration of composite targets by steel projectiles. Firstly, experiments on the impact of homogeneous polymethyl methacrylate (PMMA) targets were simulated using the finite element method (FEM) and the incubation time fracture criterion (ITFC). Next, targets were assumed to be composed of cells with weakened mechanical properties, forming a composite barrier. The composite impact problems were then used to demonstrate an approach, which can be applied to overcome the typical difficulties for impact simulations—high demands on computing resources, long computation times, and potential numerical instabilities arising from high stresses in the contact zone and high strain rates. The approach is based on the use of artificial neural networks (ANNs) trained on arrays of numerical results obtained via finite element method. Full article

The development of shale bedding and fractures exacerbates the invasion of drilling fluid, leading to significant reservoir damage. This article elucidates the strength degradation behavior of shale with bedding orientations of 0° and 90° under drilling fluid immersion, as determined through triaxial compression experiments. An improved Hooke–Brown anisotropic strength criterion has been established to quantitatively characterize the degradation effects. Additionally, a dynamic mechanism of pore pressure accumulation was simulated. The research findings indicate the following: (1) As the intrusion pressure increases from 6 MPa to 8 MPa, the penetration depth significantly increases. In the horizontal bedding direction (0°), cracks dominate the flow mode, resulting in a sudden drop in strength; (2) An increase in bedding density or opening exacerbates the degree of invasion and strength degradation in the horizontal bedding direction, with a degradation rate exceeding 40%. In contrast, the vertical bedding direction is influenced by permeability anisotropy and crack blockage, leading to limited seepage and minimal degradation. By optimizing the dosage of emulsifiers and other treatment agents through orthogonal experiments, a low-viscosity, high-shear-strength plugging oil-based drilling fluid system was developed, effectively reducing the invasion depth of the drilling fluid by over 30%. The primary innovations of this article include the establishment of a quantitative model for Reynolds number degradation for the first time, which elucidates the mechanism of accelerated crack propagation during turbulent transition (when the Reynolds number exceeds the critical value of 10). Additionally, a novel method for synergistic control between sealing and rheology is introduced, significantly decreasing the degradation rate of horizontal bedding. Furthermore, the development of the Darcy–Forchheimer partitioning algorithm addresses the issue of prediction bias exceeding 15% in high-Reynolds-number regions (Re > 30). The research findings provide a crucial theoretical foundation and data support for the optimized design of drilling fluids. Full article

Conventional bolts frequently fail under large deformations due to stress concentration in soft rock tunnels. In contrast, yielding bolts incorporate energy-absorbing mechanisms to sustain controlled plastic deformation. This study employed FLAC3D to numerically investigate the pull-out, shear, and bending behaviors of yielding bolts, evaluating their support effectiveness in soft rock tunnels. Three-dimensional finite difference models incorporating nonlinear coupling springs and the Mohr–Coulomb criterion were developed to simulate bolt–rock interactions under multifactorial loading. Validation against experimental pull-out tests and field measurements confirmed the model accuracy. Under pull-out loading, the axial forces in yielding bolts decreased more rapidly along the bolt length, reducing stress concentration at the head. The central position of the maximum load-bearing capacity in conventional bolts fractured under tension, resulting in an hourglass-shaped axial force distribution. Conversely, the yielding bolts maintained yield strength for an extended period after reaching it, exhibiting a spindle-shaped axial force distribution. Parametric analyses reveal that bolt spacing exerts a greater influence on support effectiveness than length. This study bridges critical gaps in understanding yielding bolt behavior under combined loading and provides a validated framework for optimizing energy-absorbing support systems in soft rock tunnels. Full article

Due to the difficulty of creating directional fractures efficiently and accurately with existing non-explosive rock-breaking methods, a directional fracturing technique utilizing a coal-based solid waste expansive agent, termed the instantaneous expansion with a single fracture (IESF), has been developed. IESF can generate high-pressure gases within 0.05–0.5 s and utilize gas pressure to achieve directional rock fragmentation. The rock-breaking mechanisms under double-borehole conditions of conventional blasting (CB), shaped charge blasting (SCB), and IESF were studied by theoretical analysis, numerical simulation, and in situ test. The gas pressure distribution within directional fractures of IESF was determined, and the crack propagation criterion between double-borehole was established. Numerical simulation results indicated that the stress distribution in CB was random. SCB exhibited tensile stress of −10.89 MPa in the inter-borehole region and −8.33 MPa on the outer-borehole region, while IESF generated −14.47 MPa and −12.62 MPa in the corresponding regions, demonstrating that stresses generated between adjacent boreholes can be superimposed in the inter-hole region. In CB, strain was concentrated along main fractures. SCB exhibited strains of 7 mm and 8 mm in the shaped charge direction, while non-shaped charge directions showed a strain of 1.5 mm. For IESF, strain in the shaped charge direction measured 6 mm, compared to 1 mm in non-shaped charge directions, resulting in superior directional fracture control. In situ test results from Donglin Coal Mine demonstrated that IESF can form superior directional rock-breaking efficacy compared to both CB and SCB, with the average crack rates of 95.5% by IESF higher than 85.0% by SCB. This technique provides a non-explosive method that realizes precise control of the direction of cracks while avoiding the high-risk and high-disturbance problems of explosives blasting. Full article

The Bohai Strait is a special tectonic region in North China, characterized by strong fault activity and frequent seismic events. In this study, we analyzed the stress state across the Bohai Strait in detail by integrating the stress data derived from the hydraulic fracturing measurements in four boreholes along the strait (i.e., Pingdu, Xiangli, Changdao, and Gaizhou from south to north) and evaluated its implications for seismicity. The results reveal that the gradient coefficients of the maximum (S_H) and minimum horizontal stresses (S_h) with depth in Xiangli and Changdao are over 1.59 and 1.87 times the corresponding stresses of the North China Block. However, the S_H and S_h in Pingdu and Gaizhou do not exceed 50.2% and 59.4% of those of the North China Block. The stress values increase as the distance approaches the interaction of the regional faults in the Bohai Strait. The S_H orientation in the Bohai Strait region is N68.67 ± 9.30° E, consistent with the prevailing NEE–E-W regional stress direction. According to the Coulomb friction failure criterion, the friction coefficients of the four boreholes range from 0.24 to 0.52, lower than the theoretically critical limit for inducing fault slip in the upper crust (i.e., Byerlee’s law). The faults in the strait region are considered to be contemporarily stable but need to be further evaluated, considering more influencing factors. This study provides a new, instructive understanding of the variations in the stress state in the Bohai Strait region. Full article

Variations in the warm formability of AA7075 sheets are primarily attributed to differences in precipitate morphology resulting from distinct thermal histories. To better understand this relationship, this study systematically investigates the influence of precipitate characteristics—quantified by the product of precipitate volume fraction and average radius—on forming limits across various thermal routes in warm forming processes. A modified Cockcroft–Latham ductile fracture model incorporating this microstructural parameter was developed, calibrated against experimental data from warm isothermal Nakajima tests, and implemented within a finite element framework. The proposed model enables the accurate prediction of forming limit curves with minimal experimental effort, thereby significantly reducing the reliance on extensive mechanical testing. Building upon the validated FE model, a practical methodology for rapid R-value estimation under warm forming conditions was established, involving the design of specimen geometries optimised for isothermal Nakajima testing. This approach achieved R-value predictions within 5% deviation from conventional uniaxial tensile test results. Furthermore, experimental results indicated that AA7075 sheets exhibited nearly isotropic deformation behaviour under retrogression warm forming conditions. Overall, the methodology proposed in this study bridges the gap between formability prediction and process simulation, offering a robust and scalable framework for the industrial optimisation of warm forming processes for high-strength aluminium alloys. Full article

In coal seam mining operations, the presence of overlying water bodies presents persistent challenges, particularly during multi-seam extraction, where water accumulation in upper seam goafs requires careful management. This study examined the Lingzhida Coal Mine, focusing on the geological conditions of the 3# seam (upper) and the 15# seam (lower), as well as the distribution of water accumulation in the corresponding goafs. The mechanism of water inrush from the upper goaf was studied, and the role of the water-resisting belt (WRB) is suggested. By utilizing empirical equations and field measurements, a method for calculating the floor fracture depth of the 3# seam and the roof fracture height of the 15# seam was derived through multi-linear regression analysis. Based on the relationship between the thickness of the WRB (H_w) and the protective layer (H_p), a classification criterion for the water-inrush risk (the likelihood of water entering the lower seam from the upper goaf) is proposed. The mining area was divided into four risk zones: high-risk (H_w < 0), medium-risk (0 ≤ H_w < 0.5H_p), low-risk (0.5H_p ≤ H_w < H_p), and safe (H_w ≥ H_p). Then, an adaptive zoning approach for water-preserved mining was introduced, considering the spatial distribution of goaf water. This approach incorporates water-preserved mining technologies, including the staggered layout of working faces, reduction in mining height, and the transfer–storage of water resources. These research findings provide crucial insights for ensuring the safe and efficient extraction of the multi-seam. Full article