Geological tectonic processes lead to the widespread development of joints and fractures in deep rock masses. During service, such rock masses are affected not only by rainfall infiltration and groundwater seepage but also by dynamic disturbances such as blasting and earthquakes. The combined effects of seepage, static stress, and dynamic loading alter the stress and deformation states of fracture surfaces, promoting crack initiation, propagation, and coalescence and thereby inducing complex failure responses. As structural weaknesses in rock masses, joints and fractures substantially reduce the overall load-bearing capacity and constitute key factors governing the mechanical response and failure modes of rock masses subjected to seepage and dynamic disturbances. To investigate the dynamic mechanical response and energy-absorption characteristics of bolted fractured rock under a simulated deep hydro-mechanical environment, bolts were fabricated from high-strength, high-toughness, and high-ductility negative Poisson’s ratio (NPR) steel, 45# steel, and Q235 steel. Hydro-mechanically coupled split Hopkinson pressure bar (SHPB) tests were then conducted to comparatively examine the dynamic strength, secant modulus, failure modes, and energy-dissipation characteristics of fractured sandstone reinforced with the three bolt types at different fracture inclination angles. The tests were performed under a fixed hydro-mechanical environment comprising an axial static stress of 27 MPa, a confining pressure of 27 MPa, and a seepage water pressure of 6 MPa, with fracture inclination angles of 0°, 15°, 30°, 45°, and 60°. The results show that NPR bolts markedly improve the dynamic load-bearing and energy-absorption capacities of fractured sandstone. The dynamic peak stresses of the NPR-bolted specimens were 10.22%–39.44% and 19.85%–48.12% higher than those of the specimens reinforced with 45# steel and Q235 steel bolts, respectively. For all three bolted specimen groups, the peak stress first increased and then decreased with increasing fracture inclination, while the NPR-bolted specimen reached a maximum peak stress of 80.00 MPa at an inclination of 15°. Failure-mode analysis indicates that the bolts restrained relative fracture displacement by carrying axial and transverse loads and enhancing resistance to sliding along the fracture surface. At 15°, the NPR-bolted specimen was characterized primarily by tensile cracking and slight particle spalling, without evident block instability. Based on the experimental analysis, a theoretical model incorporating dynamic loading, axial static stress, confining pressure, and seepage water pressure was established. Parameter sensitivity analysis was further conducted to examine the potential effects of environmental parameters on the distribution of axial and shear forces in the bolts, thereby revealing the governing role of the angle between the bolt and fracture plane in the mechanical response stages and energy evolution. These findings provide a theoretical basis and parameter support for the design of rock-bolt reinforcement in deep engineering rock masses subjected to dynamic disturbances.

Influenced by the superposition of mining on double key strata, the gob-side entry in the fully mechanized top-coal caving mining of extra-thick coal seams is highly susceptible to severe ground pressure phenomena, such as rock bursts and significant roadway deformations. This area represents a critical focus for prevention and control during the mining process. Therefore, this article focuses on the fully mechanized caving mining of thick coal seams at the Caojiatan mine. It analyzes the distribution and migration characteristics of the key stratum in the overlying stratum and establishes a mechanical model of the transverse pressure bearing structure in the mining area. The analysis covers the transition of the transverse pressure bearing structure through four states, from a virtually stable state to an unstable state, filling the gap left by traditional S-R theory in analyzing the transverse pressure bearing structure in the mining area, and revealing the mechanism of strong mining pressure manifestation along the gob-side entry in the ultra-thick coal seam under the influence of double key strata. The results indicate that the main factors affecting the manifestation of strong mining pressure along the goaf are the pressure-boosting effect caused by the instability of the double-key strata, the excessively long cantilever length of the lateral pressure-bearing structure, and the underfilling of the goaf gangue. To this end, a combination of directional energy accumulation blasting and enhanced blasting for roof cutting and pressure relief technology was proposed to reduce the cantilever length of the pressure-bearing structure and increase the filling degree of collapsed gangue, thereby reducing the pressure of the roadway to control deformation. The effect of this technology was comprehensively studied using numerical simulation and on-site experiments, verifying the effectiveness of this technology in controlling the deformation of the roadway surrounding rock. The peak pressure decreased by a maximum of 18.5%, and the average step distance decreased by 41%. The maximum reduction in tunnel deformation is 81.9%. This study provides a scientific basis for the deformation control of the roadway under similar conditions.

In response to the static/dynamic loading challenges faced by bolt support in deep engineering, a generalized macroscopic constitutive model suitable for Negative Poisson’s Ratio (NPR) bolts has been developed. This model integrates a generalized hardening law with the Mises yield criterion and an associated flow rule to simulate both yield and post-yield responses under a wide range of loading conditions. To facilitate numerical implementation, a subroutine was embedded into the ABAQUS environment. The model’s performance was validated against experimental results from high-temperature quasi-static (25–600 °C) and high strain-rate dynamic (0.1–1000 s−1) tensile tests, demonstrating excellent agreement with Pearson correlation coefficients exceeding 0.9984. Additionally, the Akaike Information Criterion (AIC) was employed to benchmark the model’s predictive efficiency and parameter compactness against existing formulations, revealing a superior balance between accuracy and simplicity. Sensitivity analysis indicated that the elastic modulus (E) and hardening coefficient (B) are the primary factors influencing yield strength and hardening rate, accounting for 81.47

During the excavation of a deep-buried tunnel traversing a fault zone in Daliangshan mountain, asymmetric meter-level soft rock deformations occurred. This study investigates the instability mechanisms of such deformations in the Daliangshan Tunnel and corresponding support strategies. The High-Stress Compensation Tunneling (HSCT) method was employed in this study, which was developed based on the fundamental principles of Negative Poisson’s Ratio (NPR) anchor cable technology. Through two physical model tests, comparative analyses were conducted on deformation evolution patterns of surrounding rock and mechanical responses of support systems under both conventional and NPR cable coupled supports, considering distinct rock mass conditions (non-fault zone vs. fault zone). Results demonstrate that NPR cables exert a constant resistance and yielding effect on rock masses, enabling controlled deformation. Consequently, the rock-support system was endowed with adaptive adjusting capacity, significantly reducing deformation (approximately 83.17 % reduction in field tests) and stabilizing the mass. By establishing a mechanical failure model for conventional support conditions, we elucidated instability mechanisms at the vault and arch spandrels. NPR cables enhance shear strength along dominant structural planes at the left spandrel and vault, suppressing shear slippage. Simultaneously, they reduce bending moments in rock layers at the right spandrel, inhibiting bending-shear failures. This approach effectively controls meter-scale deformations to centimeter-level magnitudes, validating NPR cable support system efficacy for surrounding rock control. The study provides new scientific foundations for supporting deep-buried cross fault tunnel.

To address the technical challenges such as long construction preparation cycles and severe roadway deformation of withdrawal roadway, taking the withdrawal roadway of Qinglong Coal Mine as the engineering research object, a rapid entry-forming technology for withdrawal roadway combining roof cutting and pressure relief with mining instead of excavation is proposed. By conducting similar physical simulation tests, the movement and evolution laws of overlying strata during the automatic entry-forming process are systematically revealed; on this basis, the required support parameters are derived by combining mechanical model and numerical simulation methods. The research results show that: through pre-splitting and slitting treatment on the roof, the technology promotes the preferential caving of the immediate roof on the slitting side, and the bulged rock forms an effective bearing support for the main roof, significantly reducing its subsidence. When the roof cutting angle is controlled between 10 degrees and 20 degrees and the roof cutting height is set between 8 m and 10 m, the surrounding rock stress can be uniformly released, the stress concentration phenomenon is significantly weakened, the deformation of the roof and two sides tend to be stable, and the overall surrounding rock structure shows a good control effect. Based on the above research conclusions, targeted suggestions for the on-site application of the technology are put forward. The results of engineering practice verification show that the roof cutting and pressure relief automatic entry-forming technology has effectively solved the core problem of surrounding rock control in the working face withdrawal roadway, and can provide technical reference and promotion application basis for other coal mines with similar geological conditions.

Expressways constitute essential lifeline infrastructure supporting regional interconnection and optimizing social spatial patterns. However, geohazards including landslides severely threaten expressway networks, making landslide-triggered risk assessment essential. Conventional static zoning-based evaluations predominantly neglect network functions and fail to effectively quantify the geohazard impacts on network connectivity. To address this gap, this study proposes a landslide risk assessment framework integrating Random Forest (RF) susceptibility modeling and complex expressway network topological analysis for validation in Guangdong Province, China. Using 13 influencing factors, the RF model produces landslide susceptibility maps with a test set Area Under the Curve (AUC) of 0.893, where relief, slope, elevation, geological units, and monthly mean rainfall serve as primary drivers. Furthermore, landslide susceptibility is converted into segment failure probability, and an undirected weighted expressway network graph with 49715 nodes and 45063 edges is established. Betweenness centrality and comprehensive risk index (Re) are adopted for quantitative characterization. One random failure and three targeted failure scenarios are developed to simulate variations in global network efficiency and the relative size of the largest connected component. Results indicate that around 22% of core segments govern network connectivity. The Re effectively distinguishes high-risk segments (20% of all edges), among which 6.5% are extremely high-risk links featured by high landslide sensitivity and vital structural importance. Municipal-level risk assessment ranks Huizhou, Yunfu, Heyuan, Meizhou, and Shanwei as the top five cities. These findings provide scientific support for provincial expressway landslide risk mitigation and optimal emergency resource allocation for critical segments.

Revealing the disaster-inducing mechanisms of fracturing instability and the evolution patterns of fracture fields in the overburden during the mining of deeply buried extra-thick coal seams serves as the theoretical foundation for preventing hazards such as water and sand inrushes in coal mine working faces. Based on the mining geological conditions of the 2301 working face in a mine in Shaanxi Province, China, this study investigated the fracture movement and dynamic distribution characteristics of the fracture field in the overburden through a combined approach of numerical simulation, fractal theory, fracture entropy theory, mechanical modeling, and field measurements. Firstly, the dynamic evolutions of fracture rate, fractal dimension, fracture length, and fracture entropy in the overburden were analyzed from the perspective of the mining-induced fracture field. Besides, the proportions of open and closed fractures, fracture length characteristics, and fractal evolution features in various sub-regions during mining were further revealed. Moreover, the anisotropy of spatial distribution of fractures in the overburden was quantified, and the equilibrium trajectory equation of the stress arch in the overburden was established. The following beneficial results were obtained. The overburden exhibits pronounced group-wise fracture movement behavior and periodic arching characteristics of the fracture arch, where the periodic arching fracture serves as the dominant fracture controlling the fracture field. The fractures within the fractured zone are distributed in an “arc shape”, and the average fracture rate and fractal dimension there are 2.40% and 0.81, respectively. The mining-induced fracture field evolves into a largely symmetrical “arc-shaped” topological structure. During mining, the fracture field successively experiences “stress field reconstruction, fracture initiation and propagation, structural instability and reorganization, and self-repair regulation”, while fractures in the overburden undergo a dynamic evolution process from “fracture opening” to “fracture closing”. In this process, dominant fracture groups merge to form interconnected fracture networks. Furthermore, the anisotropy of fracture spatial distribution in different regions of the fracture field was quantified in the light of the fracture entropy theory, and the evolution and distribution characteristics of fracture dip angles in various regions of the mining-affected overburden were statistically analyzed. Based on the three-hinged arch structure theory, the equilibrium trajectory equation of the stress arch in the overburden was established. Field measurement results disclose a water-conducting fracture zone height of 224 m and a fracture-to-mining ratio of 24.9, which closely align with the numerical simulation outcomes. The findings provide valuable insights for hazard prevention in working faces under similar geological conditions.

In this study, a series of scale-down biaxial compression tests are carried out on four typical rocks with varying strength and deformation characteristics to investigate the failure behaviors around circular openings in different lithologies. The basic mechanical properties are comparatively analyzed, followed by the failure process and mode, strain field evolution, and acoustic emission (AE) characteristics. The failure mechanisms are further discussed in terms of mineral composition and microscopic structure, as well as the strength-brittleness chart. Granite and sandstone exhibit brittle failure characterized by V-shaped spalling, small particle ejection, and tensile cracks, while marble and mudstone show more pronounced deformation failure with significant opening convergence. AE frequency distributions and b-values indicate a transition from high-frequency, large-scale cracking in high-strength rocks to low-frequency, smaller-scale failures in weaker rocks. AF-RA analysis further suggests a predominance of tensile fractures in granite and marble, whereas shear mechanisms dominate in sandstone and mudstone. Microstructural analysis reveals that mineral composition and fabric control these behaviors: granite's interlocking structure inhibits shear, marble's polygonal texture promotes tensile cracking, and weakened grain boundaries in sandstone and mudstone facilitate shear failure. A strength-brittleness chart is proposed for preliminary failure mode assessment, providing practical guidance for predicting rock behavior in engineering contexts.

Catastrophic events such as earthquakes, rockbursts, gas explosions, and terrorist attacks generate impact loads that pose severe challenges to the performance of protective materials. To meet the demands of such extreme service conditions, a novel quasi-negative Poisson's ratio (NPR) steel has been developed. This study systematically investigates its mechanical response and microstructural evolution across a broad strain-rate spectrum (10-4 to 6500 s-1) using quasi-static tensile tests, split Hopkinson tensile bar (SHTB) experiments, and electron microscopy (SEM/EBSD). The material exhibits pronounced strain rate sensitivity, with continuous yield strength enhancement, and a non-monotonic variation in both ultimate tensile strength and ductility. Notably, the steel demonstrates large deformability, suppressed necking, and excellent strength-ductility synergy. Microstructural analysis reveals that the densities of twins and dislocations are positively correlated with the increase in strain rate, which is consistent with the observed changes in mechanical properties. The excellent synergy between strength and ductility in this material is primarily attributed to the presence of nanoscale twins, which effectively impede crack propagation both within grains and along grain boundaries, while also providing ample space for dislocation slip and storage. In addition, an improved Johnson-Cook constitutive model, incorporating a modified strain rate sensitivity coefficient, was proposed to accurately capture its dynamic response. Comparative evaluations show that the NPR steel outperforms conventional high-strength steels in balancing strength and ductility under both quasi-static and high-strain-rate loading, highlighting its strong potential for applications in impact- and blast-resistant structures.

This study presents a new coal mining technique that uses top-cut unloading to induce the fragmentation and expansion of collapsed ore. Stress compensation and control are achieved by using a constant-resistance, large deformation anchor cable. The research employs laboratory physical model tests and an artificial neural network (ANN) time-series prediction model to monitor, analyze, and predict the movement and crack development of the overlying rock layers in tunnels. The results show that the support characteristics of constant-resistance, large-deformation anchor cables, combined with the filling effect of collapsed ore fragmentation and expansion, automatically form tunnel supports. This new mining method significantly reduces the displacement of the overlying rock layers and minimizes surface subsidence. Furthermore, the ANN time-series prediction model accurately forecasts displacement at multiple monitoring points in the overlying rock mass and the axial force of constant-resistance, large deformation anchors. This innovative mining method provides valuable insights for ecological protection and exploration of underground works.

Significant deformation and failure pose severe challenges to the stability of deeply buried soft rock roadways. Focusing on the soft rock roadways in the Wanfu Mine, this study elucidates the stress accumulation and release mechanisms of the surrounding rock through a combined approach of laboratory experiments, theoretical analysis, and numerical simulations. A resilience-oriented support strategy utilizing micro-NPR steel anchor cables is proposed and validated. Based on the zone failure range theory, the dimensions of the flow layer, plastic softening layer, and plastic hardening layer were calculated to optimize the lengths of long and short anchor cables. Static tensile tests and elastoplastic theoretical analysis were conducted to quantify and compare the energy absorption capacities of conventional and micro-NPR cables. Findings indicate that while conventional cables succumb to failure after energy absorption, micro-NPR cables effectively accommodate energy release without fracturing. Numerical results demonstrate that using PR and micro-NPR cables reduced roadway displacement by 13.8

The stability control of the surrounding rock in the deep coal mine roadway is of paramount importance. To this end, from the perspective of pressure relief, a novel roadway surrounding rock control technology using roof cutting by high-energy gas directional fracturing (HEGDF) has been proposed. Only one single crack surface will be generated along the preset direction of the borehole wall after HEGDF, resulting in directional fracturing and pressure relief on the roadway roof, which is beneficial for optimizing the stress environment of the roadway and improving its stability. First, a mechanical model of HEGDF was established, and the principle of roof cutting by HEGDF was analyzed. Then, taking the deep mining of Guotun Coal Mine as the engineering background, a three-dimensional finite element numerical model was established. The stress-strain-damage evolution law of HEGDF under high stress conditions was explored, and the initial circumferential stress distribution pattern of the hole wall after HEGDF was characterized. Subsequently, a roof cutting field test using HEGDF was conducted at Guotun Coal Mine. The results showed that the HEGDF can achieve an ideal directional rock fracturing effect under high stress, effectively cutting off the stress transmission path between the roadway roof and the goaf roof, thus achieving the goal of optimizing the roadway stress environment. This research offers a promising solution for the stability control of surrounding rock in deep coal mine roadways.

Flexible-formwork concrete (FFC) is widely adopted in gob-side entry retaining (GER). However, the roadside FFC wall cannot provide sufficient load-bearing capacity immediately after casting. This time-dependent strength gain induces a distinct structural and mechanical asymmetry-solid coal on one side versus a developing FFC wall on the other-which significantly amplifies advance-pressure-driven roof damage. Field inspections using borehole cameras in the N1215 panel of the Ningtiaota Coal Mine confirmed this failure mechanism, revealing severe roof fracturing and progressive degradation in the advance zone. To address this, a three-dimensional numerical model was established to reproduce the full mining process and identify the pressure zoning characteristics. Parametric comparative simulations were systematically performed considering three key design variables: advance support length, hydraulic prop spacing, and roof anchor cable spacing. To strictly quantify the control performance, a comprehensive evaluation system was defined, including roof stress increase rate, side abutment pressure increase rate, and deformation control rate. The results indicate that the advance-pressure-affected region extends significantly ahead of the face, and the marginal benefit of support intensification diminishes beyond specific thresholds. Consequently, a symmetry-enhancing "hydraulic prop-anchor cable coupled" advance support strategy was proposed to compensate for the inherent asymmetry of FFC-based GER. Field application in the belt transport roadway of the N1215 panel indicates that roadway convergence was effectively restrained, with roof-floor convergence of 13 mm and side convergence of 9 mm at the monitored section, confirming the applicability of the optimized design for maintaining entry stability during safe mining.

To investigate the influence mechanism of roof pre-splitting blasting on overlying strata movement in automated roadway formation without coal pillars, the mechanical response characteristics of the bearing structure of the overlying strata after pre-splitting blasting were analyzed. Comparative similar material simulation tests were conducted under two working conditions: with and without roof pre-splitting blasting. Combined with the proposed deformation analysis method based on settlement observation lines, key parameters of overlying strata movement under the two conditions were systematically compared. The results demonstrate that the influence of roof pre-splitting blasting on overlying strata movement is mainly reflected in three aspects: enhancing the caving and bulking effect of the overlying strata, weakening the fracturing and damage effect of the overlying strata, and reshaping the spatial effect of overlying strata fracturing. Based on in-situ borehole monitoring data obtained from the goaf surface, including flushing fluid loss, drilling speed, and core condition, the theoretical analysis and simulation test results were further validated. This study provides a scientific basis and theoretical support for precise control of strata movement, safe and efficient mining, and ecological environmental protection in mining areas under the condition of automated roadway formation without coal pillars.

The quasi-NPR (negative Poisson's ratio) steel is a new material developed for rock support design. While its superior shear resistance in small-scale unfilled joints has been experimentally demonstrated, the effects of joint length and infill thickness remain unclear. This study performs direct shear tests on quasi-NPR bolted joints with joint lengths of 100-400 mm and infill thickness-to-asperity height ratios (t/a) ranging from 0 to 2. During the shearing process, the axial force and strain of the bolts are continuously monitored, along with the acoustic emission (AE) characteristics of the joints. The experiments show that (1) the shear strength of quasi-NPR bolted joints varies more steadily compared to HRB400 bolted joints, indicating that quasi-NPR steel can mitigate the scale effect on joint shear strength. (2) The shear performance of quasi-NPR steel, including the deformation, axial strain, and axial force, shows it exhibits better deformation adaptability in large-scale joint, particularly when the joint length reaches 300 mm. (3) An increase in the t/a ratio leads to the failure mode of bolted joints to shift from sudden brittle instability to progressive plastic damage, as evidenced by AE signatures. The decrease in b value with increasing joint length shows longer joints expand the bolt's effective anchorage area, amplifying the dominance of shear cracks. Finally, the shear resistance of an 8-mm-diameter quasi-NPR steel calculated by a modified model shows the influence of t/a ratio becomes insignificant when the joint length exceeds 300 mm. These findings offer theoretical insights for the design of quasi-NPR steel in the support of rock mass with weak interlayer.

The 110 mining method is a novel coal mining approach that is environmentally friendly. To investigate the movement laws of the overburden strata under the mining conditions of this method, this study systematically analyzed the development characteristics and formation mechanisms of the “three zones” of the overburden strata (caving zone, fractured zone, and flexural subsidence zone). A predictive model for the development height of the “three zones” was established based on the mining damage invariant equation and the pressure arch theory, and a quantitative criterion for the boundary between the caving zone and fractured zone was proposed.To verify the reliability of the model, the 8302 working face of Jinjiazhuang Coal Mine was selected as the research object. A combination of theoretical analysis and on-site monitoring was employed to conduct prediction and in-situ monitoring experiments on the height of the “three zones” and the surface conditions of the goaf. The results show that the relative error between the predicted height of the caving zone by the model and the measured value is +0.38 ​m, and the relative error for the fractured zone height is −1.55 ​m, indicating a high prediction accuracy.The predictive model established in this study provides a theoretical basis for the safe and efficient mining as well as the overburden control in the 110 mining method. The research findings have significant engineering application value for promoting the development of green coal mining technologies.

Energy-focusing blasting has increasingly been applied to generate directional fractures in underground rock engineering, but the mechanistic link between the energy-focusing principle, directional fracture evolution, and practical charge design remains insufficiently resolved. This study integrates mechanics-based analytical modeling, coupled SPH–FEM simulation, and field testing to investigate the energy-focusing mechanism and its engineering application. The analytical framework identifies three localized actions governing guiding-crack initiation: focused compressive stress, circumferential tensile stress, and misaligned radial shear stress. It further distinguishes transient guiding-crack initiation from subsequent directional propagation driven by tensile opening and gas-wedge loading. The SPH–FEM reproduces the predicted sequence of stress localization, guiding-crack development, preferential detonation-product migration, and continued crack propagation. Under the modeled conditions, the directional mean peak particle velocity and effective stress in the focusing direction are 1.97 and 2.21 times those in the non-focusing direction. Five progressively charged single-borehole tests reveal a non-monotonic charge response: bilateral directional crack coverage initially increased and subsequently decreased as charging entered the overcharging regime. Furthermore, a staged three-threshold criterion is proposed to translate the mechanistic understanding into practical charge-design guidance. The criterion distinguishes guiding-crack initiation, sustained directional propagation, and the onset of non-focusing damage within a bounded operational charge window. The integrated findings advance the mechanistic understanding of energy-focusing blasting and provide a mechanism-based framework for site-calibrated charge selection under varying rock-engineering conditions.

The high-stress and intense dynamic loading conditions in deep underground engineering projects are becoming increasingly frequent. Poisson’s Ratio (PR) steel bolts, due to their weak energy dissipation capacity and insufficient impact resistance, often fail to effectively control the large deformations of caverns caused by dynamic disturbances such as rockbursts and explosions. This study focuses on a novel negative Poisson’s Ratio (NPR) steel bolt characterized by high constant resistance and high ductility, conducting a systematic comparative analysis with conventional PR steel bolts. Innovatively from the perspective of energy transfer and dissipation, it compares the dynamic response characteristics and anti-blasting capability of caverns supported by these two types of bolts. Test results indicate that the NPR bolt-supported cavern remained overall stable under blast loading, with only a few cracks appearing at the crown and sidewalls. In contrast, the PR bolt-supported cavern suffered severe damage, featuring extensive collapse and spalling of concrete at the crown. The NPR bolt support also improved the stress state within the supporting structure. Specifically, the PRMS values at the crown, energy-absorbing layer, and secondary lining in the PR bolt-supported cavern were 1.4 times, 2.8 times, and 53 times higher, respectively, than those in the NPR bolt-supported cavern. Frequency domain analysis revealed that the NPR bolt support broadened the distribution range of blast energy in the frequency domain, indicating a more dispersed energy transfer pattern. Conversely, under the PR bolt support system, energy was predominantly concentrated in the low-frequency band, reflecting severe energy aggregation that contributed to overload failure of the secondary lining. This research confirms that NPR bolts can significantly enhance the anti-blast protection capacity of underground caverns under dynamic impact, providing crucial technical support for deep underground engineering to withstand various dynamic impact loads and control nonlinear large deformations of surrounding rock.

This study investigates the coupled effects of freeze-thaw cycling (0, 20, 40 cycles) and low-frequency dynamic disturbance on sandstone with prefabricated fractures at three inclination angles (30°, 45°, 60°), using conventional and “static–dynamic–static” loading tests. Results show that inclination angle governs the failure mode: 45° specimens fail via “structural-plane-controlled” shear slip, with the lowest freeze-thaw strength deterioration (ηFT = 16.5%) and simple crack networks; 30° and 60° specimens fail via “matrix-damage-dominated” tensile cracking, with higher ηFT (27%–29%) and complex crack networks. Secant modulus degrades stepwise with freeze-thaw cycling but remains relatively stable during disturbance, consistent with the relatively stable acoustic emission (AE) b-value during cyclic loading. Across the conditions investigated, the b-value generally exhibits a late-stage rise followed by a drop as peak stress and specimen failure are approached, suggesting that this pattern may provide a specimen-scale indication of imminent instability. XRD and SEM analyses reveal freeze-thaw damage as a physical leaching process: clay mineral content decreases from 48% to 35%, while albite content drops from 14% to 8%, driving a shift from transgranular to intergranular fracture at 45°. These findings support stability assessment of open-pit cold-region slopes under coupled freeze-thaw and mechanical disturbance.

To enhance the anti-impact protective performance of armor systems and address the demands of lightweight armored vehicles and military equipment, a systematic study was conducted on the ballistic resistance of a silicon carbide (SiC) ceramic/novel TWIP (twinning-induced plasticity) steel composite structure. Samples of the SiC ceramic/TWIP steel composite and monolithic TWIP steel were fabricated for comparative analysis. Single-stage light gas gun plate impact experiments were performed at a flyer impact velocity of 500 m/s to obtain free-surface velocity profiles of both materials under high-velocity loading. The spall strength and strain rate sensitivity of the composite and monolithic steel were calculated from these profiles and statistically compared. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were employed to characterize the microstructural evolution and damage mechanisms, including microvoid nucleation, coalescence, and primary crack propagation, in the impacted samples. Numerical simulations were implemented using LS-DYNA, where the TWIP steel was modeled with the Johnson-Cook (J-C) constitutive equation, and a particle-based method was adopted to simulate the brittle ceramic phase. The simulations were extended to investigate spallation behavior at varying impact velocities and to evaluate the influence of different steel properties on composite performance. Experimental results demonstrate that the composite exhibits 22.76% and 7.09% enhancements in spall strength and strain rate sensitivity, respectively, compared to monolithic TWIP steel. Microstructural analysis reveals that both materials undergo ductile fracture characterized by microvoid coalescence; however, the composite shows significantly weaker spall damage, confirming its superior impact resistance. The numerical model achieves excellent agreement with experimental data, validating its predictive accuracy. Stress distribution analysis during the impact process identifies a critical crack-initiation velocity of approximately 225 m/s. Furthermore, the influence of steel properties on the anti-impact performance of the composite structure was analyzed, demonstrating that the novel TWIP steel exhibits superior performance.