Toppling failure is a typical type of disaster associated with rock slopes. The deformation behaviors and mechanisms underlying the evolution of rock slope toppling are complex, influenced by adverse geological conditions and external loads. Investigating the deformation characteristics, failure modes, and disaster mechanisms of rock slope toppling, as well as proposing methods for stability evolution, are urgent issues in slope engineering. Approximately 220 cases of toppling slopes in China have been collected, and the regional distribution of these cases is presented. The relationships between toppling failure and several key factors, such as slope height, slope angle, terrain obliquity, and lithology, are thoroughly analyzed. Building on existing classification methods for rock slope toppling, a four-level classification method is proposed based on the tendency relationship between the dominant discontinuity and the slope, the dominant or subordinate status of toppling deformation, the deformation characteristics of the toppling body, and the combination of toppling strata. The deformation behaviors and failure mechanisms of typical toppling types, including block toppling, flexural toppling, and composite toppling, are revealed through a combination of physical model tests and numerical simulations. Systematic presentations of stability analysis approaches, including the G&B method, equivalent continuum method, Liu method, cantilever beam method, and composite analysis method, are provided, along with discussions on their limitations and evolving trends. This research is expected to serve as an important reference for theoretical studies and engineering practices related to rock slope toppling.

Similar physical model tests in geotechnical engineering encounter significant challenges, particularly in accurately representing complex stratigraphic structures, engineering geometries, and structural plane morphologies. Conventional industrial 3D printing techniques often fail to meet the specific requirements of geotechnical modeling. To address this gap, we have developed a three-dimensional rapid prototyping system designed for fabricating large-scale similitude physical models of complex rock masses and engineering structures. This system employs a dual-nozzle pumping extrusion molding method and incorporates technological innovations in several key areas, including the pumping system, extrusion system, and dual-nozzle switching system. These advancements effectively resolve critical issues such as the extrusion of high-viscosity printing materials, material overflow during dual-nozzle switching, and frequent clogs during extended printing sessions. Functional tests demonstrate that the equipment can rapidly fabricate physical models of complex rock masses and engineering structures using multiple materials, exhibiting high forming precision, excellent printing compactness, fast printing speeds, straightforward disassembly, and ease of cleaning. Subsequently, the device was utilized to produce rock-like specimens containing weak interlayers and tunnel physical models with interlayer structures. Case study analyses confirm that the system effectively meets the demands of physical model testing in geotechnical engineering, providing valuable technical support for innovations in rock mechanics theory and the safe construction of infrastructure engineering projects.

The lateral confinement of the rock mass can significantly enhance the grout compressive bearing capacity of compression anchors. However, this bearing capacity is difficult to quantify. Current specifications adopt empirical calculation methods, which tend to result in large deviations in calculation results. To address the aforementioned challenges in quantitative calculation, this paper develops a mechanical model that considers limited cracking depth of the rock mass surrounding the grout, derives a method for calculating the grout compressive bearing capacity, and systematically analyzes the influences of relevant parameters. The results indicate that when limited cracking is allowed in the surrounding rock mass, the axial stress sustained by the grouted body increases significantly. This stress shows a marked increase with the propagation of crack depth, ultimately reaching the compressive bearing capacity at the critical cracking depth. Under identical crack depths in the rock mass, the axial stress sustained by the grouted body significantly increases with the elastic modulus of the grout and the tensile strength of the rock mass, while it decreases notably with an increase in the Poisson?s ratio of the grout and the elastic modulus of the rock mass. In contrast, the radius of the reinforcing bar and the Poisson?s ratio of the rock mass have negligible effects on the axial stress of the grouted body. To verify the method proposed in this study, field tests were conducted in moderately weathered granite. Through comparative analysis, the calculated results from this study are slightly larger than the measured values, but the overall trend is consistent with a high degree of agreement, which verifies the validity of the proposed method. This method provides valuable references for further theoretical research and engineering design related to the grout compressive bearing capacity of compression anchors.

To elucidate the full-stress-path evolution of gas permeability in deep sandstone reservoirs within the Fanjing block of the Dongying Sag, Shengli Oilfield, sandstone specimens were selected from burial depths of 1 970 to 3 375 meters, with axes oriented both perpendicular and parallel to the bedding. Systematic investigations were conducted using P-wave velocity measurements, X-ray diffraction, mercury intrusion porosimetry, and gas permeability tests to analyze permeability evolution across different stress stages and the underlying mechanisms. The results indicate that as burial depth increases, P-wave velocity rises while porosity and pore size diminish, suggesting a denser structure. Quartz is identified as the predominant mineral, with total clay content exhibiting a consistent decrease with increasing burial depth. The specimen at 2 601 meters displays a more developed pore structure and significantly higher initial permeability compared to specimens at other depths, highlighting the influence of local lithologic variations and structural complexity on permeability. During confining pressure loading, overall gas permeability decreases. In the context of triaxial compression, specimens with relatively higher permeability primarily undergo compaction, showing a continuous decrease in permeability, while denser specimens initially experience a decrease in permeability before increasing again as microcracks propagate under higher deviatoric stress. During the reconfinement phase, permeability decreases once more. The orientation of bedding has a pronounced impact on deformation and flow responses. This study reveals a stage-based mechanism characterized by confinement compaction, fracture-induced permeability enhancement, and recompaction during reconfinement, clarifying the influential roles of lithologic differences and pore structure on stress-flow coupling. These findings provide a crucial foundation for reservoir evaluation and the efficient development of deep hydrocarbon reservoirs in the Dongying Sag.

This study develops and implements a smooth joint model (SJM) within the framework of particle discontinuous deformation analysis (DDA). By integrating experimental results, the study investigates the strength and failure behavior of stratified rock samples subjected to various bedding inclinations and microparameters. Initially, seven stratified rock samples with differing bedding inclinations were created using the SJM, and a sensitivity analysis of the SJM microparameters was performed through uniaxial compression simulations. The results indicate that the compressive strength of the samples exhibits anisotropy with changing bedding inclination angles, with the highest strength observed at bedding angles of 0°or 15°and the lowest at 60°or 75°. The SJM tensile strength significantly influences samples with high inclinations, while cohesion notably affects samples in the mid-to-high inclination range. The internal friction angle of the SJM has a strong impact on samples within the 30°–75° range. In contrast, the SJM stiffness parameters have a minor effect on compressive strength. The elastic modulus of the samples is less influenced by bedding inclination and SJM strength parameters, with SJM stiffness being the primary influencing factor. Based on these findings, a microparameter calibration method for the Smooth Joint Model within the proposed framework is introduced and applied to analyze the mechanical properties of stratified rock masses. The trends in compressive strength and elastic modulus for different inclination angles observed in the simulations are generally consistent with theoretical solutions and align well with experimental data. Furthermore, the simulated failure modes correlate with the experimental results. The simulation outcomes validate the effectiveness of the proposed method, providing new tools for simulating complex jointed rocks in engineering applications, particularly in predicting mechanical behavior and analyzing failure modes.

The scientific quantification of fracture network topology connectivity is essential for advancing fundamental theories such as rock mechanics. Essentially, it involves establishing a mapping relationship between the geometric topology of fracture networks and rock mechanics variables. To develop a universal evaluation system for fracture connectivity and to quantitatively characterize the topological geometric properties of multi-fracture connectivity, we focus on two key variables: connectivity strength and spatial connectivity effect, approached from both narrow and broad perspectives. Firstly, by considering the differences in coordination numbers between X-type and Y-type topological nodes, we define a new connectivity strength index that incorporates topological parameters of the fracture network. This index serves as a universal measurement tool for comparing the connectivity strength of multi-scale fracture networks. Secondly, using the method for assessing the intersection triangles of fracture geometries, we establish a general geometric criterion for both central and non-central connectivity. We identify three core elements for evaluating planar fracture connectivity: trace length, center position, and direction. We construct a maximum fracture cluster identification method utilizing an intersection node heat map and derive the theoretical expression for the critical trace length. Finally, we establish a percolation model to quantitatively describe the spatial distribution characteristics of fracture-connected clusters.

The North Grotto Temple, constructed on weakly cemented sandstone formations, has suffered from significant weathering due to prolonged freeze-thaw cycles. To explore the structural damage mechanisms, the saturated sandstone samples were used to simulate the external temperature variations endured by the grotto. After 0, 5, 10, 15, and 20 cycles, the mass, elastic wave velocity, dry density, relative density, porosity, X-ray diffraction (XRD) mineral analysis, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) were tested. The evolution of damage was analyzed from both macro-scale and micro-scale perspectives, clarifying the structural damage mechanisms The results indicate that: (1) The macroscopic deterioration of sandstone initially manifested as granular disintegration and the cracks development. In subsequent stages, the samples showed more severe disintegration, and local block detachment was attributed to the cracks coalesce. (2) The samples displayed a decrease of mass, wave velocity, and dry density with an increasing number of cycles, while relative density and porosity increased. (3) Freeze-thaw action induced fluctuations in the volume ratio of pores of different sizes. Compared to the initial state, the final volume ratio of small and medium pores decreased, whereas the ratio of large pores increased. (4) The freezing stages of sandstone progressed from the unfrozen stage to the supercooling stage, rapid freezing stage, and stable freezing stage. Freezing pressure promoted particle breakage, pore development, and crack propagation. The thawing stages followed a sequence from the unthawed stage to the slow thawing stage and rapid thawing stage. Upon thawing, the sandstone structure lost support from ice crystals, leading to structural failure. (5) The effective frost heaving pressure in sandstone increased with the number of freeze-thaw cycles, while crystallization pressure showed a significant negative correlation with pore size. (6) The accumulation of microstructural damage ultimately resulted in macroscopic failure and the degradation of physical properties. These research findings can serve as a reference for the protection of weakly cemented sandstone grotto.temples.

Under the conditions of a composite hard roof, the risk of rockburst at the end of the working face is significantly elevated due to the coupled effects of coordinated fracturing of overlying hard strata, high-stress concentration in isolated coal bodies, and the presence of wide protective coal pillars in the retreating roadway. Analyses indicate that frequent high-energy microseismic events induced by roof fracturing, along with stress concentration in isolated coal pillars, are the primary triggers of rockburst. Through theoretical analysis and field monitoring, the mechanism of roof-blasting-based rockburst mitigation has been elucidated, and a roof blasting control strategy has been proposed to interrupt stress transmission pathways in critical overlying strata, thereby providing effective protection for retreating roadways and isolated coal bodies. Numerical simulations were conducted to compare the stress evolution and plastic zone distribution in the surrounding rock under three scenarios: no blasting, high-position single-hole blasting, and combined “high + low-position” blasting. The results demonstrate that roof blasting substantially mitigates the effects of stress concentration during the end-of-face stage, with the “high + low-position” combined blasting exhibiting optimal performance by achieving the greatest reduction in peak stress and a notable contraction of the plastic zone. Parameter optimization indicates that a combination of high-position (53 m) and low-position (33 m) hole depths, initiation heights of 19.3 m (high) and 13.0 m (low), and inclinations of 60°(high) and 40°(low) simultaneously enables optimal evolution of plastic failure in the strata and effective stress reduction in coal pillars. Field applications have shown that the peak and concentration of support pressures were significantly decreased, with the maximum monitored coal body stress reaching only 12.7 MPa and exhibiting smooth stress variation. Additionally, the frequency and cumulative energy of high-energy microseismic events were reduced by 30% and 35%, respectively, with no events exceeding 104 J. Multi-parameter monitoring confirmed that the proposed approach effectively improved the stress environment during the end-of-face stage, reduced dynamic load intensity, and achieved coordinated protection of retreating roadways and isolated coal bodies.

Rock masses exhibit significant strain-softening characteristics under high-stress conditions. During excavation, surrounding rock may undergo plastic shear failure with strain-softening. Under high internal pressure, the primary stress sequence of surrounding rock changes, leading to strain-softening in another direction, known as bidirectional strain-softening. Accordingly, an analytical method for calculating rock stress and displacement—considering the biaxial strain-softening characteristics—has been proposed from a stress path perspective. For rock masses of superior quality (e.g., Grade III and above), the effects of bidirectional strain-softening can be overlooked in the structural design calculations for caverns. However, for lower-quality rock masses (e.g., Grade V1), the calculated rock displacements during high-pressure gas storage can differ significantly—by more than a multiple—when accounting for strain-softening versus neglecting it. For rock masses classified as Grade IV1, this discrepancy is approximately 14%. Therefore, the strain-softening characteristics of medium-to-soft rock strata must be considered in the structural design of compressed air energy storage caverns. These findings offer valuable insights for the design of cavern structures within medium-to-soft rock formations.

Landslide susceptibility assessment (LSA) is critical for predicting potential landslides at regional scales. Existing machine learning based data driven models are highly dependent on data quality and generally lack physical interpretability, which often leads to limited generalization ability and physical inconsistency under complex geological and hydrological conditions. In contrast, physically-based models in mechanical principles can characterize the relationship between rainfall infiltration and slope stability, but their application at the regional scale remains constrained by spatial heterogeneity of parameters and limited model applicability. To address these challenges, this study proposes a probabilistic physics-informed machine learning (PIML) framework that explicitly incorporates geotechnical domain knowledge into the model training process. A simplified transient infiltration model and the first-order reliability method (PRL-STIM) are utilized to compute the factor of safety and failure probability, respectively. These physics-based outputs are integrated into a composite loss function designed to ensure both physical and risk consistency, thereby guiding the training of a neural network. The framework is validated using a rainfall-induced shallow landslide event that occurred in Niangniangba, Gansu Province, China, in 2013. A high-quality dataset is compiled, and a spatial cross-validation strategy is employed to assess the model′s generalization ability and predictive uncertainty in previously unseen areas. Results from five-fold spatial cross-validation indicate that the PIML model enhances the average AUC by 13.6% and reduces the scientific inconsistency index (SI) by 88.6% compared to the baseline model. These improvements demonstrate the proposed model′s enhanced robustness, physical consistency, and interpretability for regional LSA.

To investigate the excavation deformation and bearing characteristics of ultra-deep circular shafts for shield tunnels in soil-rock composite strata, this study focuses on the circular shaft foundation pits of a shield tunnel section along the Shenzhen Airport-Daya Bay Intercity Railway. By analyzing field measurement data and numerical calculation results from three adjacent shafts—one main shaft with an inner diameter of 36 m and two service shafts with inner diameters of 12.6 m—an in-depth examination of the excavation deformation characteristics and internal force responses of the ultra-deep circular shafts was conducted. The results indicate that: (1) Under the influence of groundwater level fluctuations, soil and rock excavation, and adjacent slopes, the diaphragm walls of the main shaft exhibit a composite deformation pattern characterized by “cantilever” and “bulging,” with a maximum lateral displacement of 0.52‰He (where He denotes the excavation depth). The diaphragm walls of the service shafts demonstrate overall tilting deformation, with a maximum lateral displacement of 0.18‰He, while the maximum surface settlement reached 0.37‰He. (2) During asynchronous excavation of the shafts, the ratios of the maximum circumferential normal stress to the maximum vertical normal stress for the main and service shafts are 4.8 and 4.4, respectively. In addition, the ratios of the maximum vertical bending moment to the maximum circumferential bending moment are 6.9 and 1.9, respectively. Furthermore, the diaphragm walls exhibit compressive bending per unit depth. The axial forces in the ring beam supports of each shaft are relatively high within the groundwater fluctuation zone or near the soil-rock interface due to various factors, including local overloading and uneven soil-water pressure. (3) A simplified calculation method for determining the vertical bending moment of the diaphragm wall based on inclinometer data was proposed and successfully applied in the engineering case. The calculated maximum vertical bending moment of the main shaft is 78% of the design value. This method can effectively and quantitatively assess the bearing capacity of diaphragm walls during shaft construction, particularly in cases where reinforcement meters are not installed. The findings of this research provide valuable insights for similar circular foundation pit engineering in soil-rock composite strata.

The lined rock cavern (LRC) offers a promising solution for large-scale hydrogen storage, where mechanical stability and gas tightness are essential for operational safety and efficiency. To address the challenges of evaluating LRC composite structure under complex geological and operational conditions, this study establishes a three-dimensional numerical model and identifies circumferential strain, load-sharing ratio, and structural damage ratio as key evaluation indicators. A Pythagorean fuzzy linguistic cloud (PFLC) model is developed to facilitate quantitative multi-attribute decision-making for assessing and optimizing LRC performance. Results indicate that rock mass strength is the dominant factor, with a correlation coefficient of 77%, and the critical operating pressure remains below the uniaxial compressive strength of the host rock. Based on these findings, a cooperative optimization strategy for the composite structure is proposed: in high-strength rock zones (Class≥II), the lining thickness can be reduced to 0.5 m, and the burial depth can be less than 200 m; C30–C35 ductile concrete is recommended for linings; and reducing the aspect ratio to 5:1 or applying axial reinforcement helps maintain overall stiffness. The proposed multi-objective optimization framework, which integrates geological adaptability and engineering controllability, provides a quantitative basis and theoretical support for the performance evaluation and structural optimization of LRC hydrogen storage caverns.

This study investigates the time-domain scattering characteristics of near-fault velocity pulse waves in alpine valley composite sites using the scaled boundary finite element method (SBFEM). A coupled near-field/far-field computational framework has been established, where the finite near-field region, characterized by semi-sinusoidal topography, is discretized using quadtree mesh generation. The unbounded far-field is accurately modeled through displacement unit-impulse response functions. Representative velocity pulses, extracted from the San Fernando, Northridge, and Chi-Chi earthquake records via the Hilbert-Huang transform, are converted into equivalent nodal loads at the computational interface to ensure physically consistent wave input. Parametric studies reveal that the depth of valley incision significantly influences velocity pulse wave scattering, reducing peak ground acceleration at the valley bottom by 85%–90% due to wave diffraction and shielding mechanisms. Variations in mountain height substantially amplify vertical displacements under non-velocity pulse waves, producing responses approximately 2.4 times greater than those induced by velocity pulses. The scattering of velocity pulse waves is particularly sensitive to incident angles, with peak ground acceleration amplification on the rear mountain slope exceeding that on the front slope by about 65%, highlighting directional amplification effects. These findings provide a theoretical foundation for evaluating and designing seismic safety in near-fault alpine valley terrain.

To investigate the combined effects of elevated topography and overlying soil layers on local seismic site response as well as the mechanisms of earthquake-induced hazards, a series of representative numerical site models with varying topographic heights and soil conditions were developed using the finite element method, based on post-earthquake field investigations. The Fourier amplitude spectral ratio and Fourier amplitude spectral difference were utilized to evaluate the seismic response characteristics for different site configurations. The results indicate that resonance amplification, superposition effects, and peak frequency coupling are the primary mechanisms through which topographic features and overlying soil conditions jointly influence local seismic ground motion characteristics. The relative contributions of these factors to seismic amplification are critical in determining the severity of earthquake-induced engineering damage. Furthermore, the coupling of peak amplification frequencies resulting from both topographic and overlying soil effects is identified as a significant mechanism contributing to seismic hazards. Notably, when the amplification frequencies induced by topography and overlying soils coincide in frequency and are comparable in amplitude, the coupling effect becomes most pronounced. This results in a marked enhancement of seismic response, potentially exposing structures within the site to the most unfavorable conditions for seismic performance. This study provides valuable insights into seismic design under complex site conditions and contributes to the development of more effective earthquake-resistant strategies for engineering applications.

To accurately interpret microseismic events and alleviate time localization deviations caused by background noise filtering, this study improves the time localization picking accuracy of microseismic signals is enhanced while preserving the background noise. The time window energy is calculated to quickly locate the arrival and end times of the signal, and the time-frequency characteristics of the signal are analyzed to identify instantaneous frequency mutation points, thus achieving precise time localization of the signal. We propose a time localization picking method (TWE-TFC) based on the joint integration of time window energy (TWE) and time-frequency characteristics (TFC). The performance of this method is validated using simulated signals, model test signals, and field monitoring signals, and it is compared with the STA/LTA method, the AIC method, and the two independent methods—the TWE and TFC methods. The research findings indicate that: (1) Distinct mutation characteristics in signal energy and instantaneous frequency are exhibited when mine seismic signals arrive at and depart from the geophone, which are crucial for achieving accurate time localization picking; (2) Characteristics of the arrival and end times of the mine seismic signals cannot be fully represented in a single time or frequency domain, which requires integrating time-frequency domain characteristic parameters to improve time localization accuracy; (3) Compared to the STA/LTA method and the AIC method, the proposed TWE-TFC method improves the picking accuracy of the signal arrival time by more than 67.76% and improves the capability to pick signal end time; (4) In comparison to the standalone TWE and TFC methods, the average time localization picking error of the TWE-TFC method is reduced by more than 68.11%.

The phosphogypsum-based material, composed of phosphogypsum, slag, and lime, used for solidifying sludge has been extensively studied. However, it still encounters challenges such as slow early-stage hydration and low long-term strength due to the high water content of sludge, which weakens stabilization efficiency. This paper employs phosphogypsum-based powder combined with bentonite as a regulating agent, capitalizing on the unique water conversion and expansion properties of ettringite. A combination of macro-performance tests and micro-characterization techniques was utilized to investigate the hydro-mechanical properties of the stabilized sludge and to evaluate the effectiveness of bentonite. The results demonstrate that bentonite significantly reduces the free water content in the solidified sludge, achieving a 10% reduction after both 28 and 90 days of curing. Additionally, bentonite enhances the mechanical properties of the solidified sludge during the curing process. The strength of the solidified sludge after 90 days of curing reaches 3.8 MPa, which is double that achieved after curing14 days (1.9 MPa). Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) results indicate the formation of a dense, interwoven network of needle-like ettringite alongside cementitious hydration products (e.g., calcium silicate hydrate, calcium aluminate hydrate) in the samples cured for 90 days. Mercury Intrusion Porosimetry (MIP) results further confirm the near disappearance of large pores (＞10 μm), suggesting that the expansive filling effect of ettringite significantly reduces macroporosity. The water conversion and expansion driven by ettringite accelerate early-stage cementitious formation and enhance long-term strength. Moreover, the comprehensive cost index of bentonite-solidified sludge is only 6.51% of that of tricalcium aluminate. Therefore, utilizing low-cost, readily soluble bentonite as a regulating agent in phosphogypsum-based sludge stabilization is a viable option. This study provides a sustainable strategy for the synergistic utilization of dredged sludge and phosphogypsum, thereby broadening the application scope of special soils.

To investigate the thermo-mechanical coupling for soil surrounding energy pile, an efficient mesh-free numerical model based on the physics-informed neural networks (PINNs) method is proposed. The model incorporates the heat diffusion equation and Navier stress equilibrium equation as physical constraints by embedding the residuals of the governing equations into the loss function, thereby ensuring that the training process strictly adheres to physical conservation laws. Validation against finite element simulation results indicates that the optimal configuration of the proposed PINNs model consists of four hidden layers with 50 neurons per layer and the Tanh activation function, achieving maximum relative errors of only 0.53% and 5.72% for the temperature and displacement fields, respectively. In terms of optimization strategy, the hybrid Adam+L-BFGS optimizer reduces the total loss to 4.42×10??, improving performance by 51.52% and 15.33% compared with using Adam and L-BFGS individually. Moreover, the Latin hypercube sampling strategy significantly enhances model accuracy, reducing the average relative temperature prediction error by 77.03% and 76.81% compared with uniform and random sampling, respectively. With the introduction of a transfer learning framework, the model achieves comparable accuracy to full retraining under new working conditions at only 9.35% of the computational cost, improving overall computational efficiency by 16.55% compared with the traditional finite element method. The proposed approach provides a new solution for studying thermo-mechanical coupling problems in underground engineering, combining physical rigor with high computational efficiency.

The key to ensuring effective filter performance is to allow unimpeded seepage without increasing the pressure head or decreasing the flow rate. In response, the drainage mechanism is initially described based on hydrodynamics. Numerical modeling of flow behaviors in three soil-filter columns was conducted using HYDRUS–1D, focusing on typical poorly graded sand and three granular filters. Based on Darcy′s law, theoretical equations were derived to calculate the surplus pressure head and the relative difference in flow rates between soil with and without filters. An assessment equation was proposed to determine the drainage requirements for coarse-grained filters. This equation meets the criteria of limiting the development of surplus pressure head and the reduction of flow rate under both saturated and unsaturated conditions. Furthermore, flow tests on the three soil-filter columns were conducted under constant head and free drainage conditions. The results indicated that the proposed equation outperforms previously published equations in assessing drainage performance. Finally, partial safety factors were calculated using the proposed equation, and the variability of hydraulic conductivities for both soil and filter materials was quantified to ensure compliance with targeted reliability. The proposed equations are applicable not only to internally stable soils with filters but also enhance the methods for assessing and designing coarse-grained filters.

To address the challenges of excessive thickness and high costs associated with conventional rock shed cushion layers, this study proposes a cost-effective and highly efficient sand-tire composite cushion structure designed to enhance rockfall impact protection. A numerical finite element model of the composite cushion was developed using LS-DYNA and validated through field impact tests. Subsequently, the deformation behavior and energy dissipation mechanisms of the composite cushion under impact loading were systematically investigated, with a particular focus on the influence of the number of tire layers. The results demonstrate that the sand-tire composite cushion exhibits a four-stage dynamic response consisting of compaction, diffusion, enhancement, and rebound. The primary energy dissipation mechanisms include sand compaction and frictional sliding at the sand-tire interfaces, while the tire layers significantly restrict sand deformation and provide additional energy absorption. Increasing the number of tire layers markedly enhances specific energy absorption; notably, the energy absorption per unit displacement for a three-layer tire configuration increases by approximately 50% compared to a pure sand cushion. This study elucidates the efficient energy dissipation mechanisms of the sand-tire composite cushion and proposes a novel cushioning structure that balances economic feasibility with superior performance. These findings provide robust theoretical guidance and practical support for optimized design and engineering applications in rockfall protection.

Hydraulic fill sand, an important material in coastal engineering, has been widely utilized in major projects. In comparison with conventional quartz sand, it typically contains a certain proportion of shell fragments, which significantly influence the physical and mechanical properties. Under seismic loading, hydraulic fill sand is susceptible to liquefaction, thereby posing potential risks to engineering safety. Therefore, this study systematically investigates the cyclic response and excess pore water pressure development of hydraulic fill sand with varying shell contents through undrained cyclic triaxial tests. It is found that liquefaction resistance decreases gradually as the shell content increases. Meanwhile, the development pattern of excess pore water pressure shifts from a three-stage moderated process to a two-stage rapid process. The presence and breakage of shell fragments would alter the soil skeleton fabric, permeability characteristics and force chain transmission, which collectively account for the reduction in liquefaction resistance of hydraulic fill sand.