Circulating hydraulic fracturing, a flexible transformation method for hot dry rock, is anticipated to reduce reservoir fracture pressure, enhance transformation volume, and ensure efficient and safe storage. This method holds significant promise for the economic and efficient development of hot dry rock geothermal resources. To investigate the evolution and fracture mechanisms affecting the tensile properties of reservoir rock due to cyclic hydraulic fracturing, we conducted cyclic loading-unloading Brazilian splitting tests on granite treated with high-temperature water cooling. Two test conditions were examined: varying heat treatment temperatures (200 ℃, 300 ℃, 400 ℃, 500 ℃ and 600 ℃) and different cyclic load upper limits (peak loads of 65%, 70%, 75%, and 80%). The fracture surfaces were analyzed using scanning electron microscopy. The results indicate that tensile strength initially increases and then decreases with rising heat treatment temperatures but continues to increase with higher load upper limits. The number of cycles leading to fatigue failure decreases as the load upper limit increases, displaying a trend of first decreasing and then increasing with higher heat treatment temperatures. The peak displacement experiences three stages: rapid growth, slow growth, and eventual failure as the number of cycles increases. Notably, when the temperature exceeds 300 ℃, deformation significantly increases, suggesting that granite transitions from brittleness to ductility. Overall, the fracture mode is characterized by failure along the diameter direction. Beyond 300 ℃, the crack mode shifts from a “straight line” tensile crack penetrating the center of the circle to a “curved line” mixed tensile-shear crack deviating from the center. This change is primarily attributed to the substantial softening of mineral crystals and the formation of microcracks due to high temperatures. Furthermore, microstructure analysis reveals that as heat treatment temperature and cycle number increase, the internal crack propagation mode of granite transitions from transgranular to intragranular. Concurrently, micro-damage accumulates, resulting in decreased fatigue strength and increased plastic deformation. Macroscopically, this manifests as a coupling effect of tensile strength attenuation and enhanced fracture ductility. The findings of this research provide theoretical support for the design and construction of cyclic hydraulic fracturing.

Rainfall and changes in reservoir water levels are two key drivers of degradation in the hydro-fluctuation belt. This study aims to elucidate the damage evolution mechanism and the primary control modes of bank slopes within the hydro-fluctuation belt of the Three Gorges Reservoir area under typical conditions of rainfall and reservoir level fluctuations. By enhancing the accuracy of analysis and numerical simulation of bank slope stability in the reservoir area, this research holds significant value for guiding stability assessments of bank slopes in the region.
Initially, the water pressure loading sub-matrix is derived from the equations of discontinuous deformation analysis (DDA), and a novel method of DFN-Voronoi block discretization is proposed based on the discrete fracture network (DFN). Subsequently, a simulation analysis of the damage characteristics of the hydro-fluctuation belt—considering conditions of short-term heavy rainfall (45 mm/h) and reservoir water level decline—is conducted using the DDA hydro-mechanical coupling method, exemplified by the No. 6 slope of Qingshi. Through the DFN-Voronoi block discrete DDA coupled hydro-mechanical calculation method, the evolution mechanism and characteristic patterns of bank slope damage in hydro-fluctuation belts under varying conditions are systematically revealed. This is achieved by simulating the deformation of discontinuous media, the dynamic coupling of seepage and stress, and the visualization of multi-stage damage patterns. The results indicate that during uniaxial compression simulations across different fracture types, the proposed DFN-Voronoi model achieves a reduction in maximum displacement errors of 17% and 13%, respectively, compared to the traditional Voronoi model, effectively preventing unreasonable damage surfaces resulting from stochastic discretization. In case simulation analyses, under a working condition of 45 mm/h rainfall, the continuous accumulation of hydro-mechanical coupling leads to gradual degradation of the hydro-fluctuation belt. This iWANG Linfeng1, 2, CAI Bo1, XIE Mingjun1, TANG Ning1, YANG Zhizhong1
s specifically manifested as bending and collapse of the leading edge due to flexural shear damage, alongside pushing and pulling crack damage at the trailing edge. As the reservoir water level gradually declines, discrete blocks on the slope surface become destabilized and roll down, exacerbating tension-slip damage at the trailing edge. This latter form of damage emerges as the predominant type affecting bank slopes in the hydro-fluctuation belt during periods of reservoir water decline. Based on the DDA hydro-mechanical coupling analysis, this study reveals the damage patterns of bank slopes in the hydro-fluctuation belt of the Three Gorges Reservoir area under classical working conditions. The findings can provide numerical tools and reference values for evaluating the stability of bank slopes in the hydro-fluctuation belt and for managing reinforcement efforts in phases.

To investigate the impact of bedding on the multifractal characteristics of acoustic emission (AE) signals during the tensile failure process of coal rock, Brazilian tests were conducted on coal samples with varying bedding angles. AE systems were employed for real-time monitoring, and analyses were performed on the mechanical properties, failure patterns, and ringing counts. The multifractal spectrum of the coal samples was estimated using the MF-DFA method. The time-varying response characteristics of the spectrum width Δα and the frequency spectrum measure subset Δf(?) were examined, which facilitated the identification of precursors to tensile failure in coal rock through multifractal analysis. The research findings indicate that as the bedding angle increases from 0°to 90°and subsequently to C0°, the tensile strength of coal samples initially decreases before increasing again. The failure mode transitions from bedding tensile failure to bedding shear sliding failure, and eventually to matrix tensile failure or a composite failure characterized by bedding shear sliding. Throughout the loading process, the coal samples display a fluctuating decrease followed by an increase in  , while Δf(?) exhibits an overall fluctuating decrease. The fractal aggregation activity of cracks is enhanced, and when significant primary fractures develop, both   and Δf(?) reach their extreme values, maximizing the non-uniform distribution characteristics of the signals and the proportion of large-scale fractures. The propagation mode of cracks is significantly influenced by bedding, with the bedding dip controlling the direction of crack propagation. This indicates that as the bedding dip increases, cracks transition from bedding-parallel to bedding-perpendicular propagation, resulting in a greater variety of macroscopic cracks. The evolution of crack patterns in coal samples shifts from a “unidirectional gradual” mode to a “multidirectional multifocal” mode. Consequently, the parameter   initially decreases and then increases, while the variation of Δf(?) is inconsistent. Overall, the more singular the crack propagation mechanism in coal samples, the smaller the Δf(?). The time-varying response characteristics of the multifractal parameters   and Δf(?) in coal samples are closely linked to their crack evolution, with a sudden increase in   and a sudden decrease in Δf(?) serving as precursors to tensile failure in coal rock.

The efficient and accurate acquisition of structural plane information in rock masses is critical for classifying tunnel surrounding rock. Due to the fragmented nature of sandy dolomite rock masses, traditional geological mapping methods face challenges in precisely obtaining structural plane data. This study focuses on a typical sandy dolomite tunnel from the Water Diversion Project in Central Yunnan. By employing three-dimensional laser scanning technology, the geometric parameters of structural planes are accurately characterized, and these parameters are subsequently applied to the engineering geological evaluation of the surrounding rock. The results indicate that: (1) Utilizing 3D laser point cloud data, key geometric parameters such as the occurrence of structural planes, the dominant structural plane group, structural plane spacing, roughness, and ductility of dolomite with varying degrees of sandification are quantitatively characterized. The error ranges for dip direction, dip angle, and joint spacing are within ±7°, ±5°, and ±6 cm, respectively. (2) The structural plane spacing derived from point cloud data enables the indirect calculation of the rock mass integrity coefficient (Kv) and the RQD index for classifying dolomite sandification grades. This effectively addresses the quantitative characterization of the rock mass integrity index Kv and RQD value. (3) Based on the established classification system for sandy dolomite tunnel surrounding rock, the rock mass integrity index Kv, RQD value, and structural plane roughness score index are quantitatively refined by correlating them with the volume joint number (Jv). Additionally, the structural plane extension length score is enhanced through a continuous scoring method, resulting in more accurate surrounding rock classification outcomes. The findings of this research provide a novel approach for the detailed evaluation of the engineering geological characteristics of surrounding rock in sandy dolomite tunnels and contribute to the foundational theory of disaster prevention and control in sandy dolomite underground engineering.

To investigate the microstructural evolution and strength degradation mechanisms of granite under ultra-high-temperature conditions (up to 1 000 ℃), this study employs a comprehensive suite of multi-scale characterization techniques, including nuclear magnetic resonance (NMR), micro-CT three-dimensional reconstruction, scanning electron microscopy (SEM), and rock mechanics testing. These methods systematically analyze the microstructural evolution characteristics of granite at elevated temperatures and their impacts on mechanical properties. Additionally, the energy evolution process of granite is examined based on energy dissipation theory. The results indicate that the porosity of granite initially increases slowly and then rapidly with rising temperature. Specifically, higher temperatures correlate with a more pronounced increase in porosity, with 400 ℃ identified as the threshold temperature at which significant changes occur. CT scanning results reveal that the internal pores of granite continuously develop and expand due to temperature effects, ultimately connecting to form fractures. SEM analysis demonstrates that noticeable crack formation initiates within granite at 400 ℃ and further propagates as the temperature increases. Under both uniaxial and triaxial compression conditions, the total strain energy consistently decreases with rising temperature, with a brittle-ductile transition occurring between 600 ℃ and 800 ℃. Temperature exhibits a strong correlation with peak strain, peak stress, porosity, and total strain energy. This research elucidates the internal microstructural changes and energy evolution of granite at high temperatures, providing valuable insights into the damage evolution mechanisms of rocks subjected to elevated thermal conditions.

Fracture dissolution in rock masses is a critical process in engineering applications such as solution mining of salt caverns, geological CO? sequestration, and ensuring long-term seepage safety of high dams. Rock fractures act as primary flow pathways, where dissolution occurs with particular intensity. However, conventional experiments are unable to achieve real-time dynamic characterization of this dissolution process, which limits our understanding of morphological evolution and its effects on dissolution rates. In this study, high-fidelity fracture samples of two typical soluble rocks—homogeneous salt rock and heterogeneous limestone—were fabricated using microfluidic chips embedded with real rock fractures. A flow-dissolution visualization experimental technique was subsequently developed to enable high-precision dynamic observation of dissolution morphology at various flow rates. Furthermore, an image-processing method was devised to dynamically quantify dissolution rates, allowing for the determination of dissolution rates for both rock types across different flow-rate conditions. The results indicate that the dissolution rate initially increases with flow rate and then stabilizes, suggesting that a flow-induced transition in dissolution patterns is the underlying mechanism driving the evolution of the dissolution rate. Finally, a theoretical model was developed to identify the critical threshold for the dissolution pattern transition through advection-diffusion time scale analysis under single-phase flow conditions and force balance analysis under multiphase flow conditions. This model elucidates the governing mechanisms of dissolution morphology on the evolution of dissolution rates. The study advances dynamic characterization techniques for fracture dissolution in soluble rocks, provides an effective method for quantifying dissolution rates, and enhances the mechanistic understanding of fracture dissolution in soluble rock masses.

Peridynamics (PD) encounters challenges in tunnel excavation simulations, primarily due to difficulties in determining fracture parameters, high memory consumption, and low computational efficiency. This study systematically investigates a parallel PD algorithm designed for progressive failure analysis of surrounding rock during tunnel excavation through theoretical analysis, algorithm development, and numerical experiments. The results indicate that the strain energy equivalence method for determining fracture parameters, derived from theoretical analysis and validated by numerical simulations, serves as a simplified alternative when fracture energy data is unavailable. Additionally, a GPU-accelerated algorithm based on a “point-pair” mapping strategy reduces memory usage by nearly 50% in large-scale three-dimensional models containing millions of particles, significantly improving computational efficiency by two to three orders of magnitude compared to serial implementations. Furthermore, the model, adjusted based on favorable agreement with field data from the Canadian Mine-by tunnel, analyzes the effects of the lateral pressure coefficient and tunnel cross-sectional shape on the evolution of damage and displacement fields in the surrounding rock. The findings confirm the applicability and potential of this efficient algorithm for engineering-scale problems, offering an effective and reliable computational tool for tunnel design and stability assessment of surrounding rock.

To enhance the seismic design standards of rigid-facing reinforced soil retaining walls for high-speed railway in China, this study builds upon prior shaking table tests and numerical simulations to elucidate the deformation evolution mechanisms of such walls under seismic action and establishes calculation methods for post-earthquake horizontal displacement of the facing and surface settlement. The research findings indicate: (1) The deformation process comprises three distinct stages, with increasing seismic intensity causing structural damage to propagate inward. Surface settlement distribution transitions from triangular to bimodal, with peak settlement shifting from near the facing toward the reinforcement ends. (2) The entire deformation-to-failure process can be calculated using the double-wedge method, whereas the anchored wedge method is only applicable when the pullout resistance of upper reinforcements remains effective under seismic action. (3) Based on the elastic foundation beam theory and the double-wedge calculation method, a computational method for determining horizontal displacement of rigid facing in geosynthetic-reinforced soil retaining walls was developed, explicitly incorporating reinforcement failure mechanisms under seismic action. (4) Simplified into triangular and superimposed double-triangular distributions based on surface settlement's spatial characteristics, a calculation method for seismic-induced settlement was proposed. (5) Boundary conditions at facing bottoms significantly influence structural behavior: compared with fixed hinge connections, fixed rigid connections reduce horizontal displacement but increase maximum bending moment and shear force in facing sections. These insights provide valuable references for the design of high-speed railway reinforced soil retaining walls, while also facilitating the transition from the allowable stress design method to performance-based design methods for such structures.

Aiming to investigate the seepage-mechanics coupling characteristics of coal under complex stress conditions and their impact on coal mine engineering safety, and providing theoretical and experimental support for key issues such as gas disaster prevention, efficient coalbed methane development, and surrounding rock stability control, a high-precision triaxial fluid-solid coupling test system was independently developed based on advanced image measurement technology, By integrating multi-physical field sensing modules and a real-time data acquisition system, this system enables synchronous monitoring and analysis of the dynamic mechanical responses and seepage characteristics of coal samples under coupled axial pressure, confining pressure, and seepage loading. The research first elaborates on the core components and working principles of the system, including the triaxial loading device, seepage pressure control system, digital image acquisition unit, and data processing algorithms. Subsequently, through coal failure tests designed under different stress paths and seepage conditions, combined with the non-contact strain measurement and full-field deformation visualization capabilities of image measurement technology, the study reveals the synergistic evolution laws and disaster mechanisms of coal deformation and seepage. The experimental results demonstrate that the system can accurately capture the changes in seepage-mechanics parameters during the entire process of coal fracture initiation, propagation, and penetration, quantitatively characterizing key indicators such as effective stress coefficients and dynamic permeability evolution. This provides an experimental basis for establishing a more comprehensive fluid-solid coupling theoretical model. Furthermore, the intelligent analysis method based on image measurement technology significantly improves data acquisition efficiency and reliability, overcoming the limitations of traditional point-based measurements. This study not only provides an important technical approach for the safe mining of deep coal resources and the optimization of gas extraction but also offers a referential methodology for research on fluid-solid coupling issues in similar underground engineering projects.

 The differences in rock mechanical behavior significantly influence mine disaster protection. To investigate the size effect of granite and sandstone under dynamic impact, the impact compression tests on sandstone and granite specimens with length-to-diameter ratios of 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 using split Hopkinson pressure bar (SHPB) system at an impact pressure of 0.75 MPa were conducted. The stress-strain curves, compressive strengths, peak strains, and elastic moduli of sandstone and granite specimens with varying length-to-diameter ratios were examined. The analysis of energy for rocks with different length-to-diameter ratios is included. The differences between sandstone and granite during the impact process using digital image correlation (DIC) and sketches were compared, and the rock fracture morphologies were analyzed. Furthermore, the relationship between rock failure and slab length using the Euler formula were examined. The results indicate that the two types of rock exhibit distinct and common patterns. The stress-strain curve of sandstone is relatively “smooth”, while the slope changes at each stage of the stress-strain curve for granite are pronounced. The variation in sandstone strength with length is greater than that of granite. Specifically, the compressive strength of sandstone is positively correlated with the length-to-diameter ratio, increasing as the ratio rises. In contrast, granite shows no significant size effect on strength. The peak strains of both sandstone and granite are negatively correlated with the length-to-diameter ratio, decreasing as the ratio increases; notably, the reduction in peak strain for sandstone is more substantial than that for granite. The elastic moduli of both sandstone and granite are positively correlated with the length-to-diameter ratio, with both increasing as the ratio grows. However, the increase in elastic modulus for sandstone with length is less than that for granite. In these tests, transverse cracks were observed on the surfaces of both sandstone and granite. As the length increased, the energy dissipation per unit volume of rock decreased, and the energy dissipation rate for sandstone was lower than that for granite. Additionally, as the length-to-diameter ratio increased, both rocks were more susceptible to fracturing. The buckling stress of the surrounding rock exhibited a negative correlation with length under dynamic loading conditions. The findings of this study can provide valuable insights for the stability control of roadway surrounding rock.

表土–煤柱结构联动失稳是巨野煤田深部矿井主要的冲击地压类型之一，其发生机制尚未完全明确。以巨野煤田赵楼煤矿七采区FZ14断层锯齿保护煤柱为工程背景，采用相似材料试验、数值模拟、理论分析、现场实测等方法，系统研究巨厚表土–锯齿断层煤柱组合的协调变形特征、载荷传递规律、联动失稳机制。采用相似试验研究了走向连续推采条件下采场后方围岩的巨厚表土载荷加载规律，分析了基岩拱脚与土拱结构的联动模式及对应运动阶段的采场应力演化趋势。通过数值模拟研究了倾向顺序接续条件下巨厚表土–断层煤柱结构的空间形态特征，分析了巨厚表土运动成拱过程与断层上下盘煤柱变形与受力的对应关系。基于相似试验及数值模拟结果，通过理论分析建立巨厚表土–断层煤柱协调变形模型，并推导组合结构发生断层煤柱整体失稳型和巨厚表土应力加载型冲击地压的工程判据，基于此设计了锯齿煤柱上覆承载基岩自重载荷和断层煤柱临界应力的量化方法。结合工程实践应用结果，分析了巨厚表土–锯齿断层煤柱结构失稳诱冲发生机制：下盘采场回采形成的土拱结构传递载荷导致断层煤柱承载应力高度集中，当其上覆载荷超过弹核区临界应力时即发生整体失稳型冲击地压；同时，断层煤岩柱压缩下沉引起土拱结构扩大上移，当破坏高度超过其自稳厚度时巨厚表土迅速向下加载引起应力加载型冲击地压。根据巨野煤田采场巨厚表土–锯齿断层煤柱结构的“震动场–应力场–位移场”监测结果，设计了“近场基岩微震监测–回采煤层应力反演–远场表土沉降观测”联合监测方法。

To elucidate the mechanical properties of oil shale in the Chang 7 Member of the Ordos Basin, triaxial compression experiments were conducted under various confining pressures and bedding inclinations. Based on the characteristics of the stress-strain curves of the Chang 7 Member rocks, a quantitative brittleness evaluation index was proposed. A damage constitutive model, which incorporates post-peak brittle drop, was established by integrating damage mechanics with residual strength and the Drucker-Prager criterion. The results demonstrate that: (1) The deformation of oil shale primarily occurs in three stages: elastic deformation, strain hardening, and strain softening. (2) As confining pressure increases, the compressive strength, residual strength, peak strain, and elastic modulus increase, while brittleness and fracture complexity decrease. (3) Oil shale oriented perpendicular to the bedding planes exhibits higher strength but lower stiffness and brittleness, displaying pronounced anisotropic characteristics. (4) The proposed model effectively accounts for the stress drop rate (brittleness) and outperforms Weibull distribution-based models in predicting the post-peak brittle behavior of rocks, with theoretical curves aligning more closely with experimental stress-strain curves.

The algal clotted dolomite reservoirs in the Dengying Formation of the Sichuan Basin are characterized by well-developed pores and vugs exhibiting strong heterogeneity, which complicates the accurate determination of rock mechanical parameters through conventional experimental methods. This study integrates nanoindentation tests and micro-CT scanning to assess the meso-scale mechanical properties and pore-vug distribution characteristics of algal clotted dolomite, and establishes a digital rock model with realistic pore-vug distributions based on discrete element theory. Furthermore, by utilizing digital pore-vug extraction technology from outcrops, a rock block model containing large-scale defects was developed, facilitating the upscaling from nanometer to centimeter scales. This block model was employed to simulate multi-scale coring processes in the field, elucidating the conversion laws of rock mechanical parameters from laboratory to geological engineering scales. The results indicate that the algal clotted dolomite in the Dengying Formation displays significant vug development and algal framework structures with notable dissolution effects, characterized by poor pore-throat connectivity and heterogeneous distribution. The mineral elastic moduli conform to a Weibull distribution, with discrepancies of 1.2% for uniaxial compressive strength and 5% for elastic modulus between the digital rock model and experimental results, while demonstrating good agreement in failure patterns. The upscaled coring simulation reveals that both uniaxial compressive strength and elastic modulus initially decrease rapidly and subsequently stabilize as core size increases, indicating a gradual diminishment of size effects. Failure in the block model predominantly occurs around vugs, manifested as vug deformation under external loads, the initiation and propagation of microcracks along vug edges, and eventual connection through adjacent vugs to form cavities. Edge vugs, particularly those near free boundaries, facilitate crack initiation and propagation, with their influence diminishing as the distance between vugs and edges increases. The algal frameworks tend to experience relative slippage with surrounding minerals during stress transfer, thereby promoting the formation and propagation of shear cracks.

To accurately determine the deformation of coal during the CO2 adsorption process, the pressurization experiments using non-adsorptive helium were employed to analyze the volumetric deformation caused by free gas effects. By integrating this with swelling deformation during CO2 adsorption, a decoupled computational method that accounts for the tripartite coupling effects involving swelling deformation due to adsorbed gas, as well as the compression and expansion deformation of the coal matrix caused by free gas was proposed. The results indicate that: (1) The relationship between apparent volumetric deformation (the compression deformation of the matrix) and gas pressure for both reconstituted and raw coals during the increase in helium pressure can be divided into two distinct stages: pore compaction and linear elastic deformation. Additionally, the overall volumetric deformation-pressure curve exhibits a rapid reduction followed by a gradual reduction phase. (2) The difference between the overall volumetric deformation and the apparent volumetric deformation in coals under the pressure of free gas is quantified by the coefficient of difference in volumetric deformation, VK. As helium pressure increases, VK initially increases and then decreases. The overall volumetric deformation is found to be 14.29 to 39.54 times the apparent volumetric deformation, indicating that the deformation in pores and fractures due to pressure from free gas is significant. (3) The proposed method for calculating coal deformation accurately determines the overall volumetric deformation during CO2 adsorption processes. The calculations reveal that the relationship between overall volumetric deformation and adsorption pressure follows the Langmuir function, with the maximum overall volumetric deformation ranging from 2.39 to 3.14 cm3 under the experimental pressure range, representing an increase of 3.54% to 4.22% compared to the initial volume. The maximum deformation is 1.31 to 2.06 times greater than the apparent volumetric deformation measured by the strain gauge.

To address the limitations of traditional linear seepage theory under complex fracture conditions, a novel rock mass permeability coefficient is introduced. This model integrates the empirical advantages of the Izbash equation with the theoretical framework of the Forchheimer equation. Based on the geological conditions of the Huanglong Pumped Storage Power Station project, a three-dimensional fracture network model was developed using the Monte Carlo stochastic method. Through numerical simulations and in-situ borehole water pressure test data, this research systematically examines the interaction mechanisms among fracture geometric characteristics, network connectivity, and nonlinear seepage behavior. The results reveal the following: (1) A distinct exponential relationship exists between the seepage parameter p and the water permeability rate q. Complete fracture network connectivity is achieved when p＞8.65, which is accompanied by a significant reduction in permeability anisotropy. (2) For p＜4.28, the effective seepage area decreases by 71.3%, with a maximum velocity reduction of 76.21%. (3) Compared to conventional empirical formulas, the proposed model enhances the calculation accuracy of rock mass permeability coefficients in medium to high permeability conditions (1–30 Lu) by incorporating a non-Darcy flow effect factor E. This innovation demonstrates superior performance in characterizing inertial effects and local vortex energy dissipation mechanisms.

The southwestern mountainous region of China is tectonically active and characterized by high, steep anti-dip rock slopes with weak intercalations. Under seismic action, the dynamic response characteristics of these slopes are complex, and the mechanisms of deformation and damage remain unclear, hindering effective disaster risk prevention and control. Based on extensive investigations of high and steep slopes in the upper reaches of the Jinsha River, a conceptual geological model is developed. It examines the dynamic response characteristics and deformation failure of the slopes under varying conditions of peak ground acceleration(PGA), seismic wave frequency, and loading direction through large-scale shaking table model tests. The results indicate pronounced nonlinear dynamic response characteristics of weak interlayer anti-dip rock slopes under seismic action, exhibiting significant height and surface effects. As the PGA increases, these two dynamic amplification effects become more prominent. The vertical dynamic response of slopes within the range of 1/3h to 2/3h demonstrates a surface effect when subjected to sinusoidal waves. As the frequency of sinusoidal waves increases, the region exhibiting a greater dynamic response gradually shifts from 1/3h to 2/3h towards the foot of the slope. When PGA≥0.4 g, under the action of a 2 Hz sinusoidal wave, the dynamic response in the damage area at the top of the slope shows signs of decay. Under the influence of the Wenchuan wave, the horizontal dynamic response at the slope's top and surface is significantly weaker than the vertical dynamic response. However, under the effect of high peak ground acceleration(PGA≥0.4 g) seismic waves, an opposing pattern is observed. The vertical dynamic response in the upper range of 1/2h to 5/6h of the slope is stronger when loading occurs simultaneously in the x and z directions compared to loading the Wenchuan wave solely in the x direction. The deformation and failure process of the slope model can be categorized into five stages: the tiny damage stage, the cracking stage at the slope top, the failure stage at the slope shoulder, the evolution stage of the sliding surface, and the instability stage of the sliding surface. Shaking table test on dynamic response of anti-dip rock slope with weak interlayers under seismic loading

Sand fluidization induced by leakage from water supply pipelines is a critical mechanism contributing to subsurface voids and ground collapse. Most existing studies have focused on fully saturated sands, with limited exploration of unsaturated conditions. This study employs model tests to investigate the fluidization behavior of sand under varying initial submerged water levels. The results reveal a distinct secondary expansion of fluidized cavities within unsaturated sand beds. A hydraulic criterion for complete fluidization under unsaturated conditions is proposed. Empirical relationships for the hydraulic gradient at different saturation levels are established based on pore water pressure measurements. A theoretical formula for the critical flow rate necessary for complete sand fluidization, derived from the momentum theorem, is developed and validated through experiments. The findings demonstrate that the critical flow rate is significantly influenced by the initial submerged water level. Additionally, capillary-induced matric suction inhibits the initiation and progression of sand fluidization under unsaturated conditions.

To effectively address the challenges of low efficiency and difficulties in rock-socketing construction faced by traditional large-diameter bored piles, this study pioneered the application of the steel pipe nested pile support structure to deep excavation engineering in soil-rock dual strata. A systematic in-situ test study on the support performance of steel pipe nested piles was conducted, clarifying the dynamic evolution of internal forces in pile shafts during the excavation process, revealing the synergistic load-bearing mechanisms of composite support structures, and proposing an optimized support scheme for steel pipe nested piles. The results show that as the excavation depth increases, the bending moments of cast-in-place piles evolve into a “wave-shaped” multi-peak distribution along the depth direction, with significant fluctuations near the excavation face and a gradual downward migration of extreme bending moment points; the application of prestressed anchor cables reduces peak bending moments by 11%–34%. The bending moments of steel pipe piles evolve into a nonlinear “S” shaped distribution along the depth direction, with significant increases within 1.0 m above and below the interface, accompanied by noticeable stress concentration. Front-row steel pipe piles bear the majority of hydrostatic and soil pressures, while the bending moment fluctuation range of rear-row piles is approximately 90% of that of front-row piles. The supporting effect of the reserved side ramp significantly mitigates the excavation-induced unloading effect, and the upward shift of the slightly weathered rock layer interface effectively restricts the development of negative bending moments at the base of cast-in-place piles. The variation in the interface position between cast-in-place piles and steel pipe piles significantly influences the mechanical behavior of the piles. As the interface position shifts upward, the bending moments of cast-in-place piles and steel pipe piles evolve into a “lateral-spoon-shaped” single-peak distribution and a “wave-drum-shaped” multi-extremum distribution, respectively, gradually activating the load-bearing characteristics of steel pipe piles. Under similar geological conditions, it is recommended that subsequent excavation projects prioritize the optimized support scheme for steel pipe nested piles, with the interface between cast-in-place piles and steel pipe piles set within 0.5 m below the soil-rock stratum boundary and positioned between anchor cables MG–4 and MG–5. This design can fully utilize the support performance of steel pipe nested piles, ensuring the stability of the support structure and construction efficiency.