On 15 August 1950, an Ms8.6 earthquake struck the Medog—Zayu region in the Eastern Himalayan syntaxis, with a maximum intensity of XII and an area with intensity≥VIII of about 2.19×105 km2. This mainshock-dominated event released seismic energy in a highly concentrated manner and triggered extensive landslides and related geological hazards. To systematically reveal the spatial distribution and the river-blocking patterns of coseismic landslides, we integrate multi-temporal historical imagery since 1961, archival records and field investigations to analyse the intensity distribution. For the high-intensity zone (X–XII) from Milin Wolong to downstream of Duden in the Namcha Barwa region, a coseismic landslide inventory is constructed for the first time, resulting in a dataset of 920 landslides. Quantitative analysis reveals that landslides predominantly occurred at 2 000–4 000 m elevation, on 20°–50° slopes, and within 4 km of active faults. The landslide distribution is strongly controlled by the main central thrust fault, the Motuo fault, and the Apalong fault. Based on statistical analysis and morphological characteristics, we delineate four types of earthquake-induced landslide-damming patterns: seated landslides, high-altitude remote hazards, whole gully-scale landslides and multi-landslide clusters, typified by the Gengbangla, Zelongnong Gully, the Jamaqiming Gully, and Zhaqu—Xirang landslide groups, respectively. The maximum duration of river blockage reached 15–16 hours. The unique geomorphic and tectonic environment of the Eastern Himalayan Syntaxis provides favorable conditions for the occurrence and evolution of high-altitude remote geological hazards. As the region is currently in a seismically active phase, it is critical to enhance research on the failure mechanisms and early warning of under extreme earthquake conditions, thereby improving disaster preparedness, resilience, and emergency response capabilities in the region.

When constructing tunnels in rheological strata, the creep of the surrounding rock increases the load on the supporting structure over time. Additionally, environmental influences may cause creep phenomena in the supporting structure, resulting in a complex interaction mechanism between the tunnel?s surrounding rock and support due to the coupling effects of both. This article proposes an analytical method for circular tunnels based on the theory of complex functions and Laplace transform. Unlike previous analytical solutions, the approach presented here incorporates the rheological properties of the surrounding rock, non-hydrostatic stress fields, and the creep characteristics of supporting structures. The Kelvin-Voigt model was employed to simulate the rheological properties of both the surrounding rock and the supporting structures. Displacement and stress solutions were derived from the displacement coordination equation and the stress boundary conditions of the surrounding rock and support structures. The accuracy of the analytical solution was verified through numerical simulations, followed by a parameter analysis. The main conclusions drawn from this study are as follows: (1) For simple mechanical models, the analytical method proposed in this paper is faster, simpler, and retains a degree of accuracy superior to that of numerical simulations; (2) When accounting for the creep characteristics of the supporting structure, the deformation of the surrounding rock is greater compared to existing analytical results, the contact pressure between the surrounding rock and the supporting structure is reduced, and the creep of the supporting structure diminishes its bearing capacity and deformation constraint. A higher creep rate in the supporting structure correlates with a faster rate of deformation in the surrounding rock, a lower creep modulus, and increased deformation of the surrounding rock; (3) In the context of non-hydrostatic stress fields, the coupling effects of creep between the tunnel and the supporting structure can exacerbate tunnel issues such as arch uplift or inward compression of tunnel sidewalls, thereby compromising the safety of the supporting structure. Considering these factors is crucial for the design and construction of tunnels in complex environments; (4) Engineering applications demonstrate that the analytical method proposed in this paper effectively predicts the trends in tunnel surrounding rock deformation and support structure stress, showcasing its potential for practical engineering applications.

The mechanical interaction between glaciers and the underlying bedrock is a primary factor influencing ice avalanche disasters. However, research on the mechanical properties of the ice-rock interface remains limited. To further investigate the key mechanisms involved in the initiation of ice avalanches in high-altitude cold regions and to elucidate the main controlling factors and their underlying principles, this study designed and developed a small high-speed centrifuge device suitable for conducting debonding tests at the ice-rock interface. Systematic tests on the bonding strength of the ice-rock interface were carried out under various conditions. The main findings are as follows: (1) The centrifuge device demonstrates high testing efficiency and low data dispersion, facilitating strength tests of the ice-rock interface under multiple conditions, including tension, pure shear, and compressive shear. (2) The bonding strength of the ice-rock interface is closely related to temperature, rock surface roughness, and rock lithology. Lower temperatures lead to greater bonding strength, exhibiting an overall linear relationship. The bonding strength shows a nonlinear positive correlation with rock surface roughness; however, when roughness exceeds a certain threshold, the formation of interface cavities inhibits further increases in bonding strength. Rock lithology affects bonding strength with ice through factors such as porosity and mineral hydrophilicity. (3) A computational model for the bonding strength of the ice-rock interface was established, clarifying the quantitative relationships among bonding strength, temperature, roughness, and normal pressure. This study provides a novel experimental method for analyzing the mechanical properties of the ice-rock interface, and the results offer a quantitative basis for understanding the mechanisms of disaster and assessing the risks of ice avalanches in high-altitude cold regions.

 In-situ permeability evaluation of rock masses at the engineering scale is crucial for deep energy extraction and subsurface energy material sequestration, including CO2, hydrogen, and nuclear waste storage. Compared to laboratory-scale tests, this approach more accurately reflects the seepage behavior of rocks under their original in-situ conditions. This study proposes a theoretical method for calculating the in-situ gas permeability of rock masses at the engineering scale, systematically analyzing key parameters that influence permeability results. Special emphasis is placed on determining and conducting sensitivity analyses of the effective testing radius. Through simulated engineering-scale permeability tests under in-situ conditions and comparative analysis with core-scale results, it is observed that permeability values differ by no more than a factor of three. This discrepancy is primarily attributed to the confining pressure of 0.8 MPa applied during core-scale tests and the presence of interconnected pores and microcracks induced by local air bubbles during the casting process. Based on these findings, a series of pilot field tests were conducted in a deep underground laboratory and in both coal and sandstone roadways of a coal mine in Shandong Province, utilizing a self-developed portable in-situ gas permeability testing system. The results demonstrate that the proposed method and integrated system exhibit strong adaptability, stability, and repeatability across diverse engineering scenarios, thereby facilitating effective evaluation of rock mass permeability and grouting effectiveness. This research offers a novel technical pathway and theoretical foundation for the in-situ assessment of reservoir exploitability and the sealing performance of barrier systems in deep subsurface energy material sequestration projects.

To investigate the mesoscopic crack evolution behavior and the dominant mechanisms during the failure process of sandstone, an integrated approach combining acoustic emission moment tensor inversion with RA-AF parameter analysis was employed to quantitatively characterize the types, spatiotemporal distribution, and stress response characteristics of microcracks. Based on moment tensor theory and incorporating sensor coupling coefficients calibrated through pencil-lead break experiments, microcracks were classified into five categories—shear cracks, tensile-shear mixed-mode cracks, compressive-shear mixed-mode cracks, tensile cracks, and compressive cracks—using the crack tensile angle criterion. Furthermore, an RA-AF empirical model was established to support the analysis. The results indicate the following: (1) Under various loading paths, microcracks resulting from sandstone failure are predominantly shear cracks. The number of each of the five microcrack types exhibits a positive correlation with stress level, with shear cracks showing the most significant increase. (2) As stress increases, microcracks initiate, propagate, and gradually coalesce, forming a fracture zone that corresponds to the macroscopic failure surface. (3) RA-AF analysis reveals that shear cracks account for more than 50% of all microcracks in sandstone, which aligns with findings from moment tensor inversion. (4) Waveforms generated by tensile cracks exhibit abrupt characteristics, with concentrated signal energy in the frequency domain, whereas waveforms associated with shear cracks display oscillatory behavior, featuring dispersed frequency-domain energy and higher amplitude. This distinction provides a physical mechanism that explains the heterogeneity observed in RA-AF parameters. (5) Moment tensor inversion is well-suited for theory-driven, detailed analysis of crack mechanisms, while RA-AF analysis is more appropriate for rapid identification of crack types in engineering practice. This study elucidates the dominant micromechanical mechanism of shear failure in sandstone and the co-evolutionary behavior of multiple crack types, thereby providing a theoretical foundation for rock fracture prediction.

To investigate the influence of normal stress on the seepage and damage characteristics of sandstone during dynamic constant-amplitude cyclic direct shear, red sandstone samples were subjected to dynamic constant-amplitude cyclic direct shear tests under normal stresses of 10, 15, 20 and 25 MPa. During the loading process, acoustic emission (AE) signals were simultaneously recorded, and the permeability of the sandstone was measured in real time. After testing, the fracture surfaces of the sandstone samples were scanned using a 3D scanner. The test results indicate that the permeability evolution of sandstone during direct shear exhibits distinct stage characteristics, which can be described as “gradual decrease→slow decrease→slight recovery→exponential increase.” Throughout the loading process, the permeability of samples subjected to high normal stress consistently remains lower than that of samples under low normal stress. As the normal stress increases, the initiation of AE activity in the samples is delayed. However, the Felicity effect occurs earlier and more prominently, indicating a greater extent of damage. Higher normal stress facilitates a transition in the fracture mode of sandstone from tension-dominated to shear-dominated. At the microscopic level, increased normal stress promotes the development of transgranular cracks, leading to straighter crack propagation paths. Simultaneously, crack propagation is restricted near the main shear plane, ultimately resulting in macroscopically flatter fracture surfaces with lower roughness.

Rock masses often exhibit significant size effects under uniaxial compression, yet the underlying mesoscopic controlling mechanisms and sensitivity to crack parameters remain poorly understood. In this study, we conducted uniaxial compression and acoustic emission (AE) monitoring experiments on granite specimens of various laboratory scales. By incorporating constraints from X-ray diffraction (XRD) mineral composition and AE-guided micro-crack data, we established a numerical model with a pre-existing micro-crack network using the PFC platform. The results indicate that the uniaxial compressive strength, failure mode, and crack propagation of the specimens demonstrate pronounced size dependence: peak strength decreases with increasing specimen size, and the failure mode transitions from splitting to shearing. In a homogeneous mineral matrix model (without pre-existing micro-cracks), the strength is nearly independent of specimen size, suggesting that pre-existing micro-cracks are the primary factor controlling the size effect. Furthermore, crack length has a significantly greater impact on strength degradation than crack number, with smaller specimens being more sensitive to variations in crack parameters. The established model effectively reproduces the experimental results regarding stress-strain behavior, AE event sequences, AF-RA crack classification, and failure patterns, thereby validating the reliability of the multi-scale numerical approach. These findings provide theoretical support for addressing the strength size effect and enhancing the safety design of engineering rock masses under complex geological conditions.

Accurately predicting the dynamic evolution of permeability during CO2 injection into shale reservoirs is crucial for carbon sequestration and enhanced shale gas recovery. However, traditional permeability models often fail to comprehensively describe the full-range evolution of permeability throughout the entire CO2 injection process in shale—from the low-pressure gaseous state to the supercritical state. To address this limitation, this study develops a shale permeability evolution model based on a dual-elastic system comprising both the matrix and fractures, determined by component permeability weighting. By incorporating key factors such as mechanical degradation of the matrix, secondary adsorption, and strain hysteresis effects, we establish a governing equation for permeability evolution under multi-effect coupling. Utilizing an overlapping dual-elastic medium structure, we perform parallel cross-coupling numerical solutions, achieving an accurate representation of the nonlinear permeability evolution during full-pressure CO2 injection. Furthermore, a decoupled analysis of influencing effects reveals that the degradation of mechanical parameters of the matrix material due to CO2 defines the boundary thresholds for permeability fluctuation ranges. The asynchronous response between mechanical strain and adsorption strain significantly amplifies differences across evolutionary stages, leading to clearly distinguishable phase transitions. Additionally, the strain hysteresis effect prolongs the duration of evolution. Gas adsorption and mechanical responses jointly regulate the transition points between evolutionary stages, with the secondary adsorption-induced swelling strain particularly enhancing phase differentiation throughout the evolution process. This study also provides an in-depth analysis of the fundamental framework of fluid-solid coupled permeability modeling and explores the characteristics of different numerical simulation methods. The findings not only deepen the understanding of shale permeability evolution during CO2 injection but also offer valuable insights for theoretical modeling and numerical simulation of permeability in geological fluid sequestration.

To elucidate the precursory tilt deformation patterns of tension-fractured hazardous rock masses under gravitational loading, this study conceptualizes the collapse process as subcritical propagation under stress corrosion, utilizing a bending Mode-I fracture model. A time-dependent evolution equation for tilt deformation is derived, and the theoretical characteristics of tilting behavior are examined. Based on the principles of micro-electro-mechanical system (MEMS) gravity accelerometry, a method for monitoring the cumulative tilt angle along the primary tilting direction is established using spatial vector angles. A physical model test simulating the collapse of such rock masses under predominantly gravitational loading is designed and conducted, with the resulting tilt deformation behavior analyzed. Additionally, high-low temperature tests are performed to calibrate MEMS tilt sensor drift, and automated field monitoring is implemented to capture time-series variation patterns of tilt angles during collapse events. Comprehensive analysis indicates that precursory tilt deformation transitions from a constant-rate phase to an accelerating phase. However, due to subcritical crack propagation within a heterogeneous medium, localized step-like fluctuations occur during the constant-rate stage, while trend alterations manifest during acceleration. A power-law relationship is identified between the tilt rate and its acceleration prior to collapse. Based on this relationship, a collapse time prediction equation utilizing the inverse of the tilt rate is proposed, and the predictive efficacy of both linear and nonlinear formulations is evaluated. These findings support the application of tilt-sensing technology in monitoring and early warning systems for rock collapse.

In response to the engineering challenges associated with limited construction scale and slow development speed in high-impurity salt mines oil storage, this study proposes a novel technical approach that utilizes sediment voids to expand oil storage capacity. Laboratory experiments and theoretical analyses were conducted on sediment particles from the Yunying salt mine in Hubei Province. A evaluation system encompassing sediment characterization and sediment void storage capacity was established. The mechanism of oil injection and production under the fluid-solid coupling of oil/brine and sediment was systematically studied. The sediment void clogging risk during oil injection and production was explored. The migration rule of oil and brine in sediment voids were elucidated. The results indicate that Yunying sediments possess a void ratio exceeding 40% with favourable connectivity in total, meeting the requirements for oil storage. Multiple oil injection and production cycles demonstrate low flow resistance and a linear mass-time correlation. Dominant flow channels are established only during the initial injection, stabilizing thereafter. The oil-brine interface exhibits fingering phenomena without abnormal pressure or rate fluctuations. Transient clogging events occur randomly, presenting an overall low risk. The oil injection pressure increases stepwise as the oil-brine interface descends. The hydrophilic properties of the sediments improve brine injection and oil production efficiency through capillary forces. These findings provide scientific support for the construction of high-impurity salt mines oil storage facilities.

 Ice avalanches are a primary trigger for glacier-related disaster chains in high-mountain regions. Understanding how boundary conditions influence the dynamics and deposition of ice avalanche debris flows is crucial for deciphering the evolution of such disaster chains. This study systematically investigates the motion and depositional behavior of ice avalanche debris flows under varying mass, elevation differences, slope gradients, and toe constraints, utilizing a chute-based experimental setup within a low-temperature laboratory. Key parameters, including flow velocity, basal force, and deposition morphology, are analyzed throughout the debris flow movement. Results indicate that elevation differences and mass govern the dynamic energy transfer within the flows. Specifically, elevation differences control depositional dispersion by regulating peak flow velocity, while mass influences travel duration, resulting in a positive correlation between run-out length and deposit thickness. Furthermore, topographic conditions significantly affect energy dissipation during deposition. An increased slope gradient in the run-out zone reduces basal resistance, thereby expanding the depositional area and enhancing particle scattering at the flow front. A wider slope toe promotes lateral spreading, increasing travel distance and shifting the mass center, which transforms deposit morphology from tongue-shaped to fan-shaped. Finally, theoretical analysis confirms that run-out distance is dictated by the efficiency of kinetic energy transfer among particles and their interaction with the substrate, exhibiting a positive correlation with both particle energy-transfer efficiency and fluctuations in basal stress.

This paper investigates the effect of anisotropic stress states on the small strain stiffness of red mudstone fill material (RMF). A comprehensive experimental program was conducted, including 18 triaxial-bender element tests, 4 isotropic consolidation tests, and 6 stress-controlled loading-unloading tests. The results indicate that the normalized strength is well characterized by the nonlinear strength envelope. Under isotropic stress conditions, the small strain stiffness increases with mean stress, which can be described by a power equation. During conventional triaxial shear, small strain stiffness increases at low axial strains. When the axial strain exceeds 2%, the damage point can be identified, at which point small strain stiffness decreases by more than 25% with further axial strain. A power model has been employed to characterize the small strain stiffness and shear stress at both the damage point and peak point. Unloading at stress states below the damage point results in an increase in small strain stiffness. Conversely, due to irreversible structural disturbance, unloading at stress states above the damage point leads to a progressive reduction in small strain stiffness. The difference in small strain stiffness at various unloading points can exceed 30%. Therefore, the coupled effects of stress history and stress path should be considered for accurate determination of small strain stiffness, as the conventional monotonic model is not applicable in such coupled scenarios.

Current research on tunnels crossing active faults primarily focuses on individual tunnel cases, while the group tunnel effect in tunnel groups has not been systematically addressed. The influence of high internal water pressure on deformation mechanisms is rarely considered. This study employs physical model tests and numerical analysis under high internal pressure to investigate the fault resistance of tunnel groups. The results demonstrate the following: (1) Corrugated expansion joints significantly enhance fault resistance, delaying and reducing peak longitudinal strain (with maximum tensile strain reduced by 69% and compressive strain by 48%) and converting shear failure into coordinated deformation. (2) Group effects intensify the fracturing of surrounding rock during dislocation, resulting in a complex “Y-shaped intersecting crack system.” (3) The sides of adjacent tunnels exhibit higher strain responses than the outer sides (with peak compressive strain at 87% and longitudinal tensile strain at 35%), indicating tunnel-rock-tunnel interaction. (4) Earth pressure between tunnels increases abnormally due to group effects, while the pressure on the outer sides remains largely unaffected. (5) The mechanical response of the lining (axial and shear force) strengthens with smaller tunnel spacing but diminishes and stabilizes as spacing increases. This study reveals the failure mechanisms of high-pressure hydraulic tunnel groups, providing insights for fault-resistant designs in seismic zones.

To identify the distribution differences between fractures and interlayer gravels within glutenite cores, accurately evaluate spatial heterogeneity, and enhance hydrocarbon recovery efficiency, this study employed elastic ultrasonic wave velocity—a parameter highly sensitive to variations in the internal rock structure—to measure wave velocities in 18 outcrop cores collected from the Shawan Sag in the Junggar Basin. A non-destructive evaluation method for heterogeneity was established based on stratified elastic wave velocity measurements. Fifteen samples were utilized as test cores for heterogeneity assessment using this method, while the remaining three served as validation cores, with their velocity distributions compared for verification. The results demonstrate that: (1) the proposed method effectively identifies heterogeneity characteristics, such as gravel distribution and pore-fracture networks in glutenite, enabling an accurate assessment of spatial heterogeneity; (2) the method offers several advantages over conventional heterogeneity evaluation techniques, including non-destructiveness, high sensitivity, rapid measurement, and cost-effectiveness; and (3) consistent heterogeneity evaluation results were obtained between the test and validation cores. Therefore, this method can serve as a valuable reference for heterogeneity assessment in glutenite reservoirs.

 Conventional finite element methods for large-scale numerical simulations are often constrained by high computational demands and extended runtimes. To enhance efficiency, we developed a predictive model based on a backpropagation (BP) neural network. A three-dimensional finite element model of a buried pipeline with corrosion defects crossing a reverse fault was established using ABAQUS. We systematically analyzed the effects of four key parameters—corrosion depth-to-thickness ratio, diameter-to-thickness ratio, internal pressure, and burial depth—on the seismic response of the pipeline. In this parametric study, fault displacement and the four key parameters served as inputs to the BP neural network, with the pipeline’s axial peak compressive strain as the output. The model was trained and validated using training, validation, and test datasets. Results indicate that increasing the corrosion depth-to-thickness ratio, diameter-to-thickness ratio, internal pressure, or burial depth reduces the fault displacement necessary for the lower section of the pipeline to reach its strain limit. Failure modes differ between unpressurized and pressurized pipelines, exhibiting inward local buckling and outward bulging, respectively, at stress concentration zones. The four parameters are highly correlated with the compressive strain response, with correlations transitioning from linear to nonlinear as fault displacement increases. The trained BP neural network achieves maximum prediction errors of 13.60% on the validation set and 12.84% on the test set, both below 15%, demonstrating robust accuracy and generalization in predicting the seismic response of in-service buried pipelines across reverse faults.

Significant limitations and hysteresis are presented in dynamic prediction methods driven by on-site monitored displacement data for tunnel surrounding rock deformation. By comprehensively utilizing the physical information contained in tunnel construction project documents and the mathematical information from displacement time-series curves, a modelling method based on the dynamic Bayesian network (DBN) was developed using the concept of physical information machine learning (PIML) to achieve dynamic predictions of surrounding rock deformation. Through discretization processing and reconstruction of displacement time-series curves, a static sample database was established by combining physical information data with ultimate displacement data, while a dynamic sample database was created by integrating physical information data with displacement time-series curve data. Based on the characteristics of the static samples, the K2-score algorithm was improved to construct a static Bayesian network (BN) model for ultimate displacement prediction. Utilizing the static BN model and the characteristics of the dynamic samples, physical-data dual-drive modelling methods for the Markov DBN were derived by incorporating prior information, including the constraints of steady-state random processes and Markov process constraints. By integrating prior information for constraint-enhanced optimization, the optimized Markov DBN model was established. Five-fold cross-validation tests revealed that the prediction capability of the Markov DBN model decreased rapidly over time and that the network transition direction significantly affected this capability. In contrast, the prediction ability of the optimized Markov DBN model remained robust over time, was unaffected by the network transition direction, and significantly exceeded that of the Markov DBN model, as the optimized model enhanced constraint connections between target nodes and influencing factor nodes throughout the entire timeframe. Through engineering case analysis, it was concluded that before and during the early stages of tunnel construction, the optimized Markov DBN model could effectively predict displacement time-series curves, overcoming the limitations and hysteresis inherent in traditional methods. Furthermore, during construction, self-updating of the optimized Markov DBN model and dynamic predictions of surrounding rock deformation could be achieved by inputting the on-site monitored displacement data.

Geothermal energy, a renewable resource with immense potential, has garnered significant attention. In deep geothermal reservoirs, artificially stimulated fracture networks serve as critical pathways for heat extraction. Consequently, the permeability and spatial distribution of these fractures directly impact heat extraction efficiency. This study conducted shear-seepage experiments on a single rough granite fracture under varying confining pressures, shear displacements, and fracture roughnesses. A nonlinear relationship between permeability and the aforementioned three factors was established based on the experimental results. This relationship was then integrated into the THM coupled framework TOUGH2MP-FLAC3D to assess the long-term performance of Enhanced Geothermal Systems (EGS) under varying fracture networks, fracture densities, and horizontal stress ratio conditions. The findings reveal that fracture permeability exhibits an exponential negative correlation with confining pressure, a logarithmic positive correlation with shear displacement, and a quadratic correlation with fracture roughness. Increased fracture density significantly enhances thermal performance; as fracture densities increase from 0.1 to 0.25, the thermal breakthrough time extends by up to 6.4 years, the EGS lifespan increases by up to 13 years, and total heat production rises by approximately 22.5%. Horizontal stress anisotropy negatively affects thermal performance, while higher fracture density effectively mitigates the reduction in heat extraction caused by stress anisotropy. This work provides a theoretical foundation for hydraulic fracturing during the stimulation of hot dry rock reservoirs.

How can the essential requirements of retention, hydraulic conductivity, and clogging for geotextile filters be simultaneously satisfied? Coordinating the assessment of their seepage stability performance is crucial. To achieve this, sixteen soil-geotextile column hydraulic gradient ratio tests were conducted using four typical geotextiles. The seepage stability was evaluated based on hydraulic conductivity, stable hydraulic gradient ratio, and the washout of soil fines observed during the tests. Additionally, both the grain size of the soil and the constriction size of the geotextile were treated as random variables. Utilizing soil-water interaction theory, a retention assessment approach was proposed based on the probability of ineffective retention. The performance limits of retention were determined using data from eighty-five experimentally assessed soil-geotextile columns. Furthermore, a hydraulic conductivity assessment approach was developed, considering the partial clogging of the geotextile due to the formation of a bridging structure. The results indicate that the proposed design criterion surpasses previously published criteria in effectively distinguishing between clogging or blinding in ineffective and effective systems. It was found that polypropylene long-filament geotextiles with a high mass per unit area are particularly well-suited for use as filters.

Coral sand deposits in the islands and reefs of the South China Sea are vulnerable to seismic liquefaction. Shear wave velocity provides a rapid and non-destructive method for assessing liquefaction potential; however, existing criteria, primarily developed for quartz sands, exhibit limited applicability to coral sands. This study aims to establish a specific relationship between shear wave velocity and cyclic resistance ratio for coral sand. A series of cyclic undrained triaxial tests and bender element tests were conducted using a GDS dynamic triaxial system on saturated coral sand from the South China Sea and comparable quartz sand. Systematic measurements of cyclic resistance and shear wave velocity were obtained for both materials, leading to the development of a quantitative model relating shear wave velocity to cyclic resistance for coral sand. The validity and engineering applicability of the proposed model were further validated through a case study of typical liquefaction sites, resulting in an empirical equation for the critical shear wave velocity of coral sand. The results indicate a strong correlation between shear wave velocity and cyclic resistance ratio in coral sand, with coral sand exhibiting significantly higher shear wave velocity than quartz sand at equivalent cyclic resistance ratio levels, thereby confirming their intrinsic mechanical differences. The proposed model effectively characterizes the liquefaction resistance of coral sand under varying seismic intensities and can accurately delineate liquefied layers in case analyses. This research provides a valuable reference for seismic safety assessments and foundation design in coral sand sites, such as islands and ports in the South China Sea.

Multiple drying-wetting, freeze-thaw, and drying-wetting-freeze-thaw cycle tests were conducted on intact expansive soil. This was followed by conventional shrinkage tests and controlled suction desorption tests on saturated samples under each cycle condition to investigate the differences in the effects of drying-wetting, freeze-thaw, and combined drying-wetting-freeze-thaw cycles on the soil-water characteristics and shrinkage behavior of expansive soil. The results indicate that the yield suction (sy) and shrinkage limit suction (sSL) divide the desorption process of saturated expansive soil into three zones: (1) when s＜sy, the soil is in the elastic zone, (2) when sy≤s≤sSL, the soil is in the elastoplastic zone and (3) when s＞sSL, the soil is in the shrinkage limit zone. Following drying-wetting (DW) cycles, the expansive soil exhibited the highest critical suction, water retention capacity, air entry value, yield suction, and shrinkage limit suction, with freeze-thaw (FT) cycles yielding intermediate values, while drying-wetting-freeze-thaw (DW-FT) cycles resulted in the lowest values. Under various cycling conditions, the e-Sr curves during desorption can be approximately divided into three segments: a gentle segment, a steep descending segment, and a vertical segment. The shrinkage deformation was essentially completed after the steep descending segment. The degree of saturation (or void ratio) decreased (or increased) with the number of cycles and eventually stabilized. Notably, the first cycle caused the most significant reduction (or increase), with the degree of saturation (or void ratio) stabilizing after three cycles. The dry shrinkage degree of saturated expansive soil was greatest after DW cycles, followed by DW-FT cycles, and smallest after FT cycles. A model for the Soil Shrinkage Characteristic Curve (SSCC) and Soil-Water Characteristic Curve (SWCC) of saturated expansive soil, incorporating the effects of DW, FT, and DW-FT cycles, was proposed, and the fitting results demonstrated good agreement with the experimental data.