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.

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.

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.

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.

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.

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.

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.

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 (s_y) and shrinkage limit suction (s_SL) divide the desorption process of saturated expansive soil into three zones: (1) when s<s_y, the soil is in the elastic zone, (2) when s_y≤s≤s_SL, the soil is in the elastoplastic zone and (3) when s>s_SL, 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-S_r 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.

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-FLAC^3D 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.

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.