To investigate the overall deformation mechanism of the central locked slope in cold regions, this study conducted freeze-thaw tests and nuclear magnetic resonance (NMR) experiments on sandstone samples from three rock bridges of varying lengths. By integrating multifractal theory, the study examined the evolution patterns and fractal characteristics of the pore structure in these sandstone samples during freeze-thaw cycles. Meso-damage variables were quantitatively characterized using multifractal parameters. Additionally, a predictive formula for the degradation of elastic modulus based on meso-damage was established through trans-scale damage identification and comparison. The results indicated that the evolution of the pore structure in the rock bridge samples during freeze-thaw cycles can be categorized into two stages: dynamic remodeling of the pore structure (early stage) and saturation of pore network evolution (middle-to-late stage). The peak growth rates of the primary peaks in the NMR T2 spectra for the 20 mm, 25 mm, and 30 mm rock bridge samples were 30.3%, 12.5%, and 14.7%, respectively, while the secondary peaks exhibited growth rates of 42.9%, 46.4%, and 34.3%, respectively. Notably, the growth rate of mesopores was significantly higher than that of micropores. Furthermore, with an increasing number of freeze-thaw cycles, the pore volume, heterogeneity, and pore connectivity of the sandstone samples increased, resulting in intensified damage and a more complex pore structure. In the later stages of the freeze-thaw cycles, as the length of the rock bridge increased, the degree of evolution, heterogeneity, and pore connectivity of the sandstone samples initially decreased and then increased, with the highest values observed in the 20 mm-long rock bridge, followed by the 30 mm-long rock bridge, and the lowest in the 25 mm-long rock bridge. This study defined meso-damage and macro-damage variables based on the Hurst exponent and elastic modulus, achieving a macro-meso combination of damage that successfully predicted the degradation trend of macro-mechanical characteristic parameters from the meso-scale. The findings of this study may provide valuable insights into the deformation mechanisms and stability analysis of slopes in cold regions.

Deep engineering rock masses are frequently situated in complex geological environments where water pressure, ground stress, and rock structure collectively influence the physical and mechanical properties of the rocks. Investigating the laws and mechanisms of ultrasonic wave propagation in cracked rocks under high water pressure is essential for assessing the stability of engineering rock masses in these intricate settings. By utilizing an ultrasonic testing system designed for high water pressure and high-stress conditions, we established seven levels of water pressure to replicate the hydraulic environment encountered in engineering practices. Ultrasonic propagation tests were conducted on five types of cracked rocks with varying dip angles. The initial wave of the ultrasonic signal was analyzed via Fourier transform to explore the relationships among the ultrasonic spectral curve, frequency domain transmission coefficient, quality factor, and water pressure as well as crack dip angle. An empirical model was constructed to describe the evolution of ultrasonic frequency domain parameters in cracked rocks. The results indicate that the frequency domain transmission coefficient of cracked rock initially increases and subsequently decreases with rising water pressure, conforming closely to a Gaussian function relationship. The quality factor exhibits a decrease followed by an increase as water pressure rises, showing the least sensitivity to changes in crack dip angle when the water pressure is at 2.5 MPa. Furthermore, the frequency domain transmission coefficient is determined by the size of the crack surface projection area on the rock section that is perpendicular to the direction of ultrasonic wave propagation. A larger projection area of the crack surface correlates with a smaller frequency domain transmission coefficient. As the crack dip angle increases, the quality factor first decreases and then increases, achieving its lowest sensitivity to variations in water pressure at a crack dip angle of 45°.

To achieve real-time stability evaluation and early warning for sudden unstable rock collapse, this study proposes a monitoring method for toppling unstable rock collapse based on micro-electro-mechanical systems (MEMS) sensing technology. Integrating MEMS sensing mechanisms with vibration dynamic equilibrium equations, the proposed method overcomes the limitations of traditional apparent displacement monitoring. By simplifying the toppling unstable rock into a spring-mass pendulum model, a quantitative relationship was detived, revealing a 4∶3 ratio between the natural frequency and the safety factor under limit equilibrium conditions. Indoor simulation experiments with varying degrees of detachment validated the natural frequency monitoring algorithm based on the spectral response characteristics of the bedrock and unstable rock. The applicability of MEMS sensors in acquiring time-domain and frequency-domain vibration data from unstable rocks was also verified using a laser doppler vibrometer (LDV). Furthermore, a three-parameter stability evaluation model and a hierarchical early-warning threshold criteria were proposed, which incorporate natural frequency, the inverse root mean square velocity amplitude ratio, and the inverse tilt angle as dual dynamic-deformation indicators. Key issues in the practical application of the stability evaluation model and MEMS sensing technology are also discussed. The results demonstrate that the stability of toppling unstable rock is significantly positively correlated with natural frequency, the inverse root mean square velocity amplitude ratio, and the inverse tilt angle. Moreover, the integrated dynamic-deformation monitoring approach enables multi-level early warnings (red, orange, and yellow), thereby meeting the safety warning requirements for unstable rock masses at different stability levels in engineering construction.

To investigate the influence of impact specific energy on the dynamic mechanical properties and crushing characteristics of magnetite stone, as well as to analyze the size effect of magnetite under varying loading energies, this study aims to determine the optimal loading energies for crushing ores of different sizes and to minimize energy loss. A separated Split Hopkinson Pressure Bar (SHPB) test system was employed to conduct impact experiments on magnetite ores of lengths 30, 35, 40, 45, and 50 mm, using four different impact air pressures. The analysis was conducted from five perspectives: deformation characteristics, strength characteristics, energy characteristics, cracking modes, and fragmentation degree. The results indicate that, for magnetite specimens of identical length, an increase in impact air pressure initially causes a decrease, followed by an increase in the dynamic modulus of elasticity; the peak strain and dynamic compressive strength both increase. Additionally, energy dissipation, the ratio of energy dissipation, and the unit volume of dissipated energy exhibit an upward trend. The fractal dimensions of ore lumps increase, while the average size of the fragments decreases, indicating a deeper degree of crushing. When impact air pressure is held constant, the dynamic mechanical characteristics of magnetite ore demonstrate a pronounced size effect. As specimen length increases, the dynamic modulus of elasticity increases exponentially, with a faster growth rate observed at lower air pressures. The dynamic compressive strength shows a linear increase, with a more rapid rate at higher pressures, while peak strain decreases. Furthermore, the dissipated energy and its proportion increase, and the dissipated energy per unit volume decreases. The fractal dimensions of the block size decrease, the average size of crushed pieces increases, and there is a significant increase in the number of larger fragments. The increase in specimen length inhibits the initiation of cracking in magnetite stone, alters the cracking mode, and reduces the number of cracks. The energy dissipation per unit volume is positively correlated with the fractal dimension, with a higher correlation coefficient than that observed with the negatively correlated average particle size of fragments. The increase in crushing specific energy promotes the crushing of magnetite stone, though this promotion effect gradually diminishes. As impact air pressure increases, the influence of unit crushing specific energy on the mechanical properties of magnetite stone becomes progressively weaker. Calculations suggest that the optimal crushing specific energy for magnetite stone is approximately 2.5, which yields a higher energy utilization rate. The findings of this study provide valuable guidance for the safe production of mines and the impact crushing of magnetite stone.

To investigate the fracture evolution and critical damage angle around gas pre-pumping boreholes, we conducted 3D-VIC observation tests under uniaxial compression on coal samples with varying initial fracture angles (0°, 30°, 45°, 60°, 90°). We computed time-series images of the surface deformation of the samples under different stress states, as well as their full-field strains during the destructive process. The characteristics of surface deformation and fracture evolution in borehole-fracture composite coals with differing fracture inclination angles were accurately characterized. The results indicate the following: (1) Localized bands emerge in the strain field during the elastic deformation stage. A “sudden” phenomenon occurs when the pre-fabricated fissure inclination angle is 45°, where the time interval between new crack initiation and surface penetration is relatively short. Localized zones emerge in the vicinity of boreholes and pre-existing fissures, making them more susceptible to damage during the crack initiation and expansion stages. (2) The fracture angle of the cracks significantly influences the specimen’s deformation under axial load. The tips of prefabricated fissures with varying angles concentrate and accumulate stress as axial stress levels increase, leading the samples to undergo a yielding-rupture process. The initial fracture angle of 45° represents the critical angle for destabilization damage in borehole-fracture composite coals, at which point the drilling deformation damage degree reaches a maximum of 23.42%. (3) As the initial prefabricated fracture angles increase, the damage degree of the borehole exhibits a linear upward trend when the fracture inclination angle is less than 45°, expressed as . Conversely, it follows a negative exponential downward trend for fracture inclination angles ranging from 45° to 90°, expressed as . This model demonstrates a good fit and effectively predicts the damage degree of borehole-fracture composite coals. These conclusions highlight that initial fracture angles play a crucial role in the development of fractures around boreholes during gas pre-pumping processes. The stress concentration at the crack tip is greatest, the deterioration effect is most pronounced, and the bearing capacity is lowest at the initial fracture angle of 45°, which is identified as the critical damage angle for borehole-fracture composite coals. These findings provide a foundation for assessing the destabilized damage state of gas pre-pumping boreholes.

In light of the significant impact of weak rock masses on engineering construction and the scarcity of applicable in-situ stress testing methods, an in-situ stress test method for weak rock mass based on hydraulic pillow monitoring was developed by applying the theory of rheological stress recovery. This paper provides a comprehensive summary of existing in-situ stress measurement methods for weak rock masses and their associated limitations. It discusses in detail the testing principles, devices, procedures, and result calculation processes of the proposed method. The measurement accuracy based on calibration test data is also estimated. The testing device is straightforward, allowing for in-situ stress or surrounding rock disturbance stress testing through probe combinations or distributed arrangements, thereby facilitating the acquisition of one-dimensional to three-dimensional in-situ stress data. The hydraulic pillow monitoring test has been successfully conducted in the fragmented powder rock formation of the Longpan—Qiaohou fault zone within the Xianglushan tunnel of the Central Yunnan Diversion Project, yielding monitoring data and borehole plane stress results over nearly three years. This marks the first implementation of in-situ stress testing directly within extremely soft rock in an active fault zone. A comparative test of hydraulic fracturing stress was performed at the edge of the same fault zone, with results indicating that the magnitudes of the principal stresses are relatively close. The application case and comparative testing results demonstrate the feasibility of the weak rock mass in-situ stress testing method based on hydraulic pillow monitoring. The developed hydraulic pillow device is well-designed, securely locked, and the testing procedures and calculation methods are reliable. The monitoring results from the engineering application case reflect the variations in disturbance stress within the surrounding rock, confirming that this method can be utilized for rock stress monitoring.

To thoroughly investigate the influence mechanism of lining permeability on the stability of surrounding rock in deep-buried, water-enriched tunnels that traverse weak and fractured zones, the tunnel was modeled as an axially symmetric structure. The surrounding rock was categorized into three zones based on the degree of deformation: the elastic zone, the plastic softening zone, and the fractured zone. Utilizing the Mogi-Coulomb strength criterion, which accounts for the effects of the intermediate principal stress, theoretical derivations were conducted to derive solutions for the distribution of pore water pressure, as well as the stress and deformation resulting from seepage in tunnels. This study, based on specific engineering examples, analyzed the impact of lining permeability on the distribution of pore water pressure within the tunnel, the stress and radii of the plastic softening and fractured zones in the surrounding rock, displacement of tunnel walls, and surrounding rock pressure. It discussed the reasonable range of values for the lining permeability coefficient and further explored the effects of factors such as the characteristics of the weak and fractured zones in surrounding rock, the softening modulus, and the intermediate principal stress on the stability of surrounding rock under conditions of reasonable lining permeability coefficient values. The research findings indicated that as the ratio of the permeability coefficients between the lining and the elastic zone of the surrounding rock  increased, the pore water pressure, the radii of the plastic softening and fractured zones, surrounding rock pressure, and tunnel wall displacement all decreased. Conversely, the stress in the weak and fractured zone of the surrounding rock increased. When the permeability coefficient ratio reached a certain threshold  , these parameters tended to stabilize. Considering the safety of tunnel lining structures, the stability of surrounding rock, and the capacity to resist deformation,   was deemed relatively reasonable. Further results revealed that the softening modulus of the surrounding rock had the most significant effect on the radius of the fractured zone. Additionally, the intermediate principal stress had a pronounced impact on the deformation of the surrounding rock and the expansion of the weak and fractured zone, exhibiting notable interval symmetry.

Freeze-thaw action is a primary factor contributing to crack propagation in rocks within seasonally frozen regions. To elucidate the distribution and spatial evolution of frost swelling pressure during the ice-water phase transition, freeze-thaw cycle tests were conducted on sandstones featuring a single open crack. A distributed pressure sensor was employed to monitor the values and distribution status of frost swelling pressure in real time, thereby overcoming the limitation of single-point pressure sensors that cannot accurately reflect the distribution of frost swelling pressure along the crack surface. The study investigated the evolution and distribution characteristics of frost swelling pressure, while also exploring the influence of crack depth and width on these parameters. The experimental results indicate that the frost swelling pressure curve can be categorized into five distinct stages: incubation, explosion, drop, dissipation, and disappearance. In the absence of cracks, the frost swelling pressure increases with greater crack depth and width; however, the effect of crack size on frost swelling pressure is relatively minor when cracks are present. The distribution of frost swelling pressure on the crack surface is uneven and varies with freezing duration. For deep cracks, frost swelling pressure is generated at the top of the crack, and the distribution area shifts downward as freezing progresses.

To investigate the impact of rainfall patterns on the infiltration and stability of unsaturated soil slopes, a coupled Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) analysis was conducted during rainfall infiltration. This analysis utilized the Finite Volume Method (FVM) and the Python solver FiPy. Comparisons with experimental results from model tests on granite residual soil slopes facilitated the calibration of micromechanical contact parameters in the discrete element simulation. The study examined variations in moisture content, particle displacement, and slip surfaces of granite residual soil slopes under four rainfall patterns: front-type, middle-type, uniform-type, and rear-type. The results indicate a strong correlation between the simulated and experimental data regarding infiltration rates, displacement changes, and slope failure modes, thereby confirming the effectiveness of this methodology. Rainfall patterns had a significant impact on the displacement and rotation of slope particles, particularly under front-type rainfall conditions, where the moisture content of the slope increased rapidly, accompanied by sharp rises in particle displacement and rotation, ultimately resulting in a translational failure of the entire slope. The influence of different rainfall types on slope stability is ranked from most to least significant as follows: front-type, middle-type, rear-type, and uniform-type. Slope failure initiated from cracks at the base of the slope and progressively extended upward until a complete slip surface was established. Initially, cracks were predominantly concentrated in the range of 105°to 135°, whereas, following the total failure of the slope, most particle contact fractures occurred in the direction of 90°to 120°.

Landslides are among the most prevalent geological hazards along transportation routes. During deformation, failure, and movement, they may interact with large, hazardous rock masses, significantly altering the extent and severity of the hazard. This study focuses on the Luoma slope at mileage marker K4529＋600 of the G318 National Highway in the Xizang Autonomous Region as its engineering context. Employing the Discontinuous Deformation Analysis (DDA) method, this research investigates the interaction mechanisms between landslide bodies and hazardous rock masses, along with the kinematic processes and disaster characteristics involved. Basic models of oblique and face-to-face collisions were constructed and compared with results from existing experiments, numerical simulations, and theoretical formulas to validate the accuracy of the DDA method in simulating block collisions. Considering both the intact and undamaged state of the hazardous rock mass and its unstable condition after being intersected by joints, corresponding DDA numerical models of the Luoma slope were established. By analyzing the displacement-time curves of monitoring points on the landslide body, the reliability of the DDA method in simulating landslide deformation was confirmed. Building upon this, the effects of a reduced internal friction angle of the rock mass were examined, along with the obstructive role of hazardous rock masses on the landslide body, and the impact and destructive effects of the landslide body on the hazardous rock masses were separately investigated. This allowed for a comprehensive analysis of the landslide deformation and failure processes, as well as the kinematic disaster processes resulting from the interaction between the landslide body and the hazardous rock masses. The results demonstrate that the DDA method exhibits high accuracy in simulating block collisions and landslide deformations, making it particularly suitable for analyzing interactions between landslide bodies and hazardous rock masses. Landslide deformation is primarily characterized by surface subsidence, and during this process, blocks may tilt backward or rebound. When the landslide body encounters an intact, undamaged hazardous rock mass, the rock mass serves as a barrier, limiting the extent of the disaster and illustrating its obstructive and protective role against landslide hazards. Conversely, when the landslide body encounters a dangerous rock mass that is intersected by joints, the impact accelerates the propagation of internal cracks within the rock mass, leading to its collapse and failure. This indicates that the impact of the landslide mass serves as a trigger for the destabilization and failure of the hazardous rock mass, thereby exacerbating the scope and severity of the slope disaster. This study comprehensively reflects the temporal and spatial interaction and evolution characteristics between landslide bodies and hazardous rock masses. It demonstrates that the DDA method can effectively replicate and quantitatively analyze the deformation and failure of landslide bodies, the obstructive effects of hazardous rock masses on landslides, and the impact and collision processes between landslide bodies and hazardous rock masses. By revealing the movement characteristics and deposition features of blocks, this study provides a theoretical foundation for disaster prevention and mitigation in similar slope engineering projects.

The sealing layer materials utilized in underground gas storage facilities are crucial for their effective operation. This study analyzes the impact of isophorone diisocyanate (IPDI) content on the mechanical properties of polyurethane to identify its optimal concentration. Additionally, we developed equipment to test breakdown pressure and gas permeability, enabling an investigation into the breakdown pressure, failure modes, and high-pressure gas permeability of the modified polyurethane material. Furthermore, we examined the effects of constant high temperature and thermal cycling on the gas tightness of the modified polyurethane. The results indicate that both the tensile and compressive strengths of polyurethane decrease as the IPDI content increases. When the IPDI content reaches 19.34%, the material exhibits favorable comprehensive mechanical properties and toughness, meeting the requirements for the sealing layer in artificial caverns used for gas storage. The modified polyurethane material did not fail during the breakdown pressure test, achieving a gas permeability of 7.931×10－13 cm3 STP·cm·(cm²·s·cmHg)?¹, which is approximately one-thousandth of the permeability of conventional sealing materials. When the temperature exceeds 40 ℃, the gas permeability of this modified polyurethane material increases with rising temperature; however, it continues to maintain satisfactory sealing performance.

 In China, coal mining predominantly occurs through underground methods, with over 12 000 kilometers of new tunnels constructed annually. Notably, more than 90% of these coal mine tunnels utilize bolt and anchor support systems. Enhancing the theoretical framework of tunnel bolt support has become a pressing concern in the coal mining sector. This study establishes a pre-tension reinforcement model for surrounding rock strength by introducing two key parameters: pre-tension force and pre-tension reinforcement coefficient. By integrating this model with the combined arch support theory, a coupled support theory for combined arches and surrounding rock pre-tension reinforcement is proposed. Additionally, an Excel-based design program for tunnel roof bolt support is developed. The research further analyzes the impact of support strength parameters and validates the coupled support theory through engineering case studies. The findings reveal that bolt length and spacing influence support strength by altering the thickness of the combined arch, demonstrating a positive correlation between bolt length and support strength, while a negative correlation exists between bolt spacing and support strength. Moreover, the tunnel span affects support strength by modifying the height-to-span ratio of the combined arch, which also shows a negative correlation with support strength. The pre-tension force impacts support strength by enhancing the reinforcement of surrounding rock, exhibiting a positive correlation with support strength. Finally, comparisons with actual coal mine tunnel bolt support design calculations indicate that the computed results closely align with actual values, thereby validating the proposed coupled support theory.

The critical state criterion for the rock brittle-ductile transition holds significant practical importance for assessing the forms and frequencies of engineering disasters in deep rock masses. By analyzing the critical state characteristics of the rock brittle-ductile transition as defined by the curved Mohr strength theory, this study proposes a critical state criterion that incorporates factors such as fracture modulus, uniaxial tensile strength, internal cohesion, and fracture angle, based on the Mohr-Wedge criterion derived from the aforementioned theory. The applicability of this critical state criterion is validated using data from rock triaxial compression tests. The results indicate that the critical state criterion for rock brittle-ductile transition, which quantitatively relates to uniaxial compressive strength, exhibits poor overall fitting. In contrast, the critical state criterion based on the Mohr-Wedge criterion aligns more closely with the transition trend from rock brittleness to ductility. Furthermore, the rock fracture angle included in this critical state criterion does not alter the confining pressure value at the critical state; rather, it affects the gradient of the strength curve in the ductile phase. To prevent the gradient of the strength curve in the ductile stage from exceeding that of the brittle stage, it is recommended that the fracture angle in the critical state of the brittle-ductile transition be set to 45°. The critical state criterion for rock brittle-ductile transition proposed in this work can serve as a valuable reference for understanding the transition and changes in the strength curve during the ductile phase.

With deteriorating environmental conditions and accelerating energy transformations, the development of diversified energy storage technologies has become an urgent necessity to address the imbalance between energy supply and demand. This paper proposes a novel energy storage solution that utilizes unconventional oil and gas reservoirs as compressed air energy storage sites, aiming to enhance resource efficiency by repurposing depleted or nearly depleted unconventional reservoirs. This approach leverages existing hydraulic fracturing technology to establish a compressed air energy storage system by retaining the fracturing wells and surface infrastructure, while incorporating electric motors, compressors, expanders, generators, and electrical circuitry. Comprehensive research and systematic analysis reveal several key findings: the large-scale geological reserves of unconventional oil and gas present a promising development outlook for this new method; the availability of extensive geological information and mature surface facilities can significantly lower initial investment costs; the vast number of oil and gas wells (2 677) and ample energy storage capacity (28 500 m³ per well) provide advantages for large-scale application; potential energy storage capacity within pore spaces supports low-power energy storage for extended durations (ultra-long duration); when combined with the distribution of unconventional oil and gas resources and renewable energy, the provinces of Sichuan, Shaanxi, Inner Mongolia, Liaoning, Jilin, Heilongjiang, and Shanxi emerge as optimal regions for implementing this new energy storage method; and the tight integration of several established technologies offer a stable technical foundation for realizing this innovative energy storage approach. This demonstrates the considerable feasibility of transforming depleted unconventional oil and gas reservoirs into compressed gas energy storage systems. However, several scientific and technological challenges warrant attention: the physical-mechanical degradation of reservoirs under prolonged hydration and cyclic loading, and its impact on the long-term stability of energy storage systems; the effects of rock failure or proppant flowback on the stability of energy storage spaces and equipment; the assessment of the integrity of long-term injection and production in energy storage spaces and the seal integrity of wellbores, along with their influence on storage efficiency and the safe operation of energy storage systems; the impact of compressed air temperature on the long-term stability, integrity, and downhole equipment of the energy storage system; and the influence of fracture network morphology on injection and production rates and the conversion efficiency of the energy storage system. Compressed gas energy storage systems in depleted unconventional oil and gas reservoirs present a novel solution for energy storage that could significantly enhance China′s energy storage industry.

High water pressure and high ground stress jointly control the stress state and damage accumulation evolution degree of rock, which in turn affects its static viscosity performance. In order to study the variation characteristics of the viscous properties of high water pressure and high stress rock, based on Kelvin model and ultrasonic propagation test, a method for measuring the static viscosity coefficient of high water pressure and high stress rock is proposed. Using the self-developed high water pressure and high stress rock ultrasonic testing system, the ultrasonic propagation tests of red sandstone and limestone under different water pressure and axial static stress are carried out, and the experimental value of attenuation coefficient and the theoretical value of static viscosity coefficient are calculated. The frequency correlation between attenuation coefficient and static viscosity coefficient is studied to determine the calculation frequency of rock static viscosity coefficient. The ultrasonic velocity calculated by the static viscosity coefficient is compared with the measured wave velocity to verify the correctness of the static viscosity coefficient measurement method. The static viscosity coefficient of rock with high water pressure and high stress is calculated, and the influence law and mechanism of water pressure and axial static stress on the static viscosity coefficient of rock are explored. The results show that the method proposed in this paper to calculate the static viscosity coefficient of rock with high water pressure and high stress by using ultrasonic test and Kelvin model is feasible. With the increase of water pressure, the static viscosity coefficient of red sandstone increases first and then decreases gradually, and the relationship between them is Gaussian function. The static viscosity coefficient of limestone increases rapidly and then develops slowly or decreases slightly with the increase of water pressure. With the increase of axial static stress, the static viscosity coefficients of red sandstone and limestone increase first and then decrease, and the two satisfy the quadratic function relationship.

The Dunhuang Grottoes represent a significant segment of China?s grotto temples; however, the cliff faces are highly vulnerable to weathering due to the wet-dry and freeze-thaw cycles, posing a serious threat to their long-term preservation. To investigate the deterioration mechanisms of the conglomerate rock in the Dunhuang Grottoes under these conditions, this study conducted laboratory tests simulating wet-dry and freeze-thaw cycles on conglomerate samples, utilizing regional environmental monitoring data as a reference. The findings reveal that: (1) Wet-dry and freeze-thaw cycles significantly reduce the mass, P-wave velocity, and uniaxial compressive strength of the conglomerate samples while markedly increasing their permeability; (2) Water plays a critical role in the deterioration process of the conglomerate, particularly during freeze-thaw cycles involving moisture, where the rate of deterioration accelerates and is positively correlated with water content. Compared to the fresh, dry samples, the uniaxial compressive strength decreased by 13% in the wet-dry cycle group, 12% in the dry freeze-thaw group, 36% in the saturated freeze-thaw group, and 25% in the natural freeze-thaw group; (3) Microscopic analysis indicates that the degradation of the conglomerate under wet-dry and freeze-thaw cycles results from significant changes in microstructure, including surface roughening of micro-mineral particles, structural loosening, weakening of cementation, and the formation of microcracks. These results provide crucial theoretical support for the protection of the Dunhuang Grottoes against weathering.

To accurately and efficiently predict the uniaxial compressive strength (UCS) of rock at varying depths within a borehole, an efficient UCS prediction method based on drilling process monitoring (DPM) technology and field core rebound tests is proposed. Initially, the measured DPM parameters are processed to create a pure drilling process curve, which is then averaged over specific intervals using an automatic segmentation algorithm. Subsequently, the drilling specific energy (fracture energy ratio) curve is computed along the entire borehole depth by applying a modified drilling pressure and torque model. Finally, based on core rebound tests, a functional relationship between the borehole drilling specific energy and UCS is established to obtain the rock UCS curve along the borehole depth, and the predicted results are validated by foundation bearing capacity curves obtained from cone dynamic penetration tests. The study reveals that the drilling oil pressure and the self-weight of the drill string jointly exert influence on the drill bit, with the self-weight accounting for 48.2% of the total pressure, which varies with depth. The drilling specific energy remains relatively stable despite drill bit replacements and fluctuations in drilling oil pressure, but it is more sensitive to changes in formation properties compared to drilling speed. Through the Yongchang Expressway slope drilling test, the predicted frequency distribution intervals of rock UCS for each borehole align with the foundation bearing capacity, thereby validating the effectiveness of the proposed method.

To enhance the spatial accuracy of underground temperature (UGT) prediction for deeply buried long tunnels (DBLT) in complex geomorphic environments, a pixel-level UGT prediction methodology known as the Virtual Temperature Column Method is proposed, which utilizes thermal infrared (TIR) remote sensing data. This innovative approach incorporates multi-year surface radiation data collected from TIR satellites as boundary conditions for surface temperature, leveraging a limited dataset of temperature measurements from boreholes. Key parameters such as the annual average surface temperature (AAST)，the heat flux value in the thermostat layer (THF), and the thermal conductivity of the rock (RTC) are obtained through surface temperature inversion, theoretical calculations, and indoor experiments, respectively. These parameters facilitate high-resolution pixel-level predictions of UGT in DBLT. To validate the efficacy of this methodology, a project in the Qinghai—Tibet Plateau region is used as an example to forecast the UGT of deep tunnel strata. Additionally, a gray correlation analysis is conducted to identify the key factors influencing the sensitivity of UGT predictions. The results demonstrate that the methodology improves the spatial accuracy of UGT predictions from a kilometer scale to a 30-meter scale, with prediction errors between the predicted and measured values controlled within 6%, indicating high spatial accuracy. The three key parameters affecting the sensitivity of the UGT prediction are AAST, THF, and RTC, with their correlation coefficients being 1, 0.99, and 0.489, respectively, indicating the hierarchy of sensitivity as follows: AAST＞THF＞RTC. This methodology effectively addresses the challenges posed by scarce borehole temperature measurement data and the low spatial accuracy of UGT predictions in complex geomorphic environments, providing a valuable reference for accurate UGT prediction in deep-buried tunneling projects in regions of frequent geothermal activity in China.

Crushed stone strength and particle breakage are critical factors influencing the shear behavior of soil-rock mixtures (SRM). To investigate the interaction mechanisms between rock strength, particle breakage, and shear characteristics, dyed mortar was employed to fabricate crushed stones of varying strengths, thereby preparing pure SRM. Stacked ring shear tests and sieve analyses were conducted to examine their shear behavior and particle breakage characteristics, accompanied by a proposed cumulative maximum breakage index . The results indicate that: (1) Increased crushed stone strength enhances dilatancy while reducing contraction in SRM. Particle breakage diminishes SRM dilatancy, revealing a critical dilatancy threshold under minimum top pressure. (2) Particle breakage primarily generates first-order debris, with the medium-size fraction exhibiting the highest degree of breakage, which is inconsistent with initial content distributions. (3) Higher unconfined compressive strength ( ) of crushed stone increases both the internal friction angle ( ) and the linear component of shear strength. The cohesion (c) demonstrates a quadratic relationship with . (4) The breakage index   proves to be effective in quantifying particle breakage, with its relationships to top pressure and gravel strength being mathematically describable through planar equations. Notably,  shows superior sensitivity to variations in both crushed stone strength and top pressure compared to conventional indices.

Research on surrounding rock pressure predominantly focuses on deep-buried tunnels employing the New Austrian tunneling method, with relatively little attention given to shallow-buried rocky shield tunnels. To formulate an equation for calculating surrounding rock pressure in these tunnels, a gap parameter is introduced based on the non-uniform convergence mode of the tunnel section. A two-stage numerical calculation model is developed to elucidate the key influencing factors of surrounding rock pressure, resulting in a comprehensive collection of sample results under varying conditions. A multi-factor curve fitting method is utilized to derive the surrounding rock pressure, leading to the establishment of a calculation equation applicable to different directions and locations within the tunnel. Measured data on surrounding rock pressure from several cases of shallow-buried rocky tunnels are compiled, and a comparison is made among the calculation equation, measured data, existing theories, and standardized methods to validate the proposed equation’s reasonableness. Furthermore, the differences among these methods are analyzed. The variation of surrounding rock pressure in relation to five types of influencing factors is discussed. Based on the shallow-buried rocky shield tunnel project in Wuhan, which runs beneath the Yellow Crane Tower, a fiber-optic measuring device is developed to monitor surrounding rock pressure. The measured results are compared with those predicted by the proposed calculation equation, thereby confirming its applicability. The findings indicate that: (1) The lateral pressure coefficient and gap parameters significantly influence the surrounding rock pressure of shallow-buried rocky shield tunnels; (2) The discrepancy between calculated and measured values of surrounding rock pressure remains within a 10% range. The proposed calculation equation demonstrates practical utility and provides reference value for the engineering of shallow-buried rocky shield tunnels.

The complex failure process of natural rock masses is a primary factor contributing to the unpredictability of natural disasters. To gain a deeper understanding of rock mass failure modes, we propose a numerical model that simulates the mixed tension-shear failure process of rocks, based on the ordinary state-based peridynamics method. This model integrates the maximum principal stress criterion and the Mohr-Coulomb criterion into the material damage identification process. The propagation paths of tensile and shear cracks during rock failure are determined by evaluating the ratio of fracture energy released from different failure bonds to the total fracture energy. Additionally, corresponding quantification parameters are introduced to characterize crack propagation. The model’s effectiveness in identifying crack propagation is validated through uniaxial compression tests on rock samples with prefabricated cracks. Finally, we investigate the effects of confining pressure, inclination angle of prefabricated cracks, and the height-to-diameter ratio on crack propagation morphology, peak strength, and structural damage indices of the rock. The results demonstrate that confining pressure suppresses the expansion of tensile cracks. As confining pressure increases, the failure mode of rock samples gradually transitions from tensile splitting failure to mixed tension-shear failure, and ultimately to shear failure, significantly increasing peak strength. The inclination angle of prefabricated cracks influences peak strength by altering crack propagation morphology; when the inclination angle is 30°, the rock sample exhibits more tensile cracks, resulting in lower peak compressive strength. Conversely, at an inclination angle of 90°, the increase in shear cracks significantly enhances peak compressive strength. A decrease in the height-to-diameter ratio of the rock sample prolongs the coplanar shear crack extension path and increases the number of tensile cracks. Simultaneously, the friction effect at the end face is significantly enhanced, suppressing tensile crack expansion and consequently improving compressive strength.

To investigate the effects of anchoring on deformation, failure, and energy release characteristics of slab-fractured hard rock, this study prepared slab-fractured granite specimens with prefabricated fractures and fabricated ordinary anchor cables using steel wire ropes. By integrating CCD cameras, acoustic emission (AE) monitoring systems, and axial force sensors, the deformation and failure processes, AE signals, and axial forces of anchor cables were monitored during uniaxial compression experiments on both anchored and non-anchored slab-fractured granite specimens. The results demonstrated that: after anchor reinforcement, the average peak strength of the specimens increased by 8.94%, the average energy storage before rupture rose by 9.89%, and the average energy release during rupture decreased by 12.69%. During loading, the evolution of maximum principal strain in non-anchored specimens exhibited a “central→free-surface→synchronized propagation” pattern, while anchored specimens displayed a “free-surface→central→free-surface” pattern. Compared to non-anchored specimens, which experienced violent elastic ejection instability resulting in “V”-shaped fractures, anchored specimens maintained better structural integrity despite localized fractures, spalling, and minor fragment ejection. In the failure processes, AE energy release in non-anchored specimens was characterized by sporadic high-energy events dominated by tensile fractures, whereas anchored specimens exhibited frequent low-energy events associated with shear-tensile composite fractures. Finally, based on these findings, the anchoring mechanism was systematically discussed and summarized from two key aspects: the deformation suppression effect and the energy release buffering effect. The research results not only enhance the understanding of deformation and failure characteristics in slab-fractured rock under anchorage conditions but also provide both an experimental foundation and a theoretical basis for controlling slab-related geological hazards.

As a novel type of pile foundation, the investigation into the dynamic characteristics of stiff composite piles holds substantial theoretical significance for geotechnical engineering. Grounded in the principles of soil dynamics and pile foundation vibration theory, this study systematically examines the vertical displacement response at the pile head and along the pile shaft of stiff composite piles embedded in viscoelastic saturated soil layers under the influence of vertically incident seismic P-waves. Initially, a wave equation for saturated soil is formulated in cylindrical coordinates based on Biot?s porous medium theory. Subsequently, by integrating the vertical vibration equation for strength composite piles, a closed-form series solution for the longitudinal displacement of the soil skeleton is derived, leading to an analytical solution for the vertical displacement of strength composite piles under specified boundary conditions. Finally, through computational examples and parametric studies, this work elucidates the dynamic behavior of the interaction system between strength composite piles and saturated soil subjected to vertical seismic P-wave action at the pile tip. The findings indicate that moderately reducing the radius of the concrete core pile while increasing its length can enhance its vertical seismic resistance; conversely, during high-frequency stages, an increase in elastic modulus of the cement outer pile may detrimentally affect the seismic performance of strength composite piles. In designing these structures, it is recommended that the radius of concrete core piles be maintained within 40% to 60% of their total radius while setting their length to 20 to 40 times this radius. Additionally, it is advisable that the elastic modulus for cement outer piles be established at 2% to 5% relative to that of concrete core piles.

In view of the shortcomings of the round-shaped drain approximation method for the consolidation of PVD (prefabricated vertical drain), this study presents the ribbon PVD as an equivalent to a flat elliptical cylinder with a more compact shape. The analytical solution for the consolidation of the elliptical cylinder considering the influence of vertical consolidation is provided, along with a more concise calculation formula for the dimensionless parameter Fh, derived using the symbolic deduction module of Matlab. The rationality of this approach is validated through engineering case studies, which suggest that the dimensionless parameter Fh reflects the average radial drainage distance of the PVD foundation. According to the analytical solution of elliptical cylinder consolidation, it is posited that, with a fixed width b and thickness δ of the PVD, the equivalent diameter dw is positively correlated with the diameter of a single drain de. When the diameter of the single drain is sufficiently large (e.g., de/b≥10), the equivalent diameter stabilizes. The formula for calculating the equivalent diameter of conventional size PVDs is given as, with the average consolidation error ?U of the soil foundation generally being less than 1% when this formula is applied. Conversely, when the relative diameter of a single drain de/b is smaller, the equivalent diameter is less than the value predicted by the aforementioned formula due to shape effects. If the equivalent diameter continues to be used under these circumstances, the drainage and consolidation rates of the soil foundation may be overestimated. Therefore, in the actual design of projects and indoor model tests, it is essential to consider the influence of the shape effect of PVDs.

Due to membrane penetration, the conventional water exchange method for volume measurement suffers from low accuracy when applied to triaxial testing of coarse-grained saturated and unsaturated soils. This study proposes a general-purpose method for measuring the volume of coarse-grained soil during triaxial testing by tracking the movements of the lateral surface through specially designed rigid targets affixed to the membrane surface. The 3D coordinates of these targets are obtained using a multi-media photogrammetric technique. Triaxial tests were conducted on a stainless-steel cylinder and coarse-grained soils to evaluate the performance of the proposed method. Testing on the stainless-steel cylinder demonstrates that the proposed method can directly measure soil volume with an error of 0.28%. The triaxial tests on coarse-grained soils indicate that the measurement results are reasonable when compared to predictions based on existing analytical models. The rigid targets are unaffected by membrane penetration, and their use eliminates the need for complex corrections associated with membrane penetration, enabling direct volume measurement of coarse-grained soils during isotropic and shear loading. This proposed method offers an alternative to existing techniques and has potential applications not only in triaxial testing of saturated but also unsaturated coarse-grained soils across various size ranges.

Dredged sludge can be synergistically solidified using ground granulated blast-furnace slag (GGBS), carbide slag (CS), and phosphogypsum (PG). To investigate the strength-deformation characteristics, water transformation behavior, and microstructural evolution of GGBS-CS-PG (GCP) solidified dredged sludge under varying dosages of curing agents and curing durations, a series of unconfined compressive strength tests, scanning electron microscopy (SEM) observations, and low-field nuclear magnetic resonance (LF-NMR) analyses were conducted. Furthermore, the microstructural mechanisms underpinning the strength development of the GCP solidified sludge were explored. The results indicated that the early strength development of GCP solidified sludge occurred rapidly, with the unconfined compressive strength increasing logarithmically as curing age progressed. This behavior was primarily attributed to the synergistic interactions among GGBS, CS, and PG, which facilitated the rapid generation of a substantial amount of ettringite (AFt). The produced AFt effectively filled the pores and enhanced structural density through interactions with C-(A)-S-H gels. Moreover, the formation of AFt promoted the conversion of free water in the pores into bound water, resulting in a logarithmic increase in bound water content as curing age advanced. The pore size distribution primarily ranged from 0.003 to 0.11 μm. As the dosage of GCP increased, both the amount of bound water and the number of micropores significantly rose. Additionally, a quantitative relationship was established between microstructural parameters and macroscopic mechanical properties. The unconfined compressive strength and deformation modulus exhibited power function growth corresponding to increases in bound water content and micropore quantity.

Soil radial heterogeneity significantly impacts the low-strain integrity detection of pile foundations. Conventional computational models usually simplify soil variations to linear or quadratic functions. To address the inherent randomness of soil heterogeneity, this study develops a radial multi-layer random field model. It derives semi-analytical solutions for time-domain responses at any pile depth and analytical solutions for pile head frequency-domain responses, along with a corresponding solution procedure. The model’s validity is confirmed by comparing degenerate random field cases with classical models (e.g. homogeneous soil, construction-induced hardening/softening). Furthermore, the study systematically investigates how shear wave velocity ( ), its coefficient of variation (COV), fluctuation range ( ), construction influence zone ( ), and pile length (L) on the vibration characteristics and the failure probability of pile length detection. Results indicate that the random field model’s calculations are consistent with classical models under degenerate conditions,, highlighting its broader applicability. The degree of radial variability in soil   positively correlates with the peak amplitude of the pile tip reflection velocity and the curve’s volatility around this peak. Moreover, increasing increases , while COV exhibits a dual effect. This model can be extended to analyze pile vibrations considering bidirectional and three-dimensional spatial soil variability, offering novel insights for probabilistic analysis in pile integrity detection.

The paper presents a novel structured compression model for marine sediments based on the concept of residual structure, which accounts for non-linear deformation behavior. The proposed model features a straightforward formula that includes a few parameters with clear physical meanings. The model’s performance is validated by fitting it to the oedometer test data of Gravina calcarenite. Subsequently, we conducted a series of one-dimensional numerical compression tests using the discrete element method to investigate the impact of residual structure on the compressive behavior of marine sediment samples. Post-testing, some cementation bonds remain intact, corresponding to the residual structure. Additionally, we analyzed how model parameters influence the evolution of structural degradation. The model’s predictions were compared with compression test data from various types of structured soils, including in-situ sedimentary soils, cemented soils, hydrate-bearing soils and urban soils from Mexico. The results demonstrate a strong correlation and offer new theoretical insights into the structural degradation of soils. Notably, the compressibility of structured soil samples increases rapidly with increasing load, with the compression curve approaching that of remolded samples. This characteristic may be influenced by the residual structure, and the proposed model effectively captures this behavior. The current study contributes to the planning, design, and construction of offshore artificial islands and airports by enabling accurate calculations of foundation settlement. However, a primary limitation of the proposed model is its inability to account for the effects of shear deformation on structural degradation, which necessitates further refinement.