Hydrogen is a low-carbon and clean energy source that can be produced from a wide range of sources, and the vigorous development of hydrogen energy industry is an important measure to achieve the dual-carbon goal and cope with the global energy transition. In the whole industry chain of "preparation–storage–transportation–application" of hydrogen energy, the difficulty of hydrogen storage has long been a constraint to the high-quality development of hydrogen energy industry. Salt cavern hydrogen storage has outstanding advantages such as low cost, large scale, high safety, and high hydrogen storage purity, which is an important development direction of large-scale hydrogen storage in the future, and also a major strategic demand during China's low-carbon energy transition. The current situations of hydrogen production industry and hydrogen energy consumption in China were comprehensively investigated, and the demand for salt cavern hydrogen storage in China was further analyzed. The technology and engineering status of using salt caverns to store natural gas and hydrogen in foreign countries were investigated, and the development and construction history of salt cavern storage in China were summarized. The similarities and differences of using salt caverns to store natural gas, helium, compressed air, and hydrogen were compared, and three major scientific and technological challenges that salt cavern hydrogen storage in Chin faces were proposed: hydrogen seepage and biochemical reaction in bedded salt rock, wellbore integrity control in salt cavern hydrogen storage, and pregnancy and prevention of disaster in hydrogen storage groups. The research results clearly define the rapid growth trend of hydrogen storage demand and the key research directions of large-scale salt cavern hydrogen storage in China.

Physical similarity simulation is an important method for studying the deformation and failure of underground engineering. However, the classical similarity theory, which considers the mutual constraints of geometric similarity ratio and material mechanical parameter similarity ratio between similar models and engineering prototypes, often leads to a dilemma. This dilemma arises when the size of indoor physical similarity models and the material mechanical parameters cannot fully meet the similarity criteria, resulting in mechanical distortion and difficulties in interpreting simulation test results. In this article, a principle of mechanical similarity distortion mapping processing is developed to address this issue. This principle introduces a distortion coefficient and a mapping coefficient to compensate for the influence of distortion. By coupling analytical or numerical methods, the quantitative analysis of analog physical results for underground caverns can be achieved. To demonstrate the effectiveness of this approach, circular diversion tunnels are taken as the engineering prototype, and tunnels models are created using cement-based 3D printing. Overload tests are conducted, and the analog physical results are quantitatively analyzed and compared using the proposed coupling mechanics similar distortion principle and analytical method. Furthermore, a case study is conducted on a cavern group of a hydropower station. The failure deformation of the cavern group is obtained through physical overload tests on a 3D printed sandstone cavern group physical model. The analog physical results are then quantitatively analyzed using the coupling mechanical similitude distortion method and numerical method. The results of the case analysis demonstrate that this method enables quantitative engineering mapping analysis for analog physical results of circular tunnels or complex cavern groups, even when the geometric similarity ratio and mechanical similarity ratio do not satisfy the classical similarity criterion. This method has universal applicability for physical simulation mapping analysis of underground caverns with non-constant similarity ratios.

Rock burst is a dynamic disaster that occurs during coal mining, characterized by the sudden and violent release of elastic deformation energy accumulated in coal and rock. The majority of rock bursts, approximately 90%, happens in roadways. Roadway impact failure is not only influenced by impact energy, but also by the distance from the impact source. To address this, the concept of energy distance ratio is introduced, which represents the ratio of energy released by the impact source to the distance to the roadway. By considering the static load superposition mechanism of rock bursts and the balance theory of impulse energy absorption, various factors are taken into account, including the characteristics of the impact source energy distance ratio, roadway failure degree, energy absorption of supporting components, and energy absorption of weak structures. Based on these considerations, a corresponding relationship between the energy level of rock bursts and roadway support strength is established. The roadway support technology based on “four high anchor mesh +” is determined, which includes the use of high-strength anchor mesh combined with other support elements. The safety and reliability of roadway support technology under rock bursts are classified into P1-P4 levels according to the energy distance ratio of the impact source. Each level corresponds to the “four high anchor mesh +” combined support technology with different support strength. The research findings suggest that “four high” anchor mesh support is suitable for non-impact roadways with energy distance ratios in the magnitude of 10² rock bursts. “Four high anchor mesh +1” combined support, which includes O-shaped steel sheds, energy absorption and anti-impact unit frames, and weak surrounding rock structures, can prevent 10³ magnitude rock bursts. “Four high anchor mesh +2” combined support is effective against 10⁴ magnitude rock bursts, while “four high anchor mesh +3” combined support can prevent 10⁵ magnitude rock bursts. Rock bursts with magnitudes of 10⁶ and above require remote treatment and removal from production. Engineering examples are provided to demonstrate the anti-impact support scheme and parameter design of roadways. These examples help verify the feasibility and practicality of the theoretical research results. The research outcomes have valuable implications for the theoretical research and engineering practice of rock burst roadway support in coal mines in China.

The internal temperature of municipal solid waste (MSW) landfills is chronically higher than the ambient temperature due to heat production from organic matter degradation, which leads to engineering operation and maintenance problems. Existing experimental results show that the thermally induced volume changes of MSW were stress dependent and the elastic volumetric strain was significant, the latter may affect the determination of plastic volumetric strain which is usually used as the hardening parameter of constitutive model. On the basis of the previous tests, the effect of temperature on the volumetric deformation and compression characteristics of the clay in MSW under drained conditions were investigated by using the GDS temperature-controlled stress path triaxial apparatus, and the results were compared with the volumetric deformation characteristics of MSW under the same conditions to reveal the influencing mechanism of temperature change on the volumetric deformation characteristics of MSW. The methods of determining the thermal elastoplastic compression index λ_T  and thermal elastic compression index κ_T  of MSW were derived based on the results of MSW temperature-controlled triaxial tests. By adopting the principle of equivalent stress and assuming that the elastoplastic volumetric strain induced by temperature change was equal to the elastoplastic volumetric strain induced by an equivalent stress increment, a computational model for the volumetric deformation of MSW under thermo-mechanical coupling effect was established, and the model was validated and analyzed. The results showed that the void ratio was the main factor affecting the thermal volumetric strain of MSW. The λ_T  and κ_T  of MSW reduced with the increase of the initial consolidation stress, which were one order of magnitude larger than those of clay. The ratio of compression index λ  and swelling index κ(κ/λ ) at the corresponding consolidation stress level and normal temperature could be selected to simulate the volumetric deformation characteristics of MSW under thermo-mechanical coupling effects.

CO₂-H₂O can damage the rock microstructure and change the tensile failure characteristics and fracture propagation mode during CO₂ fracturing in shale reservoirs. X-ray diffraction (XRD) tests, scanning electron microscope (SEM) observation, and Brazilian tests are conducted to investigate the microscopic damage and failure characteristics, and fracture propagation mode of Longmaxi and Chang-7 shale specimens after CO₂-H₂O treatment. The results show that the microscopic damage of bedding after CO₂-H₂O treatment is more significant than that of the matrix. The volume of bedding clay minerals is reduced due to dehydration, the organic matter is extracted and contracted, and the large-size microfractures (10−30 μm in length and 1−5 μm in width) are generated in the laminae distributed along the bedding. Carbonate and feldspar minerals in the matrix are dissolved and induce randomly distributed small-size microcracks (< 1 μm in length and < 0.5 μm in width). After CO₂-H₂O treatment, the tensile strength of shale decreases, and the anisotropy increases. The failure mode of shale changes from tensile failure to mixed tension-shear failure, and the shear action of specimens loaded vertically to the bedding is stronger. Fracture propagation is restricted by the bedding for specimens loaded vertically to the bedding, leading to fracture propagation along the bedding; for specimens loaded horizontally to the bedding, the bedding exerts stronger constraints on fracture propagation, resulting in fracture propagation merely within the bedding.

Small scale model test was conducted to investigate the technology factors related to contra-rotational shear deep soil mixing (CS-DSM) method, the effects of these factors, such as cement content, blade rotation number T, mixing energy E, rotation speed ratio of internal to external rod R_N on the uniformity and unconfined compression strength (UCS) of the mixing pile were explored. The results show that the shearing motions of contra-rotational drilling tool can reduce excessive surface spoil and prevent entrained rotation phenomenon effectively, thereby greatly improve utilization of the binder material. The results of 18 model tests also reveal the inherent connection between T-E-UCS, and the internal relationship between machine operation parameters, mixing energy and strength of the piles. Construction parameters can be determined to ensure the target design strength by the provided calculation method. There is a peak value in the UCS-R_N curve, an optimal range of R_N = 1.8−2.2 is recommended for achieving peak strength of piles in engineering application. The presented technical basis has set the cornerstone for the construction process control and quality assurance as well as quality control of CS-DSM method.

Field measurements in offshore areas have revealed that wind turbines are mainly exposed to large-amplitude and long-duration horizontal environmental loads, and those located in high-intensity areas are particularly susceptible to seismic activity during service life. However, it remains unclear how the initial horizontal loads affect the seismic behaviour of offshore wind turbines, particularly with respect to pile-soil interaction. To address this issue, this study employed the ZJU-400 centrifuge shaking table to conduct a series of centrifuge tests on a single rock-socketed pile in liquefiable saturated sands, with its prototype located in the offshore wind farm in Fujian waters. The experimental results demonstrate the bending moment and displacement responses of the pile subjected to the seismic loads in combination with initial horizontal loads. The proposed p-y model introduces a parameter related to excess pore water pressure to quantify its weakening effects on pile-soil interaction as observed in the centrifuge tests. When combined with the nonlinear Winkler foundation beam model, the proposed post-earthquake prediction model can effectively estimate the bending moment and displacement distribution of monopiles under initial lateral loading.

Geogrid is an important way to improve the bearing capacity of rubber gravel mixture. The dynamic characteristics and mechanism of geogrid-reinforced rubber gravel composites were investigated through large-scale triaxial tests. These tests involved graded cyclic loading with different layers of geogrids and were conducted using three representative rubber contents of gravel mixtures. The study focused on analyzing the development and evolution laws of cumulative plastic strain and hysteresis curves. Key parameters of dynamic characteristics, such as dynamic elastic modulus and damping ratio were compared. The influence mechanism of the coupling effect between geogrid reinforcement and rubber gravel mixtures was also discussed. The results showed that geogrid reinforcement could slow down the increase of cumulative plastic strain under the same dynamic stress. This effect became more pronounced with an increasing number of geogrid layers. Additionally, increasing the rubber content in the mixture improved the ductility of the specimen, but it greatly reduced the bearing energy of the reinforced composite. The shape of the hysteresis curve was primarily influenced by the rubber content, becoming more full, inclined, and its arrangement becoming sparser as the rubber content increased. Geogrids improved the dynamic elastic modulus of the specimens, showing a significant growth stage with an increasing number of geogrid layers. The rubber content had a major impact on the initial value and change trend of the damping ratio. These findings provide valuable insights into the behavior and performance of geogrid-reinforced rubber gravel composites under dynamic loading conditions. They contribute to the understanding of how geogrids can enhance the bearing capacity and improve the overall stability of engineering structures constructed with rubber gravel mixtures.

With the continuous innovation of construction equipment and technology, non-displacement rock-socketed prestressed high-strength concrete (PHC) pipe pile has been gradually popularized and applied. To reveal the bearing mechanism of pile toe of rock-socketed PHC pipe pile, five groups of static load destructive tests of pile toe of PHC pipe pile with pile diameter of 500 mm in argillaceous siltstone area were carried out under the background of the drilling with prestressed concrete pipe pile. The bearing capacity and macroscopic failure mode of the pile toe of rock-socketed PHC pipe piles under different conditions were analyzed, and the calculation method of the pile toe bearing capacity was proposed. The test results show that when PHC pipe pile with open pile shoe is used and the pile end is not sealed, the open pile shoe weakens the bearing capacity of pile toe of PHC pipe pile. The pile shoe pierces into the bedrock, and the settlement of the pile toe is 11−15 mm under the ultimate load. After pouring concrete to seal the bottom, the bearing capacity of pile toe is significantly improved. The ultimate bearing capacity is 340% higher than that without bottom sealing, and the pile toe resistance share ratios of bottom sealing concrete and pile shoe are 78% and 22%, respectively. The pile toe is subjected to overall shear failure. Finally, based on the Hoek-Brown strength criterion, a simplified calculation method for the bearing capacity of pile toe of rock-socketed PHC pipe piles is put forward. The calculation accuracy of this method has been verified by the tests, and the calculation method can be used as a reference for the design and construction of non-displacement rock-socketed PHC pipe piles.

The permeability of treated contaminated soil is an important factor to consider when reusing polluted soil in engineering projects. In this study, lime and fly ash were chosen as solidification materials due to their ability to both adsorb and solidify contaminants. The permeability coefficients of petroleum-contaminated soil before and after solidification, as well as the residual petroleum content within the soil, was investigated under varying parameters such as confining pressure, osmotic pressure and contamination intensity. X-ray diffraction and scanning electron microscopy were used to analyze the evolution of permeability and the migration and diffusion patterns of pollutants, providing insights into the engineering reutilization potential of solidified petroleum-contaminated soil. The results showed that the adsorption effect of the solidified product on petroleum molecules weakened the hydrophobicity of the petroleum, increasing the effective permeation pathways in the soil. The permeability coefficient of solidified petroleum-contaminated soil was two orders of magnitude higher compared to non-solidified soil. Both solidified and non-solidified petroleum-contaminated soil exhibited decreased permeability due to the enhanced adsorption and interception capacity of the soil matrix for petroleum, as well as the elevated confining pressure, osmotic pressure, and contamination level, which intensified the interception among soil particles. The solidification process effectively controlled the migration and diffusion of petroleum contaminants under permeation conditions. The residual petroleum content in various locations closely approximated the initial content, reducing the risk of pollution through permeation. Considering the mechanical properties (compressive strength of 1 280.1 kPa, shear strength of 388.88 kPa), permeability (ranging from 4.28×10⁻⁶ cm/s to 7.39×10⁻⁶ cm/s), and migration control characteristics (fluctuation rate from 0.3% to 4.9%) of lime and fly ash, it can be concluded that lime and fly ash solidified petroleum-contaminated soil can be reused in the construction of subgrade materials that require impermeability.

The morphology of the plastic zone of roadway surrounding rock has an important influence on the failure mode and degree of roadway. In order to explore the evolution of plastic zone morphology under three-dimensional stress field, this paper derives the axial stress expression based on elastic mechanics, and determines the approximate solution method of 3D plastic zone under 3D strength criterion according to the idea of solving the boundary equation of butterfly plastic zone. By determining the surrounding rock stress loading scheme through equal spherical stress p and equal deviatoric stress q with different Lode angles θ_σ , the  morphological evolution of the plastic zone under different 3D strength criteria is studied in depth, and the low sensitivity of the criterion for butterfly failure is demonstrated. Based on the butterfly failure theory, the asymmetric deformation failure mechanism and control technology of 160206 return roadway in Yangchangwan are analyzed. The results show that: 1) Under the same p, q and different θ_σ   stress loading conditions, the morphology of the plastic zone under the five strength criteria shows the evolution patterns of round, oval and butterfly shapes, and the morphology of the plastic zone of surrounding rock is basically consistent for each strength criterion under the same θ_σ  . 2) Under the loading scheme with same stress state and different stress directions, the plastic zone morphology of surrounding rock varies greatly. The shape of the plastic zone is largely determined by the horizontal lateral pressure ratio. The axial lateral pressure has a greater influence on the size of the plastic zone, but less influence on the shape of the plastic zone. 3) Under the influence of superimposed mining, the roof of 160206 return roadway presents asymmetric large deformation and failure. Based on the support idea of butterfly plastic zone, the collaborative support technology of ' asymmetric anchor cable + advanced unit support + borehole pressure relief ' has been applied, and good supporting effect has been achieved.

The deformation of foundation soil caused by freeze-thaw cycles is a typical geological disaster in engineering construction in permafrost areas. Fiber optic sensing technology provides an important technical means for accurate and distributed real-time monitoring of frozen soil deformation. To explore the feasibility of distributed fiber optic strain sensing in monitoring frozen soil deformation, this study utilized a self-developed optical cable-frozen soil interface mechanical characteristics tester to investigate the failure mechanism of the cable-soil interface in frozen soil samples with different dry densities and initial water contents. The experimental results indicate that the fiber optic strain monitoring results accurately reflect the progressive failure characteristics of the cable-soil interface, and the strain softening model can better describe the mechanical properties of the interface. During the freezing process, the liquid water in the soil becomes ice, causing the movement of the freezing front and water migration, and resulting in significant differences in the mechanical properties of the interface. The evolution process of the shear stress at the cable-soil interface at different depths reflects the deformation coordination state with the frozen soil during the cable pullout process, indicating that the measurement range of the cable and the coupling of the interface are closely related to the dry density and initial water content of the soil. This study provides a reference for the application of optical fiber sensing technology in deformation monitoring of frozen soil foundation in cold regions.

In geosynthetic reinforced soil engineering, the interaction between reinforcement and soil can be effectively enhanced by the use of geosynthetics with additional structures and the setting of coarse-grained soil layers. However, the determination method of the thickness of coarse-grained soil layer is still unclear. In this paper, based on the results of direct shear tests on the high resistance hyperstatic geogrids (HRHG) designed with convex nodes and gravel, a constitutive model of dilatancy at the geogrid-gravel interface under shear hardening condition is established, and the distribution of the additional stress induced by dilatancy in reinforced soil is further investigated. By conducting direct shear tests under different normal pressures (30, 50, 80 kPa). The effects of different coarse-grained soil layer thicknesses (60, 100, 140, 180 mm) on the interaction between reinforcement and soil are evaluated, and the dilatancy distribution at the interface between reinforcement and soil is also compared and analyzed. The results show that the established constitutive model for geogrid-gravel interfacial dilatancy agreed well with direct shear test results, suggesting that it can effectively calculate the shear shrinkage and dilatancy, and the final dilatancy decreases with the increase of normal pressure. The additional stress in coarse-grained soil layer induced by interfacial dilatancy decreases with increasing distance from the geogrid-gravel interfaces, but the scope of dilatancy increases gradually. The increase of the thickness of coarse-grained soil layer can effectively improve the interfacial shear strength, but there exists an optimal layer thickness, which rapidly reduces the increase of interfacial shear strength. The optimal layer thickness decreases with the increment of normal pressare. Through the comparative analysis of the optimal layer thickness and dilatancy ratio, a semi-empirical formula for determining the optimal layer thickness based on the modified dilatancy constitutive model is put forward, which can provide a reference for the design and application of HRHG in practical engineering.

The strength of expansive soil undergoes significant changes with saturation, and understanding the shear strength of unsaturated expansive soil is crucial for studying engineering problems related to this type of soil. This paper focuses on the expansive soil found along a highway in Nanyang City. In-situ borehole shear tests are conducted on the expansive soil under different saturation levels in its natural state, providing insights into the shear strength characteristics of expansive soil under natural conditions. The results show that as the saturation of expansive soil increases, the shear strength, cohesion, and internal friction angle gradually decrease. To calculate the shear strength of unsaturated expansive soil, two models are proposed in this study. The first model considers normal stress and saturation as variables, while the second model incorporates normal stress and matrix suction as variables. These models are developed based on field test data and the soil-water characteristic curve. The accuracy and applicability of the models are verified using the test data. Compared to commonly used shear strength calculation models for unsaturated soils, the two new models require fewer fitting parameters. They are applicable to calculating the shear strength of unsaturated expansive soils with a wider range of suctions and different normal stresses. Additionally, the results obtained using these models are more accurate.

At present, there is no suitable scale method for seepage and seepage stability test of coarse soil. Based on the equivalent alternative method, a new scale method for seepage and seepage stability test was proposed by keeping the particles finer than d30 (the grain size corresponding to 30% finer in particle size distribution) and particles finer than 5 mm unchanged. If the particle content finer than 5 mm in the original particle size distribution is larger than or equal to 30%, the oversized particles are replaced by the particles ranging from the largest allowable particle of specimen and particles larger than 5 mm; if the particle content finer than 5 mm in the original particle size distribution is less than 30%, the oversized particles are replaced by the particles ranging from the largest allowable particle of specimen and particles larger than d₃₀. A list of seepage and seepage stability tests on coarse soils was carried out to verify the proposed scale method. The results indicate that the proposed scale method is suitable and effective. The seepage failure mode does not change after scaling, the permeability of the coarse soils after scaling is also close to that of the original soils, and the critical hydraulic gradient and failure gradient of seepage instability are basically consistent with the original soils. Consequently, the seepage and seepage stability characteristics of the coarse soils after scaling can represent the original coarse soils.

The authors propose a double-layer composite straight beam model that incorporates the Euler beam theory and the state space method to account for the nonlinear interaction between concrete core, cement soil, and surrounding soil interfaces. This model allows for convenient derivation of general solutions for internal forces and deformations for different combinations of piles in layered soil. By employing the state space method, the model effectively considers soil-structure interactions and variations in local structural parameters when analyzing composite piles. To validate the proposed solution, field test results and numerical analysis findings from existing literature are compared. The obtained analytical solution aligns well with these validation sources. Additionally, using the derived analytical solution, the authors investigate the effects of various pile parameters on pile loading responses. Specifically, they analyze the impacts of pile diameter ratio, core length ratio, and Young’s modulus of the cement soil. The results indicate that increasing the diameter ratio reduces pile settlement and increases pile bearing capacity due to enhanced total side friction resistance and tip resistances. Increasing the core length ratio also leads to higher pile bearing capacity with an increasing growth rate. However, the Young’s modulus of the cement soil has a negligible influence on pile bearing capacity.

The composite foundation with combined stone columns and impervious piles can not only improve the bearing capacity of the foundation, but also accelerate the consolidation of soil, which has a strong application value in treating saturated soft clay foundation. Based on the calculation model of axisymmetric consolidation with bidirectional seepage, a consolidation differential equation of composite foundation reinforced by stone columns and impervious piles is established by considering the volume compression of central and peripheral stone columns and the disturbance effect of piles construction. The analytical solution of the combined composite foundation consolidation under the variation of additional stress with time and depth is derived by using the analytical method, including the solutions of average excess pore water pressure of stone columns and soil and the average consolidation degree of composite foundation. The correctness of the solution is verified by degradation study and comparison with existing solutions. Finally, a smaller additional stress at the bottom of the composite foundation, or a denser distribution of stone columns and impervious piles, will lead to a faster consolidation of the combined composite foundation. The disturbance effect of stone columns construction on composite foundation is greater than that of impervious piles. Ignoring the effect of the volume compression of stone columns will overestimate the consolidation rate of composite foundation; the smaller the radius ratio is, the larger the error will be. A good agreement can be observed between the predicted consolidation degree by the theoretical solution and the measured one.

Affected by global warming, the subglacial debris on the Qinghai-Xizang Plateau in China is transforming from a frozen state into a thawing state, seriously affecting the glacier shear strength and glacier stability. In order to study the influence of thawing on the shear properties of subglacial debris, this paper introduced a new variable, the thawing rate, to quantitatively evaluate the amount of melted ice, and direct shear tests were carried out on thawing samples. Subsequently, a numerical model was established based on the finite-discrete element method to study the effects of thawing rate and gravel content on the shear behavior of subglacial debris. The results show that the thawing process significantly reduces the peak shear stress, cohesion, and inner friction angle. The relationship between shear strength parameters and thawing rate can be expressed using a linear relationship. The analysis of the factors affecting the shear strength parameters of thawing subglacial debris suggests that the reduction in the contribution of cementitious force can be responsible for strength degeneration. As the thawing rate increases from 2% to 4%, the deformation mode transitions from strain-softening to strain-hardening, and the failure mode shifts from rough serrated mode to smooth circular arc mode. Additionally, an increase in gravel content leads to a significant decrease in the shear strength of subglacial debris. However, the reduction range decreases as the thawing rate increases. This study provides valuable insights for evaluating the stability of glaciers by considering the effects of thawing on the shear properties of subglacial debris.

 The determination of mechanical parameters for columnar jointed rock mass is challenging due to its complex structure. Accurately estimating the strength and deformation of such rock masses is crucial for ensuring engineering safety. To address this issue, the authors developed a photosensitive resin mould using Voronoi diagrams and three-dimensional printing technology to create regular and irregular jointed rock mass specimens. Regular and irregular columnar jointed rock mass specimens with different dip angles were prepared and subjected to uniaxial compression tests. The resulting deformation and strength mechanical behaviors of the two types of rock masses were analyzed. The failure modes and mechanisms were summarized based on the final appearance of the specimens. Furthermore, the influence of joint surface materials on the failure mode and strength of columnar jointed rock mass was explained by combining the findings with existing research results. The authors proposed a modified joint coefficient method that better accounts for the structural characteristics of columnar jointed rock mass, building upon the traditional joint coefficient method. Using this modified method, empirical relationships were established between laboratory test results of regular and irregular columnar jointed rock mass and field deformation and strength parameters. The proposed calculation formula was then applied to the Baihetan Hydropower Station project, and the predicted results were compared with field measurements as well as predictions from the RMR (RMR is a rock quality evaluation index) and Q (Q is the quality index of rock mass) methods. The results demonstrated that the modified joint coefficient method provided the closest agreement with field measurements in terms of deformation and strength parameters.

The study focused on investigating the influence of dry density and load level on the wetting creep deformation of soil-rock mixture. A total of 9 groups of compression creep tests were conducted on the soil-rock mixture under a dry-wet cycle. The results revealed that the wetting creep deformation of the soil-rock mixture increased with higher load levels and decreased significantly with increasing dry density. However, as the dry density further increased, the decrease in wetting creep deformation became less pronounced. The relationship between wetting creep deformation and the logarithm of the number of dry-wet cycles followed a linear development pattern for the soil-rock mixture under the dry-wet cycle conditions. The initial wetting strain and wetting creep rate were found to have power function distribution relationships with the load level and dry density. Based on these findings, an empirical model for the dry-wet cycle creep behavior of the soil-rock mixture was proposed. This model takes into consideration different dry densities and load levels, providing a framework for predicting and understanding the creep deformation of the soil-rock mixture under such conditions.

Compacted bentonite is a crucial material used in high-level waste engineering barriers as a buffer/backfill material. However, the high plasticity of bentonite and uneven distribution of water can result in drying shrinkage of the compacted bentonite, which negatively impacts the quality of buffer/backfill blocks. To address this issue, a new method called the alcohol method has been proposed as an alternative to the traditional water spray method. In the alcohol method, the ethanol content ranges from 5% to 35%, unlike the water spray method. Several factors were considered to evaluate the feasibility of the alcohol method in adjusting the water content of compacted bentonite. These factors included mixing efficiency, mass loss rate, agglomerate content, strength, shrinkage cracks of compacted samples, drying efficiency, and expansibility. The results demonstrated that as the ethanol content increased, at the same liquid content the mixing efficiency significantly improved, while the mass loss rate and agglomerate content decreased noticeably. Relationships between agglomerates, dry-shrinkage cracks, and the quality of compacted samples were also observed. The compacted samples produced using the alcohol method exhibited more homogeneous soil density in the compacted direction and significantly reduced dry-shrinkage cracks compared to samples produced using the water spray method. Additionally, the shear strength and expansion characteristics of air-dried samples adjusted by the alcohol method were similar to those adjusted by the water spray method. The alcohol method, along with the findings from this study, provides valuable insights for the production of buffer/backfill materials in high-level waste disposal.

Trans-Bohai passage sea area lacks basic data on measured in-situ stress. Conducting in-situ measurements in this area is challenging and carries significant risks. To obtain firsthand data on the current in-situ stress field characteristics, a comprehensive in-situ stress measurement technology is employed. This technology primarily relies on hydraulic fracturing in-situ stress measurement, supplemented by methods such as hollow inclusion, inelastic strain recovery, differential strain, and acoustic anisotropy. Three-dimensional in-situ stress measurement and research are conducted in the sea area of the study region. A linear regression equation is established, and a regression fitting curve is obtained. The results reveal certain patterns: as the test depth increases in the Bohai strait, the maximum horizontal principal stress σ_H , minimum horizontal principal stress σ_h , and vertical principal stress σ_v  all increase linearly with the increase of test depth. In the southern part of the strait, the in-situ stress state follows the relationshipσ_H＞σ_h＞σ_v  , indicating a thrust stress state. The stress field direction is NE, with the maximum horizontal principal stress exceeding the vertical principal stress, suggesting dominance of tectonic forces in the region. In the northern part of the strait, the stress state is σ_H＞σ_v ＞σ_h , which is conducive to strike-slip fault activity. The stress field direction remains NE, and tectonic forces dominate in the region. Throughout the entire engineering region, there is minimal difference in each component value of the in-situ stress. These values are significantly lower than the lower limit of the active stress value of faults in the area, indicating that the study area is currently in a stable state. These findings align with the general principles of in-situ stress measurement. The testing process adheres to the requirements of in-situ stress testing, and the obtained data can be used to analyze the regional in-situ stress state.

To analyze the spatiotemporal desalinization of groundwater in a reclaimed coral reef island, the long-term monitoring and regular sampling data of groundwater conductivity were collected from various locations and depths. The data were then analyzed in conjunction with rainfall monitoring data to examine the temporal and spatial changes in groundwater conductivity and explore the trend of groundwater desalination. The random forest model was used to predict the variation of groundwater conductivity in borehole. The findings indicate that the general trend of groundwater conductivity in the coral reef island is characterized by oscillation decline, with the relationship between groundwater conductivity and time following an exponential function. As depth increases, groundwater conductivity also increases until it reaches a level equivalent to seawater, after which it stabilizes. Moreover, the analysis reveals that at the same depth within the reef island, there is a pattern of low conductivity in the middle and higher conductivity around the periphery. This suggests that desalination starts from the central part of the island and progresses towards the periphery, with multiple initial desalination centers present in the central area. The groundwater conductivity is affected by many factors such as rainfall infiltration, tidal action and hydrogeological parameters. Based on the predictions made by the random forest model, it is anticipated that the conductivity at 8 m below the water surface will gradually stabilize at 10 000 μS/cm after 5 years, accompanied by a significant decrease in the desalination rate of groundwater.

The geometric characteristics of soil (gap ratio, fines content, relative density, etc.) not only affect the internal stability of soil but also have an important influence on suffusion development. Based on the coupled method of discrete element method (DEM) and computational fluid dynamics (CFD), a three-dimensional computation model of suffusion for internally unstable soil is established, the coupled effects of fines contents and relative densities on the suffusion are investigated, and the mesoscopic variables including soil constriction size distribution (CSD), coordination number and internal force transfer mechanism are analyzed to reveal the microscopic mechanism of the coupled influence from fines content and relative density. The results show that the increase in relative density decreases the erosion mass ratio, which is also highly related to fines content; the higher the fines content, the more obvious the effect of relative density. The specimen after erosion can be divided into “upstream erosion zone”, “central stable zone” and “downstream erosion zone”. The increment of soil permeability during suffusion decreases with increasing relative density, while it increases with increasing fines contents. The influence of relative density on the suffusion process can be attributed to three aspects: differences in flow rates under the same hydraulic gradient, variations in the distribution of internal pore sizes, and variations in the contribution of fine particles to stress transmission within the soil. The results deepen the understanding of the influence of soil geometric characteristics on suffusion processes and provide a reference for the establishment of macroscopic erosion constitutive relationship.

The 2.5D finite element method is a frequency-domain method that offers advantages such as high computing efficiency and low memory consumption. Over the past two decades, continuous improvements have been made to this method, enabling it to accurately describe the dynamic response of railway subgrades by considering complex soil constitutive relationships and geometric characteristics. Through advancements in load input methods, modeling strategies, and wave absorption boundaries, the accuracy of the 2.5D finite element method has been steadily improved. The 2D interpolation method has also been employed to enhance computational efficiency for random dynamic responses of subgrades. As a result, the 2.5D finite element method has become a commonly used approach in the study of dynamic responses of railway subgrades. To provide a comprehensive understanding of the development of the 2.5D finite element method in researching the dynamic response of railway subgrades, this paper summarizes the current development status from various perspectives, including load input, subgrade system, response output, and improvements in calculation accuracy and efficiency. The paper also addresses bottleneck problems and proposes corresponding solutions. Based on these findings, further discussions and prospects are presented regarding the algorithm’s accuracy and efficiency, as well as the research objectives and content. This paper serves as a valuable reference for future research endeavors, offering insights into the advancements of the 2.5D finite element method in studying the dynamic response of railway subgrades.

For the problem of suffosion in gap-graded sand with initial anisotropy, the Ganser drag force model, which can take into account the effect of the projected area of particles, is introduced to achieve a two-phase coupling of computational fluid dynamics (CFD) and discrete elements method (DEM) for non-spherical particles. The applicability of the numerical method in solving the interaction between the non-spherical particles and fluid is verified by comparing with single particle settlement tests. On this basis, specimens with different bedding orientations and fine contents are further generated to simulate upward seepage suffosion tests, during which both macroscopic and microscopic properties, such as the fine loss, composition of strong and weak force chains, and changes in grain fabric, are monitored to explore the seepage suffosion characteristics of anisotropic soils with various fabrics under different filling states (underfilled and overfilled). Drained triaxial tests are carried out on specimens before and after erosion to investigate the effect of seepage on the weakening of soil strength. The results show that the mass loss of the overfilled specimens increases with increasing bedding angle, while the mass loss of the underfilled specimens firstly increases and then decreases with the bedding angle. The loss of fines in the underfilled specimens is mainly due to the low connectivity fines, whereas for the overfilled specimens, suffosion leads to a simultaneous reduction in the number of both low and high connectivity fines. In addition, the triaxial tests show that suffusion causes a significant weakening of the peak strength of the soil, and the change in peak strength with the bedding angle is also influenced by the soil filling state.

Seepage in rock fractures as an important factor affecting the rock slope instability attracts more and more researchers, who have adopted various numerical methods to simulate the mechanical behaviors of slope. In present study, a coupled seepage- deformation model based numerical manifold method (NMM) is proposed, in which the fluid flow of groundwater in fracture network, the coupling effect of seepage pressure and rock deformation are discussed. A global equilibrium equation of system and a local factor of safety of arbitrary rock fractures are derived based on the principle of minimum energy and block contact algorithm, respectively. A two-dimensional flow problem in a homogeneous aquifer and fracture seepage analysis of fluid through regular fracture networks are validated and the simulation results show the robustness and effectiveness of the proposed numerical model. Finally, a collapse accident of rock slope due to seepage effect is simulated by the proposed method and the failure process of the slope is also reproduced. The simulation results show that the excessive hydraulic pressure causes the opening of vertical fractures and augments rock mass deformation, eventually leading to the failure of the slope. It can be found that the proposed method possesses more potential to simulate larger-scale engineering problems.

Rock mass disasters are caused by instability driven by energy within the rock mass. The excavation and unloading disturbance can lead to fractures and instability in the rock mass structure, which is a major cause of dynamic disasters such as water inrush in stopes. To understand the influence of excavation unloading on rock mass structure fractures and to clarify the degradation law of surrounding rock and the mechanism of dynamic disasters like water inrush, this study focuses on the characteristics of rock damage and the evolution of energy under stress-seepage coupling factors. Using the Rock Top multi-field coupling tester, the study investigates the rock damage characteristics and energy evolution under three stress paths: conventional triaxial compression (group C), conventional unloading confining pressure with different initial damage degrees (group W), and cyclic loading and unloading confining pressure (group X) under the influence of stress-seepage coupling. Based on the evolution characteristics of rock elastic strain energy, the stress-strain curve of rock under conventional triaxial compression (group C) is divided into five stages, and the characteristics of U₁, U₃, U_e, U_d and permeability change in each stage are explained in detail (U_e is the elastic strain energy, U_d is the dissipated energy, U₁ is the strain energy of the rock transformed by the positive work done by the axial stress on the rock, and U₃ is the strain energy released by the negative work). During the conventional confining pressure unloading process, the evolution law of U₁ and U₃ is similar to that of group C rock, but the negative growth of U₃ is more significant. The rock input energy gradually shifts from U_e to U_d, and the initial damage degree has no significant influence on the law. During the confining pressure unloading process, the permeability shows a fluctuating upward trend, and the confining pressure is negatively correlated with the permeability. In the process of cyclic loading and unloading confining pressure, the energy evolution law is similar to that of group W rock, with energy accumulation differing only due to time effects. On the whole, regardless of the stress path, the pre-peak rock is dominated by U_e, representing energy storage, while post-peak rock is dominated by energy release and dissipation. Axial stress loading is the main influencing factor for rapid accumulation of U_e, while the change in confining pressure is not enough to cause a large change in U_e. Axial load is the primary factor influencing engineering disasters. Furthermore, there is a significant negative correlation between rock damage variable and confining pressure. The larger the confining pressure is, the smaller the U_e release ratio of rock is, and the smaller the rock damage is. Confining pressure restraint effectively enhances the energy storage capacity of rock and inhibits the dissipation and release of rock energy.

To achieve the scientifically designed gradation composition of a salt rock aggregate base in an inland dry salt lake, this study focused on the salt rock in Lop Nur as the research subject. The analysis examined the particle breakage evolution of a single particle group of salt rock aggregate under different particle sizes and brine contents. A gradation transition model for salt rock aggregate under complex gradation was constructed, and a gradation composition design method for salt rock aggregate base was proposed. The rationality of this design method was verified, and the engineering properties of the rock salt aggregate were compared under different gradations and water loss rates. The results demonstrated that all particle groups of the salt rock aggregate experienced breakage during compaction. The gradation of uniformly graded salt rock aggregate tended to stabilize with increasing compaction work. The presence of brine reduced the particle breakage rate of uniformly graded salt rock aggregate. The Weibull distribution effectively characterized the particle breakage distribution characteristics of the salt rock aggregate. The recommended gradation composition design method of salt rock aggregate base successfully deduced the gradation characteristics of salt rock aggregate base and realized the gradation correction considering the influence of brine. Salt crystallization of brine among salt rock particles was conducive to promoting the strength formation of salt rock aggregate base. The unconfined compressive strength of the salt rock aggregate with a water loss rate of 75% reached 4.1 MPa, indicating its suitability for road base engineering in dry salt lake areas.

Due to the complexity of the pore size distribution (PSD), the variation pattern of the pore structure for clay during the drying process is not clear, which leads to an inaccurate calculation of the soil-water characteristic curve (SWCC) based on the pore distribution model. To address this issue, a study was conducted to quantitatively analyze the PSD of remodeled clay with the single or double pore structure during the drying process based on the shrinkage test and mercury intrusion porosimetry test. The results revealed that there were translational and scaling transformations of the PSDs during the drying process. The t-distribution and double t-distribution functions were proposed to describe the PSDs of clay. The degrees of freedom, the peaks and the pore diameters corresponding to the PSD peaks were extracted as characteristic parameters to characterize the variation of PSDs. Good linear relationships between the characteristic parameters and the void ratio of remodeled clay were observed. Based on these findings, the relationship of water content-void ratio-pore size distribution was further established, and a framework for calculating the SWCC of remolded clay considering the variation of pore structure was proposed. Finally, the accuracy of the proposed calculation method was verified by comparing with the experimentally measured SWCC.