The earthen sites in the arid areas of northwest China are widely affected by the salinization of foundation soils. Due to the lack of research on earthen site foundations, this study investigates the salt migration patterns of the foundation and wall roots at the Great Wall site during short-term heavy rainfall and natural drying cycles. Conductivity, moisture content, and other parameters are utilized in laboratory experiments to analyze surface deterioration, with NaCl as the migration salt. It is observed that as the number of rainfall-drying cycles increases, the facades of earthen sites exhibit phenomena such as basal collapsing (erosion), salt efflorescence, epidermal cracking, and hollowing. The phenomena of capillary rise, salt migration, and surface deterioration in earthen sites are interconnected. After several cycles, the salt supply pattern in the foundation was adjusted, the salt migrate at the root of earthen sites is limited in scope. These findings elucidate the salt migration mechanism at the foundation roots and earthen sites during the alternation of rainfall and evaporation. This study offers insights for preventing and protecting against salinity erosion in earthen sites.

To investigate the presence of pressure melting during the compression of frozen gravel soil, we conducted unconfined compression tests and resistance tests on gravel soil samples with varying water (ice) contents and freezing temperatures. The unfrozen water content in saturated gravel soil samples was quantified using nuclear magnetic resonance (NMR) spectroscopy. The results indicate that: (1) During compression, the resistance of gravel soil initially decreased rapidly, subsequently slowing down, with only the dry sample ex-hibiting an increase in resistance post-peak stress. (2) In the rapid reduction stage, the resistance reduction rate of dry samples was lower compared to saturated frozen samples. Specifically, the resistance reduction rate of −4 ℃ saturated samples was 26.8%, which was fourfold that of dry samples at the same temperature. (3) As the freezing temperature decreased, the rate of resistance reduction initially increased and subsequently decreased during the rapid reduction stage. (4) Upon temperature reduction, the relative contents of both free water and capillary water underwent rapid declines, whereas the relative content of adsorbed water initially increased marginally before gradually decreasing. Analysis reveals that the compression of frozen gravel soil elicits a pressure melting effect, resulting in an increase in unfrozen water content within the high-stress regions of the sample during loading. This meltwater subsequently migrates through the unfrozen water film into the pore spaces of low-stress areas, where it re-freezes, altering the pore structure. Notably, the pressure melt-ing effect is most pronounced within the temperature range of －2 ℃ to －4 ℃.

To study the shock compression behavior and equation of state of shallow coral reef limestone subjected to high-intensity dynamic loadings, we conducted plate impact tests using a one-stage gas gun technique at impact velocities ranging from 200 m/s to 500 m/s. Based on the particle velocity histories of samples free surface which were obtained by all-fiber displacement interferometer system for any reflectors, the interaction between the shock wave propagation and the evolution of internal pores was analyzed. The dynamic strength and the shock adiabatic relationship of shallow coral reef limestone under one-dimensional strain shock wave loading were determined. The results indicate that the shock wave expands into a two-wave configuration, comprising an elastic precursor wave and a deformation wave, within the tested samples. This phenomenon arises from irreversible plastic deformation mechanisms, including pore collapse and matrix slippage, under shock wave compression. The propagation speed and energy of deformation waves increase with rising impact pressure. The Hugoniot elastic limit value and dynamic yield strength of shallow coral reef limestone are 0.109±0.03 GPa and 0.074±0.02 GPa respectively under the strain rate range from 2.9×10⁴ s⁻¹ to 7.5×10⁴ s⁻¹.    A Hugoniot linear relationship for shallow coral reef limestone was established within the pressure range of 0.4 GPa to 1.2 GPa, and the corresponding pressure-specific volume curve exhibits distinct elastic and compaction stages. It is also found that compared with the shock adiabatic data of terrigenous porous limestone, the shallow coral reef limestone shows greater compressibility under intensive dynamic loadings. Eventually, the P-a QUOTE

The modified fibers exhibit excellent heavy metal adsorption capacity and mechanical strength, offering broad application potential in the remediation of contaminated soil. Jute was used as a fiber material, which was modified by pyromellitic dianhydride, polyaniline and hydrogen peroxide respectively. The study examined the solidification efficiency of modified jute fiber in conjunction with cement, utilizing indicators such as unconfined compressive strength, cation exchange capacity (CEC), electrical conductivity (EC), and pH value. Additionally, the toxicological evolution of this material was analyzed using the acetic acid buffer solution method. The results indicate that the optimal combination of modified jute fiber and cement co-solidification effectively enhances strength and mitigates toxicity release. The unconfined compressive strength of the co-solidified contaminated soil exceeds that of cement-only solidification by 76.78%. Furthermore, the leaching toxicity and its fluctuation under 10 freeze-thaw cycles are reduced by 64.73% and to one-third of the original level. The hydrolysis of jute produces alkaline cellulose, which effectively elevates the pH of cement-solidified contaminated soil. The modification of carboxyl acid functional groups promotes hydration reactions via neutralization, thereby enhancing the formation of calcium silicate hydrate (CSH). The introduction of jute, especially modified fibers, significantly improves the EC and CEC. Under the co-solidified function of fiber and cement, the increase of EC can reach 2.25 times that of cement-only solidification, which is the key to enhance the stability of adsorption. However, due to the influence of fiber agglomeration, particle polymerization, and electrostatic repulsion between metal ions, the strength and leaching toxicity of solidified contaminated soil are not positively correlated with fiber dosage and length. Among the three modification methods, the jute fiber modified with pyromellitic anhydride exhibits a robust adsorption and solidification effect, which is minimally influenced by fiber length and dosage. Furthermore, it demonstrates superior performance in terms of strength and toxicity control indicators. Considering both engineering applications and ecological development requirements, pyromellitic dianhydride-modified jute fiber (with a dosage of 0.9% and a fiber length of 18 mm) is more suitable for enhancing the effectiveness of cement in treating heavy metal-contaminated soil.

When the CO₂ is sealed in the unmined coal seam, the injected CO₂ will be in a supercritical state due to the influence of high temperature and high pressure, which will reduce the stability of the coal seam. In order to study the energy dissipation and failure characteristics of coal body caused by disturbance after supercritical CO₂ immersion corrosion, based on the self-developed high-pressure gas adsorption/desorption experimental system, we conducted adsorption experiments on the coal with different supercritical CO₂ immersion corrosion time (0, 2, 4, and 6 days), and impact compression tests were carried out on the coal after the action of supercritical CO₂ by using split Hopkinson pressure bar experimental system, and combined with high-speed videotape camera to film the impact process, to analyze the energy dissipation rules of the impact coal, and to elucidate the destructive cracking evolution and crushing fractal characteristics of the coal. The results show that: the stress-strain curves of coal samples after different supercritical CO₂ immersion corrosion time have similar trends under the same impact load, which can be divided into three stages: elastic energy dissipation, plastic energy dissipation, and post-peak energy dissipation. With the increased of supercritical CO₂ immersion corrosion time, the energy absorption capacity of coal samples decreased, the number of cracks on the surface of impact coal samples increased, the crack network and propagation direction became more complex, the crushing of coal samples became more intense, the crushing particle size decreased, and the crushing morphology became more complex. Finally, the linear correlation between fractal dimension and energy consumption density of coal samples after different corrosion time was determined. The results of the study have certain theoretical significance for carrying out the exploration of CO₂ injection to strengthen the deep coalbed methane extraction project.

The air temperature, pressure, as well as the temperature, stress, and strain of the sealing layer, concrete liner, and surrounding rock in the compressed air energy storage artificial cavern undergo variations during the inflation and extraction cycles. Jointly solving these variables is a key technique in engineering design and a difficulty in theoretical analysis. This article proposes a coupling calculation method between the thermodynamic of air inside the artificial cavern and the thermal conduction of the cavern wall, based on the one-dimensional basic solution of heat conduction and the basic solution of air temperature in the artificial cavern. The validity of the methodology was confirmed through a rigorous comparison with numerical simulation outcomes. An illustrative case study of a steel-sealed cavern was conducted. The findings reveal that the process of inflating and extracting air within the cavern leads to a substantial variation in air temperature, with the amplitude of pressure fluctuations exceeding those predicted under the assumption of constant temperature. The depth of the tunnel wall is minimally affected by periodic temperature fluctuations. Once the thickness of the concrete lining surpasses the influence range of periodic temperature fluctuations, the temperature of the adjacent rock mass gradually increases until it reaches a stable state. The analysis of the strength and stability of the surrounding rock can be proceed without considering the influence of periodic temperature fluctuations. The sealing layer is significantly affected by the dual effects of temperature and air internal pressure, necessitating the consideration of thermal-mechanical fatigue in its design. The characteristics of hoop stress and radial strain exhibit notable disparities between the inner and outer surfaces of concrete lining. Depending on the working conditions, the hoop stress on the inner and outer surfaces may approach the compressive and tensile strengths of concrete, both of which are crucial design considerations. Concrete lining mitigates the pressure of surrounding rock, albeit with limited effectiveness. At an appropriate burial depth, selecting the appropriate inflation pressure ensures that the surrounding rock remains in an elastic state.

Under the framework of Biot porous media theory, the fractional order Kelvin model is used to describe the rheological effect of soil skeleton, considering the coupling effect of pore pressure dissipation and skeleton rheology. By establishing a spatiotemporal analytical function for periodic cyclic loads, a three-dimensional axisymmetric dynamic consolidation control equation for a half space saturated clay foundation is constructed in a cylindrical coordinate system. The analytical solution of the control equation in the transformed domain is derived using Hankel-Laplace joint transformation and tensor operations, followed by numerical inversion to acquire the spatiotemporal solution of the physical field. By analyzing numerical examples, the dynamic consolidation characteristics of a saturated clay foundation under cyclic loading are studied. The results indicate that the settlement rate of saturated clay is slower during primary consolidation but faster during secondary consolidation. With cyclic loading, the soil's cumulative settlement development accelerates as the rheological properties of the soil skeleton strengthen. The amplitude of soil displacement fluctuations decreases as the order of viscosity increases, and the more significant the order of viscosity, the more pronounced the displacement hysteresis becomes. The rheological properties of the soil skeleton lead to a lag in pore pressure response compared to effective stress, resulting in horizontal movement of the spiral curve between pore pressure and effective stress under cyclic loading. In the unloading stage of cyclic loads, due to the decrease of normal stress with the decrease of external load, but the increase of shear stress, the soil undergoes shear dilation phenomenon, resulting in negative pore pressure in the soil.

Calcareous sand is the primary fill material used in the construction of islands in the South China Sea. Throughout the process of island construction, the calcareous sand foundation will be subjected to external loads with varying consolidation stress paths, investigating the drainage strength characteristics of calcareous sand under various consolidation stress paths is an urgent requirement in practice. By conducting triaxial consolidation drainage shear tests on calcareous sand samples obtained from a reclamation island in the South China Sea, the evolution of strength parameters and the degree of particles breakage of calcareous sand with varying consolidation stress paths are investigated. The results show that the strain softening and dilation characteristics of calcareous sand diminish progressively as the mean effective stress and the effective principal stress ratio increase. In contrast to isotropic consolidation conditions, when the effective principal stress ratio diminishes to 0.45, the reduction coefficient of peak strength for the consolidated drainage of calcareous sand spans from 0.60 to 0.95. Within the conventional stress range, as the effective principal stress ratio increases, the peak internal friction angle shows a decreasing trend, ranging from 38° to 53°. During the consolidation, the degree of particles breakage increases with the increase of the deviator stress. However, following completion of shearing, the degree of particles breakage paradoxically diminishes, with particle breakage during the shearing phase assuming predominance. The quantitative relationship is verified between the peak internal friction angle and the relative breakage potential under different stress paths. Calculations predict peak internal friction angle values that are approximately 0.8 to 1.2 times the experimentally measured values. Differences in particle crushing caused by varying consolidation stress paths and consolidation pressures are the primary reasons for the differences in the consolidation drainage strength properties of calcareous sand after shearing.

In cohesive strata, earth pressure balance shield tunneling often encounters issues such as mud cake formation and cutting edge blockage. These problems not only hinder the efficient discharge of excavated material, leading to decreased excavation efficiency, but also increase the risk of frequent silo openings during the construction process. Furthermore, heat generated during excavation can affect soil adhesion. To explore the adhesion effects on the cutter head considering cutter head temperature, water content, clay content, clay type, and other factors, a self-developed rotary adhesion test system for the cutter head was employed. The system also examined the preventive and control effects of foam agents and anti-adhesion agents at different mixing ratios to mitigate blockage. The findings indicate that an increase in temperature reduces rotational torque and soil adhesion on the cutter head's surface, but it accelerates clay hardening. The trends of soil moisture content and clay content on torque are inverse, yet they similarly affect adhesion. As moisture content or clay content increases, adhesion initially increases and then decreases. The highest adhesion occurs at 20% moisture content and 30% clay content. Furthermore, bentonite exhibits greater adhesion compared to kaolin. The adhesion effects of soil moisture content, clay content, and clay type can be assessed using a consistency index. As consistency increases, adhesion initially increases and then decreases. The soil shows the highest adhesion when the consistency index ranges between 0.5 and 0.75, and low consistency index soil is more temperature-sensitive. While the addition of foam agents alone decreases soil adhesion, substantial adhesion persists at a 70% injection ratio. However, a 50% injection ratio shows better improvement with the combined use of foam agents and anti-adhesion agents. Additionally, increasing the injection ratio has minimal impact on soil improvement. These findings offer valuable guidance for evaluating blockage risks in earth pressure balance shield tunneling through cohesive strata and choosing suitable soil improvement strategies for cohesive soil remnants.

Due to the lithology difference between layers and pronounced vertical heterogeneity, the main fractures are difficult to extend vertically in thin interbedding tight sandstone reservoirs. Increasing the fracture extension rate can effectively promote the fracture extension crossing the layer. A three-point bending fracture experiment was carried out using prefabricated cement-sandstone specimens to study the effect of extension rate on fracture path. The digital image correlation method monitored the fracture process zone (FPZ) development characteristics when the fracture extends to the bedding. A prediction model of fracture extension path considering rate effect is proposed based on fracture dynamics theory. The results indicate that at low fracture extension rates, the fracture geometry exhibits a tortuous pattern, accompanied by a short and wide FPZ. Conversely, at high extension rates, the fracture geometry becomes smooth, with a long and narrow FPZ. FPZ is discrete and has the characteristics of mutual attraction. The fracture expands from low-strength rock to high-strength rock. At low propagation speeds, a high-strain zone (FPZ) forms in advance at the bedding plane, facilitating the extension of fractures along the bedding, causing the cracks to propagate along the layers upon reaching these interfaces. In contrast, this phenomenon is not observed during high-speed crack propagation. A positive correlation exists between the tensile strength of the rock and the average tensile strength of fractures traversing the unit. Fractures with low extension rates preferentially propagate along micro-defects, leading to a reduction in the tensile strength of the rock. Conversely, fractures with high extension rates preferentially propagate along self-similar directions, causing an increase in the tensile strength of the rock due to the tearing of numerous high-strength components. As the angle between the fracture and bedding increases, the fracture's ability to traverse the layer improves. The effect of the angle is maximized when it reaches 30° between the fracture and bedding, gradually diminishing beyond this threshold. These research findings hold significant implications for optimizing hydraulic fracturing parameters, enhancing fracture height, and boosting oil and gas production in thin interbedded tight sandstone reservoirs.

To address the limited comprehension of the dynamic response characteristics of soil-rock mixture (SRM) slopes, three sets of large-scale shaking table model tests of SRM slope with different rock contents were designed and conducted based on the similarity principle. The differences in dynamic response of SRM slope with different rock contents were systematically compared and analyzed. The research results indicate that the acceleration response of SRM slopes under earthquake action conforms to the free surface effect, that is, the acceleration amplification effect of the slope is significantly stronger near the top of the slope than within the slope. However, the dynamic response of SRM slopes with different rock contents under sine wave excitation of different frequencies is significantly different, this is due to the differences in the dynamic properties of slope structures with different rock contents. Under seismic action, the dynamic earth pressure of SRM slopes with different rock contents increases continuously from the shallow surface to the interior of the slope, but due to the different degrees of deformation and damage of the slope body, the overall dynamic soil pressure response of slopes with different rock contents is different. Moreover, during the entire seismic wave grading loading process, the sudden changes in dynamic soil pressure at different parts of the slope can serve as the basis for dynamic failure of the slope. As the rock content rises, the overall deformation of the slope under seismic action decreases gradually. For instance, a slope with 20% rock content exhibits continuous sliding from shallow to deep layers, while slopes with 40% and 60% rock content have relatively small deformation. A slope with 40% rock content only experience sliding of surface rock and soil, and a slope with 60% rock content only experience peeling of shallow surface soil. This indicates that higher rock content reinforces the stability of the SRM slopes.

The back pressure saturation method, a widely adopted and efficient technique for enhancing soil saturation, can nonetheless introduce notable deviations in soil strength parameters. Standard spherical glass bead sand was utilized for conducting benchmark consolidated undrained (CU), consolidated drained (CD), and dry sample tests. Real-time accurate measurements and comparative analyses of deviatoric stress and pore pressure (or volumetric deformation) data were performed. Utilizing the p'-q stress path diagram, the influence of back pressure application on soil mechanical properties was significantly demonstrated and quantitatively analyzed, thereby preliminarily elucidating the mechanism of back pressure influence. The setting of back pressure significantly impacts the results of CU tests, where the shape of pore pressure development governs the shape of deviatoric stress development, ultimately influencing the determination of strength parameters. However, the stress path remains constrained within the framework of the revised Cam-Clay model. The mode and rate of pore pressure development are primarily constrained by the magnitude of the back pressure setting and the relative density of the sample. As back pressure increases, the potential change in pore pressure also increases, resulting in a greater amplitude of deviatoric stress change. Similarly, a higher relative density leads to a faster development rate of pore pressure and an increased rate of deviatoric stress. Under identical initial conditions, the development of pore pressure in CU tests exhibits high consistency with the development of volume deformation in CD tests, revealing the common essence of the sample’s volumetric deformation potential across different boundary conditions. A quantitative prediction formula for the residual strength of CU tests at the critical state is presented. The residual pore pressure value can be initially quantified based on the relative density and back pressure measurements, subsequently leading to the determination of the residual strength of CU.

Although the filter paper method has been widely used in the study of soil-water characteristics of unsaturated soil, the test data of the filter paper method and the pressure plate test data are always not continuous and smooth. For this reason, a series of indoor pressure plate tests, filter paper tests and soil shrinkage tests were carried out based on the water change path and volume change of the samples, and quantitative analysis of statistical indicators was conducted based on the test results of the soil water characteristic curve (SWCC). The research results show that the SWCC test data measured by the filter paper method and the pressure plate method along the drying path from saturation can be effectively connected, while the SWCC test data measured by these methods along the path without water change may be staggered or crossed during the connection, especially for the soil with significant deformation. In this paper, an improved method is proposed so as to accurately estimate the SWCC based on degree of saturation, which the soil shrinkage test is only required to supplement. A reasonable explanation is given for the differences in the performance of different filter paper method test results. The research results can not only provide important theoretical guidance for the test personnel when they deal with the test data of filter paper method and pressure plate method simultaneously, but also expand the application scope of filter paper method.

The mechanical properties of high-temperature rocks, after being cooled by various methods, significantly influence the safety of deep earth geotechnical engineering. The study primarily investigated medium-weathered granite porphyry. Uniaxial compression and cyclic dynamic impact tests were performed on specimens cooled naturally and via water immersion at 400 ℃. The aim was to compare and analyze the change in the mechanical properties of granite. Utilizing the Logistic distribution law, loading damage variables and thermal cycling damage variables were incorporated to develop a statistical damage constitutive model for granite. The corresponding parameters were determined, and the applicability and reasonableness of the model were verified. The results reveal that during uniaxial compression testing, the internal microcracks in granite expand and coalesce into macroscopic cracks as the number of thermal cycles increases. Furthermore, the mass of the rock samples and longitudinal wave velocity decrease, while the elastic deformation phase in the static stress-strain curve shortens, indicating a distinct unstable damage stage. The rate of deterioration of rock strength can be significantly affected by the cooling method, but the final static compressive strength of granite is not significantly affected. Under an air pressure impact of 0.30 MPa, the dynamic compressive strength of naturally cooled granite initially increases and then decreases with increasing impact cycles. The initial impact enhances the compressive strength of naturally cooled granite. However, when thermal cycling exceeds three cycles, granite's resistance to cyclic impacts diminishes. The dynamic damage model, formulated using the Logistic distribution, exhibits good alignment with the experimental curve. The model parameters are readily obtainable, possessing a clear physical interpretation and practical applicability. This research offers valuable references for the construction, repair, and stability analysis of rock masses in variable temperature environments.

In order to investigate the energy characteristics of Jinping marble during progressive damage, triaxial cyclic loading and unloading tests on marble samples under five different confining pressures were carried out. The evolution of elastic modulus, the rule of energy evolution and distribution, the effect of confining pressure on energy evolution, and the characteristics of progressive damage evolution of marble under cyclic loading and unloading were analyzed. Furthermore, the energy failure criteria of rock strength based on energy consumption ratio and energy consumption difference were systematically discussed. The results show that both the loading and unloading elastic moduli of the marble are monotonically degraded during the whole deformation and failure process from the initial yielding to the residual stage. The deviation of elastic strain energy calculation with the assumption of constant modulus of elasticity should be avoided. The increase of confining pressure can not only effectively enhance marble's energy absorption and storage efficiency, but also strengthen marble's energy absorption and storage limit. It can also restrain marble's energy dissipation efficiency and the increase amplitude of dissipation energy. The ratio of elastic energy decreases and the ratio of dissipative energy increases from pre-peak to post-peak, and the ratio of residual energy tends to be stable. The residual elastic energy and the residual dissipated energy increase approximately linearly with the increase of confining pressure, while the maximum elastic energy and the maximum dissipated energy increase nonlinearly with the increase of confining pressure. The modified damage evolution equation considering initial damage and residual bearing capacity can well capture the variation characteristics of damage variable based on dissipative energy under different confining pressures. The criterion of energy consumption ratio based on the definition of energy relative proportion can be regarded as the criterion of failure of marble material. While the criterion of energy consumption difference based on the definition of absolute difference of energy can be regarded as the criterion of failure of marble structure.

The permeability of gas hydrate-bearing sediments (GHBS) is an important factor affecting the gas-liquid transport characteristics during the processes of hydrate formation and decomposition, and is often selected as an indicator for evaluating the extraction capacity of natural gas hydrates. The changes in hydrate occurring habits and hydrate saturation in GHBS pores significantly influence GHBS permeability. Existing permeability models are mostly based on a single hydrate occurring habit, making it difficult to consider the impact of changes in hydrate occurring habits on GHBS permeability. Based on the parallel capillary tube models, considering the influence of the varying of hydrate occurring habits on pore structure of GHBS, a mixed occurring habit with grain-coating and pore-filling coexisting is proposed. A logical function with two parameters is proposed to describe how hydrate occurring habits change with saturation, and a permeability model of GHBS considering the variation of hydrate occurring habits is established. The correctness of the model is verified by comparing it with measurement data obtained from laboratory and in-situ permeability tests, and the effectiveness of the model is analyzed by comparing it with existing mathematical models. The results indicate that changes in hydrate saturation during hydrate formation usually lead to changes in hydrate occurring habits, affecting the trend of the GHBS permeability with hydrate saturation. The changes in hydrate occurring habits vary under different formation conditions, and the main characteristics of the changing process are reflected in the critical hydrate saturation corresponding to the transformation of the main occurring habit, as well as the direction and trend of changes. Compared to the existing models, this model can capture the changing characteristics of permeability when the hydrate occurring habit changes, and can better predict measurement data from both laboratory and in-situ permeability tests of GHBS.

To investigate the effect of unloading rate on the unloading-induced slip behavior of cement grouting-reinforced jointed granite, a constant axial pressure graded unloading perimeter pressure induced slip test was carried out on the grouting reinforced jointed granite in the state of close to critical stress by using the TATW-2000 rock triaxial test system, The unloading rates are 0.1, 0.5, 1, 5, and 10 MPa/min respectively. The study showed that: (1) During the shear slip process, the rock-slurry bond interface undergoes abrasion, leaving numerous micro-scratches on the cement section surface of the granite. As the unloading rate increases, the JRC values are 17.52, 16.25, 15.65, 12.82, and 10.72, which indicates that the larger the unloading rate is, the smaller the micro-scratches on the surface of the cement section are. (2) The relationship between the average shear slip rate and the unloading rate during each perimeter pressure unloading period conforms to a power function relationship, and the average shear slip rate increases with the unloading rate, but the rate of increase gradually decreases. Under the influence of stress-strain hysteresis effect, the average shear slip rate in each perimeter pressure holding period also increases with the unloading rate. At unloading rates of 0.5, 1, 5, and 10 MPa/min, the average shear slip rates during the perimeter pressure holding period are much smaller than those during the perimeter pressure unloading period, and the relative difference between the average shear slip rates during the perimeter pressure unloading period and that during the perimeter pressure holding period is smaller at an unloading rate of 0.1 MPa/min. (3) The average shear slip rate of dynamic slip is one order of magnitude higher than the average shear slip rate of creep slip. The average shear slip rates for creep slip and dynamic slip increase with increasing unloading rate, while the duration decreases with increasing unloading rate. (4) When the unloading rate is less than 1 MPa/min, the peripheral pressure corresponding to the slip instability of the specimen is positively correlated with the unloading rate, and negatively correlated when the unloading rate is greater than 1 MPa/min.

To study the lateral cyclic loading response of large-diameter monopiles in soft clay, the centrifugal model tests of large-diameter monopiles in soft clay under different cyclic loading forms (one-way and two-way) were carried out. The deformation characteristics of large-diameter monopiles, stiffness weakening, bending moment, cyclic p-y curves and excess pore-water pressure were relatively analyzed. The test results show that the load-displacement curves show obvious nonlinear retardation energy consumption and displacement accumulation properties. Compared with the one-way cycle loading, the two-way cycle loading causes a significant cumulative displacement, which is influenced by both the number of cycles and the loading amplitude. The cumulative displacement consists of recoverable elastic deformation and unrecoverable plastic deformation, which is related to the number of cycles and loading stress level. The two-way cycle loading causes the weakening of pile-top stiffness, thereby enhancing the bending effect of the pile. The accumulation of excess pore-water pressure is related to the cycle number and loading amplitude, with a more pronounced effect observed under two-way loading conditions.

 In order to enhance the ground strength and accelerate the consolidation rate, the technique of combined composite ground has been widely utilized in ground improvement projects. However, there are few theoretical investigations on the nonlinear consolidation behavior of this combined technique. To fill this gap, the logarithm models of are incorporated to describe the nonlinear consolidation characteristics of soils, then an analytical model for the nonlinear consolidation of composite ground with combined use of granular columns and impervious columns is established by accounting for the variation of the column-soil compression modulus ratio with consolidation. Further, the consolidation deformation of granular columns is considered by introducing a new flow continuity relationship. Based on the equal strain assumption and Darcy’s law, the governing equations and analytical solutions are then obtained with consideration of the well resistance of granular columns, disturbance effects of both impervious columns and granular columns and the coupled radial-vertical seepage within soil. Moreover, the present solutions under different loading schemes are adopted to investigate the influence of several crucial parameters on the nonlinear consolidation behavior of composite ground. Furthermore, the accuracy of the current model is verified by comparing it with the existing solutions and applying it to analyze two tests. The results reveal that ignoring column consolidation deformation leads to an overestimate of consolidation rate, with maximum error reaching up to 10.5% as the replacement ratio increases. Neglecting the nonlinearity will underestimate the consolidation rate when the soil’s compressive indices C_c are smaller than the permeability indices C_kh(v). Additionally, the variation of C_c/C_kv has little influence on the consolidation rate and can be ignored when compared with C_c/C_kh. Factors such as a denser construction site layout, a higher column-soil compression modulus ratio, a larger permeability coefficient, or a smaller smear zone area of granular columns will accelerate the consolidation of composite ground.

To further study the occurrence process and mechanism of rockburst induced by excavation of deep caverns, the true triaxial electro-hydraulic servo mutagenesis test system was used to carry out experimental research on granite with strong rockburst tendency and simulated the three-dimensional stress state at a depth of 500 meters. The excavation process near the cavern was simulated by unloading the unilateral load of the surrounding rock, and ultimately inducing rockbursts due to stress redistribution of the surrounding rock. In the experiment, monitoring equipment observed real-time tunnel wall failures. The test results revealed: (1) the rockburst process under single-side unloading can be divided into six stages - stress redistribution post-unloading, preparation period, initial cuttings ejection and spalling, calm period, secondary cuttings ejection and spalling, and severe damage; (2) Rockbursts in the cave wall exhibited distinct temporal and spatial characteristics and asymmetry under unloading influence, with cracks initially appearing at the cave roof's base post-unloading, followed by severe rockbursts on the side opposite the unloading surface, forming a V-shaped trough along the axis during subsequent loading; (3) The defined hysteresis effect coefficient indicated that compared to rockbursts under three-direction loading, single-side unloading-induced rockbursts displayed greater abruptness and were more prone to cavern collapse. To mitigate such rockbursts, support and reinforcement measures should be implemented on the existing cavern side opposite the unloading surface when excavating adjacent caverns.

Targeting the phenomenon of strong mining pressure in empty tunnels at the “three lane layout” face in deep well, the lateral fracture mode of overlying and thick-hard roof was analyzed by the methods such as theoretical analysis, similarity simulation, and on-site measurement. This analysis reveals the mechanism of strong mining pressure in empty tunnels and clarifies the characteristics of mining stress response of the working face, taking the coal seam directly overlying the hard and thick roof as the engineering background. The results indicate the formation of a lateral long cantilever-hinge structure within the working face, with the fracture line situated within the goaf subsequent to the fracturing of the overlying thick-hard roof. The rock properties and geometric configurations of the overlying and thick-hard roof layers significantly influence the magnitude of mining-induced stress in the goaf. The greater the hardness and thickness of the roof, the higher the likelihood of stress concentration occurring around the coal body within the goaf. Not only the stress concentration in the surrounding rock of the roadway is high, but also the influence range of the advance support pressure on the goaf side is wider, the degree of stress concentration is higher, and the mining pressure in the roadway is more severe, under the condition of overlying and thick-hard roof. The abutment pressure on the coal pillar exhibits a characteristic of “synchronous force and synchronous growth”. Upon reaching the stabilization phase of the goaf, the abutment pressure manifests as an L+W stress profile, featuring asymmetric stress peaks on the adjacent upcoming mining coal pillars and double stress peaks in the center of the pillars. Under the influence of high lateral stress, the middle and lower portions of the surrounding rock in the subsequent roadway section undergo significant deformation, whereas the roof remains unaffected. Based on the lateral fracture characteristics of the overlying and thick-hard roof and the mechanism of strong dynamic mining pressure manifestation, a prevention and control technology system for roof disasters is proposed, which includes advanced treatment of roof disasters and “shallow strong support+deep multi-level unloading”. This provides beneficial guidance for rock strata control in mining stope.

In tunnel construction through weak and homogeneous geological layers rich in water, such as the tertiary semi-diagenetic strata, horizontal high-pressure jet grouting piles are often used for advanced reinforcement within the tunnel. However, these horizontal jet grouting piles tend to fracture under significant loads due to their low tensile strength. Drawing on the Wangjiazhai Tunnel project of the Lincang to Qingshuihe Expressway in Yunnan, a new composite structure is put forward that involves inserting small-diameter steel pipes into the pile body. Through mechanical theoretical analysis, numerical simulations, and on-site monitoring, we conducted a comparative analysis of the mechanical mechanisms and reinforcement effects of raw jet grouting piles and composite structures on the surrounding rock. Furthermore, we optimized the layout and diameter of the steel pipes. The research indicates that under a water pressure of 300 kPa, the deflection of the composite structures decreases by 34.8%, and the maximum tensile stress decreases by 37.5% compared to the untreated piles, significantly improving the stress mode and enhancing the ultimate bearing capacity of the water pressure load to 700 kPa, while also reducing the settlement of the arch crown and stress on the surrounding rocks. Increasing the density of steel pipes arranged at the arch crown effectively reduces the tensile stress in the pile body, whereas reducing the diameter of steel pipes would lead to increased tensile stress in the pipes. For practical engineering applications, it is advisable to place 108 mm steel pipes at intervals of one pile at the arch crown, place 89 mm steel pipes at intervals of two to three piles at the arch shoulders, and steel pipes are not necessary for the sidewalls.

To improve the prediction accuracy of surface settlement around subway foundation pit, a deep attention hybrid prediction model, termed self-Attention convolutional gated recurrent units (Self-CGRU), is proposed based on the self-attention mechanism and deep learning. The Self-CGRU model can capture the spatio-temporal characteristics of settlement data. The Self-CGRU model is constructed by integrating a spatial module and a temporal module. In the spatial module, the convolutional neural network is selected to capture the spatial correlations of settlement data obtained from the adjacent monitoring points. In the temporal module, the gated recurrent units neural network is used to analyze the temporal rules of settlement data. In addition, the self-attention mechanism is introduced into the Self-CGRU model to capture the autocorrelation in settlement data. Then, the predicted values of settlement can be obtained. Surface settlement data around the subway foundation pit in Shenzhen, China are selected to verify the performance of Self-CGRU model. The results indicate that the Self-CGRU model outperforms existing models, achieving a prediction accuracy improvement ranging from 17.48% to 29.17% compared to these models. The research results can provide an accurate and stable new model for the prediction of surface settlement around subway foundation pit.

Relief wells are an important means of seepage control, and the infiltration at the bottom of shallow relief wells cannot be ignored. When utilizing the finite element method for seepage field analysis in relation to wells, a significant disparity exists between the aquifer's dimensions and the well's radius. Achieving reasonable accuracy necessitates limiting the mesh size around the well to centimeters or less, albeit at the cost of reduced efficiency. To enhance efficiency, the well bottom is commonly approximated as a point source in analytical models. The head gradient near the point source is extremely large, which is a singular point. In the finite element method, equivalent treatment is usually required to ensure the global accuracy. This paper presents a method for simulating point sources with zero-volume point elements which is based on the correction well water level method, the method uses the point source analytical solution and the tetrahedral seepage element to deduce the explicit solution of the point source element. By using this point source element to simulate the bottom of well, the point source can be simulated by using a large grid without losing the global accuracy, which greatly improves the efficiency of simulating the point source by using the three-dimensional finite element. The paper thoroughly outlines the derivation process for the explicit solution of the point element, verifies its calculation accuracy, and investigates the applicability range of simplified calculation methods. Lastly, the practical application of this method in drainage decompression and anti-floating engineering is presented.

Soil liquefaction is a prevalent seismic hazard. However, current indoor and model experiments studying the dynamic characteristics of sand liquefaction struggle to accurately represent the actual soil liquefaction process. The computational fluid dynamics (CFD) coupled with discrete element method (DEM) simulation method can accurately simulate various soil-water coupling problems. The CFD-DEM flow-solid coupling module facilitated the exchange of mechanical information between the commercial discrete element software PFC3D and the open-source computational fluid dynamics software OpenFOAM. The feasibility of this approach was confirmed through particle underwater free settling experiments. Calibration of numerical sand specimens with dynamic characteristics of real saturated sand was conducted using PFC3D software through simulated indoor cyclic triaxial tests. Based on the existing parameter information and the coupled simulation method, a site liquefaction model of saturated sand was established. The simulation results indicate that the discrete element method (DEM) can replicate indoor sand liquefaction experiments, and the calibrated parameters can be applied to site liquefaction simulations. The consistency between the settling velocity of individual particles and theoretical solutions validates the accuracy of the CFD-DEM coupling method. Under a peak acceleration of 0.25g, liquefaction occurs at various depths, and the ratio of excess pore pressure does not exceed 1 during liquefaction. The cumulative excess pore pressure increases from shallow layers to deep layers. After liquefaction, the soil strength gradually recovers from bottom to top, and the soil structure in the re-consolidated site shows a trend of homogenization.

Based on the peridynamics method, the bond model was applied to treat the thermal diffusion of rock and the conventional state model was adopt to simulate the displacement evolution. According to the number of broken bonds between material points, the material damage was determined to track real-time fracture propagation. The interaction between water and rock was realized by applying pressure and temperature of water to fracture surface. And a numerical model was proposed to simulate hydraulic fracturing in high-temperature rock considering the thermal-mechanical coupling effect. The accuracy of the proposed model was verified according to the test results of rock heating fracture propagation. Finally, the morphology of hydraulic fracturing-induced rock fractures were discussed considering the effects of water pressure, rock initial temperature and elastic modulus, the sensitivity of each factor to fracture geometry parameters was analyzed based on the comprehensive sensitivity attribute identification method. The results indicate that under conditions of low water pressure or initial rock temperature, the primary fractures exhibit a near-symmetric distribution, and there is almost no fracture branching. With the increase of water pressure or initial temperature, the number of fracture gradually increases and the bifurcation occurs, the total length and opening degree of fracture also increase. When the mean elastic modulus of rock is small, the fractures are well developed and many tiny cracks appear. With the increase of the average elastic modulus, the number of fracture branches and micro-fractures decreases obviously, and the total length and opening degree of fractures also decrease accordingly, while the rock fracture initiation time increases approximately linearly. The comprehensive sensitivity evaluation of rock material parameters and environmental parameters shows that rock fracture propagation is highly sensitive to elastic modulus and water pressure, but insensitive to water temperature.

The depth integration algorithm simplifies the three-dimensional model of landslide sliding along the surface to a two-dimensional model, enhancing solving efficiency by diminishing the number of unknowns in the governing equation. Material point method (MPM) has the advantages of both grid based method and meshless method, and can avoid mesh distortion when simulating large landslide deformation. A numerical model for landslides has been developed using the depth-integral coupled material point method, with a detailed description of the algorithm's specific process provided. Utilizing the influence domain material point method (IDMPM), two benchmark tests were conducted on typical landslide scenarios: one with a non-inclined, smooth bottom, and the other with an inclined, non-smooth slope. The depth integral coupled material point method model demonstrates high accuracy in predicting key slip parameters, including remote distance, velocity, and depth. In contrast to the conventional material point method, the depth integral coupled material point method model significantly enhances operational efficiency. Furthermore, the research outcomes offer a robust theoretical foundation and timely support for analyzing and predicting the extent of damage in landslide geological disasters, conducting hazard assessments, and facilitating emergency response.