With the continuous expansion of urban underground space development, stratum disturbance induced by shield construction has an important impact on the safety of existing underground structures and surrounding environment. Through the independent research and development of the shield tunneling test device, the load of different stratum stress levels was realized, and the change law and influence range of the stratum disturbance in shield construction under different burial depth conditions were analyzed. The results show that the change rate of earth pressure in the strata around the tunnel decreases with the increase of the horizontal distance from the tunnel. The ratio of soil pressure after shield tunneling to initial soil pressure is about 60%−80%. The change of buried depth ratio has little influence on the soil stress path at the vault and bottom. The stratum disturbance degree based on the change of stress is defined, and the stratum disturbance degree gradually decreases with the increase of the burial depth ratio, indicating that the deep burial condition will reduce the disturbance effect of shield excavation on the stratum. After the completion of the shield tunneling, the height of the vertical influence range of the disturbance is between 0.5D and 0.8D above and below the tunnel (D is the diameter of tunnel), the width of the horizontal disturbance range is about 0.5D when the shield reaches the monitoring section, and approximately 1.2D to 1.5D when the shield passes far away.

A calibration test and method for the relationship between macroscopic parameter and mesoscopic parameter, integrating shear test and particle column collapse test, are proposed based on the multi-phase characteristics exhibited by coal rock particles during collapse body excavation. The analysis of various relationships between macroscopic parameter and mesoscopic parameter in the calibration test is demonstrated using the linear contact model of the Particle Flow Code (PFC). The calibration method is validated through similar simulation and numerical tests of rescue channel excavation in collapsed body. The results indicate that: (1) the shear test and granular column collapse test effectively reflect shear damage of the collapsed body structure under quasi-static flow and energy evolution in fast flow, respectively; (2) The friction coefficient and local damping are key factors in the shear test under quasi-static flow and granular column collapse test under fast flow, respectively, among physical and mechanical parameters; (3) Based on the impact of mesoscopic parameters on macroscopic calibration experiment parameters, we suggest combining phase and weight analyses to efficiently achieve mesoscopic parameter calibration for each phase state by identifying dominant mesoscopic parameters for each phase state; (4) Numerical simulation results of rescue channel excavation in collapsed bodies using shear test and granular column collapse test closely align with similar simulation test results, validating the feasibility of the calibration method that considers phase states in collapsed body research.

Bio-cementation technology based on crude soybean urease is a new environmentally friendly foundation treatment technology emerging in the field of geotechnical engineering. The uniformity of bio-cementation is a pressing issue that needs to be addressed to advance the application of this technology in practical engineering, and soil particle size stands as a significant influencing factor. In this study, 13 types of sand with varying particle sizes were selected, along with self-extracted crude soybean urease solution, to conduct urease percolation tests, sand column curing tests, and scanning electron microscope (SEM) examinations. These experiments aimed to analyze the influence of soil particle size on the effectiveness of bio-cementation using crude soybean urease and explore its underlying mechanisms. The findings reveal that soil particle size significantly affects the migration and adsorption of urease in the crude soybean urease solution. Smaller soil particle sizes facilitate the adsorption of urease. However, excessively small particle sizes (e.g., less than 0.425 mm) lead to the concentration of most adsorbed urease in the middle and upper regions of the soil column. Conversely, excessively large particle sizes (e.g., greater than 4.750 mm) hinder urease adsorption in these regions. Both scenarios tend to result in uneven bio-cementation. Besides the amount of urease adsorption, the influence of soil particle size effect on the biocementation efficacy based on soybean urease is also associated with factors such as pore size within the soil and the number of particle contacts per unit volume of soil. Larger soil particles result in larger interstitial pore sizes and fewer particle contacts, thus hindering the formation of effective calcium carbonate crystals.

The distribution pattern of earth pressure in confined soil masses adjacent to newly excavated foundation pits near underground structures is a critical aspect of controlling the construction of retaining structures. Focusing on the three common failure modes of confined soil masses, this study qualitatively analyzes the influence of existing underground structures on the distribution of active earth pressure in confined soil masses based on the thin-layer element theory. Through a combination of model testing and field measurements, the rationality of the proposed earth pressure distribution pattern in confined soil masses is verified. The results indicate that: (1) the active earth pressure distribution in a newly excavated foundation pit adjacent to an existing underground structure and beneath semi-infinite soil masses takes on a nonlinear drum shape, with smaller values at the ends and a larger value in the middle. (2) The magnitude of increase in active earth pressure varies in the confined soil mass adjacent to the side walls of the existing underground structure, with transition points occurring at the top and bottom of the structure. (3) When the slip surface intersects the existing underground structure at its base, the distribution of soil pressure takes on a nonlinear B shape, with a sharp decrease in soil pressure at the base of the existing underground structure. (4) The earth pressure in confined soil masses increases with an increase in the area of the confined soil mass (greater depth of burial or closer proximity to the adjacent structure). The findings of this study offer new insights and qualitative analysis methods for exploring the distribution of active earth pressure in foundation pits adjacent to underground structures.

To analyze the interlayer sliding evolution patterns and deformation failure characteristics of layered composite rocks, we conducted a three-point bending test on a layered composite rock specimen composed of fine sandstone, using digital speckle correlation as the observation method. The main conclusions are as follows: (1) interlayer contact conditions (or occurrence of sliding) significantly influence the fracture sequence and peak load deformation characteristics of composite rocks. When sliding occurs at the interlayer contact surface, the upper rock layer is the first to undergo failure, and the peak load is smaller compared to the same structure without sliding. In this experiment, for instance, the peak load during sliding conditions was 56% of that without sliding. (2) During the deformation and failure process of layered composite rocks, the interlayer sliding displacement exhibits an overall fluctuating distribution. In the second set of experiments, the maximum sliding displacement reached 0.320 mm, whereas in the fourth set, it was only 0.027 mm, indicating a nearly 10-fold difference. Abrupt changes in sliding and vertical displacements were observed in different regions at the sudden drops of the load curve. However, the patterns of these abrupt changes differed between the second and fourth sets of experiments, primarily due to variations in the initial crack formation locations within the composite rock layers. (3) In our study, when sliding occurred at the interlayer contact surface of the composite rocks, the fluctuation amplitude of the ratio between horizontal and vertical stresses remained within 0.15. In contrast, when no sliding occurred, the fluctuation amplitude of the stress ratio was mostly confined to 0.5. (4) During the rupture of the upper rock layer accompanied by interlayer sliding, both horizontal and vertical accelerations were detected. Notably, the amplitude of vertical acceleration variations was approximately 50% of that of horizontal accelerations. Consequently, the energy released during the rock failure process propagates in both horizontal and vertical directions, specifically as shear waves and longitudinal waves. These research insights offer valuable implications for studying high-level rockbursts during coal mining operations and for understanding the deformation characteristics of overlying rock layers.

Waste steel slag and tires are two major industrial solid wastes. Utilizing waste tire rubber particles as a lightweight material for the heavier steel slag, the rubber-steel slag mixed filler is used to replace the drying sand and gravel, which aligns well with the national policy of energy conservation and environmental protection. Because the physical and mechanical characteristics of steel slag have the characteristic of time, in order to study the dynamic characteristics of rubber-steel slag filler considering the time effect, the resonance column test is employed to investigate the influence of hydration period, rubber particle content and rubber particle size on the dynamic shear modulus, damping ratio, and other dynamic characteristics of the rubber-steel slag filler. Based on the Hardin-Drnevich hyperbolic model, a dynamic characteristic model of the rubber-steel slag filler after curing is established. The Botlzman function is used to describe the variation law of the maximum dynamic shear modulus and the reference range of the maximum damping ratio. It is concluded that the dynamic shear modulus of the rubber-steel slag filler with a rubber mixing ratio of 5% is the largest, and the density improvement is obvious. The mixing of rubber particles with a smaller size helps to improve the hydration potential, while the mixing of rubber particles with a larger size does not significantly improve the hydration potential. The optimal ratio of rubber-steel slag filler is 0−1 mm rubber particle size and 5% rubber particle content. Compared with the dynamic properties of traditional sand, it is concluded that the dynamic shear modulus of the rubber-steel slag filler before hydration is slightly higher than that of traditional fine sand. After 90 days of hydration, the dynamic shear modulus is close to the level of Harbin medium sand and slightly lower than Fujian standard sand. Under corresponding engineering conditions, the rubber-steel slag filler can be used as a substitute for sand. Through microscopic electron microscope testing of the rubber-steel slag filler particles, it is found that the hydration reaction of the rubber-steel slag filler can be divided into five stages: latent, induced, erosion, accelerated, and slowed down. The mixing of rubber particles makes the hydration reaction lag, and its medium-term structural form changes but does not affect the hydration product changes.

To capture the influence of loading rate on the deformation process of structured soft clay, applying the approach used in the unified hardening model (UH model) to describe time effects, an equivalent time term is introduced into the yield function ( ^-t) of the structured UH model, and then a structured UH model for soft clay considering loading rate is extended. In the equivalent time term, the internal variable R of the original structured UH model is transformed into R_t to account for time-driven strain. The presented structured UH model considering time effects comprises a total of 8 parameters, all of which can be determined through routine soil tests. Comparisons between model predictions and experimental data demonstrate that the presented model is qualified to reflect the influence of loading rate on structured soft clays reasonably.

Most research on composite foundations reinforced with multiple reinforcements focuses on the combination of drainage piles with undrained piles. There is limited theoretical research on the consolidation of composite foundations enhanced by multiple drains with varying drainage capacities. In this study, we investigate a composite foundation improved by stone columns in conjunction with prefabricated vertical drains (PVDs). Assuming equal strain, we establish an analytical model for consolidation with two-way radial drainage, taking into account radial-vertical seepage within the stone column. Analytical solutions for pore pressure and consolidation degree under transient loading are derived and validated through degradation analysis and measurement comparisons. The research findings on consolidation behavior indicate that utilizing multiple types of drains can significantly expedite foundation consolidation compared to a single-drain composite foundation. Neglecting radial seepage in the stone column for larger diameter piles may lead to an overestimation of the consolidation rate. Due to the two-way seepage of water in the soil, pore pressure in the soil of multiple reinforcements composite foundations initially increases and then decreases along the radial direction. The peak radial coordinate gradually shifts towards the plastic drainage plate with depth, with the trend weakening as consolidation progresses.

The utilization of humus soil is a crucial factor influencing the feasibility and cost-effectiveness of landfill excavation. Solidification/stabilization technology holds promising engineering applications for humus soil treatment. In this study, four types of curing agents including ordinary Portland cement (OPC), sulphoaluminate cement (SAC), cement-slag mixture (OG), and magnesium oxide-slag binder (MG), were chosen for a systematic investigation of the evolution of engineering properties, permeability, leaching characteristics, and durability of solidified humus soils. The results indicate a significant enhancement in compressive strength of solidified humus soils, with SAC treatment exhibiting the highest compressive strength at 10% and 15% dosages, while OPC and OG solidified humus soils show higher strength at 20%. Additionally, the strength development of MG solidified soils is lower compared to other solidified soils. Increasing the dosage of curing agents can effectively counteract the inhibitory effect of organic matter in soil, with 15% being an appropriate dosage for both engineering and economic considerations. At a 15% dosage, solidified humus soil can meet the regulatory limit for Class IV water quality, except for OPC treatment, which is ineffective for As immobilization. Regarding durability, OG solidified humus soil exhibits the highest resistance to dry-wet and freeze-thaw cycles, while SAC solidified soil shows the weakest resistance to dry-wet cycles but superior frost resistance performance to OPC. Consequently, solidified humus soils can serve as filling materials in landfills and subbase materials in road engineering, offering theoretical and parameter support for the resource utilization of humus soils in landfills.

The reservoir water level of a high earth core rockfill dam can fluctuate by over 60 m during operation. Rockfill materials in the zone affected by water level fluctuations may undergo significant deformation due to cyclic wetting-drying cycles, resulting in longitudinal cracks on the dam’s surface and impacting its safe operation. Extensive research has been conducted on the effect of cyclic wetting-drying on the long-term deformation and deterioration of rockfill materials. Nevertheless, there is a scarcity of studies on the cyclic wetting-drying behavior of rockfill grains of varying sizes. We conducted comprehensive single grain crushing tests on slate rock grains of various sizes subjected to different wetting-drying cycles. The findings indicate that the load-displacement curves and fragmentation patterns of slate rock grains can be categorized into four types. The peak loads for grain crushing and the average crushing strengths decrease with the increase of the number of cycles. The crushing strengths of slate rock grains of varying sizes exposed to different wetting-drying cycles conform to the Weibull distribution. A power exponential relationship exists between the characteristic crushing strengths and the number of cycles, suggesting a gradual slowdown in the deterioration of the mechanical properties of slate grains. The characteristic crushing strengths exhibit a clear size effect across different wetting-drying cycles, with this effect showing a negative correlation with the number of cycles.

The effective stress method is seldom utilized due to the complexity of calculating effective stress along the sliding surface. The stability factor calculated by the effective consolidation-stress method is underestimated. A novel stability analysis method for consolidation embankments needs to be developed. The sliding body of a consolidation embankment was categorized into active shear zone, direct shear zone, and passive shear zone based on the sliding surfaces in the deformation fields of a model experiment on soft ground. The effective normal stress on the sliding surface in the active or passive zone was calculated using the Skempton equation and the Mohr-Coulomb strength criterion. The effective normal stress on the sliding surface in the direct shear zone was determined after considering the excess pore water pressure using the Skempton equation and following the principle that the increment of shear stress equals the shear strength on the failure surface. Equations for the shear strength on the failure surface, with the vertical consolidation stress as the variable and the strength coefficients composed of shear strength indexes and the coefficient of excess pore water pressure, were developed. Finally, the strength coefficient method was proposed as a new stability analysis approach for consolidation embankments based on the shear strength equations mentioned above. The study reveals that the average error in the coefficient of frictional shear strength across three zones, as determined in this paper compared to the method suggested by Shen Zhu-jiang, ranges from −7% to 7%. Furthermore, the coefficient obtained from the current code is 20% to 25% lower than that derived in this paper, and the coefficient from the vane test is 20% to 31% lower. The stability analysis of a consolidation embankment on an operational express highway demonstrates that the stability factor from the current code’s method is below 1. Both the strength coefficient method and the approach proposed by Shen Zhu-jiang align well with the engineering principles.

Lead (Pb) accumulation can pose serious threats to the environment and cause liver and kidney damage. In recent years, microbial-induced carbonate precipitation (MICP) technology has been widely used for remediating contaminated sites due to its operational efficiency. However, extreme pH conditions can degrade carbonate precipitation, increasing the risk of Pb²⁺ migration and secondary pollution. This study explores the use of spore-containing microcapsules for Pb immobilization for the first time. The results indicate that during the germination phase, the microcapsules not only shielded the spores from harsh pH conditions but also supplied inosine for their growth and reproduction. The microcapsules promoted spore growth and reproduction through nutrient supplementation, offering additional attachment sites for nucleation with Pb²⁺ and Ca²⁺. An immobilization efficiency exceeding 90% was achieved. Cerussite and calcite minerals were observed in scanning electron microscopy (SEM), SEM with energy dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffraction (XRD) analyses, while extracellular polymeric substances (EPS) were detected in both samples in Fourier transform infrared spectrum (FTIR) tests. These findings confirm the role of microcapsules in immobilizing Pb²⁺.

Sulfate saline soils are widely distributed in Xinjiang, where salt expansion often leads to road cracking and damage. This study investigated the effectiveness of a method that combines fly ash, slag, and polyacrylamide (PAM) in treating saline soils. Various tests, including salt expansion, boundary moisture content, pH, total dissolved solids (TDS), electrical conductivity (EC), sulfate ion concentration, unconfined compressive strength, and freeze-thaw cycle tests, were conducted to evaluate the mechanical and physicochemical properties of the solidified soil. Moreover, scanning electron microscopy (SEM) was utilized to explore the enhancement mechanism and microscopic features. The results indicate that the inorganic-organic combination of fly ash, slag, and polyacrylamide effectively suppresses salt expansion in sulfate saline soil, enhancing its mechanical properties, plasticity, and frost resistance. Considering economic feasibility and practicality, the optimal ratio was determined: a mixture of fly ash, slag, and PAM at 15%, with PAM at 2%. Under these conditions, the treatment exhibits the most efficient inhibition of salt expansion and improves structural integrity. The 7-day unconfined compressive strength of the treated soil reaches 993 kPa, three times higher than that of natural soil. Additionally, the soil demonstrates a significant enhancement in freeze-thaw resistance.

Under dynamic loading, the deformation and dynamic modulus of weak soil, such as soft clay, can change. This study aims to investigate the effect of long-term dynamic loads on soft clay by collecting dynamic parameters through dynamic triaxial testing. The analysis focuses on exploring the relationship between the softening index, cumulative plastic strain and cyclic stress ratio (CSR). The data exhibits a certain concentration, prompting the utilization of machine learning methods. Using a logistic regression classifier to determine soil stability, it is found that soil is less likely to collapse with lower CSR, higher loading frequency and increased softening index. The effect of frequency is observed to be less significant than that of CSR. To establish a connection between dynamic parameters and the static behavior of soil samples, a random forest model is used to predict the softening index, which is challenging to obtain directly. The prediction results demonstrate a good fit of the model and pass the significance test. The model achieves a precision of 0.93 for the training set and 0.79 for the test set. It is revealed that cumulative plastic strain plays a crucial role in predicting the softening index, outweighing other factors such as undisturbed or remolded soil, overconsolidation ratio (OCR), loading waveform, frequency, CSR and soil state type (stability/failure) based on deformation curves. This suggests promising prospects for applying the trained model and machine learning techniques.

It is extremely urgent to implement comprehensive resource utilization within the framework of the dual carbon strategy. To improve the mechanical strength properties of silty clay, three types of industrial waste slag, such as slag, bottom ash and gypsum, are utilized as primary raw materials. A waste slag-based geopolymer is then prepared through synergistic activation in an alkaline quicklime environment to stabilize the silty clay and enhance its engineering characteristics. The deformation characteristics of samples under varying waste residue geopolymer content were analyzed through unconfined compressive strength tests and X-ray diffraction (XRD) microscopic tests. The study compared and examined the influence of curing method, fiber addition, and curing age on sample performance, as well as explored the types of hydration products present. A test section of waste residue geopolymer-stabilized silty clay base was constructed for the actual project. The key findings suggest that the optimal dosage of waste slag geopolymer-stabilized silt clay is 15%, with a slag: bottom ash: quicklime: gypsum mix ratio of 8:2:3:2, polypropylene fiber content of 0.2%, and a curing method of 6 d standard curing followed by 1 d of soaking. The mechanical properties of the samples show significant improvement, particularly in the toughness region of the stress-strain curve due to fiber reinforcement. The samples exhibit excellent water stability, and extending the immersion curing age appropriately enhances the sample’s strength, with a water stability coefficient reaching up to 200% The fibers, waste residue geopolymer hydration gel and soil particles interlock closely to create a dense three-dimensional network structure, thereby enhancing the mechanical strength of the fiber-hydration gel component-soil particle interface. The curing time significantly impacts the sample, with a strength growth rate ranging from 80% to 188% at 28 d.

Artificial ground freezing technology is commonly used in tunnel construction in coastal soil regions. The static and dynamic strength characteristics, as well as the elastic modulus of freeze-thaw chloride silty clay, are crucial for predicting thaw settlement and designing the stability of artificial ground freezing technology. Hence, consolidated-undrained triaxial compression tests and cyclic triaxial tests were conducted with varying salt content, freeze-thaw cycles, and temperatures to investigate the static and dynamic strength as well as the elastic modulus in more detail. The results indicated that all static triaxial stress-strain curves and dynamic triaxial backbone curves exhibited strain-hardening behavior. The initial linear stage of the curve was more pronounced in specimens without freeze-thaw. The static strength initially decreased and then increased with rising salt content. A critical salt content of 1% corresponded to the minimum static strength. When the salt content was ≤3%, the dynamic strength showed no significant change. However, it increased significantly to 1.8 times that of other salt content specimens when the salt content reached 4% after undergoing freezing-thawing at −10 ℃. The increase in salt content led to a 1.1−2.0 times increase in the elastic modulus. The elastic modulus can be normalized as E/E_max and described using a hyperbolic model. For specimens with 2% salt content after freeze-thaw cycles, the damage rates of static and dynamic strength were 52%−66% and 69%−78%, respectively. The damage rates of static and dynamic peak elastic modulus were 90% and 81%, respectively. The impact of freezing temperature on static and dynamic strength and elastic modulus was minimal. This research can establish a theoretical foundation for the utilization of artificial ground freezing technology in marine saline formations, as well as for the prediction and control of post-construction thaw settlement to ensure the safe operation of tunnels.

To investigate the direct shear failure mechanism of rock joints, we conducted shear tests on sandstone joints under various normal stresses using the RDS-200 rock joint shear test system. Additionally, we monitored acoustic emissions with the Micro-II Express digital acoustic emission system. By analyzing the evolution characteristics of the ratio of acoustic emission rise time to amplitude (RA) and the ratio of ringing count to duration (AF), we examined the shear failure process of rock joints and discussed an early warning method for shear failure in sandstone joints. The results show that: (1) The evolution characteristics of the cumulative ringing count during the rock joint shear process reveal four distinct stages: low-speed growth, accelerated growth, extreme speed growth, and decelerated growth. For each normal stress level, both AF and RA reach their maximum values as the stage number increases, and the number of signals with higher RA values also increases with the stage number. (2) A specific method, based on JCMS-III B5706, is proposed to determine the threshold k for the tensile-shear fracture type. It is observed that both the threshold k and the tensile fracture ratio α  decrease as the shear stage number increases under each normal stress condition. (3) In the rock joint shear tests, the coefficient of variation CV(r) of the r value exhibits a decreasing trend before reaching peak shear stress, with a stage identified below the nearest CV(r)value (referred to as the early warning value CV(r)_cr) before peak shear stress. The CV(r)_cr initially decreases and then increases with increasing normal stress, showing a quadratic parabolic function relationship. The ratio of early warning time t_d to instability time t_p ranges from 5.1% to 24.5%, serving as an effective early warning mechanism. These research findings offer valuable insights for instability warning and disaster prevention in jointed rock masses.

Rigid drainage piles combine the dual advantages of high bearing capacity and drainage performance. To investigate the anti-liquefaction effectiveness of rigid drainage piles in treating liquefiable subgrade, #7 silica sand was employed as the material for modeling the liquefiable subgrade. A shaking table model test was conducted to compare the performance of a drainage pile-net composite foundation with an ordinary pile-net composite foundation, utilizing a 3×5 pile group configuration and applying bidirectional dynamic loads both horizontally and vertically. The anti-liquefaction effect of the drainage pile-net composite foundation was analyzed based on dynamic responses, including excess pore water pressure, acceleration, and settlement. Experimental results indicate that the drainage pile-net composite foundation significantly outperforms the ordinary pile-net composite foundation. Specifically, the peak excess pore pressure ratio in the drainage pile condition ranges from 0.61 to 0.79, whereas it reaches 1.0 in the ordinary pile condition, indicating complete liquefaction. In the drainage pile condition, the horizontal peak acceleration amplification coefficient increases significantly from the bottom to the top of the embankment model, with a maximum amplification coefficient of 1.60. Conversely, in the ordinary pile condition, the peak acceleration amplification coefficient demonstrates a certain seismic damping effect in liquefied ground, reaching a maximum value of 1.07. The average settlement in the drainage pile condition is 11.4 mm, whereas it is 25.7 mm in the ordinary pile condition, representing a 55.6% reduction in the final settlement. These findings suggest that drainage piles effectively accelerate the dissipation of excess pore water pressure and reduce embankment settlement, making them an effective measure for treating liquefiable foundations.

Scouring of roadbeds along river highways poses a significant threat to the safety of mountain roads. Relying on the Karakorum Highway (KKH) water damage disaster remediation project, using the erosion function apparatus and theoretical analysis, we studied the scour rate, starting shear stress, and the variation of theoretical model parameters in clay-coarse sand mixed soil samples with different clay contents. We also explored the scour characteristics and damage modes of mixed soils based on the soil skeleton theory. The following conclusions were drawn. As the clay content increases, the starting shear stress of the soil sample rises, scour resistance is strengthened, and the scour characteristics transition from non-cohesive to cohesive soil scour characteristics. The distribution of cohesive fine particles varies from filling the voids between coarse particles to bonding with them, and ultimately separating the coarse particles. The damage mode of the mixed soil samples under scouring water flow varies depending on the filling pattern of coarse particles and clays. The Wilson model exhibits a good fit with the experimental data and can be applied to predict large shear stresses, compensating for the limitations of the over-shear stress model.

Argillaceous siltstone, a common hydrophilic rock in geotechnical engineering, experiences notable variations in its mechanical properties due to the influence of water and cyclic loading. Therefore, a systematic investigation into the mechanical behavior of argillaceous siltstone under cyclic loading in different wet-dry conditions is essential for guiding engineering design and improving disaster prediction accuracy. This study conducted triaxial cyclic loading tests on dry and saturated argillaceous siltstone samples collected from Shiyan, Hubei Province, varying the frequencies and confining pressures. The research involved a comparative analysis of the strength and deformation characteristics of dry and saturated specimens, examining the influence of frequency and confining pressure on their mechanical behavior. the mechanical mechanisms of argillaceous siltstone under cyclic loading were further elucidated from the perspective of energy. The findings indicate that, (1) saturated samples exhibit a substantial decrease in strength and modulus compared to dry samples, accompanied by a more pronounced movement of the hysteresis loop towards higher strain; (2) deformation of dry samples increases slightly with frequency, while the degradation of saturated samples is markedly accelerated at higher frequencies; (3) lower confining pressures can restrict crack development in saturated samples, but the excessive confining pressure accelerates their deterioration; (4) energy consumption rate and dissipated energy of dry samples under high frequency are lower than those under low frequency, while saturated samples display an increase in dissipated energy at higher frequencies, remaining relatively constant at low confining pressures and significantly increasing at high confining pressures; and (5) the failure mode of dry samples shifts towards conjugate shear damage as the confining pressure increases, whereas the angle of the failure surface in saturated samples also increases.

In order to investigate the deformation characteristics of the clay-concrete interface under pre-peak tangential cyclic shear stress conditions, a specially developed soil-structure interface cyclic shear apparatus was utilized. Initially, direct shear tests were conducted on the clay-concrete interface under four normal pressures: 50, 100, 150 kPa, and 200 kPa. These tests determined the peak shear stress of the interface under each normal pressure. Subsequently, two shear stress amplitudes below and three shear stress amplitudes above the peak shear stress were set under each normal pressure, and cyclic shear tests of the clay-concrete interface were performed. Based on the experimental outcomes, three key indicators were established: cumulative displacement, secant stiffness and tangential plastic work. The evolution of these indicators with increasing cycles was analyzed, and a comparison was made to assess the impact of normal pressure on the cyclic shear curve at a constant shear stress amplitude. The experimental findings reveal that under low shear stress amplitudes, the shear displacement-shear stress curve of the clay-concrete interface demonstrates elastic behavior. Conversely, under high shear stress amplitudes, the curve exhibits elastoplastic characteristics. Specifically, there exists a limit value for the cumulative displacement of the interface. Additionally, the secant stiffnesses during loading and unloading gradually increase and converge, while the tangential plastic work progressively diminishes and approaches zero. The influence of normal pressure on the cyclic shear behavior of the interface is predominantly observed during the first cycle. These research findings can contribute to the deformation analysis of cyclic shear at the pre-peak stage of the soil-sensitive structure interface. Furthermore, they provide an experimental foundation for establishing the cyclic shear constitutive model of the soil-structure interface under low shear stress conditions.

Permeability reflects the ability of sand and soil bodies' internal pores to transmit fluids, and the permeability coefficient serves as a crucial indicator to assess the permeability of soil bodies. Current research on permeability predominantly focuses on aspects such as porosity, coefficient of uniformity, coefficient of curvature and particle size. Calcareous sand, characterized by its special biological origin, consists of varying proportions of coarse and fine particles. The coarse particles form the skeletal structure, while the fine particles alter the pore distribution. Additionally, the particle shapes are highly irregular. To investigate the influence of coarse particle content and particle shape on the permeability of calcareous sand, we employed the PartAn 3D particle image analyzer to obtain shape parameters of the samples. Furthermore, a constant head permeability test was conducted to explore the correlation between the physical property parameters of mixed sand and the measured permeability coefficients. The research findings indicate that the permeability coefficient of mixed sand does not solely increase with higher coarse particle content; instead, it exhibits a trend of decreasing first and then increasing. Among the quantified shape parameters, concavity (C_a), convexity (C_v), and maximum Feret length (F_L) have a greater impact on permeability. Based on the correlation analysis, a preliminary predictive model for the permeability coefficient, incorporating the shape parameters of calcareous sand particles, has been established. This model can provide a scientific basis for calculating and analyzing the seepage field of artificially filled islands and reefs in the South China Sea.

Aiming at evaluating the engineering feasibility of two self-hardening materials, slag-cement-bentonite (SCB) and magnesium oxide activated slag-bentonite (MASB), as vertical barriers for Cr(Ⅵ)-contaminated sites, the evolutions of their engineering properties and microstructures under the effect of K₂CrO₄ solution were investigated. Firstly, the changes in mass, appearance, thickness of the discoloration layer, unconfined compressive strength and permeability coefficient of the specimens after the immersion test were determined. Subsequently, based on the results of the macroscopic tests, some specimens were subjected to microscopic tests such as X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and elemental morphology sequential extraction. The results indicated that the masses of SCB and MASB specimens as well as the thickness of the discoloration layer increased with the increase of immersion time and the concentration of contaminated solution. This is mainly due to the generation of substances such as CaCrO₄ and MgCrO₄, as well as the physical adsorption of CrO₄^2- within the specimen. The unconfined compressive strengths of SCB and MASB specimens decreased with an increasing concentration, while the permeability coefficient increased with it. When the concentration of the contaminated solution reached 0.5 mol/L, the strengths of SCB and MASB specimens decreased by 42% and 60% respectively, while the permeability coefficients increased by more than 10 and 100 times respectively, which was largely due to the decrease in the generation of hydration products and the reduction of specimen densification under the effect of K₂CrO₄ solution. Comprehensive analysis revealed that although the two self-hardening materials, SCB and MASB, had good engineering performance under tap water immersion, their chemical compatibility with K₂CrO₄ solution was poor, and they were easy to deteriorate due to the effect of Cr(Ⅵ) contaminated solution. Therefore, when the concentration of Cr(Ⅵ) in the contaminated site reaches a large level, both materials can not directly meet the requirements for use, and modification studies need to be carried out.

As a novel and inexpensive material, rubber-sand mixture is commonly utilized as filler in road base and retaining wall. However, limited research has been conducted on its dynamic mechanical properties under bi-directional cyclic loading. A series of direct shear tests was conducted on rubber-sand mixture with different rubber-sand particle size ratios using a large dynamic direct shear instrument to investigate the effects of particle size ratio, normal cyclic load amplitude and horizontal shear load frequency on the shear properties of rubber-sand mixture. The findings indicate that the cyclic peak shear stress of rubber-sand mixture under normal cyclic loading increases with increasing particle size ratio, while the final shear shrinkage decreases with a higher particle size ratio. In terms of shear stress, rubber-sand mixture with large particle size ratio exhibit greater sensitivity to the change of normal cyclic loading amplitude compared to those with small particle size ratio. Moreover, the shear swelling of rubber-sand mixture with large particle size ratio becomes more pronounced with increasing normal cyclic loading amplitude. Additionally, at different horizontal shear frequencies, the shear stress of the specimens display different forms of cyclic changes over shear time, with the maximum cyclic shear stress decreasing as horizontal shear frequency increases. The shear stiffness and damping ratio of the rubber-sand mixture are positively correlated with the particle size ratio, indicating that the rubber-sand mixture with a higher particle size ratio is more capable of improving the stability of roadbed under cyclic loading.

The engineering stability of red sandstone is low, and its mechanical properties are greatly affected by the water content and dynamic load disturbance. This study focuses on typical red sandstone in the western Sichuan Plateau region. Using split Hopkinson pressure bar (SHPB) test, different water content and loading strain rate conditions were set to simulate different water contents and dynamic loads disturbance. By employing high-speed camera, digital image correlation (DIC) and other measurement means, the study revealed the influence of deformation and energy consumption characteristics of red sandstone under different water contents and different strain rates. The results show that: (1) The dynamic modulus of elasticity of red sandstone is minimally affected by strain rate but increases with higher water content; the dynamic compressive strength of red sandstone increases with lower water content or higher strain rate. (2) The dynamic Poisson’s ratio of the red sandstone is less affected by water content but increases rapidly with strain rate, ranging from 1.92 (25 s⁻¹ strain rate) to 10.55 (130 s⁻¹ strain rate) when water content is 6%. (3) As water content or strain rate increases, the average fragmentation of red sandstone decreases gradually in a nonlinear manner. An inflection point is observed at 3% moisture content and 60 s⁻¹ strain rate, leading to a significant decrease in the average rate of particle size reduction. (4) At a constant strain rate, the energy dissipation rate and reflectivity of red sandstone specimens exhibit no significant correlation with water content, whereas the energy transmittance decreases progressively with increasing water content. (5) At a fixed water content, the energy transmittance and dissipation rate of red sandstone specimens decrease with rising strain rate, whereas the energy reflectivity increases. The findings of this study offer a theoretical foundation for blasting and excavation operations in water-rich red sandstone strata, as well as for prevention and control of seismic dynamic disasters and other related engineering applications

The occurrence environment of intermittent columnar jointed basalts in water conservancy and hydropower projects in the mountainous regions of southwest China is complex. Indoor mechanical testing is a valuable method for investigating the failure pattern and degradation mechanism of columnar jointed basalts. With the help of 3D printing technology, MTS uniaxial compression test and macro camera photography, the failure pattern of columnar jointed basalts is extensively investigated, and the anisotropic effect of columnar jointed basalts is discussed and quantitatively analyzed. The research results show that the failure pattern of simulated columnar jointed basalt samples varies significantly due to the influence of the inclination angle of the cylinder. In line with the failure phenomena of columnar jointed basalts that are exposed in underground excavation engineering of dam area, three typical failure patterns of physical models of columnar jointed rock masses are presented. Axial splitting failure along the columnar joint network, shear-slide failure along the columnar joint surface, tensile-shear failure through the columnar joint network are observed. The variation curves of the peak strength and deformation modulus of simulated columnar jointed basalt samples with the change of column inclination angle present the “shoulder shape” anisotropy. The concept of strength and modulus anisotropy ratio is introduced, and the anisotropy grade of simulated columnar jointed basalt samples under different inclined angles is given. The research results have certain reference value for the analysis of deformation and failure pattern and anisotropic characteristics of actual engineering rock masses.

To investigate the hydrological response and coordinated deformation mechanism of the three-tier bridge abutment slope reinforced with basalt fiber reinforced polymer (BFRP) anchor system under rainfall conditions, indoor physical model experiments were conducted based on actual engineering cases. The experiments collected data on slope moisture content, earth pressure, anchor axial force, and strain responses. The phased evolution patterns and response process of slope rainfall-infiltration-deformation were analyzed. A comprehensive control strategy for the strength, permeability, and deformation of the slope was proposed, following the principle of “graded reinforcement, balancing overall and local considerations”. By utilizing a multi-attribute response data system, the coordinated deformation mechanism of the bridge abutment slope-BFRP anchor system was elucidated. The results indicate that under rainfall conditions, the bridge abutment slope undergoes a deformation evolution trend from three-tier to two-tier and then to one-tier. The bottom of the first-bench slope is more susceptible to cumulative damage due to water softening, unloading rebound, and stress concentration effects. When tensile cracks initially formed or expanded in the slope, the axial force of the BFRP anchors exhibited a sudden increase trend, aligning the stage deformation characteristics of the slope with the axial force trend of BFRP anchors more effectively. This index is anticipated to offer a dependable foundation for monitoring slope deformation during rainfall. The flexible reinforcement capability of BFRP anchors can efficiently mitigate slope deformation caused by rainfall. Subsequently, actions like slope drainage and implementing green slope protection should be implemented to strengthen the slope.

To investigate the triaxial creep mechanical properties of unloading-damaged sandstone, some sandstone samples with different unloading damage degrees were prepared by controlling the unloading amount using the MTS816 rock mechanics test system. Triaxial creep mechanical tests with graded loading were carried out on the aforementioned unloading-damaged sandstone to analyze the influence of initial unloading damage degree on the strain characteristics, creep rate, deformation modulus, long-term strength, and failure mode of sandstone. The results show that: (1) Under the condition of graded creep, both the axial and radial strains of sandstone with different initial unloading damage degrees stepwise grow. The axial instantaneous strains exhibit an almost linear growth trend with increasing loading levels, whereas the radial instantaneous strain shows a nonlinear growth trend. Moreover, as the initial unloading damage degree increases, the increment of axial instantaneous strain caused by increasing unit loading continuously increases. (2) The unloading-damaged sandstone undergoes three stages in the non-destructive stage: instantaneous deformation, deceleration creep, and steady creep. The steady creep rate increases exponentially with the increase of initial degree of unloading damage. In the failure stage, the sandstone experiences four stages: instantaneous deformation, deceleration creep, steady creep, and accelerated creep. Among them, the accelerated creep stage takes a very short time but can produce significant expansion deformation, leading to unstable failure of the rock sample. (3) The total creep time, average deformation modulus, and long-term strength of sandstone all show a non-linear decreasing trend as the initial unloading damage degree increases. When the initial unloading damage degree surpasses 70%, there is a sharp decline in the total creep duration, average deformation modulus, and long-term strength of sandstone, with the maximum reductions being 24.77%, 33.28%, and 21.79%, respectively. (4) As the initial unloading damage degree increases, the creep failure mode of sandstone gradually transitions from a single shear failure to a complex tension-shear mixed failure.

Flexible joint is a key factor in the seismic design of the immersed tunnel when crossing through variable strata. This paper presents a theoretical model of the seismic response of flexible joint of immersed tunnel through different strata. The analytical model consists of two flexible joints and three tube elements. The Pasternak two-parameter foundation model was used to simulate the subsoil, while the Euler-Bernoulli beam model was used to simulate the immersed tunnel. The force and deformation transmission conditions of the joint in the immersed tunnel crossing through variable strata were considered. The analysis was based on the type of immersed tunnel that connects the artificial island at both ends, and free end boundary conditions were used to simulate the connection at both ends of the tunnel. By applying the matrix transfer principle, an analytical solution was to assess the seismic response of joints in immersed tunnels, accounting for the traveling wave effect. Verification of the analysis scheme was performed using finite element simulation results, demonstrating that flexible joints can effectively reduce shear forces and bending moments at strata interfaces. Under free end boundary conditions, joint shear stiffness mainly affects the joint shear force, and joint bending stiffness mainly affects the joint bending moment. The phase angles of seismic waves differ when forces reach the maximum values. When seismic waves are vertically incident, joint experiences the minimal force.

Dynamic loading-seepage causes the migration of railway subgrade filling particles, leading to frequent engineering problems such as ballast fouling, mud pumping, settlement, and erosion. However, few studies have focused on the permeation features and internal erosion characteristics of subgrade materials, making it difficult to uncover the evolution mechanism of service performance of subgrade under complex geo-environmental conditions. Therefore, the seepage characteristics and permeability stability of subgrade materials were investigated using self-developed equipment to reveal the seepage failure mechanism under dynamic loading. The main conclusions are as follows: (1) The internal stability of the soil is affected by fluctuations in pore water pressure and hydraulic gradients in graded aggregate and gravel-sand-silt mixtures caused by dynamic loading. (2) Critical hydraulic gradients leading to the migration of fine particles (J_cr) and seepage failure (J_F) in graded aggregate and gravel-sand-silt mixtures are determined as follows: J_cr =1.30 and J_F =6.88 for graded aggregate, and J_cr =1.23 and J_F =2.71 for gravel-sand-silt mixtures. (3) The seepage failure process of subgrade materials can be divided into three stages under coupled action of train loading and seepage: stable seepage, dominant flow development, and seepage failure. The relationship between flow velocity and hydraulic gradient follows the Darcy’s law under the low hydraulic gradient. (4) The evolution process of subgrade performance was analyzed, and the mechanisms and types of railway flood hazard were summarized. The research provides theoretical support for the design and maintenance of railway disaster prevention, and has significant engineering implications.

To investigate the dynamic expansion characteristics and mechanism of three-dimensional cracks in expansive soil, a constant temperature and humidity environment box was constructed. The real-time images of rectangular and circular expansive soil cracks with thicknesses of 4 mm, 8 mm, and 16 mm were captured using binocular cameras. The three-dimensional shapes of the cracks were reconstructed using three-dimensional digital image correlation (3D-DIC) technology, and the expansion mechanism and development characteristics of the cracks were quantified. The results show that shrinkage centers vary in time and space when expansive soil cracks, and the number of shrinkage centers decreases with the increase of sample thickness. More shrinkage centers result in more complex crack network shape. The movement of the shrinkage center shows vertical settlement, and the settlement is related to the moisture content of the cracked soil block. The motion vectors of surrounding soil particles move towards the shrinkage center in a bowl shape. The uneven deformation of the soil surface varies with the spatial distribution of the shrinkage centers, causing shear stress and deflection in the development direction of some cracks, resulting in a diverse fracture network connection. The cracking process of expansive soil is accompanied by the curling of the cracked soil block. Regarding the formation and movement mechanism of the curling of cracked soil block, after the development and formation, the overall humidity difference is “dry outside and wet inside”. The resulting suction difference in the profile matrix causes a vertical contraction deformation gradient. The gradient generates a bending moment that drives the cracked soil block to sag and gathers towards the contraction center, promoting the curling formation of the soil block. The test and analysis results can provide references for the cognition, analysis and prediction methods of expansive soil crack development law.

A large area of collapsible loess area is part of a water conveyance open channel project in Xinjiang. Channel slope sliding failure often occurs due to intermittent water supply and seasonal temperature changes. To further study the deformation and failure mechanisms of canal slopes, triaxial tests and scanning electron microscope tests were conducted on loess under dry-wet freeze-thaw cycles to examine its deformation law and microscopic mechanism. Finally, the Duncan-Chang model was improved based on the deformation law of loess. Triaxial test results show that: With the increase of the number of dry-wet freeze-thaw cycles, the stress-strain curve of loess decreases, while the volume change curve increases, with diminishing change ranges. After more than 5 times, the stress-strain and volume change curves stabilize, and the cohesion and internal friction angle show an exponential attenuation trend. The cohesion is significantly affected by the dry-wet freeze-thaw cycles. Scanning electron microscopy test results show that: The microscopic analysis was conducted using scanning electron microscopy. Under dry-wet freeze-thaw cycles, large particles and aggregates split, the cementing material between particles decreased, the surface contact increased, the proportion of large pore areas decreased, while the proportion of small and medium pore areas, three-dimensional porosity and pore roundness increased, and the fractal dimension decreased. Three-dimensional porosity and fractal dimension are significantly correlated with cohesion, while the proportion of large pore area is significantly correlated with internal friction angle. The original Duncan-Chang model fails to reasonably reflect the softening phenomenon of soil. To address this, a quadratic function is used to modify the Duncan-Chang model, and Poisson’s ratio is fitted using a formula, resulting in an improved Duncan-Chang model. The improved model effectively fits the triaxial test results of loess under different cycles. As the number of cycles increases, the stress-strain model parameters k and q show an exponential decrease, while the stress-strain model parameter o shows an exponential increase. Similarly, the volume change model parameters j and l show an exponential increase, whereas the volume change model parameter t shows an exponential decrease.

Micro-piles primarily produce anti-sliding effects in soil landslides through significant bending deformations near to the slip surface. When calculating their responses, changes in bending stiffness due to plastic deformation of the pile material should be considered. This paper proposes a computationally efficient p-y method for micro anti-slide piles based on the study of the bending characteristics. Taking the micro-piles made from concrete-filled steel tubes as the object, a refined finite element numerical simulation was conducted to study the nonlinear moment-curvature relationship. This relationship was divided into three stages: elasticity, elastoplasticity, and hardening, according to the evolution of section stress distribution and plastic strain, and was modeled by a three-stage equation. Based on the p-y method for calculating laterally loaded piles, the incremental differential equation of pile deformation considering the nonlinear moment-curvature relationship was derived. Using the incremental method and updating the flexural stiffness at each incremental step, the entire process response of the pile under landslide action can be quickly solved. The proposed method was verified using finite element numerical simulation and limit analysis method. Parameter analysis shows that both ultimate soil resistance and pile flexural strength significantly influence pile response. Higher soil ultimate resistance makes it easier for the micro-pile to reach failure, with failure positions closer to the slip surface. Conversely, a higher pile flexural strength results in failure positions further from the slip surface and mobilizes a larger range of soil resistance, but also increases soil displacement required to reach failure. The proposed p-y method and the associated analysis procedure can be applied to the optimal design of micro anti-slide piles.

In order to study the mechanical properties and anisotropic characteristics of bedded sandstone, mechanical tests were conducted under different bedding inclination angles and intermediate principal stresses. True triaxial compression tests were conducted on sandstone with seven different bedding plane angles (0º, 15º, 30º, 45º, 60º, 75º, and 90º) under three different intermediate principal stresses (10 MPa, 100 MPa, and 160 MPa). The effects of inclination angle of bedding plane on the deformation, strength and failure modes of sandstone were investigated. The results show that sandstone anisotropy gradually decreases and tends to be isotropic with the increase of intermediate principal stress. Under high intermediate principal stress, both Young’s modulus and failure angle gradually increase with the increase of anisotropy angle. The peak strength is also influenced by the combined effects of bedding plane angle and intermediate principal stress. It exhibits a typical U-shaped variation with increasing bedding plane angle under low intermediate principal stress condition, and the U-shaped curve flattens with increasing intermediate principal stress. The results are significant for guiding the design and construction of deeply buried hard rock projects.

Soft rock, easily broken during mining, filling, and rolling, is used as dam filling material in some pumped storage power plants. The relationship between filling and particle composition varies, greatly affecting the strength and deformation characteristics of dam materials. Currently, research on the particle breaking characteristics of soft rock damming materials is lacking, as is the differentiation from hard rock damming materials. This paper performs particle screening, scanning, and crushing studies on soft rock damming material from a pumped storage power station. The particle crushing mode, fractal dimension, crushing strength, and size effect differences between soft and hard rock are compared. The influence of particle shape and size on particle crushing mode and crushing strength of soft rock is investigated, and the relationship between particle shape and crushing strength of soft rock is quantified. The results show that the crushing mode of soft rock particles can be classified as crushing, splitting, or mixed. For hard rock particles with low strength and soft rock, the crushing mode is unique. The fractal dimension of 2.198 for soft rock is much smaller than marble and limestone, yet it is comparable to limestone, basalt, and sandstone. More tiny pieces form on the surface during soft rock particle disintegration. The crushing strength of soft rock particles is much lower than that of hard rock particles, with an average Weibull modulus of 1.48, also lower than most hard rock particles. The size effect and dispersion of the crushing strength of soft rock particles are stronger. The crushing modes of soft rock particles are mainly affected by particle shape, while the crushing strength is mainly affected by particle size. The formula proposed in this paper describes the quantitative relationship between particle shape and crushing strength.

In response to the issue of unclear influence of slurry diffusion and soil pressure around the tunnel during grouting at the bottom of the shield tunnel, grouting unit tests and simulation tests on grouting uplift at the bottom of the shield tunnel were carried out. The analysis of the grouting unit test reveals that the slurry undergoes splitting and diffusion during grouting, leading to “slurry leakage”. Interestingly, the additional soil pressure from grouting does not increase, and in some cases, it decreases post “slurry leakage”. In the tunnel grouting lifting model test, the slurry experiences compaction diffusion and splitting diffusion with a somewhat random direction. As the splitting and diffusion of slurry solidifies in the soil layer, its fluidity decreases gradually until diffusion ceases. Transitioning from squeezing diffusion to splitting diffusion, the soil pressure around the slurry bubbles decreases significantly. After completing the grouting, the additional soil pressure diminishes due to slurry consolidation and contraction. The model shield tunnel exhibits “transverse elliptical” and longitudinal bending deformations under the additional soil pressure, inducing additional loads interacting with the surrounding soil. Hence, in practical construction, in addition to the “small amount multiple times” grouting principle, enhancing slurry consistency is crucial to prevent “slurry leakage”.

In order to study the thermal characteristics of pre-bored grouted planted energy pile groups in saturated clay foundation under different operation modes, a self-designed model test system is used to examine the thermal response of single pile and pile group. By embedding sensing test elements, data on pile top displacement, pile stress, pile and surrounding soil temperatures, horizontal soil pressure, and pore water pressure are collected. Findings show that the heated pile influences adjacent unheated piles through thermal diffusion, leading to increased pile body temperature and top displacement. Moreover, the overall heat transfer efficiency of energy pile groups is lower than that of single piles. The absolute displacement change at the pile top in energy pile groups is greater under cooling conditions than under heating conditions, necessitating safety considerations. The group effect results in larger pile top displacements and lower additional thermal stresses in energy pile groups compared to single piles. Furthermore, as the number of energy piles in a group increases, the thermal characteristics become more pronounced, accompanied by greater variations in horizontal soil pressure and pore water pressure around the piles.

To study the excavation unloading response (EUR) of the surrounding rock of grouting curtain for vertical shaft, a triaxial excavation unloading test was conducted using fractured rock-like sample of vertical shaft grouting curtain (VSGC). The strain response of the VSGC sample was measured during the simulated excavation uloading process. Furthermore, the cracking mode and damage radius of the VSGC samples after excavation unloading were analyzed using CT scanning. Results indicate that the strain response of the VSGC sample after excavation unloading decreases rapidly with the increase of radius, with the strain during the excavation unloading stage dominating the total strain. Additionally, with the deformation of the grout stone being greater than that of the rock-like matrix. Moreover, the VSGC sample filled with cement grout exhibits has stronger deformation resistance than VSGC sample filled with clay cement grout. Hence, both the tangential and radial strains at the same radius in the sample filled with cement grout are significantly smaller than those sample filled with clay cement grout. Furtherly, the initial stress level significantly impacts the EUR of the VSGC sample, and the higher the stress level, the more severe the deformation during the excavation unloading stage, and the higher the proportion of strain during the excavation unloading stage. Finally, the VSGC samples filled with cement grout are prone to cracking along the contact surface between the grout stone and the prefabricated cracks, with the damage radius being 1.2 to 1.5 times the excavation radius. On the other hand, the cracking behavior of VSGC samples filled with clay-cement grout is complex, and the damage radius ranges from 1.5 to 2.0 times the excavation radius. The research findings can offer technical insights for designing grouting curtain for vertical shaft in the prevention and control of shaft water hazards.

The shear strength of rock joints exhibits strong size dependency. Conducting multi-scale experiments on joints is of great theoretical value and practical significance for studying the mechanical properties of large-scale joints. This study focuses on the less explored issue of size effect on the mechanical properties of joints under cyclic loading, near-natural rock joints with varying roughness were obtained through cubic splitting tests. Three-dimensional scanning technology was then utilized to capture point cloud data of the joints, followed by the production of resin models of different sizes using three-dimensional printing technology. Finally, model replicas were made through mold casting. Experiments were conducted to investigate the size effect of the structural joints under different normal stresses, as well as the influence of roughness and normal stress on the shear strength of the joints. A peak shear strength formula was developed considering the size effect of the joints, utilizing the adhesive friction theory and Barton’s empirical formula. The results show that the peak shear strength of rock joints exhibits a noticeable negative size effect. Variations in peak shear strength are more sensitive in smaller-sized surfaces subjected to high normal stresses and larger-sized surfaces under low normal stresses. Moreover, the residual shear strength at low normal stresses demonstrates a distinct negative size effect. Conversely, under high normal stresses, the residual shear strength transitions from a positive size effect to a negative size effect as the joint size increases.

To address the issue of previous methods for estimating rock shear strength parameters lacking the ability to reflect and quantify uncertainties, a rock shear strength parameter uncertainty estimation method based on Gaussian process regression (GPR) is proposed for conducting probabilistic uncertainty analysis. Utilizing the rock strength parameter dataset, Gaussian process theory is employed to establish the mapping relationship between rock uniaxial compressive strength (UCS) and tensile strength (UTS) with shear strength parameters using various kernel functions. Through maximizing the logarithmic marginal likelihood function, the hyperparameter of the GPR model is optimized, and then the appropriate kernel function and GPR model are determined according to the prediction effect and uncertainty degree. The results indicate that under given UCS and UTS data, it is advisable to utilize the Matérn kernel function for developing the cohesion GPR model and the rational quadratic kernel function for constructing the internal friction angle GPR model. Compared with conventional machine learning methods, the GPR method not only provides accurate predictions of rock shear strength parameters but also offers insights into the degree of prediction uncertainty, demonstrating strong scientific validity and interpretability, thereby validating the feasibility and efficacy of the GPR model.

The wading landslides in the Three Gorges Reservoir area are widely distributed, and their movement mode and impulse wave characteristics are closely related to the wading situation. Existing methods for predicting landslide impulse waves rarely consider the influence of landslide wading. Therefore, a physical generalized model test of landslides was conducted to study the impulse wave characteristics of wading landslides and the calculation formula for the maximum wave height of the initial wave of a landslide impulse wave under varying submergence degrees (defined as the ratio of the volume of the submerged part of the sliding body to the total volume before sliding). It was observed that as submergence increases, the type of landslide impulse wave transitions from a water landslide impulse wave to an underwater landslide impulse wave, leading to a gradual decrease in impulse wave height. By analyzing experimental data, a calculation formula for the maximum wave height of the initial impulse wave of wading landslides was derived through nonlinear regression analysis. A comparison with the formula proposed by Node and Pan Jiazheng showed that the empirical formula obtained is more suitable for calculating the maximum wave height of the initial impulse wave of wading landslides, with higher prediction accuracy. This formula can serve as a valuable reference for predicting and analyzing impulse wave disasters caused by wading landslides.

Studying the development characteristics of cracks in expansive soil under the effect of dry-wet cycles is crucial for understanding the deformation and failure mechanism of expansive soil channel slopes. Addressing the current research limitations, an experiment on expansive soil crack development focusing solely on dry-wet cycles is conducted. Utilizing the block discrete element method based on the crack development pattern in expansive soil, a deformation analysis of expansive soil channel slopes is performed through programming. The study yields the following findings: (1) Water evaporation in expansive soil undergoes a transition from initial evaporation to stable evaporation, followed by deceleration rate evaporation and residual evaporation phases. (2) As the number of wet and dry cycles increases, the area ratio of expansive soil cracks gradually increases and then tends to stabilize. The total length of cracks increases progressively, while the average width of cracks continuously decreases and gradually stabilizes, and the angle between cracks transitions from T-shaped to Y-shaped. (3) The distribution of soil particles always develops towards a stable direction, the stress distribution between particles develops towards a more advantageous state, and the distribution of expansion and contraction cracks gradually stabilizes. (4) Applying the block discrete element method to analyze expansive soil slopes has successfully integrated the displacement and stress fields, taking into account cracks and hygroscopic expansion. (5) The wet-dry cycle effect accelerates crack development, with higher crack rates resulting in increased slope deformation, expansion of the plastic zone, and significant deformation at the base of expansive soil slopes.

The remediation of heavy metal contaminated sites using microbially induced carbonate precipitation is a promising technology. However, the carbonate, various minerals, and pH of the topsoil-rich surrounding environment strongly influence the heavy metal fugacity pattern during biomineralization in contaminated sites in Northwest China. The intrinsic influencing mechanism requires further investigation. In present study, contaminated loess specimens underwent one-dimensional soil column experiments with varying Cu(II) concentrations (500 mg/kg, 2 000 mg/kg, and 4 000 mg/kg). Subsequently, they were remediated by injecting different volumes (50 mL and 100 mL) of bacterial colloid. The remediation efficiency of soil samples at different depths was analyzed using Tessier sequential extraction, soil pH measurements, and X-ray diffraction (XRD). The results indicated that injecting bacterial cements converted exchangeable Cu into a less biotoxic form (e.g., carbonate-bound Cu). However, no similar transformation of Cu was observed at lower Cu(II) levels (500 mg/kg). The transformation of Cu forms in soil samples at various depths of the soil column correlated strongly with the pH of the surrounding environment. The pH, in turn, was positively associated with the volume of the injected bacterial colloid. The alkaline environment further enhanced the coordination adsorption of Cu and minerals in the loess. Nevertheless, with further alkalization, the remediation efficiency decreased significantly due to the formation of Cu-ammonia complexes. These results underscore the potential of utilizing microbially induced carbonate precipitation (MICP) technology for remediating Cu-contaminated sites.

Soil organic matter (SOM) usually occurs in mineral-associated or particulate forms, with significant variations in the physical and chemical properties among different forms of organic matter. In soil mechanics, there has been focusing on the influence of SOM content on the macroscopic engineering properties of soil. To date, limited knowledge exists regarding the influence of SOM occurrence form on soil engineering properties. In this study, soil samples with different SOM contents w_u were manually prepared, and the contents of various occurrence forms of SOM were measured using Fu’s method. Direct shear tests were conducted under drained and undrained conditions to elucidate the variation in ultimate shear strength and shear strength parameters with SOM content w_u, while also examining the impact of SOM occurrence form on the shear strength of organic soil. The experimental outcomes are as follows. The internal friction angle undergoes a notable decrease with increasing w_u under undrained conditions, which can be categorized into three distinct stages: a significant decline (Stage I), a transition phase (Stage II), and a stable change (Stage III). w_u corresponding to the endpoint of stage I approximates the threshold w_u,2, suggesting that the pronounced reduction in internal friction angle with w_u augmentation primarily occurs in organic soils dominated by mineral-associated SOM. Stage III emerges approximately after w_u > 25%. Under drainage conditions, the internal friction angle diminishes with w_u augmentation, yet its variation is independent of the occurrence form of SOM. No discernible correlation exists between cohesion of organic soil and occurrence form of SOM under drained and undrained conditions. Mechanism analysis reveals that mineral-associated SOM facilitates lubrication and diminishes friction between soil particles under undrained conditions. When the content of particulate form SOM reaches a critical threshold, the mechanical properties of the soil transforms from a frictional material to a colloidal material. Nevertheless, under drainage conditions, SOM’s susceptibility to compression results in the soil skeleton ultimately comprising primarily mineral soil particles, regardless of SOM content or occurrence form.

This study addresses the engineering geological disaster resulting from the degradation of mechanical properties of expansive soil due to changes in environmental humidity along the Middle Route of the South-to-North Water Transfer Project. Calcium carbide slag and slag are utilized as curing materials to improve the expansive soil. Comparative tests were conducted on the unconfined compressive strength, split tensile strength, and water stability of untreated and treated expansive soil to analyze the performance differences pre- and post-treatment. The strength enhancement mechanism of the calcium carbide slag-slag cured soil was investigated through the X-ray diffraction (XRD), electron microscope scanning (SEM), thermogravimetric analysis (TGA) test and nuclear magnetic resonance (NMR) test, revealing its microscopic mechanism of action. The results showed a significant increase in the overall strength and water resistance of the calcium carbide slag-slag composite modified cured soil with different slag dosage based on 6% dosage of calcium carbide slag, and a maximum value was reached when the slag dosage was 9%. Over time, the unconfined compressive strength and split tensile strength improved, while the water stability coefficient decreased notably. Hydration of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) generated by the hydration of calcium carbide slag-slag composite cured soil led to the formation of tightly bonded soil particles, enhancing the soil’s pore structure distribution and strength. The evident effectiveness of the composite curing method for calcium carbide slag-slag treated soil suggests promising engineering applications.

Unprocessed landfill waste continues to produce large amounts of hazardous gases, and the building of a cover system is an effective method to reduce the emission of landfill gas. However, the accumulation of hazardous gases may result in landfill cover breakdown or airburst accidents. This study investigates gas breakthrough pressure and emission from landfill covers by conducting tests on compacted loess specimens, commonly used as cover material in northwest China. Results indicate that at low gas pressures, gas emission from saturated compacted loess is minimal. As gas pressure reaches a threshold, emission rates rise sharply. The gas breakthrough pressure of compacted loess increases with increasing effective stress. With effective pressure increasing from 10 kPa to 20 kPa and 30 kPa, gas breakthrough pressures increase from 28.95 kPa to 30.97 kPa and 37.27 kPa, respectively. In the cyclic gas permeability test, the gas permeability characteristics of compacted loess specimens show hysteresis. In addition, An exponential relationship exists between specimen volume change and effective stress induced by gas pressure. A significant specimen volume expansion due to reduced effective stress from increased gas pressure can signal impending destruction of landfill cover systems.

Due to its distinct characteristics of instantaneity and abruptness, the stress variation characteristics of unsaturated soil under impact loads significantly differ from those under static and conventional dynamic loads. To investigate the spatial stress state under impact loads, in-situ testing was conducted on an unsaturated soil roadbed using three-dimensional stress testing technology. The three-dimensional soil pressure cells were set at depths of 0.3 m and 0.6 m below the ground surface. Continuous vertical impact loads were applied at the ground projection of the buried points. Stress testing data was collected in real time, and stress transformation methods were applied to obtain the corresponding three-dimensional stress, principal stresses, and the evolution of principal directions. Based on this, a comparison was made with existing one-dimensional stress testing methods and results, further illustrating the rationality and scientific validity of three-dimensional stress testing. The testing data revealed that under impact loads, the stress component in the impact direction (i.e., the z-axis direction) shows a notable instantaneous increase with a positive increment, whereas the increment of positive stress in the y-direction is negative. The principal stress direction angles α、β, and γ undergo considerable deviations during the impact. Specifically, α  varies within a 90º range, whileβ  and γ   rapidly decrease from their initial values to their supplements. Moreover, all three directional angles experience multiple reciprocating changes within a single impact duration. This research has theoretical significance in deepening the understanding of stress response and evolution processes in unsaturated soils under impact loads, providing valuable references for constitutive models, engineering design, and construction research related to seismic or other impact loadings.

The structure response of the underwater shield tunnel during operation is important in studying the overall stability of the tunnel. Based on the health monitoring system of Wuhan Yangtze River Tunnel, the strain and joint monitoring data of the tunnel structure over one year (from April 2022 to April 2023) were obtained. In this study, the response patterns and differences in strain and joint opening between the under-river section and the bank section were compared, and a method for calculating the normal stiffness of segment circumferential joints was proposed. The results show that: (1) the average annual amplitudes of segment strains and joints opening of the bank sections are much greater than that of the under-river section; (2) The influence of temperature on the strains and joints opening of the bank sections are greater than that of the under-river section; (3) The normal stress-joints opening curves of the circumferential joint are similar to the normal stress-displacement curve of the rock joints, but the curve shape differs at different monitoring positions. The average normal stiffness at multiple monitoring points is similar during both the opening and closing stages. The normal stiffness of the circumferential joint in the under-river section is significantly greater than that in the bank section.

In order to predict the long-term development pattern of horizontal deformation of deep foundation pit support piles, an AM-CNN-LSTM model capable of predicting the deformation of support piles was constructed based on spatial feature extraction of convolutional neural network (CNN) data combined with long and short term memory neural network (LSTM) to analyze the temporal nature of the data and the divided feature weights of attention mechanism (AM). In the context of a deep foundation pit project in Beijing, the factors affecting the maximum deformation of the supporting piles are clarified based on the gray correlation method. The constructed model was used to analyze the single-point deformation pattern of the supporting pile and to compare and analyze the results obtained from the predictions of back propagation neural network (BPNN), CNN and traditional CNN-LSTM models. The results show that the maximum deformation value of the supporting piles is highly correlated with the excavation depth of the deep foundation pit, the number of days of proximity, the internal force of the support, the nature of the soil, the size of the piles, and the embedment depth. The AM mechanism significantly improves the initial data information mining depth and deformation prediction accuracy, which is continuously updated by the gradient descent method until the error requirements are satisfied. Compared with BPNN, CNN and CNN-LSTM models, the application of AM-CNN-LSTM model is more stable for long-term deformation prediction of supporting piles. By comparing with the measured data, the prediction accuracy of the AM-CNN-LSTM model is within 5% to 10% error.

A super-deep foundation pit project in Nanjing is constructed with a double diaphragm wall of shaped enclosure structure. The soil between the double walls is in a non-limit equilibrium state, and the evolution of soil pressure distribution and the mechanism of wall-soil interaction are not well understood. To investigate the soil pressure variation within the limited soil body between the double walls caused by deep foundation pit excavation, and to examine the influence of the soil arching effect on the soil pressure distribution outside the walls, this study employs a combination of on-site measurement analysis and physical model calculations. Initially, earth pressure monitoring points are established within the soil layers through field testing, aiming to capture the evolution of earth pressure between the walls during the excavation process. Subsequently, a curved conical soil arch model is established, taking into account the layering of the soil body. This model calculates the changes in earth pressure outside the walls due to the development of lateral soil arches. The accuracy of the model’s results is then discussed through parameter inversion and error analysis of the experimental data. The findings reveal that the excavation process predominantly impacts the soil between the double walls by causing compressive deformation. The lateral constraints imposed on this limited soil body contribute to further enhancing its shear strength. Among various excavation stages, the soil excavation process significantly disturbs the geological layers. The lateral soil arching effect further increases the earth pressure on the shallow soil retaining wall, while there is almost no development of lateral soil arches in the middle and deep soil layers. When considering the lateral soil arching effect, the calculated soil pressure aligns more closely with field measurements compared to the traditional Coulomb theory method, which separately calculates soil and water pressures. This study can provide insights and suggestions for the design and construction of deep foundation pit projects with special-shaped enclosure structures.

Soil failure criteria in theoretical research and engineering applications have a significant impact on research and design outcomes. Additionally, the discrepancy in experimental results between plane strain tests and conventional triaxial tests, attributed to the influence of intermediate principal stress, has been widely acknowledged. In this study, the unified strength theory, unified slip line field theory, and soil arch failure theory are employed to investigate the anti-slide pile spacing of unsaturated loess slopes. Based on experimental data, the intermediate principal stress parameter b of unsaturated loess is determined, and the anti-slide pile spacing expression for unsaturated loess slopes is derived using the soil arch theory. Furthermore, the relationship between anti-slide pile spacing variation, intermediate principal stress parameter b, and matrix suction of unsaturated loess slopes is explored through engineering case studies. The analysis indicates that considering the effect of intermediate principal stress can lead to an increase in the design spacing of anti-slide piles, thereby reducing engineering costs. This research provides valuable insights for optimizing anti-slide pile spacing in unsaturated loess regions.

Expansive soil is prevalent in the Chengdu area, and rainfall is a significant factor triggering deep foundation pit engineering accidents. Through the investigation of engineering cases, the typical deformation and failure processes of deep foundation pits in the Chengdu area, supported by piles under rainfall infiltration, were analyzed and summarized. The measured horizontal deformation curves of supporting piles in foundation pit engineering were categorized into three types: steep, gradual, and stable types. The early risk prevention of deep foundation pits in Chengdu’s expansive soil area can be based on the horizontal deformation of supporting structures, as indicated by the deformation developments of unstable pits and the three types of measured deformation curves during early rainfall after excavation. Using wavelet analysis, artificial neural networks, and Copula random variable correlation analysis, a prediction model for the horizontal deformation of supporting structures in foundation pits, considering rainfall influence, was established. The actual deformation curves of deep foundation pits were predicted based on this model. Finally, the prediction results enable early risk warnings based on deformation predictions. The predicted deformation results align well with the measured data, preliminarily confirming the validity of the proposed model. Using the same deformation warning index, the risk warning based on predicted deformation can significantly advance the warning time, providing a basis for optimizing the treatment scheme.

The application of shield docking method in soft clay can greatly shorten the construction period of long tunnels, but the excess pore water pressure generated by the first and second shield construction in the shield docking section can affect the soil stress state and formation stability. The fluid-structure coupling model for the shield docking method is established in soft clay. In terms of time, the time distribution of excess pore water pressure at different distances on the shield docking cross-section is analyzed. In terms of space, the longitudinal distribution of excess pore water pressure and the cross-sectional distribution of excess pore water pressure caused by the first and second shield construction are analyzed. In addition, the disturbance law of pore water pressure caused by shield docking construction is analyzed, and the construction parameters are analyzed. The analysis results show that when the shield docking is completed, the disturbance range of shield construction on the top of the arch is the largest, followed by the sides, and the bottom is the smallest. The influence range of excess pore water pressure generated by shield construction in front of the excavation face is 1.5 times that generated by the first shield construction, and its value is approximately 3.4 times the tunnel diameter. When the permeability difference of layered soil is too large, a sudden change in excess pore water pressure will occur. During the shield docking process, the disturbance caused by the first shield construction stage is significantly greater than that caused by the second shield, and the pore pressure disturbance index of the first shield to the arch is about twice that of the second shield at the docking position. When no grouting reinforcement is carried out at the docking position, it is recommended to reduce the supporting force of the tunnel face to 0.8 times the standard supporting force 2D (D represents the outer diameter of the tunnel) away from the docking position for both the first and second shields, or to perform advance grouting reinforcement before the first shield reaches the docking position, in order to reduce the disturbance during the shield docking process.

Gradation is crucial factor influecing the mechanical properties of high dam rockfills. During the filling period of a high dam, frequent particle breakage due to heavy equipment rolling leads to significant changes in the grading curve. Exceeding the design values of rockfill grading can result in unqualified areas, posing a risk to the safe operation of the dam. The traditional grading evolution research is mostly based on the reduced rockfill materials with a maximum particle size smaller than 60 mm, making it challenging to effectively describe on-site grading of rockfills with large particle sizes and multiple groups. This paper provides a novel approach to developing a prototype rockfill gradation evolution model. By utilizing the Weibull distribution of particle-crushing energy consumption of each particle group of rockfill body, the proportion of particle crushing amount of each particle group under different rolling passes was obtained. A fractal distribution matrix of crushing particles was developed to estimate the particle content of each new group, resulting in a new grading curve. Model parameters were determined through laboratory single grain strength test and field rolling test. The validity of the new model is verified by comparing with the measured values of the on-site rolling test pit of Shuangjiangkou Hydropower Station, the world's highest rockfill dam (315 m) currently under construction.

Saturated loess exhibits significant physical property variations and distinctive sedimentation, and strength and deformation patterns under natural sedimentary conditions. With the combined action of water, force, and time, saturated loess undergoes a continuous transformation from an uncompacted state to a compacted state. Pressuremeter testing is a reliable in situ technique for determining the strength characteristics of saturated loess without being affected by sampling procedures. The pressuremeter curve, with three characteristic pressure values and two characteristic strength indicators, was correlated with indicators such as burial depth, initial pore ratio e, and liquid index I_L. Therefore, the key influencing factors behind saturated loess strength were obtained. Based on this, the water sensitivity parameter m_ω applicable to saturated loess was defined. The corresponding relationship between fundamental physical properties indicators and characteristic strength was established. Additionally, the criteria for distinguishing between the properties of two types of saturated loess and the principle for categorizing the strength of uncompact saturated loess were suggested. The results showed that: 1) The characteristic strength of saturated loess is influenced by several factors, including uncompact state and consistency characteristics. Thus, relying solely on a single physical property indicator would not lead to an effective and reasonable assessment of its characteristic strength. 2) The strength difference between the two types of saturated loess can be distinguished by using the critical characteristic value (m_ω = 0.5) of exponential decay of the characteristic strength of saturated loess as the dividing index. 3) The long-term development of uncompacted saturated loess can be categorized into initial, intermediate, and later stages according to water sensitivity parameter boundary (m_ω = 0.75/1.3). The corresponding characteristic strength range values for each stage have been identified.

With the development of urban underground spaces, the horizontal deformation of retaining wall induced by braced excavations has increasingly become a focal point for engineers and technicians. Due to the lack of comprehensive studies on the horizontal deformation of retaining walls and their characterization methods, this paper introduces set of characterization functions and an indicator system suitable for the deformation curve of braced excavations. Through extensive data analysis, the deformation of retaining walls caused by braced excavations is categorized into four modes: upper concave-type mode, lower concave-type mode, upper and lower concave-type mode, and no concave-type mode. By considering the deformation modes and characteristics of the upper and lower segments of the retaining wall, a representation method for the horizontal deformation curve of the retaining wall is proposed using the piecewise normal distribution function. An indicator system for characterizing the deformation curve of retaining walls is presented, focusing on the maximum value of horizontal deformation, the position value of two segmented reverse bending points and the envelope area of deformation curve. Finally, the least square method is applied to carry out regression analysis to verify the characterization method of piecewise normal distribution function, demonstrating its applicability and effectiveness in characterizing the horizontal deformation of retaining walls. Although the proposed deformation characterization method using the piecewise normal distribution function does not currently involve deformation prediction, it offers a new perspective for future research on predicting horizontal deformation of retaining walls.

The traditional theory for plane pile support computation is limited to calculating the internal forces and deformations of the pile body on the supporting plane. It does not address the calculation of axial forces on the xoy horizontal plane support. Deriving a true three-dimensional solution is overly complex, often necessitating reliance on finite element software for three-dimensional model calculations. This study builds upon prior research to derive displacement and force matrix solution equations for the support surface, accounting for excavation processes, pile-soil-crown beam-support structure interactions, and the calculation method of axial forces on the xoy horizontal plane. These equations are solved using a FORTRAN program. Based on an engineering project, this study analyzes and compares the behavior of crown beams, waist beams, support piles, support displacements, and internal forces under spatial effects with the finite element method, LiZheng’s deep foundation pit calculation results, and monitoring data processed through nonlinear regression. The results indicate that the crown beam displacement, calculated using a matrix analysis method that accounts for the excavation process and pile-soil-crown beam-support structure interaction, exhibits a pronounced spatial effect. This effect is most prominent near the corner of the foundation pit. Within approximately one-fourth of the distance from the pit angle along the span of the crown beam, the pile spacing can be increased appropriately. The axial force on the support at the xoy horizontal pit angle is significantly lower than that at the center, aligning well with the monitoring data. Targeted optimization of the support section and reinforcement calculations can lead to reduced engineering costs. The displacement of the crown beam and pile body aligns well with the monitoring data and the results computed by LiZheng software, further validating the method’s rationality and feasibility. This can serve as a novel optimization design approach.

To control the stability of waste dump slopes with soft soil base during dumping and heightening process, the relationship between heightening rate and shear strength parameters of the soft soil is established, and a method for analyzing slope stability under different heightening rates is proposed. Based on a practical case, a series of quick shear tests for soft soil with different consolidation degrees is conducted. Results show that the internal friction angle gradually increases as a hyperbolic function with increasing degree of consolidation, while the cohesion remains almost constant. The evolution of consolidation degrees of soft soil layers under surcharge loading is studied using the finite element method and the hardening soil model. The relationships between consolidation duration, surcharge loading layer thickness, and strength parameters are established. Results indicate that a thicker soft soil layer has a lower internal friction angle under the same surcharge loading and consolidation duration. A lower surcharge loading results in a higher internal friction angle of the soft soil layer under the same consolidation duration. The slope failure mode changes from sliding along the base to sliding within the waste mass as the consolidation duration extends from 50 d to 100 d. Further extension of the consolidation duration has no effect on slope stability.

The reinforcement of fissure grouting with lime pile in earthen sites is effective, but the mechanism remains complex and unclear. A three-dimensional thermal-hydrological-mechanical model is established and calculated using finite element method, based on the theory of heat conduction and unsaturated permeability, combined with the non-isothermal hydration process of quicklime and the dynamic relationship of the lime pile, slurry, and rammed soil. By comparing the monitoring results of in-situ grouting test process and the finite element simulation results, the reinforcement mechanism is revealed. The results show that the quicklime in the lime pile and slurry reaches a high degree of reaction in a very short time, achieving 87% and 76% reaction degrees at 60 min, respectively. The physical fields in rammed soil around the fissure indicate that the slurry and lime pile act as the center, with values decreasing as the distance from the fissure increases. In this process, 80% of the water in the pile and slurry and 69% of the hydration heat are effectively utilized. After normalization, the quantitative effective influence ranges of temperature, water and expansion stress are determined to be 2.4 times, 0.7 times and 1.4 times the width of the fissure, respectively. This paper provides theoretical support for the new method of fissure grouting in earthen sites under pile-slurry combination.

Based on seismic damage survey data from 155 earth-rock dams in typical earthquakes worldwide, we analyzed the earthquake subsidence pattern of earth-rock dams and investigated key influencing factors using grey relational analysis. The results show that the upper envelope of earthquake subsidence rate increases with the increase of peak ground acceleration and earthquake magnitude, and decreases with the increase of epicenter distance. The subsidence rate is higher in the near-field range, and becomes minimal at an epicenter distance of 100–150 km. The maximum upper envelope value of earthquake subsidence rate is observed in filled earth dams, followed by core rockfill dams and face rockfill dams. The earlier the construction time, the higher the upper envelope value of earthquake subsidence rate, which reflects the differences in dam filling quality due to varying construction equipment and methods. The effects of peak acceleration, magnitude, dam type, construction year and epicenter distance on the subsidence rate decrease successively, with no single factor being absolute dominant. The prediction and control of seismic residual deformation of earth-rock dam are discussed according to the earthquake subsidence patterns and the analysis results of key influencing factors, in conjunction with the seismic code of hydraulic engineering. Control standards and design principles for seismic safety deformation of earth-rock dam are provided.

Land subsidence is a globally recognized important disaster, with different disaster areas experiencing various stages of development. Accurate understanding of the development of land subsidence is crucial for effective prevention and control. Aiming at the different characteristics of land subsidence at each development stage, a clustering method (improved adaptive density peak clustering algorithm based on K-nearest neighbors, IADPC-KNN) was proposed. Combining with granular computing theory, the development patterns of land subsidence and their mapping laws were summarized. Firstly, the dynamic time warping (DTW) method was used as the distance metric between data. IADPC-KNN and other five clustering algorithms were tested on seven public datasets. The results show that IADPC-KNN has higher accuracy and better robustness. Secondly, the land subsidence monitoring data from 14 affected regions around the world were collected, and four types of land subsidence patterns and their mapping relationships were obtained through data processing, sequence extraction, cluster analysis, granular model construction, and rule generalization. Finally, monitoring data from 2017 to 2019 for a specific site were used for validation. The results show that the land subsidence pattern for the site after 2018 has a probability of 0.359 2 of belonging to Mode 4, which is good agreement with the actual subsidence development. The research results provide a theoretical reference for predicting and preventing land subsidence disasters.

The liquidity index is a critical parameter for studying soil stability, deformation, strength, and related issues. Accurate prediction of the liquidity index is crucial. In this study, we evaluated the liquidity index using support vector regression (SVR), particle swarm optimization-based SVR (PSO-SVR), genetic algorithm-based SVR (GA-SVR), and simulated annealing-based SVR (SA-SVR) algorithms. The assessment utilized the piezocone penetration test (CPTU) dataset from Nanjing and Hefei regions, with the liquidity index derived from liquid limit and plastic limit tests as a reference. Predicted results were compared with laboratory tests and the CPTU empirical formula. Single-hole prediction analysis was conducted to align with engineering practice, and sensitivity analysis explored input parameter effects. Results showed that both the SVR model and optimized SVR models effectively predicted the liquidity index of cohesive soil, with the optimized models outperforming the original. Among these, the SA-SVR model excelled in wave smoothing and moderate peak values, enhancing prediction accuracy. For improved engineering predictions, normalized parameters (cone tip resistance, frictional resistance, pore pressure parameter ratio), overburden stress and effective overburden stress should be used as input variables. Sensitivity trends of PSO-SVR, GA-SVR, and SA-SVR models aligned with theoretical expectations, with SA-SVR exhibiting narrower span and greater consistency, confirming its accuracy. Thus, the proposed SA-SVR model offers superior prediction of cohesive soil liquidity index and guidance for engineering practice.

To reveal the cross-sectional shape effect of a deeply buried roadway under dynamic load, cement mortar rock-like material samples with five different hole shapes (rectangular, R, circular, C, straight wall arch, S, vertical, E_∥, and horizontal ellipse, E_⊥) were prepared, and the dynamic response characteristics of the samples were studied by using the drop weight impact test system. The influence of hole shape was discussed from three aspects: strain time history curve, crack propagation process around the hole, and failure mode. The dynamic compressive strength and meso-cracking mechanism were analyzed by PFC^2D. The results showed that the ultimate strain of the specimen with E∥ was the largest under the same impact load. The crack initiation position of the hole roof’s macroscopic crack was in the middle. The cracks at the bottom of specimens with the R and S were more likely to extend downward from the corner point, while the other specimens extended downward from the middle of the bottom. The roof of R, S, and E⊥ specimens was dominated by tensile-shear composite failure. In contrast, the tensile failure of the roof of C and E∥ specimens was more significant. The dynamic compressive strength of E∥, S, C, R, and E⊥ specimens decreased sequentially, therefore, the E∥ specimen had the best impact resistance. During the initial dynamic loading stage, the tensile stress was mainly concentrated at the roof of the hole, and the concentrated area was proportional to the transverse span of the upper boundary of the hole. When the stress was close to peak, the tensile stress gradually diffused to both sides of the specimen. In the post-peak stage, the rebound modulus of the E∥ and C samples was close to the elastic modulus, the plastic deformation was small, while the other samples showed a higher residual strain.

The physical and mechanical properties of rockfill materials significantly deteriorate when subjected to cyclic wetting-drying. Based on the three-dimensional scanning results of rockfill particles, a comprehensive template library featuring a wide range of particle sizes has been established. Considering the effects of wet-dry cycles on particle strength, effective modulus, and inter-particle friction, a particle crushing simulation scheme has been proposed, taking into account the degradation of rockfill particles caused by wet-dry cycles. On this basis, using the coupled FDM-DEM method, a series of triaxial compression tests have been conducted on rockfill specimens subjected to cyclic wetting and drying. The results reveal that the initial modulus and peak strength of the rockfill materials decrease nonlinearly with an increase in the number of wet-dry cycles (N). Wet-dry cycles exert an inhibitory effect on volumetric strain during the initial stages of shearing and dilation in later stages of loading. However, as N increases to a certain value, the impact of wet-dry cycles on the macroscopic deformation and strength of rockfill materials becomes less significant. As the number of wet-dry cycles increases, both the average coordination number and contact slip ratio within the specimen rise. Additionally, the deviatoric fabric inside the specimen exhibits a nonlinear decrease, indicating a gradual reduction in anisotropy. This suggests that wet-dry cycles have an inhibitory effect on the development of anisotropy within the specimen.

In complex service environments involving water and soil loads, hydraulic geotechnical structures are highly susceptible to suffusion disasters, potentially triggering structural failures. This study employs the computational fluid dynamics-discrete element method (CFD-DEM) to investigate poorly graded soils, which are commonly encountered in engineering projects such as earth-rock dams and slopes. By considering three different levels of fines content and three distinct particle shapes, we explore the process of suffusion in poorly graded sand. Through an analysis of particle migration trajectories, displacements, and contact numbers, we elucidate the micro-scale characteristics of fines movement during the suffusion process. The migration effects of particles are categorized into four types: clogging, voiding, detouring, and washout. Upon statistical analysis of the evolution of migration effects throughout the entire process, it is evident that during the initial stages of suffusion, most fines are in a detached state. However, as seepage flow takes effect, particles gradually come into contact with each other, resulting in a significant decrease in detachment effects. Consequently, other non-steady-state effects, primarily detours and washouts, gradually increase as moving particles become constrained by their neighbors. The clogging rate of particles escalates, and ultimately, the majority of particles settle into a clogged state, indicating that the sample has reached a steady state.

Richards equation is the fundamental equation in unsaturated seepage theory. It is commonly solved using numerical methods combined with effective iterative techniques. Time step adjustment methods are frequently used to enhance computational efficiency. To investigate the numerical performance of different adaptive time step methods, a finite element procedure employing the FEM combined with the adaptive relaxed Picard method and adaptive time step methods was developed. The effects of different adaptive time step methods on the computational accuracy and efficiency were assessed through simulations of unsaturated seepage problems. The results demonstrate that the developed procedure is practical and reliable, and it can guarantee the stability even when the time step changes significantly; the heuristic method is simple and efficient but may struggle to ensure high computational accuracy in problems with challenging iterative convergence; the numerical performance of the truncation error method is influenced by the truncation error threshold, with a smaller threshold leading to higher accuracy but lower efficiency, while a larger threshold resulting in lower accuracy but higher efficiency, and by adjusting the threshold, the truncation error method can achieve a better balance between computational accuracy and efficiency. The research findings are valuable for advancing and applying efficient unsaturated seepage finite element programs.

To investigate the evolution of thermal fracture cracks in granite under varying pressure conditions, numerical methods were employed in conjunction with microscopic damage theory to establish a rock thermal elastic constitutive model. A mineral particle morphology extraction technique tailored for Comsol Multiphysics software was introduced, facilitating numerical simulations on thermal fractures in granite under static water and uniaxial pressures. The dynamic progression of tensile and shear cracks was analyzed. Findings suggest that the sequence of thermal fractures in granite minerals is contingent upon their individual mechanical properties and strength, with the rupture sequence of the three minerals is mica, feldspar and quartz. The thermal fracture network comprises both tensile and shear fractures, with tensile fractures predominantly shaping the network. Fracture evolution unfolds in three stages: micro-fracture initiation, fracture eruption, and stable growth. The thermal fracture threshold is governed by the minimum principal stress, with uniaxial pressure exerting a minor influence compared to hydrostatic pressure. Fracture development under hydrostatic pressure lacks clear directionality. Uniaxial pressure propagates perpendicular to the minimum principal stress, with directionality becoming more pronounced as pressure increases.

During the process of rock fragmentation assisted by free surfaces using cutters of tunnel boring machine (TBM), once the disc cutters complete breaking the rock near the vertical free surface, the vertical free surface transforms into an inclined one. To investigate the impact of the inclined free surface on rock fragmentation by disc cutters, three-dimensional models were created using peridynamics. A series of numerical studies was conducted, considering variations in the inclination degree of the free surface and the distance between the cutter and the free surface. The simulation results indicate two rock fragmentation modes: internal crack extension and internal crushed zone expansion. With the distance between the cutter and the free surface fixed at 40 mm, the rock fragmentation mode transitions from internal crack extension to internal crushed zone expansion as the tangent cot θ of the inclination angle θ of the free surface increases. The peak normal force of the disc cutter and rock fragmentation energy consumption increase as the cotangent of the free surface angle increases. The rock fragmentation efficiency of the internal crushed zone expansion mode is lower than that of the internal crack extension mode. Furthermore, within the increase of distance range from the cutter to the free surface, the peak normal force of the disc cutter, rock fragmentation energy consumption, and rock fragmentation volume increase gradually, leading to an improvement in rock fragmentation efficiency.

To predict the cumulative plastic deformation characteristics of ballasted tracks under contaminated conditions, we utilized cyclic loading triaxial tests and a revised subloading surface model to investigate the cumulative plastic deformation characteristics of fouled ballast under cyclic loading. The findings revealed a synergistic effect of fine fraction content and moisture content on the hydro-mechanical properties of ballast. Particularly, simultaneous increases in fine fraction content and moisture content lead to a continuous decline in the mechanical properties of ballast, exacerbating the cumulative settlement of railway ballast under cyclic loading. Additionally, a modified subprogram for the subloading surface model was developed based on its constitutive theory and finite element software. The model’s validity was confirmed through comparison with results from cyclic loading triaxial tests. Numerical simulations demonstrated that the proposed model effectively predicts the evolution of cumulative plastic deformation of railway ballast under varying moisture and fine fraction content. Hence, the revised subloading surface model can be applied in future studies to establish a comprehensive engineering analysis model for predicting the long-term settlement of railway tracks under different fouled conditions.

In field plate loading tests for the ground, the recommended size specified in the Technical Code for Testing of Building Foundation Soils (JGJ 340―2015), the commonly used size, and the actual size of the foundation often differ significantly, leading to discrepancies in determining the ground bearing capacity. A finite element model was established based on the results of the field tests to validate its reliability. Subsequently, the model was utilized to study the size effect on bearing capacity and deformation of both homogeneous and double-layered soil foundations under loading plates of varying widths. Furthermore, the impact of the reaction pier employed in the field test was analyze. The results indicate that with varying widths of the loading plate, the bearing capacity of homogeneous ground undergoes gradual changes, accompanied by noticeable settlement increments. The bearing capacity of double-layered ground, with a soft upper layer and a hard lower layer, increases with the width of the loading plate, resulting in reduced settlement. The presence of the reaction pier enhances the determination of bearing capacity. In the current testing code, the bearing capacity determined by ground relative deformation shows a significant size effect when the loading plate width is limited. It is recommended to adjust the upper limit of the loading plate width from 2.0 m to 3.0 m.

Composite cutoff walls are commonly used in projects aimed at preventing pollution and permeation in contaminated areas. For a composite cutoff wall made of geomembrane and soil-bentonite, a theoretical model is developed to analyze the two-dimensional transport of organic contaminants in a buffer layer-composite cutoff wall-aquifer system. This model takes into account the presence of a buffer layer and the non-uniform distribution of organic contaminant concentrations at different depths in the source zone. The model is solved using the finite difference method. Subsequently, the rationality of the proposed theoretical model is confirmed through comparison with experimental data, calculations from an existing analytical model, and simulations using COMSOL software. The study investigates the transport characteristics of an organic contaminant in a composite cutoff wall. Results show that the organic contaminant concentration in the wall is lower under the two-dimensional transport model compared to the one-dimensional model, attributed to horizontal transport slowing due to vertical diffusion. The presence of a buffer layer slows down transport in the wall, with a thicker buffer layer leading to a longer breakthrough time to and lower total transport flux at the wall exit. Increasing the geomembrane permeability coefficient from 0.5×10⁻¹² m/s to 5.0×10⁻¹² m/s reduces t_b from 172.8 years to 28.2 years. Greater cutoff wall thickness and linear adsorption coefficient enhance barrier effectiveness, allowing selection of wall thickness based on adsorption performance.

In the numerical simulation of the discrete element method (DEM), the porosity field has been employed to observe the width of shear bands, which aids in understanding the relationship between shear band width and particle characteristics. The porosity field is obtained by measurement circles. However, the measurement circle radius is usually determined empirically, lacking theoretical and numerical simulation research. Therefore, a study was conducted to investigate the relationship between the accuracy of porosity measurement and the measurement circle radius. Furthermore, the “1/2 width estimation method” and “1/2 curvature extremum method” based on the porosity field were proposed and applied to measure the shear band width in direct shear and biaxial compression tests. The measurement results were compared with those obtained using the particle rotation method and grid method. The DEM numerical results show that the proposed methods are effective for measuring the shear band width in direct shear and biaxial compression tests. In the direct shear test, the shear band width gradually increases with the increase of particle size. Due to the asymmetry and non-uniformity of the specimen, the two shear band widths in the X-shaped shear band of the biaxial compression test are not equal, and the shear band widens gradually during the axial loading process.

Cement grout, commonly applied in engineering, is a type of non-Newtonian fluids, which exhibits complex macroscopic nonlinear flow characteristics when diffusing in fractures and presents special structures such as plug flow due to the existence of yield stress. This study involved preparing artificial grouts following the Herschel-Bulkley (H-B) model and conducting visualization grouting tests on flat fractures using particle image velocity (PIV) measurements. Grout flow numerical simulations were performed using the finite element method (FEM) to solve the H-B-P (H-B-Papanastasiou) equations. The nonlinear correlation between pressure gradient and flow rate was theoretically, experimentally, and numerically analyzed and confirmed using the analytical solution of the single-phase yield-power-law for fluid flow in flat fractures. Plug flow features of H-B fluids were examined by comparing velocity profiles obtained through various methods. Comparison with the Bingham model proved that the H-B model aligns better with real grout flow. This study comprehensively verified the theory and numerical model based on an originally developed visualization method and laying the groundwork for parameter determination, which may help improve the grouting technique in complex engineering rock masses.

Currently, the prediction of ground consolidation settlement through inversion is primarily based on the assumption of soil homogeneity or stratification. However, it is a well-established fact that the hydrological and mechanical parameters of natural ground exhibit spatial variability. To address this issue, an iterative co-Kriging inversion method that utilizes settlement and pore pressure monitoring data for high-resolution inversion is introduced, aiming to depict the spatially non-uniform distribution of ground soil parameters. The resolution of the data employed for inversion characterization is coupled with sensitivity analysis to elucidate the underlying mechanism. The findings indicate that the parameter field obtained through this method represents the optimal unbiased estimate. Employing both settlement and pore pressure observation data for inversion to characterize the heterogeneous ground proves more effective than utilizing solely settlement or pore pressure data for such analysis. Furthermore, a higher resolution leads to improved predictive accuracy of ground consolidation and settlement. The inversion resolution of various observation information types for different parameters is positively associated with the sensitivity magnitude of observation information to parameters.

This paper developed a subgrade discrete element model and a geocell finite difference model. A series of coupled finite difference method-discrete element method (FDM-DEM) numerical calculations was carried out to study the compaction behavior of geocell-reinforced subgrade under vibration loads. The contribution of geocells to the horizontal residual stresses after vibration compaction was further revealed. Additionally, the prestressing effect of the geocell-reinforced subgrade was proposed to reflect the reinforcement improvement due to the stretching of geocell pockets induced by the infill materials after loading and unloading during construction. The mechanism of the prestressing effect of geocell-reinforced subgrade was discussed by combining the microscopic particle contact, the changes in coordination, and the stress path during compaction process. The results suggest that geocells can improve the resilient modulus of reinforced subgrade and significantly increase the horizontal residual stress compared to the unreinforced subgrade. Under vibration loading, the geocell shows a flared shape with an upper opening. After compaction, the geocell pockets stretch wider, and the maximum tensile strain in the geocell walls ranges from 0.17% to 0.21%. The distribution of contact force also indicates that the force chain develops from a vertical to horizontal direction after vibration compaction, reflecting the increase of horizontal residual stresses. The geocell further enhances the development of lateral contact forces among particles.

As a new type of geological investigation technology, free-falling penetrometer (FFP) can obtain the mechanical properties of seabed sediments efficiently and quickly. During the FFP penetration process, the measured cone tip resistance is significantly influenced by the penetration rate. To process the data, it is essential to convert the dynamic penetration resistance into a quasi-static penetration resistance equivalent to the static penetration resistance of the cone penetration test (CPT). A rate factor correction related to the penetration rate is crucial for data analysis. This paper conducts theoretical analysis of rate effect based on Newton's Law of Motion, and examines mucky soil on the northern slope of the South China Sea through laboratory testing. Logarithmic function and power function are employed to fit the relationship between cone tip resistance and penetration rate, a calibration method for the correlation coefficient of free-falling penetration instrument rate is proposed. Findings indicate that both the release height and the probe quality affect the final penetration depth, but the change of cone tip resistance during penetration is less affected by the probe quality. The method proposed in this paper accurately determines the rate correlation coefficient of FFP penetration. The coefficient, calibrated through laboratory tests, can rectify in-situ test data in practical scenarios, offering technical support for FFP applications.