[Objective] The aim of this study is to explore the deformation and failure mechanism of rock anchor body anchorage. [Methods] Engineering geological analysis, in-site rock anchor body anchorage entity model testing, and finite difference numerical simulation were adopted to systematically study the distribution of stress and deformation, rock mass fracture process, and failure mode of jointed rock mass rock anchor anchorage. The displacement and fracture evolution process of the model anchorage were observed during the loading process. Combined with numerical simulation inversion analysis, the deformation and failure mechanism of the model anchorage displacement-fracture-overall instability under overload was investigated. [Results] In-site entity model test results show that when the load is 1P (P=3 243.46 kN), the deformation of rear anchor plate is the largest, with a displacement of 0.085 mm, and the upper part of the rock mass of the rear anchor plate experiences local initial tensile cracking. When the overload reaches 7P, the displacement of the rear anchor plate is 3.63 mm, and the trailing edge tensile fracture surface extends and penetrates the surface. The two side fracture surfaces track the steeply inclined joint surface and undergo tensile shear failure. The deep rock mass at 5.7 m below the surface begins to undergo displacement deformation, and the bottom sliding surface is subjected to tensile shear stress and begins to shear along the gently inclined joint, forming the embryonic form of overall instability and failure. When overloaded to 9P, the displacement of the rear anchor plate is 8.73 mm, and the crack width of the trailing edge tensile fracture surface continues to increase. The crack width of the steeply inclined joint surface tensile shear failure on both sides continues to expand outward, and the bottom sliding surface tensile shear fracture penetrates. The deep rock deformation at a depth of 3.7 m below the surface reaches 0.8 mm. When overloaded to 11P, the displacement of the rear anchor plate was 22.013 mm, and the bottom sliding surface continued to expand and rupture due to tensile and shear stress. The deep rock mass below the surface of the ground had a displacement deformation of 8.5 mm, and the overall model anchorage was unstable and failed. The load displacement full process curve, tensile and shear stress distribution, and plastic zone development results revealed by numerical simulation of model anchor anchorage are in good agreement with the spatiotemporal relationship of overload rupture evolution in in-site entity model tests. [Conclusions] Under the action of overload, the deformation and failure of the model anchorage are affected and controlled by many factors including tensile shear stress state, tensile shear strength of rock mass, and joint occurrence. It is generalized into the initial tensile shear failure stage (0-1P), the tensile shear failure expansion and penetration stage (1P-7P), and the tracking joint tensile shear overall slip instability failure stage.

[Objective] To address the unclear influence mechanisms of multi-point contact states and irregular particle shapes on particle breakage modes and crushing strength in rockfill dams, and to fill the research gap in systematically integrating meso-scale mechanical features with data-driven machine learning algorithms, this study establishes a robust framework for failure mode classification and crushing strength prediction of single rockfill particles. The framework is intended to overcome the inherent limitations of traditional empirical formulas that rely on idealized spherical geometries and fixed two-point elastic contact modes. [Methods] Uniaxial compression tests were conducted on artificial gypsum particles with varying particle sizes, aspect ratios, and loading angles. Digital image correlation (DIC) technique was employed to acquire full-field surface displacement data and capture crack evolution characteristics during compression. A grid search strategy combined with stratified 5-fold cross-validation was applied to optimize hyperparameters and mitigate overfitting. Support Vector Machine (SVM), Multilayer Perceptron (MLP), Random Forest (RF), and eXtreme Gradient Boosting (XGB)—were systematically evaluated and compared for both failure mode classification and crushing strength regression tasks. [Results] Three distinct failure modes were identified: splitting, crushing, and shear. Shear failure occurred exclusively under three-point or higher contact conditions, while two-point compression produced only splitting or crushing. Crushing strength exhibited a pronounced size effect and shape dependency: strength decreased as particle size increased, aspect ratio increased, or loading angle increased. Among the four algorithms, XGB demonstrated the best overall performance. In the classification task, XGB achieved a macro-average AUC of 0.96 on the independent test set, with a macro-average precision of 0.90 and an F1-score of 0.88. In the regression task, XGB yielded the lowest RMSE and MAE of 0.9 MPa and 0.8 MPa, respectively, with R² of 0.92. Compared with four traditional strength criteria (splitting, crushing, shear failure theories, and Hertz contact theory), the XGB model demonstrated superior prediction accuracy across all particle sizes. Under the 20 mm particle size condition, the absolute deviation between the XGB-predicted value and the experimental value was only 0.06 MPa, compared with 0.09 MPa for the Hertz contact theory. [Conclusions] Particle shape and contact state exert significant nonlinear regulatory effects on the crushing characteristics of granular materials. The XGB-based machine learning model effectively overcomes the oversimplified assumptions of traditional theories regarding idealized spherical geometries and fixed contact modes. By autonomously learning from high-dimensional meso-mechanical features, the model exhibits superior generalization ability and prediction accuracy under complex conditions involving irregular particle shapes and multi-point contacts.

[Objective] This study addresses the challenge of predicting sudden subsidence of sedimentary layers caused by drilling and sand extraction in the Dongting Lake ecological restoration project. By analyzing the development process of soil deformation, a prediction model for surface subsidence induced by drilling sand extraction was established to achieve rapid prediction of surface subsidence deformation width and maximum subsidence depth. The aim is to reveal the collapse patterns of sediment layers in the ecological dredging project of Dongting Lake and predict the collapse areas, providing theoretical references for safe construction and disaster risk management. [Methods] Based on a self-designed sand extraction visualization test apparatus, physical model experiments of drilling sand extraction were conducted under different sand gradations, extraction depths, and water levels. The sand soil collapse process was recorded using a high-speed camera, and the data were processed using PIV (Particle Image Velocimetry) technology to obtain the collapse curve and quantify the soil deformation process. [Results] Experimental results revealed:(1)The collapse zone exhibits an elliptical shape, with its eccentricity decreasing as the characteristic particle size D₉₀ or extraction depth increases, while increasing with greater water depth.(2)In terms of the goodness-of-fit between the Peck curve and the surface collapse curve, when the soil loss rate is below 20%, the goodness-of-fit is relatively low, showing a scattered distribution (R²=0.78-0.96). As the extraction process continues, the goodness-of-fit of the Peck curve to the surface collapse curve gradually increases, reaching a maximum at around 55% (R²=0.98). Thereafter, the collapse curve gradually evolves into an inverted triangular shape, and the goodness-of-fit of the Peck curve correspondingly decreases.(3)The developed collapse prediction model has good applicability within the range of collapse depth <15 cm, with a collapse depth prediction R²=0.73 and a surface collapse width prediction R²=0.65. [Conclusions] This research demonstrates that:(1)Water depth will increase the range of sand soil collapse and accelerate the speed of sand soil collapse.(2) The eccentricity is affected by sand soil particle size, extraction depth, and water depth.(3)The Peck curve is suitable for the range of moderate sand soil loss and needs to be modified when the sand soil loss rate is small or large.

[Objective] Riverbed overburden, which is characterized by significant thickness and complex composition, constitutes a poor coarse-grained soil foundation. Works built upon such overburden require reinforcement treatment. Dynamic compaction is a rapid and effective ground improvement technique. However, when applying dynamic compaction to riverbed overburden, there is currently a lack of reasonable methods for evaluating its reinforcement effectiveness, and it is difficult to accurately obtain the engineering mechanical properties after compaction. [Method] Based on a dynamic compaction project for overburden reinforcement and drawing on the concept of the pressuremeter modulus equivalent density method, this study employed a combination of in-situ density tests, field pressuremeter tests, laboratory model pressuremeter tests, and laboratory unit mechanical tests. A comprehensive evaluation method for the effectiveness of dynamic compaction treatment on overburden was proposed by comparing and analyzing the in-situ density and pressuremeter modulus of the overburden before and after dynamic compaction to evaluate the reinforcement effect. The mechanical property indicators of the overburden after compaction were obtained. [Results] (1) The in-situ dry density in the shallow layers of Test Zone Ⅰ and Test Zone Ⅱ increased by 7.8% and 5.3%, respectively, after compaction, indicating that dynamic compaction significantly improved the in-situ density of the shallow overburden. (2) Within the upper 6 m, both the in-situ density and pressuremeter modulus of the overburden showed improvement. Below 6 m, the pressuremeter modulus remained close to pre-compaction levels. This demonstrated that dynamic compaction primarily enhanced the shallow layers of the overburden, with negligible reinforcement effects observed in deeper layers. [Conclusion] The proposed comprehensive evaluation method combines qualitative and quantitative assessment by comparing the pressuremeter modulus and in-situ density before and after dynamic compaction; together with laboratory unit mechanical tests, it can accurately obtain the mechanical parameters after compaction and provides an economical and efficient approach for assessing overburden treatment effects and engineering characteristics.

[Objective] The crack initiation mechanism of saturated frozen sandstone under compression remains insufficiently understood, particularly regarding the quantitative relationship between initiation stress and peak stress under varying confining pressures, failure mode transitions, and the influence of micro-crack orientation on fracture resistance. This study aims to: quantify initiation stress via the volumetric strain inflection method; establish its relations with confining pressure and peak stress; characterize failure mode evolution; reveal the anisotropic effect of crack orientation; and interpret the initiation mechanism from an energy dissipation perspective. [Methods] Cylindrical saturated sandstone specimens (50 mm×100 mm) were frozen at -10 ℃ for 48 hours. Triaxial compression tests were conducted under confining pressures of 0, 2, 4, and 6 MPa at 0.1 mm/min. Axial and circumferential strains were continuously monitored. Crack initiation stress was determined from the inflection point on the crack volumetric strain curve. At least three parallel specimens were tested at each pressure to ensure reproducibility. [Results] (1) Both peak and initiation stresses increase with confining pressure. Initiation stress ranges 25%-35% of peak stress across all confining pressures, while peak stress shows a greater growth rate.(2) Strain evolution differs by stress state. Under uniaxial compression, circumferential strain stabilizes and volumetric strain dilates while axial strain continues increasing. Under triaxial compression, both strains continue increasing with different offsets, reflecting lateral constraint.(3) Failure modes transition with confining pressure. Uniaxial compression produces axial splitting (mode I tensile) with vertical cracks and flat surfaces. Triaxial compression shifts to shear-dominated failure with inclined shear bands and stepped surfaces.(4) Micro-crack orientation significantly affects fracture resistance. When the long axis of pre-existing micro-cracks is oriented at 30° to the loading direction, crack initiation occurs most readily. This angle matches the internal friction angle of the sandstone matrix, indicating that stress concentration is maximized when cracks align with the potential shear plane, promoting wing crack nucleation. [Conclusions] Based on the experimental findings, the following conclusions are drawn. (1) The crack initiation stress of saturated frozen sandstone, as determined by the volumetric strain inflection method, represents a reliable and practical indicator of the damage threshold. The finding that initiation stress consistently comprises 25%-35% of peak stress across different confining pressures provides a quantitative basis for engineering design, enabling conservative estimates of the safe loading range in frozen rock masses.(2) The anisotropic control of fracture resistance by micro-crack orientation is a critical factor in assessing the stability of frozen rock engineering structures. The identification of 30° as the most unfavorable angle, consistent with the internal friction angle of the rock matrix, implies that geological surveys should prioritize the characterization of micro-crack fabric when evaluating potential failure planes in frozen sandstone formations. Ignoring this anisotropy may lead to non-conservative stability predictions.(3) The initiation of cracking in saturated frozen sandstone is fundamentally an energy-driven damage evolution process rather than a simple stress-induced failure. Strain energy progressively accumulates at the grain-ice crystal interfaces, primarily in the form of elastic strain energy stored in the frozen bonds, until reaching a critical threshold at the volumetric strain inflection point. Beyond this threshold, the stored energy is dissipated through two concurrent micromechanisms: tensile micro-cracking and shear micro-cracking. The competition and synergy between these two mechanisms control the overall macroscopic failure behavior. This energy-based interpretation provides a unified framework for understanding the coupled effects of stress state, micro-crack fabric, and ice bonding on the mechanical behavior of frozen geomaterials.(4) These findings have direct practical implications for the design and stability assessment of cold-region geotechnical infrastructure, including tunnels, slopes, and foundations in permafrost areas. Future work may extend the present methodology to variable temperatures, different degrees of saturation, and cyclic loading conditions to more comprehensively capture the time-dependent and environmental-dependent cracking behavior of frozen rocks.

[Objective] This study systematically investigates the synergistic interaction between the lining structure (comprising the steel liner, concrete lining, and flexible sealing layer) and the surrounding rock mass of compressed air energy storage (CAES), and proposes optimization methods for key design parameters to enhance the technical feasibility and economic viability of such storage caverns under broader geological conditions. [Methods] Comprehensive finite-element simulations were performed to evaluate the effects of critical variables, including surrounding rock mass grade, lining parameters (thickness, concrete strength, and reinforcement ratio), and sealing layer characteristics (thickness, structural form, and material properties), on the structural mechanical responses (stress distribution, strain evolution, and cracking behavior). In particular, to address the common engineering challenge of concrete lining cracking, this study quantitatively assessed the risk of crack indentation failure in the flexible sealing layer. On this basis, a novel thickness design criterion for the rubber sealing layer based on an anti-indentation criterion was proposed for the first time. [Results] (1) Baseline design suitability and geological constraints: A composite structure consisting of a 24-mm-thick Q235 steel liner and a 500-mm-thick C40 concrete lining demonstrated sufficient capacity to meet the sealing and strength requirements for a storage cavern at a burial depth of 200 m in Grade Ⅰ and Grade Ⅱ surrounding rock masses. However, in Grade Ⅲ surrounding rock mass, the maximum tensile stress in the steel liner exceeded the yield strength of Q235 steel, indicating a potential risk of structural failure. In Grade Ⅳ and Grade Ⅴ surrounding rock masses, neither the sealing structure nor the surrounding rock provided the conditions required for constructing a storage cavern that was both safe and economically feasible. (2) Effect of lining reinforcement: Simply increasing the lining thickness or improving the concrete grade had a negligible effect on enhancing the structural stress-deformation behavior. In contrast, reinforcement measures effectively controlled the crack width of the lining. With a reinforcement ratio of 0.5%, the maximum crack width was controlled within 2 mm. Notably, as the reinforcement ratio increased from 0.5% to 1.5%, the maximum crack width decreased to below 1.0 mm, and the number of cracks within the 0.5-1.0 mm range decreased. However, this was accompanied by a redistribution effect, where the number of fine cracks (0.1-0.5 mm) increased significantly from 20 to 38, suggesting that reinforcement effectively dispersed concentrated macro-cracks into distributed micro-cracks. (3) Steel liner optimization and groundwater challenges: Increasing the steel liner thickness to 30 mm still failed to meet the strength requirements; further thickening produced diminishing returns while significantly increasing construction costs. Additionally, in areas with abundant groundwater, a 24-mm-thick steel liner provided limited resistance, withstanding an external water pressure of only 0.23 MPa. If the external water pressure reached 1.0 MPa, the critical thickness required to prevent buckling instability would exceed 100 mm, making the design economically infeasible. (4) Innovative structural forms and sealing layer criterion: Adopting segmented or corrugated steel liner structures could decouple liner deformation from the surrounding rock mass, reducing tensile stress and strain by more than 70%. Regarding the rubber sealing layer, its circumferential strain under an internal pressure of 10 MPa remained far below the material limit. However, to prevent the rubber from being extruded into cracks and causing indentation failure after the lining cracks, it was determined that the thickness of the rubber sealing layer should not be less than 6 mm. [Conclusion] Constructing CAES caverns in Grade Ⅲ surrounding rock mass with sufficient burial depth is feasible, provided that optimized steel liners, reinforced concrete lining for crack-width control, and a flexible sealing layer of adequate thickness are employed to ensure sealing reliability and overall stability. Since reinforcement cannot completely eliminate lining cracking, the engineering objective should shift towards controlling the crack width within an allowable range that prevents indentation failure of the sealing layer. For areas with active groundwater, relying solely on increasing steel liner thickness to resist external water pressure is uneconomical. Instead, proactive waterproofing or drainage measures around the cavern are necessary. Most significantly, this study proposes, for the first time, a quantitative design criterion for rubber thickness to prevent crack indentation failure. This contribution provides direct design guidance for engineering practice, thereby improving the technical adaptability and safety of lined rock cavern gas storage facilities under complex geological conditions.

[Objective] In numerical simulations of deep tunnels based on strain gradient theory, the infinitely remote boundary is commonly approximated using a thick-walled cylinder model with a finite outer radius. However, the quantitative influence of the selected outer boundary radius on the computational accuracy of surrounding rock deformation, as well as the existence of a critical radius ratio that ensures computational reliability, remain unclear. This study quantifies the effect of the radius ratio (k) on the computational accuracy of the thick-walled cylinder model for deep tunnels within the framework of Toupin-Mindlin strain gradient theory, with emphasis on characterizing the associated scale effect. [Methods] A plane-strain thick-walled cylinder model based on Toupin-Mindlin strain gradient theory was established. The governing equation was a fourth-order linear homogeneous ordinary differential equation, with boundary conditions involving both Cauchy stresses and higher-order stresses. To solve the high-order boundary value problem, the governing equation was transformed into a system of first-order ordinary differential equations. Using the MATLAB ODE45 solver combined with the quasi-Newton iteration method, an iterative feedback scheme was developed to simultaneously satisfy the stress boundary conditions at the inner and outer boundaries. The validity of the numerical strategy was verified by analyzing the behavior of the model solution as the intrinsic length scale approached zero. By varying k, the strain-gradient numerical solution was compared with the classical elastic analytical solution, and the computational accuracy was quantified using the mean absolute error. [Results] Numerical algorithm showed stable convergence in solving this high-order boundary value problem. As the intrinsic length scale diminished, the numerical solution consistently approached the classical elastic solution, thereby validating the reliability of the proposed methodology. strongly affected the computational accuracy. The numerical error decreased progressively with increasing. When k≥10, the absolute error of the model was effectively controlled to the order of. Parameter sensitivity analysis indicated that the ratio of in-situ stress to support pressure exerted a more pronounced influence on numerical error than the ratio of elastic modulus to the gradient elastic constant. The critical radius ratio criterion of remained valid across various parameter combinations. Based on comprehensive numerical results, an empirical correlation between model error and radius ratio was established. [Conclusion] The findings demonstrate that significantly influences the computational accuracy of strain gradient models for deep tunnels. When k≥10, the computational error induced by finite-domain approximation can be reduced to an acceptable level for engineering applications. The empirical correlation between and provides a quantitative criterion for boundary configuration and practical guidance for determining the minimum computational domain size required to achieve the target error threshold in strain gradient-based numerical simulations of deep tunnels.

[Objective] The primary objective of this research is to develop and optimize a novel, sustainable, and cost-effective binder for the stabilization/solidification (S/S) treatment of cadmium (Cd)-contaminated soils by utilizing a multi-component system comprising red mud (RM), granulated ground blast furnace slag (GGBS), carbide lime residue (CCR), and phosphogypsum (PG), all of which are industrial waste materials. A secondary objective is to compare the effectiveness of response surface methodology (RSM) with traditional orthogonal experimental design (OED) in optimizing the binder composition for achieving both high unconfined compressive strength (UCS) and low Cd leaching concentrations. The study also aims to elucidate the mechanisms governing Cd stabilization within the treated soil matrix via advanced microstructural characterization. [Methods] Artificially Cd-contaminated soil was prepared and treated with varying proportions of the RM-GGBS-CCR-PG binder. Two parallel optimization approaches were used: (1) OED (L9 (3⁴) orthogonal array) to identify the key factors affecting the S/S performance and (2) RSM (Box-Behnken design) to model the complex relationships between binder components (CCR, PG content, and RM/GGBS ratio) and responses (UCS and Cd leaching). Following curing, the treated soil samples were subjected to UCS testing and leaching tests. The experimental data obtained from RSM were used to develop quadratic polynomial models, perform analysis of variance (ANOVA), and generate response surface plots. The optimal binder composition was determined by maximizing UCS and minimizing Cd leaching. X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), was performed to identify the reaction products and elucidate the Cd stabilization mechanisms. [Results] The RM-GGBS-CCR-PG binder effectively stabilized Cd in the contaminated soil. Both OED and RSM identified the RM/GGBS ratio as the most significant factor influencing both UCS and Cd leaching. RSM provided a more refined optimization, leading to a binder composition of 13.77% CCR, 10% PG, and a RM/GGBS ratio of 0.57∶1. At this optimal composition, the treated soil achieved a UCS of 2.12 MPa and a Cd leaching concentration of 1.57 mg/L. ANOVA results for the RSM models showed that the models were highly significant (p<0.000 1) and exhibited a good fit (R²>0.99). XRD analysis revealed the formation of hydration products such as C-(A)-S-H, ettringite (AFt), and Cd-containing precipitates (Cd(OH)₂, CdCO₃, Cd₃(PO₄)₂). SEM-EDS confirmed the encapsulation of Cd within the C-(A)-S-H gel matrix and the formation of Cd-bearing precipitates. Replacing 1 kg PC with 1 kg of the waste-based binder lowered CO₂ emissions by 0.81 kg, embodied energy by 3.93 MJ, and natural resource consumption by 1.73 kg. At a 10% dosage, material cost for S/S was approximately 24.7 CNY/m³ for the RM-GGBS-CCR-PG system versus approximately 99.95 CNY/m³ for PC—an approximately 75% reduction—reflecting the low processing burden of industrial by-products (with GGBS requiring only modest grinding) relative to clinkerized binders. Therefore, the optimized mix simultaneously advanced mechanical performance, contaminant immobilization, and environmental-economic metrics. [Conclusion] This study demonstrates the feasibility of utilizing a novel multi-component binder composed entirely of industrial waste materials (RM, GGBS, CCR, and PG) for the effective stabilization/solidification of Cd-contaminated soils. The RM-GGBS-CCR-PG binder exhibits superior performance compared to Portland cement in terms of both mechanical strength and Cd immobilization. The application of response surface methodology (RSM) proves to be a powerful tool for optimizing the binder composition, providing a more precise solution than the traditional orthogonal experimental design. The study elucidates the mechanisms of Cd stabilization, highlighting the roles of physical encapsulation, chemical precipitation, ion exchange, and surface complexation. Furthermore, the carbon footprint and cost analysis demonstrate the substantial environmental and economic benefits associated with the use of this waste-based binder.

[Objective] Fractured strata during deep foundation pit excavation can easily lead to instability in the surrounding soil. To investigate the deformation response patterns of nearby subway stations during deep foundation pit excavation in fractured strata, this study examines a deep excavation project in fractured strata near Shenzhen Metro Line 5. [Methods] We conducted an in-depth investigation into the deformation of nearby subway stations caused by unloading during foundation pit excavation, employing theoretical analysis, numerical simulation, and field monitoring. Mindlin solution was employed to calculate additional stresses. Based on the stress release method, assuming full or partial stress release in the surrounding and pit-bottom soils caused by excavation, we comprehensively considered the support effect of the excavation retaining structure. Stresses were multiplied by a reduction factor to derive equivalent released stresses for the sidewalls. A theoretical formula for station deformation calculation was established, revealing its deformation mechanism. Three-dimensional modeling analysis was conducted through numerical simulation. Grey relational analysis was employed to perform sensitivity analysis on factors influencing station deformation, determining the sensitivity of each factor to station deformation. [Results] According to numerical calculation results, the maximum settlement deformation of the main structure of the subway station during each construction process was approximately 2.5 mm, and the maximum horizontal deformation was approximately 4.5 mm. Excavation unloaded the soil adjacent to the station structure, inducing horizontal displacement toward the pit center. Numerical simulations indicated that significant longitudinal deformation occurred primarily near the excavation zone, while structures farther away exhibited negligible deformation. Vertical deformation followed a pattern of greater displacement at the top and smaller displacement at the bottom. Comparative analysis between measured data from the central excavation zone and theoretical calculations/numerical simulations yielded the following station horizontal displacement results: Compared to monitoring curves, numerical simulation results were approximately 6% smaller; compared to theoretical calculation curves, numerical simulation results were approximately 8% larger. [Conclusion] Comparative analysis demonstrates that numerical analysis methods provide a reliable basis for subsequent factor impact assessments. Simplified calculations omitted factors such as peripheral loading around the excavation pit and delayed support construction, resulting in monitoring values exceeding both numerical and theoretical calculations. Therefore, construction must strictly adhere to avoiding peripheral loading and promptly installing supports to minimize impacts on station deformation. Sensitivity analysis of factors affecting station deformation using grey relational analysis reveals high correlations with diaphragm wall moment of inertia (0.874), overburden thickness (0.816), and excavation depth (0.759). Among these, diaphragm wall moment of inertia warrants particular control emphasis. During excavation, factors such as economy and safety must be comprehensively considered. Selecting a reasonable structural stiffness can achieve good deformation control, but beyond a certain threshold, this control effect diminishes significantly. The horizontal displacement of the station decreases as the moment of inertia of the diaphragm wall increases, the excavation depth decreases, and the overburden thickness increases, exhibiting a nonlinear relationship. Grey relational analysis identifies that diaphragm wall moment of inertia is the major influencing factor.

[Objective] The effectiveness of microbially induced carbonate precipitation (MICP) in saline soils is frequently compromised by the high-salt environment. The presence of salt ions inhibits microbial activity and disrupt ion migration, leading to reduced calcium carbonate precipitation efficiency and non-uniform spatial distribution. These limitations hinder the enhancement of mechanical properties in the stabilized soil and undermine the reliability of engineering applications. To address these challenges, this study introduces sodium alginate (SA) to develop an SA-MICP composite stabilization system aimed at improving the curing performance of saline soil. [Methods] The research focuses on investigating the variation patterns of calcium carbonate precipitation behavior and mechanical properties under different SA dosages, while elucidating the mechanism of SA-mediated synergistic regulation of microbial mineralization through multi-scale experimental approaches. Sodium alginate was incorporated at varying mass fractions (0% to 6%) relative to the dry soil weight. The quantity of precipitated calcium carbonate was quantified using both solution-based precipitation assays and soil column reaction tests. Mechanical performance of the stabilized soil at curing ages of 3, 7, and 14 days was evaluated via unconfined compressive strength (UCS) and Brazilian tensile strength (BTS) tests. The morphology, mineralogical composition, and spatial distribution of calcium carbonate were systematically analyzed using particle size analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD). [Results] The incorporation of sodium alginate significantly enhanced the MICP-based stabilization of saline soil, with the extent of improvement being strongly dosage-dependent. Calcium carbonate precipitation initially increased with SA dosage, reaching a maximum at 3% SA, where the yield was approximately 58% higher than that achieved by MICP alone. Beyond this threshold, further increases in SA dosage resulted in decreased precipitation, suggesting that excessive SA elevated system viscosity and excessively sequestered calcium ions, thereby impairing reaction efficiency. Mechanical test results aligned with this trend: both UCS and BTS increased with SA dosage up to 3%, peaking at 14 days of curing. Specifically, UCS improved by approximately 35.2%, while BTS exhibited a substantial increase of up to 194.8%. The pronounced enhancement in tensile strength indicated that SA played a critical role in improving fracture resistance and inter-particle bonding continuity. [Conclusion] Microstructural analyses further validate the synergistic stabilization mechanism of the SA-MICP system. SA-MICP-treated soil displays a continuous and dense “crystal bridge-encapsulation” cementation structure, with more uniform calcium carbonate distribution effectively filling interparticle voids. This study demonstrates that sodium alginate effectively synergizes with MICP to overcome key challenges such as low mineralization efficiency and heterogeneous precipitation in saline environments. The overall SA-MICP stabilization process follows a synergistic pathway characterized as “microbial mineralization-polymer-confined regulation-crystal bridging cementation,” ultimately yielding a densely structured soil matrix with superior mechanical performance. At a 3% SA dosage, the system achieves optimal balance between precipitation efficiency and mechanical enhancement, particularly excelling in tensile strength and crack resistance. However, excessive SA adversely affects reaction kinetics and structural homogeneity, underscoring the importance of precise dosage control. Overall, the SA-MICP composite approach significantly improves the applicability and engineering reliability of MICP in high-salt conditions.

[Objective] To address the insufficient understanding of the mechanical contact behavior at the interface between a cut-off wall and a clay core wall in earth-rockfill dams, this study aims to investigate the nonlinear normal contact relationship developed during the penetration of a cut-off wall into a clay core wall. The mechanical interaction between the cut-off wall and the core wall is a key factor affecting the deformation compatibility and overall stability of seepage-control systems in earth-rockfill dams. However, the wall-end resistance mobilization mechanism and its dependence on overburden pressure have not been fully clarified. Therefore, this study focuses on establishing an experimentally validated nonlinear normal contact model that can describe the relationship between wall-end pressure and penetration displacement, and further evaluates its applicability through numerical simulation. [Methods] A self-developed model test apparatus was designed to simulate the penetration process of a cut-off wall into a clay core wall. Clay specimens were prepared to represent the core wall material, and three levels of overburden pressure (100, 300, and 500 kPa) were applied to investigate the influence of vertical stress conditions on the penetration behavior. A hyperbolic nonlinear normal contact model was proposed and calibrated to describe the mechanical relationship between wall-end pressure and penetration displacement. The proposed model was introduced into finite element numerical simulations to reproduce the penetration process to verify its effectiveness and applicability. [Results] The relationship between wall-end pressure and penetration displacement exhibits significant nonlinear characteristics during the penetration of the cut-off wall into the clay core wall. Under a constant overburden pressure, the wall-end resistance increases rapidly at the initial stage while the penetration displacement changes only slightly, indicating that the clay core wall provides a high initial resistance to wall penetration. As penetration continues, the increase rate of wall-end pressure gradually decreases, and the displacement begins to increase more noticeably. At the later stage, the penetration displacement increases substantially, whereas the growth rate of wall-end pressure becomes much smaller. This behavior indicates that the soil structure near the wall end is progressively disturbed and damaged, and large deformation of the clay core wall can occur without a proportional increase in contact pressure. The test results also demonstrate that overburden pressure has a significant influence on the penetration behavior. As the overburden pressure increases from 100 to 500 kPa, the overall bearing stiffness of the clay core wall increases markedly. This pressure-dependent behavior reflects the compaction effect and pressure-hardening characteristics of clay under higher vertical stress conditions. The proposed hyperbolic normal contact model effectively describes the measured relationship between wall-end pressure and penetration displacement. The coefficient of determination of the model fitting reaches 0.936 9, indicating good agreement between the fitted curves and the experimental data. The finite element results obtained using the proposed nonlinear normal contact model are generally consistent with the model test results, further confirming the rationality and effectiveness of the proposed contact model. [Conclusions] The penetration of a cut-off wall into a clay core wall is governed by a strongly nonlinear normal contact mechanism, rather than a simple linear pressure-displacement relationship. The wall-end resistance develops rapidly at the initial stage and then gradually approaches a slower growth trend as soil disturbance and local structural damage progress. Overburden pressure is a key controlling factor in this process, because higher vertical pressure enhances the compactness, stiffness, and resistance capacity of the clay core wall. The hyperbolic nonlinear normal contact model proposed in this study provides an effective mathematical representation of the wall-end pressure-penetration displacement relationship and can reasonably reflect the pressure-dependent deformation characteristics of clay. Its successful application in finite element analysis indicates that the model can serve as a reliable theoretical and numerical tool for analyzing the interaction between cut-off walls and clay core walls.

[Objective] The strength characteristics and underlying mechanical mechanisms of expansive soil treated with microbially induced calcite precipitation （MICP） remain insufficiently understood. Investigating the effect of varying calcium ion concentration on the strength of MICP-treated expansive soil can provide critical guidance for its engineering applications. [Methods] Sporosarcina pasteurii （CGMCC 1.3687） was selected for microbial solidification using the mixing method. This study systematically investigated the mechanism by which different calcium ion concentrations—the core variable—affect the strength characteristics of treated expansive soil. Through a series of consolidated quick shear tests， the relationship between calcium ion concentration and strength parameters was analyzed to elucidate the mechanism by which regulating calcium carbonate formation enhances soil strength. [Results] The results indicate that MICP treatment significantly enhances the shear strength of expansive soil， altering its mechanical behavior from the strain-hardening mode of untreated soil to a dual-mode response： strain-softening under low confining pressure and strain-hardening under high confining pressure. Soil treated with Ca²⁺ solution exhibited higher shear strength than the untreated control. Specifically， cohesion （c） and the internal friction angle （ϕ） followed a unimodal trend with increasing Ca²⁺ concentration， peaking at 1.5 mol/L （c=42.5 kPa， ϕ=18.4°）. This represents a 269.6% increase in cohesion and a 10.2% increase in the internal friction angle. A concentration of 1.5 mol/L was identified as optimal， maximizing calcium carbonate yield and cementation. Lower concentrations resulted in insufficient Ca²⁺， while higher concentrations inhibited bacterial activity； both scenarios reduced calcium carbonate production and soil strength. [Conclusions] This study confirms that MICP technology significantly improves the strength of expansive soil. The strengthening mechanism is attributed to a significant positive correlation between calcium carbonate content and strength indices.

[Objective] While the mechanical properties of rock-concrete composites and basalt fiber-reinforced concrete have been widely studied， research on their combined performance after high-temperature exposure remains limited. This study investigates the use of basalt fibers to enhance the high-temperature performance of granite-concrete composites， aiming to evaluate their efficacy in mitigating thermal damage. [Method] Granite， plain concrete， and granite-basalt fiber concrete （GBFC） composites with four fiber volume fractions （0%， 0.1%， 0.2%， and 0.3%） were tested. Following high-temperature treatments at ambient temperature and 200 ℃， 400 ℃， and 600 ℃， static uniaxial compression and splitting tensile tests were conducted to evaluate compressive strength， tensile strength， failure modes， and damage factors. Scanning electron microscopy （SEM） was also employed to analyze microstructural evolution. [Result] （1） The composites exhibited continuous medium mechanical behavior， characterized by plastic failure under uniaxial compression and brittle failure during splitting. Their compressive and tensile strengths fell between those of pure granite and concrete， trending closer toward the concrete values. （2） Basalt fiber incorporation improved both strength metrics and failure modes at elevated temperatures， with a 0.2% fiber content identified as optimal. （3） The damage factor increased progressively with temperature； specifically， the GBFC damage factors were 0.103 5 at 200 ℃， 0.339 1 at 400 ℃， and 0.702 7 at 600 ℃， indicating severe structural degradation at the highest temperature. （4） SEM analysis revealed that uniaxial compression primarily damaged the concrete matrix， while the interface and granite remained relatively intact. High-temperature treatment exacerbated concrete deterioration but had minimal impact on the interface and granite. Basalt fibers acted as bridging and crack-arresting agents within the concrete matrix， effectively mitigating crack initiation and propagation when added in appropriate amounts. [Conclusion] These findings provide valuable references for understanding composite mechanical properties， optimizing tunnel construction， and guiding post-fire evaluation and repair strategies for tunnel infrastructure.

[Objective] To address the stability issues of rock ridges during the blasting demolition of the large cofferdam for the unit expansion project at Wuqiangxi Hydropower Station， this study proposes an optimized blasting scheme， aiming to prevent the sliding instability of the remaining thin rock ridge after layered blasting under the influence of fracture seepage. [Method] A discrete fracture seepage-stress coupling model was employed to evaluate the excavation sequence， slope height-to-width ratios， and seepage stability of the downstream slope of the rock ridge. The stability of the rock ridge under various blasting schemes and slope height-to-width ratios was analyzed considering fracture seepage. By integrating safety factors and failure slip modes， the optimal blasting sequence and a reasonable downstream slope height-to-width ratio were determined， providing precursor information on potential failure modes of bedded rock masses under seepage conditions. [Result] （1） Based on the engineering characteristics and blasting challenges， a demolition design for the intake cofferdam was formulated： blasting the outer earth-rock cofferdam during the dry season， thinning the inner side of the cofferdam， removing the top concrete cofferdam， and blasting the remaining rock ridge in a single pass. This scheme prevents the instability of the remaining thin bedded rock ridge under fracture seepage while minimizing risks to existing structures. （2） At slope height-to-width ratios of 1∶0， 1∶0.3， and 1∶0.5， the failure mode was global， with failure boundaries comprising a composite slip surface of the concrete-rock interface， weak interlayers， and bedding planes. At ratios of 1∶0.7， 1∶0.9， 1∶1.1， and 1∶1.3， the failure mode transitioned to local bedding slip instability. As the ratio increased， the tensile failure boundary at the trailing edge moved further from the toe of the excavated slope， and the thickness of the unstable rock layer decreased， indicating an evolution toward shallow bedding slip failure. [Conclusion] Considering both the safety factor and the failure slip mode， a slope height-to-width ratio of 1∶0.7 was determined to be optimal for the downstream slope excavation， as the safety factor exceeded 1 and the failure mode transitioned from global to local. The proposed scheme effectively controls the deformation and instability risks of the reserved thin-walled rock ridge. These findings provide valuable references for the demolition of large cofferdams and the stability evaluation of rock ridges under fracture seepage conditions.

[Objective] Based on suction-controlled triaxial isotropic compression tests on compacted loess， this study establishes a soil-water characteristic curve （SWCC） and hydraulic conductivity prediction model that accounts for compression deformation. This work aims to provide an accurate and convenient method for predicting the SWCC and hydraulic conductivity of compacted loess under compressive deformation， facilitating seepage analysis in loess embankment engineering. [Method] This study takes the Q₂ compacted loess samples from the Phase I Project of mountain flattening and city construction in Yan’an New Area as the research object. Four sets of isotropic compression tests under different constant suctions （y=25， 37， 50， 100 kPa） were conducted by using a GDS unsaturated triaxial apparatus. Building upon the test findings， a power function related to the void ratio is introduced into the four-parameter Fredlund-Xing model to establish a SWCC model considering compressive deformation. The model has fewer parameters， requiring only 7 parameters； the tests are simple， as the model parameters can be obtained only through suction-controlled compression tests and saturated permeability tests； （3） the model also considers the influence of adsorbed water on the hydraulic conductivity. The proposed model is applied to predict the SWCC and hydraulic conductivity curve of Yan’an compacted loess within a wide suction range， and the predicted results are compared with measured test data. [Results] （1） Compressive deformation causes a significant mechanical wetting effect， specifically manifested as follows： a. during the constant suction loading process， the degree of saturation of the samples increases significantly with the development of compressive deformation； b. in the process of compressive deformation， the SWCC of the samples shifts overall to the right as the void ratio decreases， and the air entry value increases significantly. （2） The proposed model can accurately predict the SWCC and hydraulic conductivity of compacted loess under any void ratio within a wide suction range， and its prediction accuracy in the high suction range is significantly higher than that of the Gallipoli model and the CCG model. In addition， the proposed model is used to predict the influence of compressive deformation. During compressive deformation process， as void ratio decreases， the soil-water characteristic curve of compacted loess gradually shifts to the upper right， and the air entry value increases significantly. In the low suction range， the hydraulic conductivity of compacted loess decreases with the decrease of void ratio， while in the medium and high suction ranges， the hydraulic conductivity increases with the decrease of void ratio. The response of the hydraulic conductivity of compacted loess to compressive deformation is essentially caused by the change of the cross-sectional area of water flow and flow paths due to the change of micro-pores. [Conclusion] The proposed model provides a reliable tool for understanding the soil-water characteristics and permeability behavior of compacted loess under compressive deformation. It not only improves the accuracy of seepage analysis in loess filling projects but also provides a theoretical basis for evaluating the stability and safety of engineering structures built on compacted loess.

[Objective] In typical plain tidal river networks at the Yangtze River Delta front， dense waterways and frequent navigation significantly impact levee safety through channel operations and bed scour. Focusing on two typical levee structural types along the Huangpu River and its main tributaries， this study investigates the scour response under the coupling of structural dimensions and scour depth. The findings aim to provide a scientific basis for accurately identifying high-risk bank sections， optimizing bank protection structures， and enhancing the targeted management of levee engineering in tidal navigable rivers. [Methods] To examine the scour resistance sensitivity and its variation of levee structures in tidal navigable rivers， the theoretical scour depth was calculated based on the actual operating conditions of a navigable tributary in the upper Huangpu River. Using these calculated values as a reference， finite element models were developed to analyze the displacement responses of gravity-type and pile-founded levees under coupled conditions of varying structural dimensions and scour depths. This approach allowed for the determination of the scour resistance sensitivity and evolutionary trends for different levee structural types. [Results] The scour resistance sensitivity of gravity-type levees is primarily influenced by the base slab width and embedment depth. When the base slab width is <4 m or the embedment depth is <2 m， a toe scour 0.5-1.0 m triggers a sharp increase in the displacement rate at the wall top. Conversely， when the base slab width exceeds 5 m or the embedment depth exceeds 2 m， further increasing the dimensions yields significantly diminishing returns in scour resistance. The scour resistance sensitivity of pile-founded levees is mainly governed by the pile length. When the pile length is <15 m， the displacement growth rate accelerates markedly once the scour depth 1.0-1.5 m. Beyond a pile length of 15 m， the effectiveness of increasing pile length to enhance scour resistance weakens. [Conclusion] （1）The sensitivity of different structural types to toe scour must be fully considered during the selection and sizing of levee structures in tidal navigable rivers. Under the given typical boundary conditions， the scour resistance sensitivity increases with the base slab width， embedment depth， and pile length. However， beyond certain thresholds， the marginal gain in sensitivity decreases， making it economically inefficient to further improve scour resistance solely by enlarging structural dimensions. Instead， altering the structural type or controlling the scour depth is recommended to enhance levee safety. （2）For the design of gravity-type levees， it is advisable to maintain a base slab width of ≥4 m and an embedment depth of ≥3 m. If the anticipated scour depth exceeds 1 m， gravity-type structures are not recommended. For existing gravity levees， the impact of scour should be mitigated through strengthened vessel traffic management and the installation of protective structures. （3）For the design of pile-founded levees， the pile length should be controlled at ≥15 m. When the anticipated scour depth reaches 1 m， measures such as enhanced vessel traffic management and protective structures should be implemented to reduce scour impacts. The proposed structural dimensions and structural adaptability under varying scour conditions provide a scientific basis for the design and management of levees in tidal navigable rivers.

With the increasing internationalization of geotechnical engineering projects in China and the growth of international engineering cooperation， the demand for referencing and applying foreign technical standards in engineering practice is growing. As a widely used in-situ testing method， the technical requirements and application of plate load test （PLT） results vary across different standard systems. To facilitate international engineering practice and standard alignment， this paper provides a comparative analysis of the similarities and differences between current domestic and foreign PLT standards from three aspects： standard systems， testing methods， and data interpretation. The analysis reveals the following：（1） In terms of standard systems， foreign standards typically focus on specific fields by proposing mandatory provisions and technical requirements， featuring a relatively concise structure. （2） Regarding testing methods， foreign standards are primarily principle-based and guidance-oriented， imposing higher requirements on engineers to conduct tests based on actual field conditions. （3） In data interpretation， domestic standards usually determine the allowable bearing capacity directly from the load-settlement curve. In contrast， foreign standards derive the allowable bearing capacity by back-calculating strength parameters under specific conditions and applying ultimate bearing capacity theories. This study provides a valuable reference for conducting PLTs and analyzing results under foreign standard frameworks.

[Objective] The Bishan-Tongliang Line is an east-west municipal express railway in the suburbs of Chongqing， aimed at promoting rapid development in the western Chongqing area. During the construction of the Yunwu Mountain Tunnel—a critical control project—a sudden water inrush occurred in the adit. This study aims to accurately identify the causes of the water inrush， providing a scientific basis and technical support for waterproofing measures during construction and the identification of water inrush sources in similar tunnel projects. [Method] Taking the water inrush in this tunnel as a case study， potential water-conducting channels were analyzed based on a comprehensive review of regional engineering geology， hydrogeological characteristics， and the features of the adit water inrush. Through laboratory and field tests， as well as physical and chemical analysis methods， the differences and correlations between water samples from regional aquifer channels and the inrush water were investigated to achieve accurate and efficient identification of the water inrush source. [Result] The regional groundwater primarily consists of red bed fissure water， detrital rock pore-fissure water， and carbonate karst water. Potential sources of the adit water inrush include surface water leakage， bedrock fissure water， water accumulated in mined-out coal areas， water inrush from water-conducting faults， and karst water. Through a comprehensive multi-factor analysis combining field investigations， physical methods， and chemical methods， it was identified that the water inrush originated from confined fissure water in sandstone strata interbedded within impermeable shale， supplemented by reservoir water recharged through water-conducting faults. [Conclusion] This study provides a universal methodology for identifying water inrush sources in tunnel engineering under complex geological conditions. This approach involves predicting potential water inrush factors by integrating regional engineering and hydrogeological characteristics， followed by systematic investigation and comparative analysis of each factor using field surveys， physical methods， and chemical methods to accurately and effectively identify the source of tunnel water inrush.

[Objective] The particle size distribution of fine-grained loess is a key indicator for evaluating its engineering mechanical properties. The traditional hydrometer method is limited by theoretical assumptions, experimental procedures, and dispersion effects, leading to insufficient measurement accuracy and long testing periods, which makes it difficult to meet the requirements for precise determination of particle size distribution of fine-grained soil. To address these issues, this study takes fine-grained loess from Lanzhou, Gansu Province, as the research object, and proposes a wet sieving test method suitable for fine-grained soil by modifying standard test sieves and using nylon filter cloth as a fine sieve medium. The study systematically investigates the determination of key test parameters and micromorphology. [Methods] After modifying the standard test sieves, multiple comparative tests were conducted focusing on key indicators including soil mass, water volume, test duration, and soil mass loss rate. Scanning electron microscopy (SEM) was employed to observe the micromorphology of particles in different size groups after separation. On this basis, comparative tests between the wet sieving method and the hydrometer method were conducted under conditions of full gradation and single-particle-size groups. [Results] The test results of key indicators determined the optimal test parameters as 30 g of soil and 4 000 mL of water. The duration of a single test was approximately 12 h, with the soil mass loss rate stably controlled within 3%. In contrast, the hydrometer method required approximately 48 h, indicating a fourfold improvement in efficiency. SEM results showed that the wet sieving method could achieve physical separation of fine-grained loess particles. The short-axis dimension of particles was identified as the key parameter controlling the sieving process. A high proportion of particles in the corresponding size groups after separation verified the reliability of the method. Comparative test results showed that the contents of clay and colloidal particles measured by the wet sieving method were significantly higher than those obtained by the hydrometer method, indicating that the traditional hydrometer method markedly underestimated the content of particles smaller than 0.005 mm in fine-grained loess. Further tests on single-particle-size groups confirmed that the hydrometer method exhibited large deviations in particle size determination for fine fractions, whereas the proposed method could directly and accurately reflect the particle size distribution. [Conclusion] This study indicates that the modified wet sieving method based on nylon filter cloth can accurately determine the particle size distribution of fine-grained loess and effectively compensate for the limitations of the traditional hydrometer method in fine particle testing. This method provides reliable technical support and experimental basis for precise geotechnical testing, engineering disaster prevention, and structural safety assessment in loess regions.

[Objective] Among numerical simulation methods for blasting fragmentation, the continuous medium simulation method has high efficiency, but its mechanical mechanisms are not rigorous and errors are significant when dealing with discontinuous problems; the discontinuous deformation analysis (DDA) method performs well for discontinuous problems, but when the fragment size becomes too small, excessively long computation time and non-convergence are likely to occur. This study aims to propose a numerical simulation method for blasting fragmentation that considers both computational efficiency and mechanical rationality. [Methods] Field tests were conducted to reveal the formation characteristics of blasting fragmentation, and the necessity of selecting appropriate numerical simulation methods for different fragment size ranges of blasting fragmentation was clarified. A continuous-discontinuous numerical simulation method for blasting fragmentation based on LS-DYNA+DDA coupling was proposed. In the near-field region of the blast hole, a continuous medium numerical simulation based on LS-DYNA was used to improve the computational efficiency of the crushing zone. In the middle- and far-field regions, a discontinuous method based on DDA was used to achieve discontinuous characterization of blasting fragmentation. The accuracy of using stress and velocity components as coupling parameters was compared. Finally, the LS-DYNA+DDA coupling method was validated based on the mining and blasting practice of Zhoushan Green Petrochemical Mine. [Results] Through field experiments and numerical simulation, it was determined that small-sized fragments were mainly concentrated within a very small range near the blast hole. The continuous medium method could efficiently simulate the distribution of small-sized fragments while ensuring accuracy. It was more reasonable to use DDA method to simulate the fragmentation of medium- and large-sized fragments. Using peak velocity as the coupling parameter between different methods could reduce the pressure loss during computation transmission. [Conclusion] Based on the measured results, comparison and validation between existing numerical simulation methods and the proposed LS-DYNA+DDA coupling method show that the proposed method improves the accuracy of blasting fragmentation prediction and has advantages in balancing the mechanical rationality of fragmentation mechanisms and computational efficiency. However, this method is currently applied in limited engineering scenarios, and its prediction efficiency needs further summary and optimization for different lithologies and blasting parameters.