The shear deformation characteristics of the pile-soil interface is significantly influenced by the water content due to the structural strength and water-sensitive nature of loess, leading to strain-softening behavior during shear deformation. Effective saturation and Bishop’s effective stress were employed as direct driving variables to reflect the effects of saturation on the structural strength of loess, based on the water-stress coupling characteristics of the pile-loess interface. Structural parameters such as cohesion, friction angle, and compression index, along with their evolution equations, are developed to reflect the degradation of structural strength with plastic strain and effective saturation. On the basis, by equating the plastic deformation of unsaturated structural loess with saturated non-structural loess under lateral confinement, a load-collapse function is developed for the pile-loess interface in the effective stress-effective degree of saturation space. An elastoplastic hydro-mechanical coupling model for the pile-loess interface is developed by integrating a soil-water characteristic curve. The model is validated using direct shear test data from unsaturated structural Lanzhou loess and field pile test data from Shanxi unsaturated loess. The results show that the proposed model effectively represents the hydro-mechanical coupling behavior of the pile-unsaturated loess interface, reflects the effects of saturation on shear strength, and captures the variation of strain-softening characteristics at the pile-soil interface with saturation. The model offers an effective approach for disaster prevention design, analysis, and assessment of the load-carrying behavior of piles in unsaturated loess.

The phenomena of “dry shrinkage and wet expansion” and “frost heave and thaw settlement” in expansive soils in seasonally frozen regions have caused numerous engineering problems. This study focuses on the strength degradation and slope instability in expansive soil water channels of the Northern Xinjiang water supply project. Using drying-wetting and freezing- thawing cycles as experimental conditions, the research includes moisture content monitoring at various depths to analyze soil moisture variation patterns during different stages. Additionally, laboratory experiments are conducted to study the effects of these cycles on non-uniform deformation, strength degradation, and microstructure damage in expansive soils. The results reveal that: 1) Under drying-wetting and freezing-thawing conditions, expansive soils at certain depths of the channel foundation exhibit significant moisture content fluctuations. The most significant variations occur during the freeze-thaw phase, establishing a “phase change dynamic zone” within the expansive soil. 2) Drying-wetting and freezing-thawing cycles cause significant microstructural damage in expansive soils, marked by continuous crack development and expansion with increasing cycle frequency. The soil experiences persistent “dry shrinkage and wet expansion” and “frost heave and thaw settlement” effects. In the early stages of drying-wetting and freezing-thawing action, expansive deformation significantly contributes to total deformation. However, after a certain number of cycles, both volumetric and expansive soil deformation gradually stabilize. 3) Expansive soils exhibit varying degrees of degradation in shear strength and strength parameters. Cohesion degrades more significantly, following an exponential decrease, while the internal friction angle experiences a less pronounced reduction. In the early stages of dry-wet and freeze-thaw cycles, cohesion degradation accounts for 41.2% to 48.6% of the total degradation rate. The significant decrease in soil cohesion leads to shallow landslides in expansive soil slopes of channel foundations, highlighting the crucial role of cohesion in slope instability.

This study proposes using a xanthan gum-biochar-coconut fiber composite, termed bio-matrix, to amend the topsoil of expansive soil fill slopes, addressing issues of cracking and poor vegetation growth. The response surface methodology (RSM) was employed to analyze the cracking and strength characteristics of expansive soil amended with bio-matrix at different ratios during dry-wet cycles. The analysis revealed the effects of individual factors and their interactions on the crack ratio and shear strength of expansive soil. Underlying mechanisms were further investigated using scanning electron microscope (SEM), X-ray diffraction (XRD), and tensile tests. Results indicated that all factors significantly influenced the crack ratio and shear strength of expansive soil. The primary interactions were observed between xanthan gum and coconut fiber, with negligible interaction among other factor pairs. The high viscosity and colloidal properties of hydrated xanthan gum enhanced the interfacial bonding between soil particles and fibers, intertwining with coconut fiber to form a stable three-dimensional network, thus improving soil tensile strength. Multi-objective satisfaction function optimization identified the optimal bio-matrix ratio: 0.60% xanthan gum, 3.60% biochar, and 0.24% coconut fiber. Compared to unmodified expansive soil, the optimized bio-matrix reduced the crack ratio by 71.04%, increased shear strength by 93.73%, and enhanced vegetation coverage by 223.77%. These findings enhanced a theoretical foundation for the application of bio-matrix in ecological protection of expansive soil slopes.

Ili loess is susceptible to substantial collapsible deformation due to water infiltration, leading to various engineering failures. To investigate the characteristics of water infiltration and the mechanisms of collapsible deformation, a field immersion test was conducted in the collapsible loess region of Ili. The changes in water content, water diffusion form, infiltration water volume, and surface collapsible deformation during immersion were analyzed. Numerical simulations explored surface collapsible deformation characteristics under varying saturation infiltration ranges. The results showed that the average vertical diffusion rate in the experimental area was 0.38 m/d, while the average radial diffusion rate was 0.17 m/d. Over time, the water diffusion pattern transitioned from elliptical to conical, with a wet front angle of 41° and a saturated front angle of 20°. The quantitative analysis of the vertical and radial water diffusion rates and infiltration water volume of Ili loess over time was conducted. A mathematical relationship between infiltration range and cumulative infiltration volume per unit area was derived. The correction coefficient β₀ for collapsible in the experimental area was determined to be 0.74, exceeding the recommended value of 0.5 in the specifications. The surface collapsible deformation correlates with water infiltration and can be divided into four stages: stable immersion, severe collapse, slow collapse, and consolidation settlement. As the saturation front angle increases, the surface collapsible deformation value maintains good consistency with the calculation results of the subsidence trough formula. The variation in the width of the subsidence trough aligns with the influence range of surface collapsibility, both following an exponential increase.

 To address the challenge of determining parameters for the hardening soil (HS) model in engineering practice, a database named HS-CLAY/9/196, which includes HS parameters, is established. A multivariate probability distribution for HS parameters is constructed based on the database. The probability distributions of HS parameters are updated using the available measured data of common soil parameters. The effects of the types and quantities of measured soil parameters on the estimation of HS parameters are studied. In addition, the probabilistic transformation models of HS model parameters (i.e., oedometric tangent stiffness  E^ref_oed, triaxial secant stiffness E^ref₅₀, and unloading/reloading stiffness E^ref_ur) are proposed based on the given measured data. The results show that the established multivariate probability distribution model effectively characterizes the statistical characteristics and cross- correlations of HS parameters. Based on the constructed multivariate probability distribution model, various measured data can be integrated to enhance the accuracy of parameter predictions through Bayesian updating. The prediction uncertainty can be reduced as the variety of measured data increases. To achieve accurate predictions forE^ref_oed,E^ref₅₀ , and E^ref_ur with low uncertainty, priority should be given to collecting the measured data of soil parameters that are strongly cross-correlated with the target HS parameters, such as the compressibility modulus E_s1-2, water content w, and void ratio e.

Cyclic loading significantly affects coal seepage; however, the quantitative characterization of seepage channels in fractured coal under cyclic loading is inadequate, and a matrix structure model for the fractured coal is absent. Therefore, seepage tests involving pore pressure and confining pressure cyclic loading were conducted on fractured coal with different grading conditions. The results indicate: 1) Under both pore pressure and confining pressure cyclic loading, the initial permeability of the coal mass varies with grading. As the Talbol power exponent increases, permeability successively increases, exhibiting clear stratification. 2) The sensitivity of effective stress to permeability K under cyclic loading is represented by effective stress variation Δσ^s_e . It is observed that the value of Δσ^s_e decreases in an “L-shaped” manner as permeability K increases during pore pressure cyclic loading. When K≤0.75×10⁻¹² m², the smaller Talbol power exponent corresponds to a lower the value of Δσ^s_e  is. 3) A method to calculate the average seepage pore area of graded coal is proposed, and a tortuosity model is developed to describe the evolution of tortuosity in fractured coal under cyclic loading. This research provides a theoretical basis for understanding the permeability evolution mechanism of fractured coal under cyclic loading and establishing a seepage model.

The stress state is the fundamental for evaluating the soil strength and stability，playing a crucial role. However, during the stress testing, local damage and other uncertain factors may lead to partial sensor data missing, causing the existing three-dimensional stress calculation method to fail. To accurately restore the soil stress state during data missing, a three-dimensional stress calculation method was developed based on three-dimensional stress testing principles, incorporating axisymmetric and one-dimensional compression characteristics. The three-dimensional stress, principal stress, the first invariant of stress I₁, the second in variant of stress J₂ and stress Lode angle of a sandy soil foundation under one-dimensional compression conditions with different data missing were calculated and compared to results with complete data. The results show that the method is highly accurate; as the load increases, the relative error decreases and converges. The principal stresses, the first invariant of stress I₁, the second invariant of stress J₂ and the stress Lode angle align with one-dimensional compression response, suggesting that this calculation method supports advanced data mining. This study offers a novel approach and a practical method for fully utilizing the test data.

The effects of near-fault pulsed and non-pulsed ground motions on structural responses differ significantly, yet their impacts on site ground motion parameters remain unclear. Therefore, a centrifuge shaking table model test of a dry sand site under 50g (g represents the acceleration caused by gravity) centrifugal acceleration was designed and conducted. The model site consisted of Fujian standard fine sand with a relative density of 50%. The pulsed acceleration record from Saratoga Aloha Ave station and the non-pulsed record from Capitola station, both within the near-fault range in the east-west direction of the Loma Prieta earthquake, were selected as inputs for the shaking table. An accelerometer vertical array and surface settlement gauge were placed at the center of the site, while horizontal displacement gauges were fixed on the lateral outside of the model box. This setup was used to compare the response differences of the dry sand site under near-fault pulsed and non-pulsed ground motions and to evaluate the correlations between site ground motion parameters and the peak acceleration values of the input ground motion. The model test results show that compared to non-pulsed ground motions, pulsed ground motions significantly reduce the amplification factors of peak acceleration but increase the final surface settlements of the site. For peak horizontal displacement, pulsed ground motions increase the peak displacements in the deep soil layer (> 15 m) but significantly reduce them in the shallow layer (< 5 m). Statistical results reveal high correlations between site seismic response parameters (amplification factors of peak surface acceleration, surface settlement, shallow peak horizontal displacement, Arias intensity) and the input peaks acceleration of ground motion, with all fitting coefficients R² greater than or equal to 0.97. These results provide a reliable experimental basis for further numerical simulations to study the impact of near-fault pulsed ground motions on site seismic response.

Sandstone is a crucial rock type for CO₂ aquifer storage. The clay minerals within it expand upon adsorbing CO₂ or H₂O, which affects the rock’s mechanical properties and may threaten the reservoir’s mechanical stability. A type of quartz-cemented sandstone with low clay content was studied. Triaxial compression experiments were performed under dry, H₂O, and supercritical CO₂ (scCO₂) saturation conditions, maintaining a constant pore pressure of 10 MPa. The effects of various fluids on the peak strength, cohesion, friction angle, and both macroscopic and microscopic failure characteristics of sandstone were compared and analyzed. Results indicated that, compared to dry conditions, scCO₂ and H₂O presence significantly reduced the peak strength of sandstone samples by 7.61% and 18.02%, respectively. Under different confining pressure levels, the weakening effect of scCO₂ on sandstone peak strength remained nearly constant, whereas the weakening effect of H₂O first increased and then decreased with rising confining pressure. The cohesion of sandstone decreased by 12.11% and 16.03% under scCO₂ and H₂O saturation, respectively, while the friction angle was remained nearly unaffected by the fluids. Both scCO₂ and H₂O reduce the failure angle of sandstone.

Expansive soil, a commonly distributed clay, is unsuitable for direct engineering applications. This study proposes a method to produce foam lightweight soil from expansive soil, effectively mitigating its expansive properties. The physical and mechanical properties of expansive soil-based lightweight soil (E-LS) were systematically investigated under varying water-solid ratios, wet densities, and expansive soil contents, using tests for flow value test, drying shrinkage test, pH test, and compressive strength test. An orthogonal experiment was conducted to quantify the influence of these factors on unconfined compressive strength (q_u), leading to the development of a strength determination method. The results show that the preparation of E-LS modifies the expansive soil structure, completely eliminating its expansiveness. Compressive strength of E-LS increases with both wet density and curing age. For expansive soil contents ranging from 30% to 60%, the unconfined compressive strength at 28 days (q_{u-28 d}) varied from 0.21 MPa to 1.58 MPa. Specifically, for E-LS with 50% expansive soil content, a water-to-solid ratio of 0.8, and a wet density of 900 kg/m³, the q_{u-28 d} reached 0.92 MPa, meeting the requirements for embankment construction. The factors affecting compressive strength are ranked as expansive soil content > wet density > water-solid ratio, and a predictive model for E-LS strength was developed. E-LS exhibits the capability to fulfill diverse embankment filling requirements in engineering applications, while demonstrating distinct advantages including expansive property mitigation, compaction-free implementation, and construction efficiency, thereby presenting significant potential for practical engineering deployment.

The slip effect can significantly enhance the permeability of fractured rock, and understanding its influence is crucial for comprehending gas flow dynamics within reservoirs. Most existing theoretical models treat intrinsic permeability and slip coefficient as constants and lack a method to define the critical pore pressure where the slip effect becomes significant. Thus, a dynamic apparent permeability model was developed based on equivalent fracture and rock bridge models, considering slip coefficient and intrinsic permeability as functions of effective stress and adsorption swelling. Using the established dynamic apparent permeability model, we analyzed variations in intrinsic permeability and slip coefficient under different confining stresses and permeable media. Additionally, we introduced the concept of the slip effect contribution rate to identify the critical pore pressure where the slip effect becomes significant. The results indicate that: 1) Intrinsic permeability increases with rising pore pressure, while slip coefficients decrease;   2) For different permeable media, the increase in intrinsic permeability with pore pressure is linked to gas adsorption properties, and slip coefficient variation is more complex; 3) A power function relationship exists between the slip effect contribution rate and pore pressure, with the critical pore pressure order being N₂<CO₂<He. This study offers theoretical guidance for predicting permeability and extracting resources from fractured rocks.

A computational model for the seismic response of end-bearing pipe piles in saturated soil under vertically incident P-waves is established by considering the coupled vibration among pile, outer and inner soils. The soil is treated as a saturated two-phase medium, and the pile is modeled as a one-dimensional Euler bar. Considering wave scattering effects in the pile-soil system, the resultant soil displacements are expressed as the sum of scattered and free-field displacements. Based on the Biot’s dynamic consolidation theory, the governing equations of scattered and free-field soils are formulated, and expressions for the displacements and frictional forces of outer and inner soils are subsequently derived. Analytical solutions for the vertical seismic response of end-bearing pipe piles in saturated soil are obtained by incorporating soil frictional forces into the governing equation of the pipe pile and applying continuity and boundary conditions of the pile-soil system. The proposed solution is verified by comparing it to existing studies. Parameter analyses are conducted to examine the differences in seismic response of pipe piles in saturated versus single-phase soil and to investigate the influence of major pile-soil parameters in saturated soil on the seismic amplification factor at the pile top, kinematic response factor, and frictional forces of outer and inner soils.

Upon completing large-area layered filling, the foundation soil exhibits transverse isotropy and is predominantly unsaturated, making post-construction settlement prediction challenging. Additionally, the creep model considering transverse isotropy and unsaturated characteristics has not been proposed. Therefore, the true triaxial apparatus for unsaturated soil was enhanced, and transversely isotropic unsaturated loess samples were prepared. The relationship between matrix suction and moisture content at various depths in transversely isotropic unsaturated loess was determined using soil-water characteristic curve tests. The creep characteristics of loess fill under varying moisture content, degree of compaction, deviatoric stress, and net confining pressure were examined using a consolidation drainage test system. According to the creep curve, the expressions for six parameters in the modified Burgers element model were determined, establishing a post-construction settlement prediction method for transversely isotropic unsaturated loess fill foundations. The results show that the transversely isotropic unsaturated loess exhibits distinct creep characteristics, primarily nonlinear attenuation creep. The degree of compaction, moisture content, deviatoric stress and net confining pressure significantly affect its creep characteristics. Creep stability strain is linearly related to the degree of compaction. Enhancing soil compaction can effectively reduce post-construction settlement of the fill foundation. A prediction algorithm based on the modified Burgers model, which reflects the influence of degree of compaction, moisture content, and stress level, and accurately describes the post-construction settlement behavior of transversely isotropic unsaturated loess fill foundations, is established. Actual engineering monitoring results demonstrate that the proposed settlement prediction algorithm is simple, practical, and effective. The research results can enrich and advance the creep model of unsaturated soil, and provide a scientific basis for solving the problem of deformation calculation of high fill foundation.

To characterize the distribution law of vertical earth pressure for a trench-buried culvert, backfill soils were subdivided into distinct regions with varying effects of the soil arching direction, which referred to the analytical method of vertical stress for silo granular materials. The formula of vertical earth pressure for a trench-buried culvert was then presented based on the binomial distribution mode for backfill soil load transfers, and its application steps were outlined along with determining both the load transfer coefficient and the height of an equal settlement surface. Finally, discussions were carried out on the thin layer thickness, comparing verifications, and influencing factors. The results show that the proposed formula of vertical earth pressure with the maximum uniform thickness of thin layers is not only straightforward and practical without complex integrals, but also it reasonably accounts for comprehensive influences of soil arching, backfill soil partitions, load transfers, and an equal settlement surface. The validity of the proposed formula is demonstrated by comparing it with the theoretical formula, model tests, and numerical simulations. At the culvert top, the vertical earth pressure increases with increasing the trench width or the backfill soil height, and its distribution is not uniform on the horizontal plane. However, it changes in contrast to that of the load transfer coefficient, when the internal friction angle of backfill soils increases. In addition, the height of the equal settlement surface is not constant, and it should be evaluated against the backfill soil height to choose the proposed formula under different conditions.

Slip zone soil, a crucial factor in landslide stability, is essential for understanding the initiation mechanisms and stability assessment of reservoir bank landslides. This study investigates the strength characteristics of slop zone soil under drying-wetting (D-W) cycles to inform research on reservoir bank landslides. As an illustration of this phenomenon, the Shilongmen landslide in the Three Gorges Reservoir serves as a case study. Taking into account the impact of both D-W cycles and the overlying load on the soil, the strength characteristics of the slip zone soil are investigated. Experimental results show that slip zone soil exhibits strain softening during D-W cycles, becoming more pronounced with more cycles. D-W cycles cause deterioration in shear strength and cohesion of slip zone soil, especially in the first four cycles, while the internal friction angle remains largely unchanged. The compaction effect of the overlying load mitigates the deterioration caused by D-W cycles. The findings reveal the weakening pattern of mechanical strength in slip zone soil under combined effects of overlying load and D-W cycles, offering valuable insights for studying mechanical properties of slip zone soil in reservoir bank landslides.

Grouting is a widely used and effective method to enhance the strength of soft, fractured surrounding rock and maintain engineering stability. In order to evaluate the impacts of grouting on mechanical properties and fracture damage of coal and rock, uniaxial compression tests were conducted on samples before and after ultrafine cement grouting. Digital image correlation and acoustic emission technologies were employed to monitor damage evolution and crack growth in coal and rock. The process of crack tip grouting expansion was discussed using fracture mechanics theory. The results show that: 1) Compared to intact coal samples, the strength increase post-grouting. Coal samples with more cracks exhibit lower strength, potentially due to stress concentration at crack tips. 2) Post-grouting, internal pores in the coal sample are filled, reducing brittleness and enhancing plasticity and deformation resistance. However, grouting minimally affects post-peak deformation, and the cementation between grout and coal is suboptimal. 3) The failure of intact coal samples primarily exhibits a single high-strain concentrated zone. In grouted coal samples, grouting enhances the isotropic of the mechanical properties failure lacks a in distinct strain concentrated zone, and strain evolution is relatively disordered. 4) The horizontal displacement damage factor Dw is proposed to characterize the damage evolution degree of coal under uniaxial load, the horizontal displacement damage variable is defined, and the damage piecewise constitutive model for uniaxial compression coal sample is established.

In order to obtain the temperature field evolution in the mud silo during the freezing process for shield rescue, a model test of horizontal freezing inside the shield was designed based on similitude theory. This was applied to the tunneling project in the Yangtze River corridor of the Xinjizhou water supply pipeline in Jiangning District, Nanjing. The temperature evolution and distribution characteristics in the mud silo during freezing were studied, leading to the following conclusions. Firstly, using 20 freezing pipes arranged through geological exploration and grouting holes, the slurry chamber of the shield (diameter 6 480 mm) could be completely frozen within 75 days, with a maximum pipe spacing of 3.12 m. After 135 days of freezing, the average temperature of the frozen soil in the slurry chamber reached −13 ℃, with a longitudinal temperature difference of approximately 4.4 ℃. The overall freezing effect was uniform, meeting the water sealing and bearing requirements for shield chamber opening, thus facilitating shield rescue construction. Secondly, temporary suspension of freezing during construction led to temperature redistribution in the frozen soil of the slurry chamber. A 10-hour suspension caused the frozen wall temperature to rise to −14 ℃ to −10 ℃, but it returned to its pre-suspension state after 20 hours of resumed freezing. Thirdly, 45 days post-freezing, the average temperature of the frozen soil in the shield slurry chamber rose to −4 ℃, meeting the requirements for shield re-pushing construction. It took about 20 days for the frozen soil temperature at the freezing pipe position to rise back to 0 ℃, remaining around 0 ℃ for approximately 125 days. During construction, auxiliary measures like forced thawing or circulating mud can accelerate the thawing of frozen soil in the shield’s slurry chamber. The horizontal freezing method in tunnels is an effective technique for improving formation to construct a maintenance environment in the shield chamber.

Slope topography can significantly amplify seismic effects, threatening the seismic safety of pile foundations on slopes. To elucidate the mechanism by which slope topography affects pile foundation vibration, an analytical method is proposed to solve the dynamic response of slope-pile under SH wave incidence. Firstly, based on the wave function expansion method, the free field displacement of slope soil under SH wave with arbitrary incident angle is solved. Then, the interaction between pile and vibrating soil is simulated by the beam on Pasternak foundation model, and the dynamic response of pile is solved by applying the boundary conditions of pile foundation. The calculation results are compared with the finite element simulation results, showing good agreement, which effectively verifies the method’s accuracy. The effects of pile-soil modulus ratio, pile slenderness ratio, slope gradient and SH wave frequency on the vibration of slope-pile system are examined through parameter analysis. The results show that the topographic effects significantly increase pile foundation vibration when the pile-soil modulus ratio (100) is low, the pile slenderness ratio (10) is low, at specific slope gradients (90°, 150°), and specific vibration frequencies. This study provides a scientific basis for further improving the seismic design theory of slope bridge piles in high-intensity mountainous areas in the west.

Through several centrifugal model tests and result analyses, the characteristics of bearing capacity failure envelope of pile foundations under horizontal, vertical and bending moment loads (H, V, M) were studied. The research results indicate that: vertical and horizontal loads affect each other. When the pile foundations are subjected to combined vertical and horizontal loads, the interaction between these loads must be considered in the design. The H-V failure envelope curve of pile foundation is approximately elliptical, with the center not at the origin but located on the upper half of the V-axis, biased towards the downward load. The failure envelope curve equation can be expressed mathematically. This curve on the V-H load plane helps determine the safety state of the pile foundation. The spatial failure envelope surface under the combined action of horizontal load H, vertical load V, and bending moment load M is approximately ellipsoidal, with the center not at the V-H-M origin but on the upper half of the V-axis. The spatial failure envelope surface of pile foundation bearing capacity provides a basis for judging and verifying whether the pile foundation is in a safe state under horizontal load H, vertical load V, and bending moment load M. Utilizing failure envelope surface addresses some shortcomings of traditional design methods, making it a reasonable and necessary approach in pile foundation design.

High-intensity wave loads in marine environments can induce stress changes in the seabed soil surrounding piles, affecting the bearing capacity of the embedded sections of single piles. Consequently, the wave-induced dynamic response of the seabed significantly affects the horizontal impedance of single piles in marine environments. This study models ocean waves as harmonic waves of specific frequencies and analyzes the seabed soil’s dynamic response under linear wave loads using a fully dynamic (FD) model based on the soil’s porous elastic assumption. The seabed soil’s dynamic response results in a horizontal external load on the pile section. An analytical solution for calculating the horizontal impedance of a single pile is proposed using the Winkler foundation and Euler beam models to simulate the pile-soil system, and the transfer matrix method to address soil stratification. This formula comprehensively considers the impact of wave-induced seabed dynamic response on the pile’s horizontal impedance. The validity of this method is verified through comparison with previous experimental results. Finally, the primary factors affecting the horizontal impedance of single piles under seabed dynamic response conditions are analyzed. The results show that the horizontal dynamic impedance of single piles in marine environments is related to wave intensity, pile diameter, and seabed soil parameters. The impact of seabed dynamic response on the horizontal impedance of single piles is mainly characterized by a wave in stiffness K_h and an increase in damping C_h within a certain frequency range. Outside this range, the pile impedance is similar to result obtained without considering the seabed dynamic response. Additionally, the impact frequency range expands with increasing pile diameter, pile-soil stiffness ratio and permeability coefficient.

To enhance the effectiveness of the enzyme-induced carbonate precipitation (EICP) technique in solidifying aeolian sand, EICP was combined with polyacrylamide (PAM). Initially, the effects of PAM on urease activity and calcium carbonate production were examined, followed by determining the optimal PAM concentration through sand solidification tests. A wind tunnel test compared the wind erosion resistance of aeolian sand solidified by EICP and EICP+PAM, while the impacts of PAM on EICP water retention and absorption were also assessed. The results show that PAM has a minimal effect on urease activity and calcium carbonate production within the studied concentration range (0−1 g/L). As PAM concentration increases, the surface strength and crust thickness of sand specimens initially rise and then decline. When the PAM concentration is 0.6 g/L, both parameters reach their maximum, identifying 0.6 g/L as the optimal PAM concentration. The wind erosion resistance of sand solidified by EICP+PAM is superior to that of sand solidified by EICP alone. The wind erosion rate of EICP+PAM solidified sand is merely 13.28 g/(m²·min) at a wind speed of 30 m/s. Additionally, the surface crust of PAM-enhanced solidified sand provides improved water retention and long-term stability, suggesting that combining PAM with EICP technology effectively enhances the performance of solidified aeolian sand.

The construction of underground powerhouses for hydropower stations has always been a focal point and challenge in design and construction due to their large scale, high side walls, extensive spans, and complex geological conditions. This study relies on the Shuangjiangkou hydropower station, known for having the highest geostress globally, to investigate the engineering issues related to hard rock deformation and failure under extremely high stress, along with stability control methods. The research is divided into two main aspects: Firstly, we estimate and adjust the in-situ stress field of underground caverns in deep-cut valley areas using limited geostress test data and the brittle failure phenomena observed in the pilot tunnels. Secondly, we examine the typical failure phenomena of underground caverns under extremely high stress, including global issues from high-stress failure and block instability due to localized rock veins cutting, along with corresponding failure mechanisms and control measures. The findings offer valuable case studies and references for constructing large underground caverns in high-stress hard rock environments.

Uniaxial compressive strength σ_cm of rock mass is a crucial mechanical parameters affecting the excavation and support optimization of tunnel boring machine (TBM) surrounding rock. To rapidly and accurately evaluate in-situ rock mass mechanical parameters in TBM engineering, a comprehensive TBM database with 159 sets of rock mass characteristics, tunneling parameters, and technical indexes was developed from four typical long-distance hard rock tunnels in China. Additionally, the specific energy SE_TBM theoretical equation, suitable for the TBM cutterhead rock breaking system, was proposed and derived. The empirical model between SE_TBM and σ_cm was established, and its validity was verified and discussed. The results show that, compared to FPI, SE_TBM effectively eliminates the influence of varying TBM excavation parameters and technical indexes, serving as a new reliable index for accurately evaluating rock mass excavatability. The empirical relationship of uniaxial compressive strength of rock mass derived from four rock mass classification criteria demonstrates strong performance (coefficient of determination R²>0.84), with the prediction model based on rock mass integrity index K_v exhibiting the best performance. The new model’s average relative error for predicting uniaxial compressive strength of rock mass, modified by upper and lower limit equations, is 11.37%, indicating high overall prediction accuracy. Utilizing extensive TBM tunneling parameters offers a novel approach to quickly estimate the uniaxial compressive strength of in-situ rock mass.

 To address the challenge of absorbing outgoing waves in geotechnical dynamic analysis, an explicit mixed finite element time-domain perfectly matched layer (PML) based on the central difference integration scheme is proposed. The two-dimensional and three-dimensional semi-discrete finite element equations suitable for explicit integration were derived. A two-dimensional stress-displacement mixed element Q4/4 and a three-dimensional stress-displacement mixed element HEX8/8 were developed for spatial discretization. An extended central difference explicit integration scheme was proposed to solve the third-order dynamic equations arising from the three-dimensional PML formulation. The implementation was carried out in ABAQUS/Explicit, and several numerical experiments were conducted to analyze the absorption performance of the artificial boundary under varying conditions, including soil types, wave types, wave frequencies, and boundary thickness. The results indicate that the PML achieves conditional convergence under all computational conditions. When the PML thickness exceeds 10 elements, the normalized root mean square deviation between the truncated and enlarged model responses is less than 2%. The proposed integration scheme and numerical implementation exhibit good stability and computational accuracy. For different soil types, the PML demonstrates excellent absorption performance for outgoing waves of various types and frequencies. The research findings have broad applications in the geotechnical dynamic analysis.

The soil-rock mixture is a heterogeneous material consisting of high-strength rocks and a low-strength soil matrix, with complex interactions among its mesoscopic components under loading. Considering the mesoscopic structural characteristics, the interface between soil and rock, as well as the interior of the soil matrix, are identified as the material’s weak points. Using the cohesive model, the initiation, expansion, and fracture of cracks at weak points are described, and a cohesive element insertion program is developed. Subsequently, using the results of direct shear tests, the material parameters for the cohesive elements in the soil matrix and at the soil-rock interface are determined. A mesoscopic numerical method for soil-rock mixtures based on the cohesive model is then established. Based on this, biaxial compression numerical tests on soil-rock mixtures with varying mesoscopic structures were conducted. The influence of different mesoscopic factors on mechanical properties was clarified by analyzing the failure state of cohesive elements. Results indicate that the maximum nominal stress in shear direction of cohesive elements can be determined by the peak shear stress of the load-displacement curve in direct shear tests. The maximum effective displacement is determined by one-fifth of the maximum shear displacement, and the tangential friction coefficient is calculated by the ratio of residual shear stress to normal stress. The numerical method based on cohesive elements can effectively describe the mechanical properties and deformation behavior of soil-rock mixtures, particularly for the strain softening behavior under low confining pressure.

To investigate the impact of rainfall on the stability of granite residual soil slopes, indoor model box tests were conducted at three rainfall intensities (30, 60, 90 mm/h) and two rainfall durations (3, 12 h). The variations in wetting front and vertical displacement were monitored. PFC discrete element software was used to simulate direct shear tests of granite residual soil, calibrate the mesoscopic parameters of granite residual soil for varying moisture contents, and develop a discrete element slope model. The analysis concentrated on the displacement and rotation fields, instability indicators, force chains, and fabric anisotropy to reveal the mesoscopic deformation and mechanical mechanisms underlying slope instability in the model box tests. The results show that when the rainfall intensity reaches 60 mm/h or above, the slip and disturbance range of the slope expand significantly, and the slip body exhibits a circular arc shape along the slope face. The slip loss rate of the slope initially decreases and then increases with prolonged rainfall; short-term low-intensity rainfall can stabilize the slope, but continuous rainfall significantly increases the slip loss rate. After 9 hours of rainfall, the displacement and rotation angle of soil particles in the slope increase markedly, forming a distinct circular arc slip failure surface. Furthermore, after 9 hours of rainfall, the distributions of force chains and contact force anisotropy within the slope change significantly, with force chains on the slip surface breaking and densely concentrating in stable regions.

To address the challenges in rock acoustic emission localization, such as difficulty in picking up arrival times and unsolvable equation systems leading to low accuracy and even inability to locate, a novel localization algorithm was proposed. This algorithm is based on vector auto regressive -Akaike information criterion (VAR-AIC) time-of-arrival pickup and integrates an intelligent optimization algorithm. The improved VAR-AIC method enhances arrival time accuracy by utilizing instantaneous frequency to define the arrival time range and selecting a feature function for precise determination. The nonlinear positioning equations are transformed into an objective function using the Newton-Raphson method, enabling iterative solutions through optimization algorithms. Broken lead test results indicate that the VAR-AIC method significantly enhances acoustic emission arrival time pickup accuracy by determining the arrival time range through instantaneous frequency and selecting the feature function for precise determination. Comparing the performance of the atomic orbital search, gray wolf, and adaptive particle swarm algorithms reveals that the atomic orbital search algorithm not only ensures localization precision but also accelerates iteration speed. Consequently, a rock acoustic emission localization method of improve vector auto regression -Akaike information criterion-atomic orbital earth (IVA-AOS) combining VAR-AIC accurate time-to-time pickup and the atomic orbital search algorithm was proposed. Compared to traditional methods like the mutual correlation+Geiger algorithm, Newton iterative algorithm and PCI-Express8 machine self- contained algorithm, the IVA-AOS localization algorithm exhibits smaller localization errors and higher precision. This innovation effectively addresses the frequent unsolvable cases in traditional localization algorithms, offering new insights and methodologies for rock acoustic emission localization.