Desaturation method is an innovative method to reduce the liquefaction risk of sandy grounds. The mechanism is to reduce soil saturation by introducing gas into soil pores, thereby increasing liquefaction resistance. This method provides a simple but economical solution to liquefaction of sandy soils. However, the long-term stability of the unsaturated state of the treated sand is a critical issue affecting the anti-liquefaction efficacy and economical efficiency of the desaturation method, and there are few related studies currently. In this study, an originally saturated sandy ground was desaturated by electrolytic desaturation method, and the change in saturation was investigated under different conditions, including hydrostatic and hydraulic gradient flow conditions. Additionally, the effects of hydraulic gradient, particle size distribution, relative density, and initial saturation degree on the saturation change of the specimens were analyzed. The results show that pore-water seepage gradually increases the saturation degree of the specimens until it stabilizes. A larger hydraulic gradient yields a higher final stable saturation degree. Under the same seepage conditions, smaller relative density and finer particle size lead to smaller final changes in saturation. In addition, decreasing the saturation of the specimen after electrolysis reduces the final stable saturation degree.

The red mud has a huge stock and high increase, which brings serious problems such as safety, environmental protection and land occupation. To expand red mud resource utilization and advance green composite foundation technology, we propose a red mud–fly ash geopolymer (RFG) pile technology. This study evaluated the material preparation, construction method, pile quality, vertical bearing characteristics, and environmental impact of the RFG pile, based on laboratory tests, an in-situ pile installation test, and a static load test on a silty-clay foundation. The results show that: 1) RFG piles can be formed by pumping and underwater casting using conventional wet drilling. When the mass ratio of red mud: fly ash: medium sand: gravel: blast furnace slag powder is 1:2:2:4.94:0.1, with a liquid-solid ratio of 0.55, the RFG mixture exhibits good workability suitable for pumping and underwater pouring. The slump can be controlled in 220−225 mm, and the strength can reach 13.9 MPa after 28 days of curing at room temperature. 2) RFG piles exhibit strong compressive bearing performance. For a single RFG pile 10 m long and 0.52 m in diameter, the vertical ultimate bearing capacity is 753 kN; the bearing capacity of a single-pile composite foundation with a spacing of 3 diameters is 240 kPa. 3) On-site formation quality of the RFG pile is good, and core samples collected along the pile length are largely intact. The coring rate of the six piles is more than 99%, and the compressive strength of the core samples at different depths is more than 10 MPa, up to 19.5 MPa. 4) The implementation of RFG piles has no adverse impact on the quality of surrounding water bodies and has not changed the evaluation results of groundwater corrosivity. The research results lay a foundation for the engineering application of RFG pile, and also provide a new idea for improving the utilization rate of red mud

To ensure the stability of the borehole surrounding rocks during geothermal energy extraction and improve the efficiency of the process, single radial compression mechanical tests were conducted on energy-storing granite with internal sleeves. Using multiple monitoring devices, including the VIC-3D non-contact full-field strain system, a static strain testing and analysis system, this study investigated the damage characteristics and internal energy evolution of the borehole surrounding rocks under complex geological conditions such as high temperature and thermal cycling. Additionally, a failure criterion was established. The results indicate that the load-displacement curve of the single radial compressed energy-storing granite with internal sleeves exhibits a distinct pre-peak concave segment and linear segment under various conditions. Post-peak behavior is influenced by the sleeve and rock heterogeneity, showing two patterns: a rapid steep drop, or a drop followed by recovery, or leveling off before dropping again. The final failure mode is fragmentation into three or four pieces. Damage initiates with cracks at the inner borehole wall, parallel to the loading direction, followed by cracks at the outer borehole wall, perpendicular to the loading direction. Adding sleeves reduces crack width; fracture morphology and crack growth are partly influenced by the bonding between the rock sample and the sleeve. Energy evolution analysis reveals that the total pre-peak energy grows exponentially. We analyzed the relationship between energy and sleeve thickness by examining the proportions of elastic and dissipated energy relative to total pre-peak energy. A sleeve thickness of 1.0−1.5 mm provides the optimal enhancement. Based on theoretical analysis, we developed a failure criterion for energy-storing granite with internal sleeves and validated its accuracy.

The penetration response of cone penetration test (CPT) depends on the stress and density states of sand and is also influenced by the non-linear stress-strain relations of soils from very small (10−5) to relatively large (10−1) strain levels. Accounting for these key soil behaviours is crucial for accurate numerical simulations of CPT responses. For this purpose, an intergranular strain (IGS)-based elastic model is introduced into a state-dependent plasticity model to capture the full-strain-range non-linearity behaviour of sand. A numerical model of the CPT penetration process is then established by combining the aforementioned constitutive model and the arbitrary Lagrangian-Eulerian (ALE) large deformation finite element technique. The latter is adopted to handle the problems of large deformations of soil and mesh distortion. Then the computed response of CPT is compared with 1g test observations, and the numerical model is utilized to analyse the influences of the full-strain-range non-linearity behaviour of sand on the penetration response of CPT. The results indicate that the non-linear stress-strain relations at small strains can have noticeable impacts on the tip resistance of CPT, in particular for loose sand, while having a relatively small influence on the penetration depth required to reach a steady-state penetration resistance. The above influences might be attributed to a rapid decay of soil strains with the distance from the cone tip, and consequently high stiffness and strong constraints effects of far-field soils on core soils adjacent to the cone tip. Furthermore, this paper explores the strong constraint effects of far-field soils through the analysis of the cavity expansion problem, highlighting the significance of full-strain-range non-linearity of sand in addressing large deformation issues related to deep compression failure.

The enzyme-induced calcium carbonate precipitation (EICP) technique strengthens soil and reduces permeability by cementing soil particles with calcium carbonate. However, limited penetration of solutions between soil particles hinders cementation in saturated environments, necessitating systematic investigation of EICP reinforcement in underwater, unconsolidated sandy layers, such as seabed and lakebeds. In this study, we developed a model test system for underwater EICP grouting and implemented controlled pore-water flow in underwater sandy layers using a perfusion–drainage liquid cycle. During EICP reinforcement, we measured the conductivity, pH, and Ca²⁺ concentration of the reaction solution in embedded and drainage pipes to characterize changes in mineralization efficiency in saturated sand. Additionally, by tracking the model’s overall permeability as a function of reinforcement cycles and applying electrical-resistance tomography, we systematically characterize reinforcement effects and the spatiotemporal evolution of grout diffusion in underwater sands. 1) The perfusion–drainage system enables EICP grouting reinforcement in water-rich sandy layers. The saturated-sand permeability decreases from 1.28×10⁻² m/s to 9.66×10⁻⁵ m/s after 10 EICP treatments. 2) The slurry diffuses from both sides of the grouting pipe toward the center pumping pipe, with high conductivity, low pH, and Ca²⁺ enrichment, indicating continued diffusion and mineralization as resistivity declines toward stabilization and pore space becomes filled. 3) Resistivity varies significantly with depth and location, indicating uneven reinforcement in large-scale soil masses. These findings provide a theoretical basis for applying EICP technology to seabed foundation reinforcement and submarine landslide mitigation.

The counterpressure pile sheet retaining walls are a novel type of slope support structure. Although engineering practice has demonstrated their excellent performance, systematic studies on their deformation characteristics and mechanical behavior remain limited. Through model tests comparing counterpressure piles and cantilever piles, this study investigates the evolution of pile-top displacement, pile deformation, internal force distribution, and earth pressure during the sandy backfill process. Key findings are as follows: (1) The top displacement of the cantilever pile was 81.76 mm, which is 6.69 times that of the counterpressure pile (12.22 mm), resulting in cracking in the soil mass 51 cm horizontally away from the pile top. (2) The counterpressure pile exhibits a typical S-shaped distribution of bending moment, with a distinct reverse bending phenomenon and a reduction in the peak moment. (3) The excessive deformation of cantilever piles leads to an increase in the gravitational component of soil weight perpendicular to the pile shaft direction. The soil pressure on the counter-pressure pile is about 15% lower than that on the cantilever pile, reflecting its good stress redistribution ability. (4) Three primary working mechanisms are identified: provision of anti-overturning moment through soil reaction on the counterpressure plate, enhancement of horizontal resistance via friction between the plate and soil, and increase of passive earth pressure in front of the pile. The counterpressure platform significantly enhances overturning resistance, mitigates slip, and improves long-term structural stability. These findings offer experimental validation and a theoretical basis for optimizing counterpressure pile sheet retaining wall designs.

Deformation of the deposit bank slope is intensified due to reservoir water regulation and rainfall, threatening reservoir operation. To investigate the deformation and failure mechanisms of bank slopes, as well as their infiltration characteristics, a large-scale physical model test was conducted to simulate rainfall and its interactions with water level fluctuations at the Sanbanxi Reservoir in Guizhou Province. The parameters such as pore water pressure in slope and the whole process of slope deformation evolution are obtained. The results show that: (1) The final shape of the modeled wetting front is determined by the slope shape, and the different infiltration effects are mainly manifested in the change of migration depth, and the seepage field characteristics and slope gradient have a greater influence on the migration rate. (2) The soil pressure curve changes gently under both conditions, the pore water pressure changes with a lag, and the soil pressure and pore water pressure in the deeper layers of the slope body fluctuate more than those in the shallower layers in the saturated state. (3) Slope deformation during rainfall is dominated by erosion pits and localized slides, while erosion channels dominate during coupling, and the scale of slope erosion during coupling is about twice as large as that during rainfall, but multi-stage slip traction damage occurs at the foot of the slopes in both conditions. (4) Based on the experimental results, the deformation and damage mechanism of the modeled bank slope under the coupled rainfall and water level is summarized into five stages: softening and settling of the slope surface, development and expansion of erosion gullies, and development of erosion channels and collapse at the foot of the slope. The results of this study fill the gap in the study of bank slope stability under the above conditions in Sanbanxi Reservoir area, and it is useful for the study of similar deformation damage of gravel soil bank slopes and their prevention and control.

The use of catalysts under high-temperature steam conditions enhances oil shale pyrolysis efficiency and increases the permeability of flow channels, serving as a prerequisite for the industrialization of in-situ thermal extraction of oil shale. An experimental approach was used to investigate how catalysts affect microscopic pore-structure parameters and the extent of damage to oil shale during high-temperature steam pyrolysis. We independently constructed the oil shale pyrolysis experimental system, and results show that adsorption capacity, specific surface area, pore volume, and mechanical properties vary with catalyst concentration. The main conclusions are as follows: (1) The mass loss rate of oil shale treated with MnSO4 and CrCl3 solutions increases significantly relative to untreated shale, by up to 6.9% and 4.7%, respectively. As catalyst concentration increases, oil shale pores become predominantly small mesoporous (2−10 nm); the Barrett–Joyner–Halenda (BJH) pore volume and specific surface area increase. Owing to the predominance of small mesopores, the average pore size initially increases and then decreases. The fractal dimension decreases. (3) Catalytic pyrolysis reduces the elastic modulus of oil shale to varying degrees, with greater deterioration at higher catalyst concentrations. The maximum decreases in elastic modulus are 2.43 GPa and 3.35 GPa, respectively, and the corresponding peak energy-storage densities are below 0.12 MJ/m3. Higher catalyst concentrations lead to more extensive pyrolysis, with weaker energy absorption, storage, and release, and greater energy consumption

Solute ions migrate, collide with and associate with both free water and bound water, indicating a virtual semi-permeable membrane effect in pore water. Electrostatic attraction draws some mobile ions into bound water, converting them into immobile ions. Spatially nonuniform ion distribution creates a chemical potential in pore water, causing a discrepancy between the actual pore-water pressure and its measured value in unsaturated saline soil. Therefore, the effective osmotic suction is used to characterize the chemical factors to describe the mechanical behavior of unsaturated saline soil. By clarifying the types and characteristics of pore water and ions in soil, considering the non-movable ions in liquid water, the calculation method of effective osmotic suction is determined by a representative elementary volume (REV). The contribution of chemical potential in pore water to Gibbs free energy of gas-liquid interface is analyzed. Based on soil-skeleton stress-balance analysis and the fact that the surface tension of the gas–liquid interface satisfies the Young–Laplace equation, we propose a generalized effective-stress equation for unsaturated saline soil that accounts for capillary and physicochemical effects. For loess with varying salinity and matric suction, isotropic compression and shear tests under controlled suction were conducted using an unsaturated true-triaxial apparatus. The relationship between the effective stress and isotropic deformation, the shear strength under different intermediate principal stress parameters of the saline loess is obtained, and the accuracy of the generalized effective stress equation is verified.

The permeability of coral sand is related to the formation of freshwater lenses in blown-in islands and reefs, and is an important parameter describing the permeability characteristics of reef sand strata, which is of great significance to the sustainable development of islands and reefs. The permeability of coral sand is affected by the percolating solution pH and permeation duration in addition to the particle size, gradation, and pore characteristics. To investigate the effects of permeate duration, particle size and gradation on the permeability of coral sand in different pH environments, we carried out conventional permeability tests, and analyzed the changing rules of mineral content and particle fraction of the sand columns before and after the tests by using D8Advance X-ray diffractometer and laser particle sizer. Results show that, under neutral percolating solution and fixed porosity, the initial hydraulic conductivity increases with the effective grain size. The initial hydraulic conductivity coefficient and the curvature coefficient follow a negative logarithmic relationship, while the initial hydraulic conductivity coefficient and the uniformity coefficient follow a logarithmic relationship. Under acidic conditions, hydraulic conductivity has a quadratic relationship with time; under neutral conditions, hydraulic conductivity remains largely unchanged. The increase in hydraulic conductivity intensifies as pH decreases. In acidic environments, the calcite content of coral sand increases, while aragonite, calcium and magnesium calcite, and rock-salt contents decrease; mineral changes are not obvious under neutral conditions. The percolating solution first passes through a layer with a significantly increased fine-particle content; under the same layer conditions, a lower pH leads to a more pronounced increase in the fraction of fine particles. We developed a preliminary regression-based model to predict the initial and final stabilized hydraulic conductivity. A machine-learning model incorporating time effects and percolating solution pH was also developed. These models can be used to assess reef-sand permeability and to analyze the evolution of freshwater lenses.

To investigate the creep characteristics of loess, we conducted consolidation–drainage triaxial creep tests on undisturbed Malan loess at different moisture contents, while monitoring axial, radial, and volumetric deformations throughout. The test results show that the creep deformation of Malan loess with different moisture contents is characterized by axial compression, radial expansion, volume compression, and then axial accelerated compression, radial accelerated expansion, and volume accelerated compression to damage. Based on the mechanical response and microstructural evolution of loess under creep, we conclude that creep macroscopically reduces loess strength and increases deformation, while microscopically causing structural damage to the soil. The mechanism involves three synergistic effects—water-induced reduction of interparticle resistance, load-induced space release, and time-dependent processes—that promote creep-slip of soil particles. Based on memory-dependent derivatives and damage mechanics, we propose a creep-damage constitutive model. The applicability of the new model has been verified by fitting the theoretical model to the creep test data. These results deepen our understanding of loess creep and have practical value for the long-term safety assessment of loess engineering.

The soils in the hydro-fluctuation zone on the Three Gorges Reservoir are exposed to dynamic environments of long-term wet-dry cycles and suction variations, leading to its changes in their unsaturated shear strength and failure modes. This study investigates the effects of wet-dry cycles on the unsaturated shear strength characteristics of red soil in the hydro-fluctuation zone of a landslide area on the Three Gorges Reservoir, using nuclear magnetic resonance (NMR) and triaxial shear tests. The study also reveals the variation in the critical saturation at which the failure mode transitions from strain-softening to strain-hardening. Results indicate that matric suction significantly contributes to shear strength at low saturation levels, exhibiting obvious strain-softening and shear failure characteristics. Under high saturation conditions, the soil exhibits strain-hardening and swelling failure characteristics. Taking into account pore-size distribution and suction, we propose a critical-saturation model for the transition from strain-softening to strain-hardening. The model’s applicability and reliability are verified through a comparison of predicted results and experimental data. The critical saturation degree increases with the number of wet-dry cycles, suggesting that the repeated wet and dry cycles cause particle rearrangement, destruction of the original aggregates, and the evolution of the pore structure from dense to loose. The increase in pore size requires a higher saturation state to form continuous water distribution, causing the transition from shear failure to swelling failure.

For the safety and long-term stability of underground engineering, it is important to clarify the shear time-dependent performance of deep-seated anchored and filled jointed rock masses. Shear creep tests on anchored and filled jointed rock masses under constant normal stiffness (CNS) boundary conditions were conducted, and the influence mechanisms of different combinations of filling degree Δ, joint roughness coefficient JRC, filling material strength σ_cj , and normal stiffness kn on the tangential and normal creep characteristics of the anchored and filled jointed rock masses were analyzed. A fundamental relationship equation among macroscopic stress difference, mesoscopic stress, and time was established. Combined with mesoscopic computed tomography (CT) experiments, the evolution law of pore volume fraction was analyzed. On this basis, an improved nonlinear shear creep equation of the Nishihara model considering the combination of macroscopic and mesoscopic scales was established. The research results indicate that: 1) The four influencing factors of Δ , JRC,σ_cj  and k_n mainly lead to the differential evolution of the climbing-shearing behavior between rough asperities and the wear behavior of the filling material, which in turn affects the tangential and normal creep characteristics of the anchored and filled jointed rock masses; 2) Δ  is the main factor affecting the tangential creep performance of the anchored and filled jointed rock masses, and the influence degrees of JRC, σ_cj and k_n  on the tangential creep performance of the anchored and filled jointed rock masses are relatively close; 3) A localized coordinated deformation failure mode of the anchoring-induced compression and fragmentation zone was proposed to reflect the overall time-dependent deformation evolution characteristics of the anchored and filled jointed rock masses; 4) An improved Nishihara nonlinear creep model was constructed, and its parameters were verified and subjected to global sensitivity analysis. The model can effectively describe the accelerated creep stage of anchored and filled jointed rock masses and can provide theoretical guidance for the long-term structural slip failure prediction of deep-seated rock masses.

Laboratory testing has become the most direct and accurate method for determining the mechanical properties of rocks. The mineral-rock multiscale analysis technology, using digital core modeling and discrete element simulation, reveals the regulatory mechanism of microscopic mineral mechanical parameters on macroscopic engineering responses, providing a theoretical tool for the assessment and prevention of geological disasters. Nanoindentation is an important technique for studying micromechanics, and current nanoindentation studies on rocks focus mainly on shale and granite; few studies address basalt, gneiss, schist, slate, or other rocks, and little is known about whether the same rock-forming mineral exhibits different micromechanical properties across rocks. In this study, the compositions, contents, apparent morphology and micromechanical properties of the main rock-forming minerals in ten categories of rocks are obtained by means of powder X-ray diffraction test, optical microscope surface observation, electron probe test and nanoindentation test, and the suitable peak loads of different rock-forming minerals for nanoindentation test are selected experimentally. A large body of literature on nanoindentation is compiled to compare the micromechanical properties of the same mineral across rocks and to reveal underlying causes. The indentation results indicate a significant linear relationship between fracture toughness and the elastic modulus; the relationship with hardness is not statistically significant. The appropriate peak load for quartz, potassium feldspar and plagioclase is 7 mN, that for mica is 3 mN, and that for calcite and dolomite is 4 mN. Nanoindentation curves differ substantially among minerals. Quartz data show the least dispersion, followed by potassium feldspar; plagioclase, dolomite, and calcite exhibit moderate dispersion. Compared with published studies, the granite data show strong concordance; for other rocks, the results can guide the selection of nanoindentation parameters. This further provides a basis for parametric modeling of rocks from the perspective of micro-mechanical properties, which is of great significance for studying the micro-macro mechanical behavior of rocks. In addition, in combination with environmental geology and sustainable development needs, multi-scale analysis technology can reveal the mechanical response mechanism of minerals and rocks in complex environments, further expanding its application prospects in the development of new energy materials and ecological restoration engineering.

We conducted a one-dimensional vertical infiltration test on a loess soil column considering the effects of vibration to examine how combinations of vibration frequency and amplitude affect the temporal variation of volumetric water content and the evolution of the wetting front. Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests were used to reveal microscopic evolution. Using the experimental data, we determine the unsaturated permeability coefficient of loess with three methods—the VG-M model, the wetting-front advancement method, and the instantaneous-profile method—and perform a comparative analysis. The results indicate that vibration accelerates the water infiltration rate. Under vibration, the depth of the wetting front increases with higher vibration frequencies, and the time required to transition from unsaturated to stable infiltration decreases as the vibration frequency increases. All three methods effectively capture the enhancement of the permeability coefficient due to vibration. The results from the instantaneous profile method and the VG-M model are relatively close, while the unsaturated permeability coefficient calculated using the wetting front advancement method is slightly lower. In the initial stage of the loess soil column’s microstructure evolution, medium pores dominate the soil's internal structure. During the intermediate stage, under the coupled effects of vibration and seepage, the proportion of large pores increases, forming seepage channels. In the later stage, the soil’s microstructure stabilizes, with a significant reduction in large pores and an increase in small and micro pores.

To characterize the deformation and internal force distribution of the hard roof during coal seam mining and to assess the sensitivity of key parameters on its mechanical response, we model the coal seam and the immediate roof as an elastic foundation and select a unit width rock beam at the center of the working face as the research object. Based on the theory of elastic foundation beams and key strata, we establish an elastic foundation beam model for the main roof and obtain analytical solutions for roof deflection, bending moment, and shear force prior to initial fracture. We analyze the influence of five key parameters—the elastic modulus; the stiffness of the coal seam and the immediate roof; the thickness of the overlying soft-rock strata; the influence range of the advanced abutment pressure; and the main-roof thickness—on roof deflection, bending moment, and shear force Finally, using Design-Expert software, we design a five factor, three level response surface scheme and perform a sensitivity analysis of single factors and factor interactions on the hard roof’s mechanical characteristics. Results show that (1) the stiffness of the coal seam and the immediate roof significantly affect the overall roof deformation, while other factors primarily influence the goaf roof. Additionally, increasing the thickness of the overlying soft-rock strata increases roof deflection, whereas other factors have the opposite effect. (2) If the thickness of the overlying soft-rock strata increases linearly, the goaf roof bending moment and shear force also increase linearly. The influence range of the advanced abutment pressure and the main-roof thickness significantly affect the bending moment and shear force in the roof in front of the working face, whereas the elastic modulus and the stiffness of the coal seam and the immediate roof have little to no effect. (3) Factors governing geometric characteristics and load distribution—such as the thickness of the overlying soft-rock strata, the influence range of the advanced abutment pressure, and the main-roof thickness—generally have a greater effect on rock-beam deflection and internal forces than the mechanical properties of the rock mass (e.g., elastic modulus and the stiffness of the coal seam and the immediate roof). The model accounts for the dynamic variation of the upper load during coal-seam mining, providing a theoretical basis for studying the deformation and internal-force distribution of the main roof throughout mining.

Pile groups with members of different lengths can mitigate differential settlement among foundation piles, prevent basin settlement, and ensure consistent reliability indicators across individual piles. This paper presents an approach for analyzing the reliability of pile groups with dissimilar pile lengths in spatially variable expansive soils under rainfall. The variation of soil matric suction with depth under rainfall infiltration conditions was analyzed by numerical simulation software. The Karhunen-Loève (KL) expansion method is used to discretize random fields. The pile-pile and pile-soil interactions in a pile group with dissimilar pile lengths, and the influence of the reduction of matric suction on the ultimate bearing capacity of the piles are analyzed using the modified load transfer method (LTM). The first-order reliability method (FORM) is employed to solve the reliability indices of each pile in a pile group, and the sequential component method (SCM) is adopted to estimate the reliability index of the pile group. Parametric studies show that increasing rainfall intensity and duration reduce the reliability indices of both individual piles and the pile group.

This study uses the composite pile-sheet wall introduced into the Lanzhou hub project by the Zhongwei–Lanzhou passenger dedicated line as the research object, and employs a combined field monitoring and numerical simulation approach to systematically investigate the passive soil-arch effect in front of piles in the embedded section of the existing–new side-by-side pile-sheet wall. Field monitoring yields measurements of pile deformation, bending moment, and soil pressure in front of the new pile, and a three-dimensional finite element (FE) model is constructed for comparative verification. Based on the numerical simulation results, an in-depth analysis is conducted of the formation mechanism, evolution, geometric characteristics, and spatial configuration of the passive soil arch in front of the composite pile-sheet wall. The results show that the contact soil pressure in front of both the existing and the new piles follows a parabolic distribution, with larger values near the surface and smaller values at depth. Under embankment widening and train loading, the increase in contact soil pressure in front of the existing piles is smaller than that in front of the new piles. As the loads on the new pile increase, both piles experience greater displacements, creating a substantial displacement difference with the soil between them. This causes the principal-stress direction in the inter-pile soil to deviate and leads to the formation of a passive soil arch in front of both the existing and the new piles. The evolution of the passive soil arch can be divided into the following stages. Under the load from the existing embankment, a stable soil arch forms in front of the existing pile. The stress relief caused by excavating the new pile holes is limited in extent, and the soil arch in front of the existing piles remains intact. With the increase of new load, the stress of the soil in front of the new and the existing piles overlaps, resulting in stress redistribution. The original soil arch in front of the existing pile disappears, and a new passive soil arch forms progressively between the new and existing piles. Before and after the embankment widening, as the load increases, the thickness of the passive soil arch remains relatively constant, but the rise-span ratio gradually increases. Under the same working conditions, the soil arch thickness and the rise-span ratio decrease with increasing burial depth. The research results can provide reference for the design and construction of new composite pile-sheet wall.

Low-strength, highly compressible soft clays are widely distributed in coastal areas of south China, where their engineering characterization is critical for infrastructure development. Although cone penetration test (CPT) efficiently acquires geotechnical parameters, data interpretation exhibits regional variability, and the applicability of existing methods requires urgent validation. Focusing on coastal clay sites in Dongguan, Guangdong, and surrounding regions, this study integrates in-situ CPT testing, consolidated undrained triaxial tests, and consolidated quick shear tests to analyze the mechanical behavior of coastal clays. Based on CPT data from Dongguan’s coastal soft clays, the modified soil behavior index (IB) is demonstrated to quantitatively characterize soft clays and enhance soil classification. A preliminary assessment of stress history is conducted using normalized cone tip resistance and the modified soil classification index, with a combined application of Mayne and Robertson’s methods recommended for determining the over-consolidation ratio (OCR) of soft clay layers. Comparative analysis of consolidated undrained triaxial tests and consolidated quick shear tests reveals that CPT-derived mechanical indices necessitate calibration against laboratory data. State parameters interpreted from CPT align with Robertson’s soil classification chart. Five methodologies are employed to evaluate the compressibility modulus, showing that CPT-derived results fall within code-recommended ranges, with the K-M1990 method shows high accuracy in coastal silt soil layers. The research outcomes provide regionally optimized solutions for CPT data interpretation in south coastal soft clays, offering practical guidance for geotechnical investigations. This work bridges the gap between conventional CPT interpretation frameworks and region-specific geotechnical conditions, advancing reliability in coastal engineering applications.

This study investigates the deformation characteristics of ultra-deep circular shaft excavation in soil–rock composite strata, based on a shaft project for the Shenzhen Airport–Daya Bay Intercity Railway. Monitoring data collected during excavation were statistically analyzed, and orthotropic plate elements were used in the numerical model to capture differences in the circumferential and vertical stiffness of the diaphragm wall. A comparison of measured and simulated results yielded insights into the deformation and load bearing mechanisms of large diameter shafts in complex urban environments. The results indicate that: 1) Due to the uneven distribution of composite strata, groundwater levels, and surface overloads, the excavation induced two opposite deformation modes in the diaphragm wall. The maximum deformation of the “outward bulging” type diaphragm wall was 0.50‰H_e (where H_e is the excavation depth), while that of the “inward bulging” type reached 0.55‰H_e. 2) This case study shows that shaft deformation changes as the depth-to-diameter ratio r increases. When r ≤ 1.1, the shaft deformation is in the circumferential compression stage. When the excavation depth exceeds the soil-rock interface (r > 1.1), and the shaft enters the elliptical deformation stage. 3) In the numerical simulation, the reduction coefficients for the circumferential and vertical stiffness of the diaphragm wall were set to 0.3 and 0.8, respectively. The relative difference between the calculated results and the measured data was within 13%. Finally, an elliptical deformation mode and mechanism that can explain this behavior were proposed. The research findings provide valuable references for the safety assessment of similar large-diameter circular shaft constructions in soil-rock composite strata.

The traditional analysis method of self-balanced pile test has many shortcomings. Based on load-displacement curves of upper and lower piles, a total displacement method of self-balanced static loading test is proposed. Preliminary numerical analyses show that, when the load-cell position deviates from equilibrium, the total-displacement method yields smaller deviations than the equivalent-displacement method. The analysis of various cases with different displacement conditions shows that the results obtained by the total displacement method are highly consistent with those of the conventional methods. When the displacement difference between the top and bottom piles is large or exhibits abrupt changes, the total-displacement method is more appropriate than the conventional method. The total displacement method can solve the problem that the conventional method cannot analyze the upper and lower piles as a whole pile. Moreover, the equivalent-displacement method may be inapplicable when the upper-section displacement is smaller than the lower-section displacement; the total-displacement method remains applicable. The load-displacement curve obtained by the total displacement method is more complete than that obtained by the equivalent displacement method. For ultimate bearing capacity and displacement values not reported in the literature, the total-displacement method provides corresponding results. In addition, the total-displacement method can effectively mitigate site- and environment-related disturbances in obtaining the ultimate bearing capacity of self-balanced pile tests, providing theoretical guidance for similar projects.

We develop a time-domain analysis framework that couples the indirect boundary element method (IBEM) with the discrete element method (DEM) to investigate the dynamic response patterns and failure mechanisms of rock slopes subjected to near-fault ground motions. This framework enables a nonlinear dynamic simulation approach for near-fault slope systems, capturing the discontinuous deformation characteristics of rock and soil masses. Firstly, we construct a high-precision numerical model of the kilometer-scale, semi-infinite near-fault seismic wavefield using IBEM. Subsequently, based on Green’s function theory and the IBEM solution of the wavefield, we derive an explicit formulation of the equivalent seismic loads on the boundaries of the DEM computational domain. This enables cross-scale energy transfer within the IBEM-DEM coupled system. Finally, the DEM resolves the nonlinear dynamic response of meter-scale rock slopes, yielding a multi-scale nonlinear seismic simulation framework that spans from kilometer-scale faults to meter-scale slopes. Numerical simulations combined with dynamic monitoring results demonstrate that the IBEM-DEM coupling algorithm can accurately capture the dispersion characteristics and energy attenuation patterns of near-field seismic wave propagation. Under near-fault seismic loading, progressive shear failure first occurs within weak interlayers, leading to strength degradation, the formation of through-going rupture surfaces, and subsequent accelerated instability of the sliding mass along the shear plane. This process induces significant displacement and velocity responses, ultimately forming a typical debris accumulation at the slope toe. The surface velocity of the sliding mass is markedly greater than that at the base, with the mean surface velocity reaching 3.6 times that of the base, and peak X- and Z-direction velocity components of 4.98 m/s and 5.92 m/s, respectively, exhibiting a pronounced surface-acceleration effect. The monitoring points of the sliding mass exhibit maximum displacements of up to 41 m in the X-direction and 35 m in the Z-direction from the initial slope surface to the final accumulation position, with the displacement-time history showing a distinct step-like growth pattern, indicative of abrupt sliding behavior during the alternating transformation of kinetic and potential energy. The IBEM-DEM coupled method developed in this study reconstructs the full evolutionary sequence from rock mass rupture to landslide formation, providing an innovative analytical framework for the dynamic failure analysis of landslides induced by near-fault ground motions, as well as theoretical and technical support for identifying landslide mechanisms and mitigating seismic hazards in complex geological settings.

Accurate and reliable seismic input is a prerequisite for seismic response analysis of engineering structures. Based on the artificial boundary substructure method, the frequency-wavenumber domain (FK) semi-analytical method was integrated into the open-source finite element platform OpenSees. Combined with message passing interface (MPI) parallel computing technology, this integration enables equivalent input of P-waves, SV-waves, and SH-waves at arbitrary angles. After verifying the correctness of the developed seismic wave input methodology, a nuclear island structure located in a non-bedrock site was selected to analyze the effects of soil nonlinearity and geotechnical medium properties on its seismic response under oblique SV-wave incidence, considering soil-structure interaction (SSI). The research findings indicate: (1) Soil nonlinearity reduces the peak ground acceleration of the containment structure and significantly alters the internal force responses at the top and bottom of the pile foundation; (2) Variations in the dynamic properties of geotechnical media lead to changes in the stiffness of the soil-pile-nuclear island system, profoundly impacting the structural dynamic response. Specifically, sandy or silty soil layers with dynamic characteristics exhibit strong filtering effects on high-frequency seismic components, amplifying the bending moments in pile foundations adjacent to such layers. This study provides an effective tool for addressing external seismic input problems using the OpenSees platform.

Traditional assessments of active earth pressure are typically deterministic and assume a homogeneous soil layer. However, soil properties exhibit inherent random variations due to geomorphic processes or poor construction control. To address this limitation, we employ the random limit analysis method (RLAM) to investigate the influence of spatial variability in soil strength parameters on the active earth pressure. We enhance the conventional three-dimensional (3D) rotational failure mechanism by applying a spatial discretization technique that enables rigorous coupling with random-field simulations. We derive an explicit equation for 3D active earth pressure based on the upper-bound theorem of limit analysis. The validity of RLAM is verified by comparing it with a deterministic numerical method and with the random finite difference method (RFDM). Furthermore, through extensive uncertainty analyses, a reliability assessment framework is established for gravity retaining walls that explicitly incorporates the spatial variability of soil strength parameters. It is found that under different random field design scenarios, the decay curves of system failure probabilities for the retaining wall intersect within a specific range, providing valuable guidance for the design and construction of retaining walls.

One of the important tasks in the study of sand liquefaction is to assess soil liquefaction likelihood. Based on the field liquefaction investigation cases, the correlation degree between each factor and liquefaction was given by grey relational degree method, and the relationships between factors from seismic load, soil environment, soil properties and liquefaction were analyzed. The support vector machine (SVM) algorithm and Platt scaling principle were then used to construct a probabilistic model for liquefaction assessment, and comparative study was conducted with existing deterministic and probabilistic liquefaction assessment methods to analyze its effectiveness. The model was then applied to actual engineering cases and its practicality was explored finally. The results indicate that it has a significant correlation with liquefaction and the influence relationship between each factor and liquefaction is complex. The overall classification accuracy of the SVM-based soil liquefaction assessment model was 89.41% for the test set and 86.67% for the validation set, higher than that of existing liquefaction assessment methods. The depth range of applicability is extended, and the model can also provide the soil liquefaction probability. The results provide a reference for probabilistic assessment of soil seismic liquefaction.

The decomposition of municipal solid waste released heat energy, leading to temperature increase in vegetated soil covers and thus changed and even deteriorated the function of rainwater regulation of landfill soil covers at municipal solid waste landfills. To investigate rainfall infiltration in vegetated soil covers under temperature effects, we developed an automatic, multi-point temperature-control system for soil-column tests. Temperature-controlled soil-column model tests were then conducted under rainfall conditions. Using the nonisothermal soil–water retention curve model for rooted soils, we conducted finite-element simulations of nonisothermal seepage in vegetated soil covers through secondary development of COMSOL. Test results and numerical simulations are well consistent and show that temperature significantly affects the spatiotemporal distribution of soil water content. Higher temperature caused deeper positions of wetting front and peak water content as well as reduction in water content of surface layer in vegetated soil covers of municipal solid waste landfills. Derived from the nonisothermal soil water retention curve model of rooted soils, the numerical model of vegetated soil covers shows satisfactory usability and predictability. Ignoring the temperature effect likely induces misleading prediction of leachate pollution and landfill stability in municipal solid waste landfills. This study provides references for the hydraulic-thermal coupling analysis and design of vegetated soil covers for municipal solid waste landfills.

Hydropower projects, pile foundations of bridges and tall buildings in western China are primarily constructed on deep overburden layers within high mountainous valleys. To accurately determine the physical and mechanical parameters of these deep overburden layers, in-situ borehole testing technology has gained significant attention. This paper systematically reviews the current research status and achievements from the aspect of the test instrument, test technology and process, theoretical analysis and data interpretation of various in-situ testing techniques for deep overburden drilling, including static cone penetration test, pressuremeter test, borehole shear test, dynamic penetration test, and standard penetration test. The findings indicate that the main advantages of static cone penetration test are continuous rapid testing and high data accuracy, and its disadvantages include difficulty penetrating gravel soils and an inability to observe soil layers directly. The combined drilling-penetration exploration method and multi-casing penetration technology can effectively obtain cone-tip resistance, side friction resistance, and permeability for dense silt, sand, gravel, pebble and cobble layers in deep overburden. The pressuremeter test can measure in-situ mechanical parameters at different depths, but results are strongly affected by the pore-forming quality, with a lower testing precision in soft soil. Compared to pre-drilling and press-in pressuremeter methods, self-boring pressuremeter minimizes disturbance to the borehole walls, effectively preventing collapse in non-cohesive soils and shrinkage in cohesive soils within deep overburden layers, thereby rapidly and accurately obtaining static lateral pressure, plastic pressure, ultimate pressure, and lateral pressure modulus. The main advantage of the borehole shear test is that the strength parameter is measured under the natural stress state of the overburden, but the main disadvantage is that the shear mechanism and drainage conditions are not easy to control. Borehole shear tests are suitable for saturated fine-grained soils in deep overburden, with results closely approximating consolidated undrained shear strength parameters. The main advantages of dynamic penetration test and standard penetration test are wide application range and identification of sand liquefaction, but the main disadvantage is that the transmission of hammer energy is not easy to determine. In deep overburden at considerable depths, the relationship between dynamic penetration and standard penetration hammer numbers is nonlinear, necessitating appropriate correction of hammer numbers through monitoring hammer energy. Current challenges include a lack of in-situ drilling testing technologies and robust data-interpretation methods for deep overburden characterized by high-stress levels, complex structures, and overconsolidation. It is recommended to develop multifunctional in-situ testing equipment, integrate various in-situ testing technologies, and enhance the multi-source data correlation analysis of test parameters using machine learning. This approach is an effective solution to the problems.