Dolomite is formed via dolomitization, a process that enhances porosity. Investigating the influence of dolomite as a characteristic mineral on the deterioration of the physical and mechanical properties of siltstone is significant for the design and stability prediction of deep underground engineering. This study employs X-ray fluorescence spectrometer (XRF), X-ray diffraction (XRD), microscopic analysis, ultrasonic wave velocity measurements, and nuclear magnetic resonance testing to quantify dolomite’s impact on siltstone’s physical parameters. Brazilian splitting tests, monotonic loading, and cyclic loading-unloading experiments reveal the evolution of mechanical parameters, including tensile and compressive strengths. An apparent elastic-viscous-plastic damage model is developed, and dolomite-induced deterioration mechanisms are investigated using computed tomography (CT) and scanning electron microscopy (SEM). The results indicate that: 1) Dolomite content enhances particle roundness, weakens intergranular interlocking, and creates distinct boundary pores with calcite, leading to enhanced pore connectivity and a 2.77-fold increase in porosity. 2) Dolomite presence reduces maximum tensile strain, decreases compressive strength by 14.5%, extends the compaction phase by 9%, and shortens the stable crack propagation phase by 12%. 3) A larger cyclic loading-unloading difference correlates with higher damage values. Dolomite-free rocks exhibit significant damage variation, with rapid early-stage increases followed by slower growth, whereas dolomite-containing rocks show more stable damage progression, with dolomite inducing more pronounced elastic-viscous-plastic damage accumulation. 4) Cracks in dolomite-free samples are bent, dissipating more energy with lower energy storage values, while those in dolomite-containing samples are straight, dissipating less energy with higher energy storage values. Dolomite enhances porosity, facilitating crack propagation and increasing the proportion of tensile cracks.

To further investigate the unloading mechanical response and yield failure mechanism of tunnel surrounding rock, we analyzed the strength law and failure mechanism of thick-walled cylinders using the Mohr-Coulomb yield criterion. Unloading deformation and failure comparison tests were conducted on thick-walled cylindrical specimens made of natural sandstone and cement mortar materials, aiming to explore the unloading deformation and failure mechanism of tunnel surrounding rock. The results indicate: 1) Compared to loading and unloading experiments on rock core specimens, the surrounding rock at the most dangerous point around the roadway in thick-walled cylinder unloading tests reached the material’s elastic limit more rapidly, making it more susceptible to yielding and failure. 2) The unloading deformation of cement mortar specimens was consistent with that of natural sandstone specimens. Unloading deformation was essentially complete when the unloading ratio reached approximately 95%. 3) Under high initial stress conditions, failure occurred in the surrounding rock during unloading. The inner wall of the specimen first reached an unfavorable stress state, leading to failure. 4) Unloading induced the surrounding rock to squeeze and expand toward the free surface of the circular hole, producing extensive spalling of “fish-scale” rock flakes and rock blocks (characterized by thin edges and thick middles) from the inner wall, resulting in localized damage. These findings provide theoretical support for stability control and supporting design of tunnel surrounding rock in deep underground engineering.

In fully grouted bolt systems for roadway rock support, rod yielding and interface slip failure pose critical challenges. To investigate stress transfer mechanisms under these failure modes, we developed a bolt-rock interaction model incorporating surrounding rock deformation and rod loading boundary conditions. We derived analytical expressions describing axial force and shear stress distributions along the rod under support equilibrium conditions. By integrating the rod’s stress-strain constitutive model with a trilinear bond-slip model, we analyzed stress distribution patterns caused by rod yielding and interface slip during surrounding rock deformation. The theoretical framework was validated through comparison with field monitoring data from a representative tunnel project. The analytical results indicate: 1) Initial yielding occurs preferentially at the neutral point. Subsequent to yielding progression, both axial force and interfacial shear stress stabilize, forming a distinct yielding platform in the axial force distribution profile. This mechanical transition converts the neutral point into an extended “neutral segment” along the rod axis. Yielding deformation magnitude exhibits positive correlations with surrounding rock strain, anchor length, and bearing plate reaction forces. 2) Interfacial slip initiates at the loading end and propagates distally through progressive softening and debonding mechanisms. Enhanced rock deformation and extended rod length markedly expand the interfacial slip zone, consequently reducing constraint effectiveness on rock mass displacement. Interfacial degradation can be mitigated through two key measures: optimizing interfacial shear strength parameters, and strategic installation of bearing plates. These findings offer critical insights for mechanized analysis and performance-based parameter optimization in fully grouted bolt support systems.

Wetting deformation, one of the primary types of deformation in core wall rockfill dams, significantly affects the stress-deformation behavior of the dam structure and its safety during initial impoundment. To perfect the theory of wetting plasticity, it is essential to develop a plastic model for rockfill wetting deformation. A new plastic model for wetting deformation is proposed in this paper based on the modified Cambridge model and a wetting dilatation equation derived from the wetting strain law. Based on the test data, the parameters are determined and the model is verified. The model’s calculation results are in good agreement with the test data, confirming the accuracy and rationality of the modified Cambridge model for rockfill wetting deformation proposed in this paper. Additionally, the variation rules of model parameters under different confining pressures and porosities are analyzed, and calculation methods for each parameter under varying conditions are provided. These findings enhance the plasticity theory of rockfill wetting deformation and provide valuable reference and support for future research in this area.

To investigate the evolution of permeability characteristics of geotextile materials in woven soilbags under compressive deformation in hydraulic protection engineering, a self-developed vertical permeability device and image analysis were utilized to study pore structure and seepage behavior under 0%−10% uniaxial tensile strain. The results demonstrated that tensile strain has a significant impact on the pore distribution of soilbag geotextiles. Porosity exhibited a weak exponential increase, while specific surface area showed a weak logarithmic increase with tensile strain. These relationships were quantified using a woven geotextile single-pore model. The hydraulic gradient-velocity relationship during seepage conformed to the Forchheimer equation. The critical Reynolds number exhibited non-monotonic variation, decreasing initially and then increasing with tensile strain. Inter-fiber spacing significantly influences flow regime transitions under low tensile strain. Based on the flow regime classification, the permeability coefficient corresponding to the Darcy flow regime was extracted. A predictive model for the permeability coefficient under tensile deformation was developed using porosity and specific surface area as predictors. The model’s predictions showed good agreement with experimental measurements. The study elucidates the underlying mechanism by which tensile strain modulates the permeability of soilbag geotextiles through changes in porosity and specific surface area.

The seepage phenomenon of water in multi-layered unsaturated soils is ubiquitous in natural environments and engineering practices. To accurately describe the one-dimensional transient seepage behavior of water in the two-layered unsaturated soil under a time-varying rainfall scenario, based on the exponential soil-water characteristic curve and permeability coefficient function, the corresponding analytical solutions are derived for the first time via the approach of variable substitution, separation variable, and Fourier series transformation. The solutions also account for the arbitrary initial water content distribution and two types of bottom boundary. On this basis, the correctness of the proposed analytical solutions is validated by comparing them with existing two analytical solutions and corresponding numerical solutions. Finally, taking the simplified two-layered soil cover as an example, the one-dimensional transient seepage laws of water in the two-layered unsaturated soil are analyzed. The results indicate that, for the same total rainfall, water storage in the cover is smaller and cumulative leakage CQ_b is larger under the “previous-peak” rainfall pattern, while the opposite occur under the “post-peak” pattern. Compared to the case where the soil cover with a smaller saturated permeability coefficient is located above the two-layered cover, the corresponding water storage is larger and the value CQ_b is smaller when it is located below. When the initial total water storage is the same, the larger volumetric water content at the bottom zone, the smaller water storage in the cover after a period of rainfall, and the larger value of CQ_b. A larger initial effective saturation of the cover S_ini leads to a larger value of CQ_b during the rainfall, and at the same time, the value of CQ_b increases linearly with an increasing S_ini.

The loess in Shaanxi Province exhibits heavy metal contamination, primarily concentrated in the Guanzhong region. In addition, the main heavy metal ions in loess are Pb, Cu, Ni, Cd and As. Among them, the Pb concentration is the highest, reaching up to 545.6 mg/kg. To mitigate pollution spread at contaminated sites, a loess/bentonite cutoff wall was implemented, and its hydraulic conductivity and pollution retardation behavior were experimentally investigated. Experimental results demonstrate that increasing bentonite content in the cutoff wall significantly reduces both hydraulic conductivity (k) and pollution retardation coefficient (C_ad). To aid in subsequent engineering design, quantitative models for predicting k and Cad were formulated. Using this characterization, the minimum bentonite addition required to meet cutoff wall permeability standards was calculated (28.52%), exceeding the project’s specified value. Consequently, bentonite modification is necessary. Simultaneously, colloid migration during polluted liquid seepage through the cutoff wall was identified, contributing to pollution diffusion and pollution retardation coefficient reduction. Consequently, subsequent research should focus on developing a cost-effective modified material to enhance colloid fineness and reduce its mobility within the cutoff wall. This approach would reduce hydraulic conductivity, improve pollution retardation coefficient, and prevent pollution spread caused by colloid migration.

The natural topography of karst regions is favorable for pumping and storage projects, however, karst development creates heterogeneous engineering geological rock groups, which can compromise project stability. Therefore, accurately estimating the mechanical characteristics of such heterogeneous rock masses in karst areas is crucial. Existing methods for estimating rock mass mechanical parameters fail to adequately quantify dissolution-induced heterogeneity, referred to here as dissolution characteristics. This study analyzes the impact of dissolution on rock masses and introduces the dissolution rate, inhomogeneity coefficient, and degree of variation to characterize these dissolution-induced features. A method for preparing karst rock samples is proposed, and rock samples with specific karstification characteristics are prepared for uniaxial compression tests. The findings reveal a negative exponential relationship between mechanical parameters and dissolution rate. Additionally, the inhomogeneity coefficient and degree of variation influence these parameters by modifying dissolution impact coefficient, establishing a relationship expression linking mechanical parameters to dissolution characteristics. A field method for quickly determining dissolution characteristic indices is developed. By integrating the Hoek-Brown criterion with the established relationship expression, a rapid estimation method for mechanical parameters of heterogeneous rock masses in karst areas was created. The method is applied to the upper reservoir site of a proposed pumped storage power station in Hubei Province’s karst region, demonstrating the validity of the estimated mechanical parameters and the strong engineering applicability of the developed method.

The physico-mechanical properties of suspended and fluid mud differ significantly from those of conventional soft soils. Therefore, using only the method of “correction by empirical coefficients of settlement calculation based on classical formulae” for calculating settlement in large areas of suspended and fluid mud foundations is unscientific. In response, this study established a total settlement calculation method for the intermittent settlement stage and the subsequent low-pressure (0−100 kPa) consolidation stage through theoretical derivation. Static intermittent settlement modeling tests were conducted to evaluate the validity of the batch settlement calculation method, and low-pressure consolidation tests were performed to assess the validity of the low-pressure consolidation settlement calculation method. The study results indicate that, 1) The cumulative change rate of average void ratio (r_e) and the low-pressure consolidation compression index (C_C-low) are two key technical parameters. The former can be determined by combining theoretical formulae with long-term static intermittent settlement modeling tests, while the latter can be determined through indoor low-pressure consolidation tests. 2) For suspended and fluid mud with a clay content of 40% to 60%, if static intermittent settlement modeling tests cannot be conducted, a “cumulative change in the average void ratio of 60% to 75%” can serve as a criterion for determining the stable state of static intermittent settlement. Specifically, when the clay content is 40%, r_e is 75%, and when the viscous grain content is 60%, r_e is 60%. This criterion also applies to Bingham bodies with no initial structure. 3) Determining the value of the low-pressure consolidation compression index based on the e-lgP (e is the pore ratio, P is the vertical compressive stress) using the slope averaging method is more reasonable. 4) The total settlement formula integrates the static intermittent settlement behaviors and low-pressure (0−100 kPa) consolidation behaviors, meeting the requirements for engineering accuracy. This study addresses the shortcomings of current research and provides scientific support for the design and construction of suspended and fluid mud foundation treatments.

The damage and failure of a rock mass is the inevitable consequence of the initiation, propagation, and coalescence of internal cracks within it. This process can be characterized by changes in acoustic emission and infrared radiation signals, highlighting the importance of studying the acoustic-thermal response characteristics of the damage evolution in fissured rock masses. To investigate the acoustic-thermal response characteristics of crack extension and its precursor law during the cyclic loading and unloading of fissured sandstone, tests were conducted on prefabricated fissured sandstone with varying crack inclination angles. The study analyzed the acoustic-thermal response characteristics of crack propagation, identified precursor laws of various acoustic and thermal signals, and proposed a coefficient of variation index to quantify crack evolution. The main conclusions are as follows: 1) As fissure dip angles increases, the shear-induced damage effect on the specimen becomes more pronounced, with infrared and acoustic emission signals exhibiting distinct stage characteristics during loading and unloading. 2) With increasing cyclic loading and unloading cycles, precursor laws of acoustic and thermal signals became evident, characterized by prefabricated cracks forming around high-energy acoustic emission localization points, accompanied by infrared thermal image temperature anomalies; a sudden change in acoustic emission counts, RA(the ratio of acoustic emission rise time to amplitude), and AF(the ratio of ring counts to duration time) values during unloading, with these parameters maintaining higher values and more concentrated distributions. 3) Infrared temperature and acoustic emission RA, AF anomalies appear earliest, followed by acoustic emission localization. Acoustic emission counts show changes later, with infrared thermal images being the latest indicators. Acoustic emission localization and thermal image anomalies can provide spatial early warnings of crack formation. 4) A novel acoustic-thermal coefficient of variation (CV) index is proposed to quantify crack evolution. This index integrates crack evolution characteristics, optimizes weighting ratios, and reflects fluctuations in acoustic and thermal parameters over time, thereby characterizing crack evolution intensity. It overcomes the limitations of single acoustic or infrared signals, such as hysteresis and spatial constraints. This research provides valuable references for understanding rock disaster mechanisms, rock control strategies, and geological disaster prevention and mitigation.

To enhance the adoption and application of modular waste tire-faced retaining walls in earthquake-prone areas, we introduce the concept of geogrid-wrapped tire-faced retaining walls. A shake table test model was designed for this wall, considering the dynamic similarity ratio between soil and structure. Several factors were considered, such as geogrid wrap types, tire binding modes, foundation depth, and reinforcement length, to assess the wall’s seismic performance under strong earthquakes. The dynamic response characteristics, including wall acceleration, lateral displacement, and dynamic earth pressure on the wall back, were analyzed and compared to those of geogrid-stripped reinforced tire-faced retaining walls and traditional retaining walls. Key factors influencing the seismic performance of geogrid-wrapped walls were identified, revealing that the non-folded and full-bound mode provides superior seismic performance. It was found that, compared to foundation depth, reinforcement length more significantly enhances the seismic performance of the wall. A correlation between geogrid dynamic strain and local wall deformation was established, providing a reference value for wall design based on lateral displacement.

To address the low dewatering efficiency and prolonged occupation period of traditional dredged sludge yards, a novel ring-type tube stockyard sludge storage and dewatering technology was proposed. Long-term laboratory experiments were conducted to investigate the dewatering dynamics, focusing on the synergistic effects of geotextile filters and dimensional parameters. The mathematical expressions for each stage of the sludge dewatering process in the ring-type tube stockyard were clarified. The results indicate that in a double-layer ring-type tube stockyard without a geotextile membrane, the sludge dewatering process consists of three stages: solid-liquid separation, seepage, and evaporation, which change linearly, exponentially, and linearly, respectively. In a double-layer ring-type tube stockyard with a geotextile membrane, the sludge dewatering process is divided into four stages. The dewatering rates in the solid-liquid separation and seepage stages are significantly accelerated, leading to improved overall dewatering efficiency. Mechanistically, this acceleration results from the geotextile membrane’s effectiveness in preventing solid sludge particles from clogging the inter-thread gaps in the ring-type tubes. In an eight-layer ring-type tube stockyard, the sludge dewatering process is divided into five stages, introducing a linear change stage of sudden settlement compared to the double-layer stockyard. The mathematical descriptions of the other stages are similar to those of the double-layer stockyard. As the ratio of yard height to inner diameter increases, the sludge settlement distribution takes on an “inverted cone” shape, with maximum settlement occurring at the center, thereby enhancing overall dewatering efficiency. These findings are crucial for the efficient utilization of limited storage space for dredged sludge.

Due to its unique composition and fabric characteristics, loess exhibits structural and hydrological sensitivity, with its mechanical properties, including yield stress, shear strength, and deformation characteristics, being closely related to saturation and structural integrity. Considering the influence of saturation on the structural strength of loess, structural parameters such as yield stress, friction strength, and cohesion strength are introduced, and a functional relationship between these parameters and initial saturation was established. An evolution equation for structural parameters during plastic deformation was derived based on the structural degradation characteristics observed in shear deformation of loess. On this basis, the yield function for structural loess was developed by drawing inspiration from the Cambridge model. By taking yield stress and structural parameters as hardening parameters, an elastoplastic constitutive model for loess, accounting for saturation and structural evolution, was proposed using the associated flow rule, and the corresponding constitutive matrix was derived. Based on triaxial consolidation drainage test data for undisturbed Q₃ loess from Dongjiahe Town, Tongchuan City, Shaanxi Province, stress-strain curves under varying confining pressures and saturations were predicted, and the model’s rationality was verified. The results indicate that under low saturation conditions, loess exhibits high structural strength, which decreases significantly after yielding, accompanied by pronounced strain softening characteristics. As soil saturation increases, structural strength and corresponding yield stress decrease, with stress-strain curves becoming less steep, indicating increased plastic deformation and progressively less pronounced softening characteristics. The model effectively captures the relationship between loess structure and initial saturation, enabling a more accurate description of mechanical behavior under varying saturation conditions and reflecting how strain softening characteristics vary with saturation.

Rock residual strength is a critical parameter for engineering projects such as tunnel excavation, mining operations, and slope stabilization. The calculation of residual strength using strength criteria often yields inaccurate results, and the required parameters are difficult to obtain. In this study, we introduce the energy reduction ratio parameter to quantify the strength reduction and propose a novel method for determining residual strength. To validate the method, triaxial compression tests were conducted on sandstone samples in a region. The results indicate a significant negative correlation (0.943) between the energy reduction ratio and confining pressure. Subsequently, experimental data from 20 different rock types were collected and analyzed. Compared with two existing methods, the proposed method provides more accurate calculations of rock residual strength. Based on the slope characteristics of the energy reduction ratio fitting curve, two distinct types of curves can be identified: concave downward and convex upward curves. Finally, the correlation between these curve types and rock brittleness-ductility transitions, as well as their relationship with rock failure modes, is established. These findings offer valuable references for evaluating the stability of rock mass engineering.

To investigate the influence mechanism of synchronous grouting in shield tunnel on vertical displacement and earth pressure of sandy soil stratum, model tests were conducted to study the vertical displacement and earth pressure of the upper stratum during synchronous grouting. The results indicate that with the same filling coefficient of synchronous grouting material, the upper stratum rises and earth pressure increases after injecting small water content slurry, whereas it settles and earth pressure decreases after injecting large water content slurry. Similarly, with consistent water content in the grouting material, reducing the filling coefficient significantly decreases the uplift of the upper stratum and reduces the extrusion pressure on the upper stratum of the tunnel. Vertical earth pressure increases and passive soil arching occur when the upper stratum uplifts, while vertical earth pressure decreases and active soil arching occur when the stratum settles. During on-site synchronous grouting, the filling coefficient should be determined based on the consolidation shrinkage of the slurry and stratum permeability, and grouting parameters should be adjusted according to on-site monitoring results.

Supercritical geothermal systems are at the forefront of enhanced geothermal system (EGS) development. Investigating fracture seepage evolution in supercritical environments is crucial for the sustainable exploitation of geothermal resources. To reveal the evolution of seepage characteristics in hot dry rock fractures under the action of supercritical water, we examined the permeability of fine- and coarse-grained fractured granite under varying temperatures (25−500 ℃) and triaxial stresses, using a self-developed high-temperature, high-pressure rock triaxial mechanical testing system capable of reaching 600 ℃. The results indicate the following:1) Temperature significantly influences crack permeability, which can be divided into two distinct stages as temperature increases, with peak permeability observed at 250 ℃. 2) Under combined effects of temperature and supercritical water-rock interaction, fracture permeability evolves through four distinct stages as temperature increases, with peak permeability occurring at 250 °C and 400 °C. Near the supercritical state, water-induced weakening of rock properties and dissolution of free surfaces enhance permeability, with 350 °C identified as the critical threshold for permeability evolution under supercritical aqueous conditions. Following exposure to supercritical water exposure, the fracture’s surface morphology is redistributed due to mineral dissolution, precipitation, and recrystallization. The fracture’s filling rate after water-rock interaction is 14%, which alters the seepage pathways and consequently affects permeability. 3) Coarse-grained granite exhibits reduced permeability at low and medium temperatures, attributed to its high thermal expansion and low elastic modulus. At high temperatures, the extensive water-rock reaction area in coarse-grained granite leads to a 32.67% higher permeability reduction compared to fine-grained granite. This study provides valuable insights for the efficient development of enhanced geothermal systems under supercritical conditions.

To investigate the mechanical properties and damage mechanisms of typical glacial soil in Yunnan, triaxial shear tests were conducted using a TSZ-2 automatic strain control triaxial apparatus under various influencing factors. The mechanical properties of glacial soil were analyzed under varying temperatures, confining pressures, and water contents. A statistical damage constitutive model incorporating a coupling damage variable D (freeze-thaw and load) was employed to characterize the deviatoric stress-strain relationship. The results indicate that under low confining pressures, variations in initial water content significantly affect the deviatoric stress-strain curves and failure strengths. However, the magnitude of these discrepancies diminishes progressively under increasing confining pressures. Under high confining pressures, freeze-thaw cycles have minimal impact on soil with optimal water content w_opt of 19%, which exhibits high cohesion and low failure strength damage. As freezing temperature increases, the deviatoric stress-strain curves soften, and soil strength decreases; however, the overall deviatoric stress strength remains unchanged. Confining pressure reduces the deterioration effect, and the damage caused by the first freeze-thaw cycle is particularly significant. The total damage rate increases with rising freezing temperatures, while soil at optimal water content exhibits the lowest total loss rate. An increase in the number of freeze-thaw cycles reduces deviatoric stress strength, with the first decrease being the most pronounced and influenced by water content. The internal friction angle and cohesion significantly decrease as freeze-thaw cycles progress, whereas soil specimens at optimal moisture content exhibit lower degradation rates. The statistical damage constitutive model, incorporating coupling damage variable D effectively characterizes the deviatoric stress-strain relationship based on triaxial test results. Studies have shown that the effect of freeze-thaw cycles on damage is greater than that of freezing temperature.

Through unidirectional gradient cooling tests on indoor soil columns, we analyzed changes in temperature distribution, water replenishment, water redistribution, and frost heave deformation under two soil types. We also examined how median particle size affects interlayer water migration in coarse-grained railway subgrade fillers. The results indicate that altering the lower layer soil while keeping other conditions constant during unidirectional freezing results in a similar temperature change process and no significant difference in freezing depth under the same temperature boundary. Focusing on the median particle size d₅₀ of the upper and lower layers of soil, we propose the ratio F₅₀ of their median particle sizes to assess the impact of particle size variation between these layers on interlayer water migration. When the ratio of median particle sizes between the upper and lower layers falls within the range of 1.40−3.24, water replenishment is relatively limited, leading to water accumulation at the interlayer interface. With an increasing ratio, water replenishment decreases further, enhancing interlayer accumulation, impeding water movement from the lower to the upper layer, and reducing frost heave deformation in the soil column. Additionally, notable disparities exist in flow rate and density of water migration pathways between the upper and lower layers, with the upper layer exhibiting lower density and the lower layer higher density. Water migration is slower in the lower layer but faster in the upper layer. The extent of interlayer water accumulation is significantly influenced by the density of water migration pathways. Extreme ratios of median particle sizes between the upper and lower layers can result in water breakthrough across interlayers during upward water migration within the soil column.

To consider the effect of nonlinear changes of the shear strength of unsaturated soil in the two dimensions of net normal stress and matric suction on the passive earth pressure, a calculation method for the passive earth pressure on the back of retaining walls for unsaturated backfill is proposed based on the nonlinear shear strength envelope shell and the classical Rankine earth pressure theory. First, employing the generalized Mohr-Coulomb failure criterion, we applied the variable tangent technique to determine equivalent cohesion, equivalent friction angle, and their correlations at arbitrary points on the envelope. Subsequently, through iterative analysis combining Mohr’s circle stress states, we determined the equivalent cohesion and friction angle under passive limit equilibrium conditions. Finally, we derived Rankine passive earth pressure expressions for unsaturated soils that maintain formal consistency with classical soil mechanics formulations. The method’s reliability was validated through comparative case studies with established models. Parametric analysis revealed that increasing matric suction and overburden pressure enhances equivalent cohesion and passive pressure, while reducing equivalent friction angle. In the case study, the envelope shell model yielded lower passive earth pressures than the plane model at low matric suction levels, but higher pressures at elevated suction levels.

The erosion degree at the root of the earthen site often exhibits variations with the height, correlating with the soil’s moisture content. This study investigates the effects of freeze-thaw cycles on the apparent morphology, mass loss, unconfined compressive strength, color difference, phase composition, and microstructure of lime-metakaolin (L-MK) improved soil under varying moisture (0−3%, 0−6%, 0−9%, 0−12%). All experiments used natural hydraulic lime (NHL) improved soil as the control. Results indicate that the surface deterioration and mass loss of L-MK and NHL improved soil samples correlate positively with the number of freeze-thaw cycles and moisture content. A threshold exists in the influence of moisture content on the compressive strength of L-MK improved soil samples. At a 0−3% moisture content range, compressive strength increases with freeze-thaw cycles. Beyond this, strength decreases inversely with freeze-thaw cycles, with the most significant drop occurring in the first cycle. In earthen site restoration projects, the soil at high moisture positions should be closely monitored and reinforced during the initial freeze-thaw stage. Microscopic analysis reveals that increasing moisture content leads to pore development in the improved soil’s microstructure after freeze-thaw erosion, accompanied by a noticeable reduction in hydration products like calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH). NHL improved soil exhibits recognizable color differences, while L-MK improved soil shows slight or perceptible changes. L-MK improved soil satisfies the restoration requirements for earthen heritage sites.

The complex geological structure of the fractured rock surrounding a water-sealed cavern reservoir and the presence of an unsaturated zone of an inaccessible unsaturated zone of groundwater are the primary causes of oil leakage, leading to groundwater contamination. To evaluate the scope of oil leakage and its transport within the rock body, the impact of the water curtain system on oil transport was numerically analyzed using the pore-fracture dual medium model in a subterranean water-sealed oil cavern reservoir located in Liaoning Province, China. The geometric effects of fractures on oil transport were evaluated through the fracture’s inclination angle, degree of openness, and permeability. The study revealed that while the water curtain system could not entirely prevent oil leakage, but compared with no water curtain, it significantly reduces environmental impacts. Over a 50-year period, leakage distance remained stable at 2.20 m, with corresponding 69.11%, 80.40%, and 81.05% reductions in leakage area, maximum migration distance, and migration rate, respectively. The leakage area is maximized only when a horizontal water curtain is added, with the maximum leakage point in each condition occurring in the rock column between the caves (the area between the right and left adjacent chambers, as defined below). The presence of near-field fissures influences the spatial distribution of oil transport, with the leakage area reduced in the intersection zone with the cave reservoir. The maximum vertical oil transport distance is positively correlated with the inclination angle of near-field fissures. The oil leakage range initially increases and then decreases with increasing fracture permeability, while the fracture aperture has a negligible impact on the oil transport range. The study’s findings provide theoretical guidance for the operational design of water-sealed oil cavern reservoirs.

The damage progression in retained rock masses during high rock slope excavation is attributed to cumulative effects from repeated multi-step blasting. Understanding the damage formation mechanism under frequent blasting disturbances is critical for ensuring slope stability. This study examines the excavation of rock slopes at the Baihetan Hydropower Station. Initially, single-hole and multi-hole acoustic wave tests were conducted on the arch shoulder slope blasting. Continuous assessments of the cumulative damage to the retained rock mass after multiple blasts revealed that, in homogeneous rock slopes, damage primarily originates from blasting at the same step, followed by lower steps. Beyond three to five steps, the influence on cumulative damage becomes negligible due to increasing distance from the blast center. Additionally, the complete restart technology in LS-DYNA was employed to model the excavation of rock slopes on the left bank of the Baihetan Hydropower Station (at elevations between 700 m and 650 m), simulating cumulative damage evolution under five-step cyclic blasting. Results demonstrate that cumulative damage in homogeneous rock slopes exhibits localized characteristics, with the current step accounting for 70%–82% of damage and adjacent steps contributing 10%–20%. Numerical simulations corroborate field data in terms of cumulative damage extent. The blasting damage formation mechanism was analyzed based on strain discrimination. Cumulative damage in high rock slopes results from the combined effects of step-local compression damage, middle/far-area tension damage, and tensile stress induced by blasting stress waves from lower steps. A damage prediction model was developed using regression analysis, correlating blasting frequency with damage severity and depth. The results indicate that the cumulative damage during stepped excavation is closely related only to the current and two adjacent blasting steps. The damage severity in the affected zone exhibits an exponential decay characteristic as the number of blasting load disturbances increases. Consequently, stricter safety control standards for blasting vibrations, accounting for cumulative damage effects, are proposed. Compared to single blasting events, the safety control standards under frequent blasting disturbances are stricter, implying current standards may inadequately ensure safety.

Numerical simulation technology is crucial in underground engineering for predicting the long-term deformation of rock rheology. A numerical simulation analysis method for rock aging is proposed, utilizing a generalized fractional derivative component based on fractional calculus to capture generalized stress relaxation characteristics, where the parameters are employed to describe the dynamic stress change process of rock. The generalized fractional derivative component is connected in series with the improved Burgers model for strain correction, allowing the model to describe the different rheological directions of rock when stress changes. The established model is further derived into a three-dimensional central difference format for a computational time step, then compiled using C++ and FISH languages, and embedded into the numerical simulation software FLAC3D. Simulation results are compared with the generalized stress relaxation test conducted on tuff. The results show that the secondary development of the generalized stress relaxation rheological model can well simulate the strain change law in different rheological directions of rock, reflecting the generalized stress relaxation characteristics of the rock. This helps to determine a reference range for the rheological deformation of the rock, aiding in more accurate prediction of the long-term deformation of engineering rock masses caused by disturbances such as excavation that leads to changes in the stress field environment.

To address the construction requirements of heavy-load transmission line foundations in loess regions, this study proposes a novel composite foundation configuration consisting of an upper short column and multiple lower batter piles. A validated numerical simulation method, supported by experimental results, was employed to optimize structural configurations of various composite forms and analyze their load-bearing mechanisms. Through orthogonal experimental design, the influence ranking of the quantity, length, and inclination angle of inclined piles on bearing capacity was systematically clarified. Under equivalent volume conditions, increasing the embedment depth of the short column while appropriately reducing the length of inclined piles was found to enhance uplift bearing capacity without significantly compromising compressive capacity. Based on extensive numerical simulations, preliminary recommendations for the structural dimensions of the composite foundation were proposed. During upward loading, the short column reaches ultimate capacity first; during downward loading, the inclined piles reach ultimate capacity first. The bearing capacities of the short column and inclined piles are asynchronous across different loading conditions. A calculation methodology incorporating bearing capacity mobilization coefficients was developed for short column-inclined pile composite foundations, providing valuable references for related foundation designs.

To investigate the macro- and meso-mechanical evolution of pebble-soil mixtures, we developed a Python-based random generation algorithm through ABAQUS secondary development, creating morphologically representative models of natural pebbles. Through triaxial compression numerical simulation tests, the influences of characteristic parameters such as pebble content, distribution inclination angle and roundness on the macroscopic and microscopic deformation and failure forms of pebble-soil mixtures were analyzed, and the variation laws of key mechanical parameters were revealed. By integrating 3D digital image correlation (3D-DIC) technology, we tracked real-time surface and internal deformation during laboratory testing, thereby validating the rationality of numerical simulation results. Fracture propagation exhibits pebble-content-dependent characteristics: low-content specimens predominantly show “unilateral flow around with rock penetration” and “envelopment with rock penetration”, whereas high-content specimens demonstrate “single rock rotation” and “strike-slip” mechanisms. Increasing pebble content drove shear zone evolution through three distinct phases: initial smooth planes progresses to X-shaped configurations, ultimately developing arc-network structures. Force chain networks transition from diffuse X-cross patterns to well-defined vertical orientations with increasing directional alignment. With the increase of pebble content and the improvement of roundness, the compressive strength, internal friction angle and cohesion of the specimens show an increasing trend; as the pebble inclination angle increases, the compressive strength, internal friction angle and cohesion show a decreasing trend. DIC-recorded uniaxial compression tests confirm congruence between experimental observations and numerical simulations across all pebble concentrations, particularly in surface crack initiation, propagation, and internal failure patterns. Our findings advance the mechanistic understanding of pebble-soil composites and establish a theoretical framework guiding future geotechnical applications involving these materials.

With the development of underground space and uplift resistance issues arising during urbanization, the application of uplift pile technology in high water table clay areas, such as the southeast coastal regions, has become increasingly prevalent. However, conventional drilling techniques face significant challenges, including difficulty in achieving the required side resistance due to the mud cake effect and challenges in expanding the bottom hole. To address these challenges, a novel calculation method for the uplift bearing capacity of constrained grouting pile groups, accounting for disturbance effects, has been proposed. Taking the ⑤1 layer of grey clay in Shanghai as a case study, a clay and sand elastic-plastic-disturbed state concept(CASM-DSC) model was developed to accurately simulate the mechanical behavior of the soil around the pile. Numerical simulations were performed using a user-defined material constitutive (UMAT) subroutine to analyze the disturbance effects of the foundation soil around the pile and the influence of expansion size. The simplified calculation method for the uplift resistance of grouted and expanded steel pipe piles, as proposed in previous research, was revised. The results indicate that drilling excavation significantly reduces the side resistance of clay soils and influences the mechanical performance of the pile-soil interface. The disturbance coefficient and range exhibit a quadratic relationship with stress state and a linear reduction trend, respectively, in the foundation soil. At varying expansion lengths, the ultimate uplift bearing capacity of the model pile exhibits a “V” shape characteristic as length increases. Additionally, the expansion process alters the distribution of side force and axial force along the pile. Field tests at the Xuhui Binjiang site in Shanghai confirmed the effectiveness and applicability of the simplified calculation method, with a calculation error controlled within 15%. This provides reliable theoretical support and a practical calculation method for pile foundation engineering design.

Improving tunnelling efficiency and reducing cutter wear are challenging objectives when tunnelling in hard rocks, determining optimal cutting parameters is crucial for practical projects. Laboratory tests are essential for understanding the load performance of disc cutters. In this study, a novel full-scale rotational cutting platform is employed to investigate cutting force characteristics and determine optimal cutting parameters. Additionally, the finite element method is applied to enhance experimental analysis and provide new insights. Based on experimental results, the variations in cutting forces and rock-breaking efficiency with cutting depth and installation radius are identified. Subsequently, an optimal cutting depth of 6 mm is determined at a cutter spacing of 100 mm. The distribution of rock chips is analyzed using an indicator of cumulative percentage below a given grain size, which decreases and then increases with increasing cutting depth for any cutting radius. The numerical model is validated as reliable based on crack development caused by disc cutter intrusion. The numerical results for disc cutter rock-breaking performance are consistent with experimental findings. The findings provide valuable data for optimizing cutterhead layout and reducing cutter wear.