The surrounding rock of a compressed air energy storage (CAES) salt cavern experiences both creep and fatigue during operation. Ensuring the safety of the CAES salt cavern requires studying the mechanical response of salt rock under the combined effect of creep and fatigue. Developing a creep constitutive model that considers cyclic loading and unloading can more accurately predict the long-term stability of the cavern. This paper introduces a fatigue damage body to describe the impact of cyclic loading on the creep characteristics of salt rock. It then integrates this component with an elastic body, Kelvin body, and nonlinear visco-plastic body to propose a new creep-fatigue constitutive model. The model is validated with experimental data, showing good agreement between model predictions and experimental data. The finite difference form of the model is derived and implemented in FLAC3D software for a uniaxial creep simulation experiment. The simulation results for axial strain closely match the experimental data. Finally, a three-dimensional geomechanical model of a domestic CAES salt cavern is established using the proposed creep-fatigue model. The deformation of the salt cavern during long-term operation is analyzed and compared with results from the static Norton Power model, highlighting the differences and improvements provided by the new model.

A thick layer of soft clay is widely distributed in the coastal area. Coastal soft clay is characterized by high compressibility, high water content, high organic matter content, low bearing capacity, low permeability and prolonged stabilization time. Solidification treatment is one of the most popular and effective methods for improving the mechanical properties of coastal soft clay. Cement solidified coastal soft clay faces challenges such as poor durability, high energy consumption and carbon emissions. Alkali-activated cementitious material (AACM) is a green and low carbon cementitious material. Utilization of AACM for stabilizing coastal soft clay has become a research focus in the field of geotechnical engineering. However, several critical issues remain unresolved in the study of AACM solidified coastal soft clay. This study reviews the strength and water stability of AACM solidified coastal soft clay. The multiscale coupled solidification mechanism of AACM in coastal soft clay is elucidated. The shortcomings of current research on AACM solidified coastal soft clay are discussed. The sustainability of AACM solidified coastal soft clay is analyzed, and potential research suggestions are discussed. This study can provide new ideas and insights for the subsequent research and promotion of AACM solidified coastal soft clay.

For gas storage in abandoned coal mine hard-rock tunnels, the bonding performance between concrete lining and surrounding rock is crucial for maintaining the bearing capacity and air-tightness of the containment structure. However, cyclic internal pressure variations can cause degradation of the interfacial bond. To study the fatigue deterioration characteristics of rock-lining interface strength under cyclic high pressure, direct shear tests were conducted on rock-concrete composite specimens with different interface roughnesses after fatigue loading under varying normal stresses. Strength characteristics were analyzed through interface morphology evolution, stress-displacement curves, peak strength and failure patterns. The results show that shear stress-strain curves can be divided into three stages: crack closure stage (plastic-elastic deformation), crack propagation stage (elastic deformation), and brittle fracture stage (failure). Higher interface roughness and normal stress facilitate more complete development of each stage. Concrete embedded in rock grooves and sandstone columns exhibit mutual extrusion and interlocking effects. Horizontal strain and principal strain display distinct zonal dislocation characteristics. Under cyclic loading, particle breakage occurs accompanied by microcrack propagation. Both rock debris and cracks increase with higher upper stress limits. This study demonstrates that the interface strength characteristics are closely related to fatigue degree, interface roughness and internal pressure magnitude. The findings can provide experimental basis for stability analysis of lined caverns in abandoned mines under compressed air energy storage conditions.

Cyclic loading induces crack formation in rock, which weakens its structural integrity. It is crucial to investigate the damage evolution process. Acoustic emission (AE) and resistivity monitoring technology can effectively track rock damage by detecting changes in fracture patterns. Integrating AE and resistivity parameters allows for a comprehensive characterization of damage progression during cyclic loading and unloading. This study employed AE and resistivity monitoring to examine damage in sandstone specimens with varying moisture contents under cyclic loading. Computed tomography (CT) scans were utilized to map crack distributions post-fracture. Using AE and resistivity parameters, damage variable equations were developed, leading to the derivation of a constitutive model for uniaxial cyclic loading and unloading. The results demonstrate that the damage variable equations accurately capture the damage evolution of sandstone during loading and unloading. The close agreement between the constitutive model’s predictions and experimental data highlights its practical utility for studying cyclic damage in sandstone.

This study aims to analyze the anchoring characteristics of 2G-NPR anchor rods and determine the reasonable matching range between the anchor rod diameter and the anchoring aperture. Based on laboratory pull-out tests, the failure modes of the anchoring system under different anchoring apertures were analyzed. A mechanical model was established to match the anchor body and anchor aperture, and theoretical formulas for axial force and interface shear stress along the anchoring direction were derived. Using the finite difference program FLAC3D, pull-out models for different anchoring apertures were established, and the stress distribution of the anchoring system was analyzed. The results indicate that: 1) Under different anchoring apertures, with a diameter matching difference of 8 mm as the boundary, the failure interface of the anchoring system at maximum bearing capacity differs. 2) The load-displacement curve of the anchoring system during loading can be categorized into five stages: preloading, elastic deformation, plastic deformation, interface debonding initiation, and complete debonding. 3) Under a pulling force of 30 kN, as the anchoring aperture increases, the shear stress distribution at the anchor rod-anchoring agent interface shows little variation with hole diameter, but exhibits significant stress concentration at the spiral rib. At the same position, the shear stress at the anchor rod-anchoring agent interface is 2-3 times that at the anchoring agent-surrounding rock interface. Additionally, the shear stress distribution at the anchoring agent-surrounding rock interface decreases significantly with increasing hole diameter. 4) The optimal anchoring aperture difference for diameter of 18 mm 2G-NPR anchor rods has been determined to be 8-12 mm.

The spatial stress mechanism of circular diaphragm walls persists as a critical research focus in foundation pit engineering. Previous theoretical studies predominantly address axisymmetric loading conditions, with limited investigation of non-axisymmetric loading scenarios. However, eccentric pressure frequently develops in circular foundation pits due to soil heterogeneity and uneven pile loading. To analyze spatial mechanical behavior under non-axisymmetric loading, we deconstruct the column-shell system into vertically oriented elastic foundation beams and circumferentially arranged curved beams using load decomposition principles. We present a rigorous derivation process for calculating internal forces and displacements under circumferential non-axisymmetric loading. The curved beam configuration matches the horizontal geometry of diaphragm walls, enabling simultaneous consideration of spatial arching effects and simplified solution of three-dimensional structural problems while clarifying parameter-deformation relationships. Numerical validation through two case studies confirms theoretical derivations, with cloud distribution plots illustrating circumferential and vertical load-sharing coefficients. Results demonstrate that circumferential stiffness predominantly governs soil-water load resistance in circular diaphragm walls.

Heavy metal contamination is a growing problem with increasing industrial and urbanization processes. This has created a requirement for field-applicable and effective stabilization/solidification (S/S) methods. Therefore, the long-term leaching behavior and leaching mechanism of zinc from activated magnesium oxide (MgO) carbonation-cured contaminated soils in strong (pH = 3), weak (pH = 5), and neutral (pH = 7) environments were investigated. The semi-dynamic leaching test method was used to evaluate the effect of S/S treatment under different pollution concentrations, active MgO dosages, and carbonation times by effective diffusion coefficient (De) and leachability index (Lx). The results showed that the dissolution of Zn ions in the strongly acidic (pH = 3) environment was significantly greater than that in the weakly acidic (pH = 5) and neutral (pH = 7) environments, both of which were 4−5 orders of magnitude lower than that in the untreated contaminated soil samples. The De of the carbonation-treated soils were all less than 3×10−13 m2/s, and the Lx were all more than 9, fulfilling the condition of controlling the contaminated site underutilization. Under prolonged acid attack, the carbonated Zn was eventually leached out by dissolution. Based on these findings, the remediation of Zn-contaminated soils by the activated MgO carbonation method lays a solid foundation for safely treating and reusing heavy metal-contaminated land resources.

To explore the correlation mechanism between the macroscopic strength and microscopic structure of undisturbed loess containing Na2SO4 salt under freeze-thaw cycles, loess samples were subjected to different freeze-thaw cycle tests, permeability tests with different Na2SO4 salt contents, microscopic tests (scanning electron microscope tests), and macroscopic tests (consolidated-undrained shear tests). The grey correlation analysis method was used to determine the correlation between the shear strength index and microscopic tissue parameters of the samples under different salt concentrations and freeze-thaw cycle times. The strength index changes and microscopic pore damage changes were analyzed from a macro-micro perspective. The research results indicate that: 1) Changes in Na2SO4 salt content and freeze-thaw cycles can cause a redistribution of the proportion and area of pores in the soil. As the salt content increases, large pores transform into small and medium-sized pores. As the number of freeze-thaw cycles increases, small and medium-sized pores transform into large pores. 2) Under freeze-thaw conditions, as the number of freeze-thaw cycles or salt content increases, the strength, cohesion, and internal friction angle of the soil significantly decrease. When the number of freeze-thaw cycles increases to 5 or more, the internal disturbance of the soil tends to stabilize. 3) According to the grey correlation analysis, the change in particle distribution has the greatest impact weight on the change in cohesion, and the change in soil particle area circumference has the greatest impact on the internal friction angle. During the freeze-thaw cycle, the correlation between the microstructure characteristics of particles and the internal friction angle is high, while the correlation between cohesion is low. As the number of freeze-thaw cycles increases, the fractal dimension of the area perimeter method has the greatest impact on cohesion and internal friction angle. The particle morphology plays a dominant role in the microstructural characteristic parameters and has the greatest impact on the shear strength of loess.

In response to the damage and failure of surrounding rock caused by different amplitudes of loading and unloading, red sandstone from a certain water conveyance tunnel was selected for pre-peak and post-peak loading and unloading tests with different stress amplitudes, and the stress-strain curve, hysteresis loop evolution, and macroscopic failure characteristics during the loading and unloading process were analyzed. Based on the shear damage mechanics process that takes into account compaction deformation, the four-stage mechanical evolution characteristics of red sandstone were revealed, and the theoretical calculation formulas for loading and unloading moduli were derived to explore their evolution laws. The results show that the larger the amplitude of loading and unloading stress prior to the peak of red sandstone, the larger the hysteresis loop area. Under the same stress amplitude, the hysteresis loop area before the peak is less than that after the peak. The hysteresis loop before the peak shows a development trend of “sparse-dense-sparse” with axial strain, while the hysteresis loop after the peak shows a development trend of “dense-sparse”. Red sandstone exhibits overall single slope shear failure under loading and unloading conditions, with considerable irreversible deformation occurring throughout the process before and beyond the peak. The mechanical evolution characteristics of red sandstone are manifested in four stages: pore crack compaction, stable development of microcracks, unstable development of cracks, and rock failure. The strength and deformation characteristics of red sandstone may be better described using the shear damage mechanical mechanism that takes into account compaction deformation. The analysis of the loading and unloading moduli shows that the pre-peak loading modulus generally increases with the increase in stress amplitude, while the unloading modulus tends to stabilize. The research results have certain reference values for analyzing tunnel surrounding rock damage and stability.

The second-generation negative Poisson’s ratio (2G-NPR) bolts are increasingly being applied in the reinforcement of fractured rock masses. Direct shear tests were conducted to compare and analyze the shear mechanical behaviors of 2G-NPR anchor bolts and conventional steel (Q235) bolts in anchored joints with different filling thicknesses. The results showed that, under the same filling thickness, the 2G-NPR bolts exhibited lower shear stiffness in the elastic stage, higher peak shear strength, and greater peak shear displacement compared to the Q235 bolts. As the filling thickness increased, although the changes in peak shear strength between the two types of anchor bolts were not significantly different, the 2G-NPR bolts displayed a notable advantage in peak shear displacement due to their high energy absorption and high ductility characteristics, resulting in improved specimen ductility. Axial force monitoring data revealed that the 2G-NPR bolts effectively compensated for the sudden axial force drop caused by decoupling with the grout and demonstrated more sustained load-bearing capacity. Their average peak axial force was 3.14 times that of Q235 bolts, and the peak axial force continued to increase with the filling thickness, indicating more stable anchoring performance. Acoustic emission (AE) monitoring further revealed that, under the same filling thickness, the 2G-NPR bolts had lower maximum cumulative counts and maximum cumulative energy, with a later decrease in the b-value (the ratio of small to large AE events), leading to less damage to the specimens. This indicates that the enhanced ductility of the specimens reinforced by 2G-NPR bolts is due to their effective absorption of shear strain energy, which slows the propagation of cracks. These findings provide guidance for the application of 2G-NPR bolts in supporting rock masses with weak interlayers.

At present, theoretical analyses on double-arch tunnel construction effects have rarely considered the construction impacts induced by the middle guide tunnel, despite its prevalence in practical designs. During construction, the middle guide tunnel is excavated first, sharing its lining boundary with adjacent left (tunnel 1) and right (tunnel 2) caverns, while requiring backfilling and reconstruction of the central diaphragm wall. Based on complex variable function theory and the Schwarz alternating method, this study proposes a calculation approach for stress and deformation in lining-surrounding rock systems of double-arch tunnels incorporating middle guide tunnel effects. For the shared lining boundary between the middle guide tunnel and lateral caverns, the Cauchy integral method transforms boundary integral conditions into the difference between complete single-cavity integrals and shared boundary integrals. This aligns with the Schwarz alternating method’s concept of “additional surface forces” generated during three-cavity interaction analysis. Validation against monitoring data and numerical simulations from the Suzhou Qizi Mountain double-arch tunnel project confirms the feasibility of this complex function approach. Parametric sensitivity analyses were conducted for Poisson’s ratio, surrounding rock elastic modulus, middle guide tunnel aspect ratio, and double-arch symmetry. Key findings include: elastic modulus variations exhibit consistent impacts on Tunnel 1 and 2 lining displacements-higher modulus correlates with reduced total displacement at equivalent angles, showing “W”-shaped profiles with inflection points at arch springings. Increased middle guide tunnel aspect ratio (toward “tall-narrow” geometry) elevates maximum principal stresses in both surrounding rock and lining. Symmetrical enlargement/reduction of adjacent cavern sizes while maintaining middle guide tunnel dimensions amplifies/reduces original cavern lining displacements, particularly in shared lining regions.

To address the challenges of solid waste disposal and utilization, this study employed solid sodium silicate to activate a binary precursor system (comprising slag and fly ash) for synthesizing geopolymers. These geopolymers were then used to stabilize sludge with an 80% moisture content, transforming it into recycled fine aggregate for geotechnical engineering applications, such as railways and roads. The research initially examined the effects of precursor proportions, precursor content, sodium silicate molar ratio, and sodium silicate concentration on the unconfined compressive strength, splitting tensile strength, and electrical resistivity of the stabilized sludge (aggregate matrix). Subsequently, confined compression tests were conducted to evaluate the compressive properties of the recycled fine aggregate, considering the influence of these factors. Afterwards the relationship between the physical and mechanical properties of the aggregate matrix and the compressive characteristics of fine aggregates was established. The results demonstrate that precursor proportions, content, molar ratio, and concentration significantly affect both the physical and mechanical properties of the matrix and the compressive performance of the aggregate. There is an optimal range for these parameters: when the precursor consists of 90% slag and 10% fly ash, the precursor content is 30%, the sodium silicate molar ratio is 0.8, and the concentration is 1.8 mol/L, the matrix achieves its maximum unconfined compressive strength, splitting tensile strength, and electrical resistivity. Under these conditions, the fine aggregate exhibits the lowest initial strain rate under confined compression, the smallest final strain, and the highest yield strength. Furthermore, the physical and mechanical properties of the matrix are positively correlated in a nonlinear manner with the yield strength of the aggregate. This suggests that the aggregate not only inherits the physical and mechanical characteristics of the matrix but also retains the matrix’s pore structure. This study demonstrates how controlling the properties of the aggregate matrix can improve the geotechnical properties of the aggregates, thereby enhancing the resource utilization potential of solid waste in geotechnical engineering. It also offers new approaches for achieving sludge reduction, stabilization, harmlessness, and resource recycling.

The recognition of strain information for rock deformation localization and fracture precursors was studied through experiments. The digital speckle correlation method was employed as the observation technique. Three types of sandstone specimens were subjected to uniaxial compression tests. The study focused on the evolution of non-uniformity statistical indices, the increment of maximum shear strain, and the direction of maximum principal strain during loading. Additionally, methods for identifying deformation localization and rupture precursors based on strain information were analyzed and discussed. The results show that: (1) The abrupt change point of the evolution curve of the non-uniformity statistical index Sw coincides with the initiation time of deformation localization, and reaches the maximum value in the early stage of rupture. This behavior can serve as an indicator for identifying the initiation of deformation localization and rupture precursors. (2) The maximum shear strain increment within the localized deformation band increases abruptly in the early stage of rupture, serving as a precursor signal of rupture. (3) The direction of the maximum principal strain exhibits a sudden change during the early stages of deformation localization and rupture, showing obvious change around the localized deformation band. The magnitude of this directional change decreases with increasing distance from the localized deformation zone.

Rock masses in underground engineering are subjected to three-dimensional in-situ stress, which influences their physical and mechanical properties by controlling pore compaction, crack initiation, and propagation. These processes result in varying degrees of change in different ultrasonic parameters. To investigate the sensitivity of various ultrasonic parameters to three-dimensional in-situ stress and their attenuation characteristics, ultrasonic wave propagation tests were conducted on red sandstone using a three-dimensional static stress ultrasonic testing system. By analyzing the selected head waveforms, the variations of ultrasonic wave velocity, head wave amplitude and head wave energy with the three-dimensional static stress were investigated. Empirical models of rock ultrasonic parameters were developed. The sensitivity of each parameter to the three-dimensional in-situ stress was assessed, and the attenuation mechanism was explored. The results indicate that under constant confining pressure, ultrasonic wave velocity increases rapidly with increasing axial static stress and then stabilizes, following an exponential relationship. The head wave amplitude of red sandstone initially increases and then decreases, exhibiting a Gaussian distribution. Similarly, head wave energy shows an overall trend of first increasing and then decreasing. Under constant axial static stress, ultrasonic wave velocity, head wave amplitude, and head wave energy all increase with rising confining pressure, indicating that confining pressure enhances ultrasonic wave propagation. Different acoustic parameters exhibit varying sensitivities to rock damage evolution. Compared to ultrasonic velocity, head wave amplitude and head wave energy are more sensitive to both initial pore compaction and damage evolution, making them more suitable for characterizing the damage evolution of engineering rock masses.

The mechanical behavior of interfaces is a hot research topic in the field of geotechnical engineering. The soil-rock contact surface, as a widely existing interface in various geological bodies, its mechanical behavior is closely related to engineering stability and geological hazard development. Geometric shape is an important factor affecting the mechanical behavior of soil-rock interfaces. Different shapes of soil-rock interfaces were regarded as objects, and the natural contact surface morphology was restored through 3D printing technology. Bedrock models containing rectangular, serrated, and arc-shaped contact surfaces were printed, and soil-rock samples with different interface shapes were prepared. On this basis, indoor shear tests were conducted to investigate the influence of regular interface morphology on the shear behavior of specimens under different asperity widths. The results indicate that: (1) For the same material, natural interfaces have obvious shear peaks, while regular interfaces have no significant peaks. When the proportion of asperity width is less than 35%, the curved interface exhibits the highest shear strength, followed by the serrated interface and then the rectangular interface. When the proportion of asperity width exceeds 35%, the serrated interface shows the highest shear strength, followed by the curved interfaces and then the rectangular interface. Additionally, as the asperity width increases, the shear strength gradually increases. (2) Interface cohesion decreases in the order: serrated>arc-shaped>rectangular, whereas the internal friction angle decreases in the order: rectangular>serrated>arc-shaped. (3) During shear process, two shear planes form at the interface of a protruding body: a primary shear plane at the soil-rock interface and a secondary shear plane within the protrusion. The secondary shear plane primarily accounts for the differences in shear behavior of interfaces with different shapes.

Currently, the flocculation-solidification combined method (FSCM) is a significant approach for the treatment and resource utilization of high-water-content dredged mud slurry (HW-MS). Extensive experimental evidence has demonstrated that flocculants significantly enhance the dewatering performance of slurry-like mud and amplify the strength multiplier effect through dehydration promotion. However, due to the complexity of the involved physicochemical processes, it remains unclear whether flocculants have additional effects on the curing reaction, shear behavior, and deformation characteristics of solidified mud beyond their role in enhancing dehydration and strength. Based on this, one-dimensional consolidation tests, unconfined compressive strength tests, and triaxial undrained shear tests were conducted to compare and analyze the compression, deformation, and triaxial shear characteristics of FSCM- and pure cement solidification method (PCSM)-treated slurry-like mud under no-dewatering conditions. Additionally, the study investigates the influence of flocculants on the strength and deformation characteristics of modified slurry-like mud under varying cementitious binder contents, focusing on the underlying mechanisms and patterns. Furthermore, field acoustic emission scanning electron microscope (FESEM) analyses revealed the intrinsic mechanism at the microscopic level. The results show that, even without dehydration, flocculant addition does not adversely affect the strength development of modified slurry-like mud but significantly enhances its toughness. Under similar peak strength conditions, FSCM solidified slurry-like mud exhibits significantly higher failure strain compared to PCSM solidified mud, with its stress-strain behavior transitioning from brittle to ductile. Flocculant-induced toughness enhancement improves the safety and freeze-thaw resistance of modified slurry-like mud fills.

The mechanical characterization of dynamic direct damage in brittle rock under pre-tension stress is crucial for evaluating the safety and stability of deep rock engineering. However, due to the harsh experimental conditions associated with dynamic direct tension of pre-tensioned rocks, experimental studies in this area are relatively scarce, and theoretical investigations into the macro-micro mechanisms are even rarer. Based on the wing crack extension model under quasi-static direct tensile loading, the static and dynamic fracture toughness relationship models, and the dynamic-static coupling function of strain rate and strain, a constitutive relationship model for dynamic direct tensile damage of brittle rock under pre-tension is proposed by introducing the fracture toughness modification parameter  related to pre-tension stress. The relationship between the enhancement of dynamic crack fracture toughness and dynamic direct tensile strength in pre-tensioned rock is established. The dynamic direct tensile strength increases with pre-tension stress, provided that the pre-tension stress does not exceed the crack initiation stress in rocks. By comparing the magnitude of axial pre-tension stress 1pre with the crack initiation stress 1ci, the expansion of wing cracks is categorized into three cases, each corresponding to a different constitutive relationship. The effects of pre-tension stress on the mechanical properties of brittle rock are analyzed, along with the influence of the rock’s initial state (initial damage, crack size, density, and angle) on the mechanical properties of pre-tensioned brittle rock. The findings provide theoretical references for the construction and design of deep underground engineering.

To investigate the characteristic differences between soft clay cyclic softening and silt liquefaction, as well as the effects of plasticity on dynamic strength and pore water pressure, and the influence trend of pore water pressure on the dynamic modulus and damping ratio of fine-grained soils, a typical silt and two types of silty clay from Handan, along with silts mixed with varying montmorillonite clay content, were tested using a cyclic triaxial apparatus. The test results indicate that the silt sample (FT) exhibits typical liquefaction behavior, with a pore pressure ratio reaching 1.0. Once the ratio exceeds 0.6, dynamic stress attenuates significantly, and the stress-strain hysteresis loop becomes progressively flatter. For silts with 5%, 10%, 15%, and 20% clay content, the pore pressure ratio exceeds 0.8, and the dynamic stress and hysteresis loop characteristics are similar to those of the silt sample (FT). The peak pore pressure of silty clays does not reach the confining pressure, with pore pressure ratios below 0.7. These samples exhibit significant pore pressure fluctuations, slow attenuation of dynamic stress, and broader hysteresis loops. The cyclic strength of silts with varying clay content and constant dry density first decreases and then increases. The strength of silty clays is significantly higher than that of silts. The pore pressure ratio for cycles producing 5% double amplitude axial strain decreases gradually with increasing plasticity. The modulus ratio of the five silts decreases rapidly as pore pressure increases. Once the pore pressure ratio reaches 0.8, the modulus approaches 0 and tends to stabilize. The modulus ratio of the two silty clays is higher than that of the five silts at similar strain levels. The damping ratio of the most cohesive silty clay (FN1) increases with rising pore pressure. Other samples initially increase and then decrease in damping ratio, while the damping ratio of the silt sample (FT) approaches 0 upon liquefaction. In this study, the damping ratio of soils during cycles producing 5% double amplitude axial strain increases gradually with increasing plasticity.

To enhance the strength of red clay reinforced by microbial-induced calcium carbonate deposition (MICP) in a single mixing process, it is necessary to increase the concentration of the cementing solution in order to enhance the amount of calcium carbonate deposited and address the resulting decrease in microbial activity. The nonionic surfactant D-sorbitol increases the permeability of cell membranes, allowing the exocytosis of intracellular urease and enhancing enzyme activity, thereby promoting calcium carbonate synthesis. The three factors of D-sorbitol dosing, cementing solution concentration, and cementing solution-to-bacteria ratio were selected to determine the optimal dosing for the maximum calcium carbonate deposition, and the red clay soil was mixed and reinforced with this optimal dosing. The results showed that (1) The addition of D-sorbitol to bacillus subtilis enhances the urease activity; (2) Response surface tests were conducted to determine the optimal conditions for the maximum calcium carbonate deposition: D-sorbitol concentration of 0.48 g/L, cementing solution concentration of 3.72 mol/L, and cementing solution-to-bacteria ratio of 1.03:1; (3) After indoor curing for 14 days, the unconfined compressive strength of the red clay soil compacted and reinforced to 95% compaction was 979, 1 675 kPa, and 1 931 kPa for the untreated, microbial, and D-sorbitol-added groups, respectively; (4) The addition of D-sorbitol led to an increase in the calcite content in Bacillus subtilis from 14.4% to 38.8%, as determined by X-ray diffraction (XRD) analysis.

This study used a fulvic acid (FA) solution with a pH of 6 to simulate the weakly acidic groundwater environment typically caused by humic acid in peat soil. The FA solution soaked soft soil containing humic acid that had been solidified with ordinary Portland cement (OPC). Various methods, including visual observation, microscopic analysis, loss on ignition testing, and osmotic pressure tests, were employed to investigate how this environment influenced the structure and permeability of the humic acid-containing soil-cement. The results indicate that FA undergoes complexation reactions with cement hydration products and polyvalent metal cations released during hydration, leading to the formation of organic metal colloids. This process depletes the hydration products and inhibits further hydration. When the OPC content is low, the quantity of organic metal colloids formed is insufficient, which may cause migration and result in the softening and detachment of the surface soil from the specimens. Additionally, the internal structure of the specimens, influenced by humic acid (HA) and FA, develops granular or blocky interconnected structures with numerous large pores. These changes increase the permeability coefficient (k) of the specimens, with the effect becoming more pronounced with extended immersion. Increasing the OPC content inhibits FA infiltration into the specimen and promotes the deposition of organic metal colloids on the surface, resulting in a dense surface layer. Higher OPC content enhances the bonding of hydration products to soil particles and improves pore filling, increasing the overall integrity. This reduces the number of pores and consequently lowers the k of the specimens. To balance engineering safety with environmental and low-carbon requirements, the OPC content used to solidify humic acid-containing soft soil should be controlled between 23.3% and 30.0%.

Electro-chemical stabilization (ECS) is an innovative soft soil treatment technology that effectively combines drainage and soil cementation. Previous studies on the modification mechanisms of soft soils via ECS remain scarce. This study systematically investigates changes in the physico-mechanical properties, chemical characteristics, and microstructural morphology of soil pre- and post-ECS through vane shear strength tests, pH measurements, total organic carbon (TOC) analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results demonstrate that ECS induces drastic alterations in the soil environment, triggering electrolysis, ion adsorption/desorption, and cation exchange reactions. These processes (1) facilitate the expulsion of abundant organic matter, and (2) generate cementitious compounds (e.g., calcium silicate, calcium aluminate, ettringite). Consequently, the soil structure evolves from a dispersed state to a denser sheet-like configuration, with increased aggregation of soil particles. Collectively, these transformations contribute to a rapid and marked improvement in soil strength.

The soil-rock mixture-bedrock contact surface represents as the primary control interface for the stability of accumulated landslides, and the morphological characteristics of bedrock interface represent a pivotal element of the design. Large-scale direct shear tests were conducted on the contact surface under varying morphological parameters of the bedrock interface. The objective of these tests was to investigate the influence of the aforementioned parameters on the shear mechanical properties of the contact surface. A generalized model was developed to describe the movement of soil and rock particles at the contact surface. A simplified composite power exponential (CPE) model was established to describe the shear behavior of the contact surface. Results show that as the roughness of the contact surface increases, the shear strength of the contact surface progressively enhances. This is accompanied by a nonlinear upward convex growth trend in the apparent internal friction angle and a quasi-linear increase in the apparent cohesion. As the sawtooth height increases, the shear strength of the contact surface initially rises and subsequently declines. The impact on apparent cohesion is more pronounced when sawtooth height increases. The relationship curve between shear stress and shear relative displacement at the contact surface generally exhibits a weak hardening pattern. The compactness of the soil-rock particle skeleton is observed to decrease with increasing roughness, but to increase initially and then decrease with the elevation of sawtooth height. The movement of soil-rock particles at the contact surface is primarily characterized by interlocking, rolling and slipping, while particle fragmentation and shear failure at the bedrock tips occur under conditions of higher normal stress. The model parameters k, b, and n are found to exhibit a linear relationship with the dimensionless normal stress n/Pa. n is normal stress, and Pa is standard atmospheric pressure. The fitting coefficient ai (i = 1, 2) remains unaffected by the morphological parameters of the bedrock interface. Moreover, fitting coefficients bi and gi demonstrate a linear relationship with roughness R and sawtooth height D, respectively. The simplified CPE model effectively simulates the entire process of shear deformation at the soil-rock mixture-bedrock contact surface under varying morphological parameters of the bedrock interface. The model demonstrates good applicability, and the method for determining the parameters is both reasonable and feasible.

The variation of the disintegration characteristics of red-layer soft rock with changes in water content has significant engineering importance. To accurately describe the disintegration characteristics, it is necessary to propose appropriate disintegration indices. Currently, widely used disintegration tests under drying-wetting cycles cannot measure the continuous process of disintegration rate as water content changes. Commonly used disintegration indices, disintegration resistance index Id and disintegration rate DR, are unable to accurately measure the degree of disintegration or distinguish differences in disintegration characteristics. To address this issue, a method for calculating the surface area of granular materials was derived. A new disintegration index, the disintegration surface release rate (DS), was proposed, and the differences between various disintegration indices were compared. Water immersion and disintegration tests were conducted to study the impact of the number of drying-wetting cycles on D_S. Discrete element method (DEM) simulations were performed to study the impact of moisture content on D_S. The results show that DS has an accurate physical meaning and accurately describing the influence of particle size on the disintegration rate. With the increase in the number of cycles, the DS change rate reaches its maximum after the second drying-wetting cycle, and DS tends to stabilize after the fifth disintegration cycle. As disintegration time (t) increases, D_S exhibits a nonlinear change, initially increasing and then stabilizing. D_S shows a linear relationship with saturation (Sr). This research is of great significance for the engineering application and disintegration prediction of red-layer soft rock.

This paper intends to describe the confining pressure correlation of the mechanical behavior of sand in a reasonable way. Firstly, the relationship between the mechanical properties of sand and the confining pressure is analyzed and summarized. As the confining pressure decreases, the basic mechanical properties of sand show a stronger confining pressure dependence, the critical state stress ratio changes from a constant to a sensitive variable with the confining pressure, and the dilatancy changes from gentle to a sharp increase. Then, under the theoretical framework of unified hardending model for clays and sand, namely CSUH model, the occlusal stress parameters are introduced to describe the critical state strength characteristics. The concept of uncoupled plastic volumetric strain is proposed, and the mechanism of strong dilatation under low confining pressure is explained from the microscopic level. Based on the analysis of the influence of confining pressure on compression-shear coupling, the expression of uncoupled plastic volumetric strain is constructed, and then a unified hardening (UH) model of sandy soil which can consider the confining pressure effect is established. Compared with CSUH model, UH model considering confining pressure effect only adds two parameters, and the parameters are easy to determine. Finally, the rationality and applicability of the model are verified by comparing with the experimental data and the prediction results of CSUH model.

Current theoretical studies on ground settlement induced by small curvature shield excavation generally consider the foundation as linear elastic bodies, neglecting the rheological behavior of soil. Therefore, the time-dependent settlement changes of shield excavation along curved path cannot be accurately predicted. A mechanical model for small curvature tunneling in a Boltzmann viscoelastic foundation was established. Time domain parameters of the viscoelastic ground were obtained through Laplace transforms of the Poisson’s ratio and shear modulus for the linear elastic ground parameters. Then, the solutions for ground loss and Mindlin displacement were converted by positive and inverse Laplace transforms. During small curvature shield construction in the viscoelastic ground, a settlement solution was derived that accounts for the combined effects of over-excavated ground loss, shield tail ground loss, cutterhead face thrust imbalance, shield shell friction imbalance and slurry pressure at the shield tail. Finally, field measurements and three-dimensional numerical simulation results are compared with the analytical solution to verify its relative accuracy. In addition, the parameters of tunnel curvature radius, shield cutterhead face radius and viscoelastic ground shear modulus ratio are analyzed. The analysis results show that the transverse surface settlement inside and outside the small curvature tunnel is asymmetrically distributed, with the peak settlement shifting inward. The settlement trough curve shifts downward and the settlement volume increases with time. A smaller tunnel curvature radius has a more significant effect on ground settlement compared to a larger tunnel radius curvature with equal changes. Reduction in tunnel curvature radius and viscoelastic ground shear modulus ratio, along with growth in cutterhead face radius and over-excavated value, result in the increase in transverse surface settlement at the shield tail, as well as the increase in uplift and settlement of the longitudinal surface both before and behind the cutterhead face.

ChatGPT, an advanced natural language processing model based on the GPT-4 architecture, has shown remarkable potential across various fields. This study explores the application potential of ChatGPT in developing computational programs for three-dimensional slope stability analysis. This research integrates natural language processing with civil engineering calculations, proposing a novel ChatGPT-Python intelligent programming methodology for three-dimensional slope stability evaluation. The method enables automated implementation of Python-based computational programs for safety factor calculations using both the limit equilibrium method and the strength reduction method. The methodology comprises three main steps: problem definition (detailing the engineering scenario and guiding ChatGPT to generate a conceptual diagram), algorithm design (elaborating the computational problem and prompting ChatGPT to provide effective solutions), and code implementation (generating feasible programming solutions based on computational theory). At each stage, ChatGPT provides intelligent suggestions, which are supplemented by manual review to ensure the theoretical accuracy and engineering feasibility of the calculation results. As demonstrated through three-dimensional slope stability analysis, the Python algorithm generated based on ChatGPT achieves a maximum relative error of 4.99% when compared with commercial software results, confirming its high calculation accuracy. This study introduces an innovative approach to engineering computations, underscoring the significant application prospects of artificial intelligence in civil engineering.

Shaft construction in clayey soils typically induces ground movements. This study develops a cavity contraction theory-based analytical framework to predict three-dimensional ground displacements during shaft excavation. The validity of the proposed method was first verified through comparative analysis with published monitoring results. Subsequent parametric analyses systematically quantified depth-dependent variations in surface and subsurface soil deformations induced by circular shaft construction. Surface settlements outside the shaft exhibit a spandrel-shaped profile. This configuration gradually transitions to a concave morphology with increasing depth. Horizontal displacement curves demonstrate an evolutionary pattern: initial hump-shaped distributions progressively develop into arched configurations with depth. Deep soil deformations adjacent to retaining walls exhibit complex patterns, characterized by initial settlement accumulation followed by abrupt stress-release-induced reduction. Horizontal deformation profiles adopt distinctive bow-shaped configurations, featuring maximum magnitudes at mid-depth positions. Soil displacement magnitudes demonstrate linear attenuation with both increasing depth and horizontal distance from the excavation. The spatial influence zone of horizontal displacements extends significantly beyond the vertical extent of surface settlements. Monitoring data emphasize that frequently neglected deep-seated horizontal displacements could potentially affect adjacent infrastructure elements, particularly bridge abutments and subsurface utilities.

Tropical soil slopes are highly susceptible to geological disasters such as collapses and landslides under extreme weather conditions. Therefore, microbial-induced calcium carbonate precipitation (MICP) is considered an environmentally friendly method for slope stabilization. Following large-scale cultivation of Bacillus pasteurii, a combination of drip and sprinkler irrigation was applied for on-site reinforcement of tropical soil slopes. The reinforcement effect and solidification mechanism of typical yellow clay in tropical soil slopes were investigated through macro, micro, in-situ tests and laboratory tests. After on-site reinforcement with different dosages of MICP bacterial solution, subsequent tests were conducted accordingly. In-situ tests included rebound test and penetration test. Laboratory tests included calcium carbonate generation, unconfined compressive strength test, direct shear test, permeability test, as well as observations via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results show that: (1) The surface strength and penetration strength of the reinforced soil have been significantly improved, and they increase with the dosage of bacterial solution. However, the strength is discrete, indicating the reinforcement is uneven. (2) The compressive strength characteristics of the soil have also been improved to a certain extent. The compressive strength characteristic indexes have the largest increase and the most obvious change at the medium reinforcement strength. (3) With the increase of bacterial solution dosage, the shear strength gradually increases, and both the internal friction angle and cohesion rise, contributing to effective soil consolidation. (4) In terms of anti-seepage performance, permeability coefficient decreases by up to 63.5%, mitigating slope erosion and degradation caused by rainfall. (5) Through SEM-EDS observation, three specific reinforcement forms of calcium carbonate crystals on soil particles are obtained and proved by quantitative analysis. Therefore, MICP treatment can significantly improve the strength properties of clay and effectively enhance the stability of the slope.

Environmental changes cause the surface evapotranspiration rate of naturally preserved sandstone to vary, resulting in capillary water migration within a specific range. This process not only induces repeated hydration expansion and drying shrinkage of minerals within the sandstone but also accelerates rock deterioration due to capillary migration, including salt crystallization, dissolution cycles, freeze-thaw effects, and biological weathering. To provide a reliable reference for the preservation of historical stone buildings, this study investigates the capillary water migration mechanism, focusing on the stone archway of “Jingnanxiongzhen” in Enshi, Hubei Province. Long-term microenvironment monitoring and laboratory experiments were conducted. Numerical simulations using Comsol Multiphysics software integrated microenvironment monitoring data with rock weathering patterns, establishing a research framework under partial continuous immersion conditions. The results show that: 1) From the perspective of liquid volume fraction distribution at different times, in the long time dimension, the hydraulic gradient near the wetting front is gentle, and the volume water content of sandstone changes most sharply, and the deterioration phenomenon of rock is most obvious in this height range. 2) Once capillary water reaches dynamic equilibrium, vertical water content varies, with higher values at the bottom and lower at the top. Horizontally, water content decreases from the center to the sides. The wetting front fluctuates with evapotranspiration rate changes, aligning with observed weathering patterns. 3) Reducing the pressure head at the base of historical stone structures significantly decreases water infiltration. Lowering groundwater levels around the stone archway achieves this reduction, mitigating capillary-induced deterioration.

Based on the interaction mechanism among the surrounding rock-shield-grouting-lining segments during the construction of tunnels using the shield tunnel boring machine (TBM) method, utilizing a longitudinal deformation curve of the surrounding rock that accounts for the interaction with the shield-surrounding rock, in conjunction with the Drucker-Prager yield criterion, we propose a method for calculating the surrounding rock pressure in deep-buried tunnels constructed using the shield TBM method, considering the interactions among the surrounding rock-shield-grouting-lining segments. The proposed method is compared with field-measured data and results from other surrounding rock pressure calculation formulas. Research shows that the surrounding rock pressure in Shield TBM tunnels primarily manifests as deformation pressure. The calculated surrounding rock pressure values using the deformation pressure formula, which considers the interactions among the surrounding rock-shield-grouting-lining segments, show better agreement with field-measured data compared to other formulas based on loose pressure. The surrounding rock pressure is influenced by factors such as the properties of the surrounding rock, tunnel depth, cutter-head overcut, shield length, and grouting timing. The surrounding rock pressure initially increases and then decreases with the increase in rock cohesion. It shows a similar trend with the increase in the internal friction angle of the surrounding rock. The surrounding rock pressure decreases with the increase in the elastic modulus of the surrounding rock and increases with the increase in tunnel depth. It decreases as the cutter-head overcut increases, as the shield length increases, and as the delay in grouting behind the shield tail increases. When the surrounding rock interacts with the grouting and lining segments, a larger initial displacement released by the surrounding rock results in smaller surrounding rock pressure on the structure. The proposed surrounding rock pressure calculation method provides valuable guidance for the structural design of deep-buried TBM tunnels.

The caisson foundation is widely used in large bridge projects due to its high overall stiffness and strong bearing capacity. The key to successful sinking construction is to maintain a safe and stable sinking process. Accurately predicting the sinking rate and tilt degree of the caisson foundation during soil excavation is crucial for effective sinking control. During the sinking process, extensive real-time monitoring data of soil pressure at the cutting edge are collected. These data exhibit high dimensionality, and the underlying mechanisms linking soil pressure to sinking rate and tilt degree are complex, posing challenges for traditional analytical methods. Therefore, the extra trees algorithm from machine learning is employed to establish a sinking state prediction model. This model extracts temporal and spatial features from the monitoring data, captures the complex relationships between cutting edge soil pressure and sinking behavior, and enables intelligent prediction of sinking rate and tilt degree. The model was applied to the northern anchor caisson project of the Zhangjinggao Yangtze River Bridge, with model evaluation parameters calculated to verify prediction accuracy. Additionally, the extra trees algorithm was compared with other common machine learning methods, and the influence of model parameters on prediction accuracy was analyzed. Results show that the established model achieves high prediction accuracy, with R2 values consistently greater than 0.9 in engineering applications, meeting project requirements. The extra trees algorithm outperforms other machine learning methods, and prediction accuracy improves with an increased number of individual decision trees and greater maximum tree depth. These findings provide valuable reference for controlling sinking rates and tilt degrees in similar caisson foundation projects.

The ballastless track structure, reknown for its superior geometric stability assurance capability, has significantly contributed to the rise and development of high-speed railway technology. It is a key factor in ensuring the safety and smooth operation of high-speed railway. However, its limited adjustment capacity imposes stringent requirements on the deformation control of the underlying foundation. In recent years, some sites have experienced track upheaval deformation, which disrupt normal high-speed railway operations and present a new technical challenge. Therefore, investigating the heaving of ballastless tracks on high-speed railway subgrades holds important engineering significance. This study begins by systematically summarizing the mechanisms behind subgrade heaving in ballastless tracks, identifying three major contributing factors: foundation lithology, subgrade fill characteristics, and environmental conditions. Next, techniques including rail fastener adjustment and track gradient adjustment methods, are thoroughly reviewed, with their advantages, disadvantages, and applicable conditions outlined. Countermeasures and suggestions for effective prevention of upward deformation in the stages of railway surveying, design, construction, and operation are proposed. Finally, combining with a typical project case of a high-speed railway, the causes of its upheaval deformation; and remediation maintenance strategies are analyzed. The results can provide technical support for the prevention and remediation of upheaval deformation; diseases of high-speed railway subgrades.

Curved pipe jacking bottom curtain method is a new type of underwater shipwreck salvage technology. As this method adopts a new type of vertical small curvature radius pipe jacking, the theoretical calculation of variable-depth jacking force during the tunneling process and the disturbance to the hull and surrounding areas remain unclear. Based on the analysis of pipe-soil interaction, a more realistic pipe-soil interaction model is established by simplifying the shear failure of pipe and soil, and the theoretical thrust of vertical curved pipe jacking is deduced. The calculated thrust values from this model are compared with field-measured data and existing theoretical formulas, validating the rationality and accuracy of the proposed thrust calculation model. Additionally, a refined finite element salvage model for curved pipe jacking bottom curtain method is developed. By incorporating the theoretical thrust as input parameters into numerical simulations, the disturbance distribution law of surrounding soil layer and shipwreck during jacking process of curved pipe jacking bottom curtain method under different construction sequences is obtained. The results show that when the underwater curved pipe jacking is advancing, the pipe joint behind the shield head is mainly in contact with surrounding soil and causes friction, which is the largest resistance source in the jacking process. Unilateral construction and symmetric construction result in vertical ground settlements of −15 cm to −16 cm upon completion. However, symmetric construction induces more uniformly distributed ground disturbances, with significantly reduced disturbance and deflection on the shipwreck compared to unilateral methods. The thrust calculation model of the underwater curved pipe jacking bottom curtain method proposed in this paper is closer to the field measurement results. The research outcomes provide a theoretical basis for jacking force calculation and refined assessment of construction-induced disturbances in underwater curved pipe jacking bottom curtain method.

Under the influence of rapid developments in artificial intelligence, machine learning, as an important component of it, has significantly enhanced the intelligence, informatization, and automation in many scientific research fields. Geotechnical engineering needs to accurately predict and analyze actual engineering, so efficient and accurate processing and analysis of huge data is the key technical requirement. Machine learning is becoming an important driving force for the development of geotechnical engineering because of its advantages in processing huge amounts of data. To fully understand the progress and effectiveness of machine learning in the field of geotechnical engineering, this paper reviews a large number of relevant literature and uses CiteSpace visualization analysis tools to organize them, deeply exploring the current research status and hot issues, and identifying existing challenges and development bottlenecks. Through literature review, it is found that extensive and in-depth research on machine learning has been carried out in the field of geotechnical engineering. However, the development content and research direction of this field show a certain degree of limitation; although new algorithms have injected new vitality into the field of machine learning, the application of the latest algorithm results in geotechnical engineering is not widespread. In view of this, it is urgent to find ways to resolve its limitations and strive to apply the latest achievements to practical engineering to further promote the intelligent level of geotechnical engineering.

The dynamic evolution of fracture permeability is a critical issue in understanding the hydraulic characteristics of engineering rock masses. Investigating the dynamic evolution mechanisms of rock mass permeability is crucial for engineering design and operation, as it clarifies the factors influencing this process. Using the discrete element method and finite element method, this study establishes a numerical simulation framework for shear seepage in rough granite fractures to investigate the dynamic evolution of fracture aperture and permeability under varying confining pressures during shearing. The study reveals the dynamic evolution law of fracture permeability in rough granite during the shear process. Numerical simulations were conducted to analyze the shear and seepage processes of rough fracture samples under confining pressures ranging from 1.9 to 20.0 MPa, monitoring the evolution of fracture aperture and permeability. The numerical simulation results align with experimental observations, indicating that shear processes and confining pressure conditions significantly influence permeability evolution. Additionally, the magnitude of confining pressure determines the trend of permeability changes. Under confining pressures of 1.9–10.0 MPa, permeability initially increases significantly but decreases after shearing. When confining pressure exceeds 10.0 MPa, fracture permeability exhibits a downward trend throughout. Shear numerical simulations reveal that high confining pressures restrict fracture shear expansion, promote rock debris formation, and reduce the fracture’s water-carrying capacity. This study systematically proposes an equivalent aperture correction coefficient based on the Barton formula, provides a physically meaningful permeability calculation method, and establishes a standard evolution equation linking fracture equivalent aperture and effective confining pressure. These formulations enable accurate predictions of initial, peak, and minimum equivalent apertures under varying confining pressures and facilitate permeability calculations. The shear seepage numerical simulation method offers an effective approach to elucidate the dynamic evolution mechanisms of fracture permeability.

Renovating abandoned mines for compressed hydrogen energy storage can enable the utilization of waste resources and safety of large-scale storage of hydrogen. A theoretical framework of thermo-hydro-mechanical (THM) coupling for compressed hydrogen energy storage in abandoned mines is established. The numerical model is validated by using a previous analytical solution. A three-dimensional modeling study on an abandoned mine is conducted to analyze the THM responses and damage characteristics during compressed hydrogen energy storage. The study indicates that the established theoretical framework of THM coupling for compressed hydrogen in abandoned mines can be used for precisely describing the multi-field responses of caverns for compressed hydrogen energy storage. The ultimate storage pressure of the abandoned mine cavern after modification is significantly higher than that of the unmodified abandoned mine. Because the tunnel surrounding rock is affected by the support of anchor cables, the overall damage on the surface of the cavern rock appears mottled. The plastic zone in the surrounding rock of the energy storage cavern evolves downward. Radial and hoop displacements are observed on the cavern surface. Upon crack initiation, tensile, shear, and torsional cracks develop. Relatively high temperature and pressure gradients are observed at the junction between the lane and the main lane. The temperature gradient has an influence range of approximately 1 m. The temperature gradient ranges from −25.8 K/m to 48.8 K/m in the main lane and from −22.8 K/m to 43.8 K/m in the contact lane. The pressure gradient has a relatively large influence range of approximately 7.5 m, with a gradient of 2 000 Pa/m.

Material failure has a direct impact on the reliability and safety of the components of engineering equipment. Accurately predicting fracture behavior using traditional measurement techniques is challenging. Peridynamics (PD) is an integral nonlocal continuum mechanics theory that effectively simulates material fracture failure. However, PD does not rely on pre-generated mesh to construct the governing equations. Nevertheless, it suffers from low computational efficiency when solving large-scale problems. This paper presents an improved grid-based mesh generation technique based on bond-based PD finite element method. An improved grid-based mesh generation method is proposed for complex geometries with arbitrary cracks. Additionally, an efficient orthogonal quadrilateral-dominated automatic surface mesh generation scheme is developed. The boundary fitting algorithms are adopted to achieve high-quality entity boundary fitting, which successfully solves the problem of entity boundary fitting of the traditional out-side-in mesh method. In addition, peridynamics-based finite element method combines the advantages of bond-based PD and unstructured mesh generation techniques. This method fully exploits inherent advantages of PD in representing the non-local action effect and discontinuous deformation characteristics of materials, while maintaining the characteristic of fast node traversal of the finite element method. Combined with the improved grid-based mesh generation method, numerical examples have demonstrated the effectiveness and reliability of the peridynamics-based finite element method (PeriFEM) in conducting damage analysis of finite width plates, L-shaped plates, double-notched plates and centrally notched disks.

The analysis of tunnel seismic fragility serves as the foundation of seismic risk assessment for tunnels in high-intensity zones. The composite lining structure is commonly adopted in tunnels located in high-intensity zones. Most existing seismic fragility analysis methods for tunnels neglect the displacement discontinuities at the interface between the initial primary-secondary lining, particularly in the presence of a waterproofing board. Consequently, direct shear tests were performed on the primary-secondary liner interface incorporating a waterproofing board. A contact model was developed for the interface, along with its corresponding simulation code. Subsequently, the incremental dynamic analysis method was employed to evaluate the seismic fragility of a composite-lined tunnel. The results reveal that shear stress-shear displacement curves can be categorized into four distinct stages: linear growth, nonlinear growth, damage-induced decrease, and friction slip. The waterproofing board decreases the stiffness and strength of the interface. Under normal stress ranging from 0.3 MPa to 2.0 MPa, shear strength increases linearly with normal stress, with a friction angle of 23.7º and cohesion of 0.18 MPa. The waterproofing layer absorbs deformation during earthquakes, acting as a buffer. Compared with the displacement continuity assumption, considering displacement discontinuities at the primary-secondary liner interface increases damage index thresholds across different damage levels. Ignoring the primary-secondary lining interface effect leads to overestimation of tunnel damage states. This study provides a valuable reference for seismic risk assessment of composite-lined tunnels in high-intensity regions.

To evaluate the feasibility of geological CO2 storage in saline aquifer and overlying coal mining in Ordos Basin, the safety risk study of coal mining with CO2 injection was carried out. Based on the finite element numerical simulation software, the two-dimensional fluid-structure coupling numerical simulation of CO2 injection cooperation in coal mining is realized, and the effects of different CO2 injection rates, injection times and coal mining degrees on CO2 migration, formation pore pressure and vertical deformation are studied. Considering the CO2 injection rate of 100 000−700 000 tons per year and the half and complete excavation of coal, the numerical simulations of 9 different conditions are carried out according to the control variable method. The results show that the injection rate is the main factor affecting the variation of pore pressure, displacement and the migration range of CO2, and the migration range of CO2 is less affected by the overlying load, while the pore pressure and deformation increase with the decrease of the overlying load. The study shows that when injecting CO2 at an annual rate of 200 000 tons for 20 years: (1) The impact on the stability of the formation is relatively small. The change in pore pressure during the injection process in the upper formation is 3.4 MPa, and the change in effective stress is relatively small compared to the in-situ stress. (2) The degree of ground uplift is relatively small. The maximum deformation is 10 mm, located at the top of the injection well, and the deformation in the coal mining area is 7 mm. (3) The range of CO2 migration is relatively small. The migration distance is 540 m, which is far from the mining area and has a relatively small impact on the coal mining area. The study shows that the rate of CO2 injection is the main factor affecting the changes in pore pressure, deformation, and the range of CO2 migration. An increase in the injection rate will increase the pore pressure, deformation, and the range of CO2 migration. The degree of coal mining is relatively small compared to the impact of CO2 injection, the range of CO2 migration is almost unaffected by coal mining, and pore pressure and deformation show a slight increasing trend with the increase in the degree of coal mining. The research findings provide a reference basis for assessing the safety risks associated with the synergistic operation of CO2 injection and coal mining.

A coupled particle flow code (PFC) and computational fluid dynamics (CFD) method was adopted to study the transport and loss process of sand under pipeline orifice seepage erosion and to identify the main factors influencing ground subsidence. Orthogonal tests with three levels were designed to conduct mesoscopic numerical simulations for five factors: pipeline diameter, orifice size, buried depth of pipeline, sand internal friction angle, and groundwater depth. The numerical simulation results show that sandy ground settlement exhibits a V-shaped funnel distribution, with subsidence expanding both horizontally and vertically over time. Range analysis and variance analysis of the orthogonal test results indicate that groundwater depth hw has the greatest and significant impact on subsidence depth. Specifically, greater groundwater depth correlates with reduced subsidence depth. The subsequent ranking of influencing factors is: orifice size d, internal friction angle  and pipeline diameter DN. Pipeline buried depth has no significant impact on ground surface settlement. Based on these findings, an estimation formula for ground subsidence range induced by pipeline leakage under various conditions was proposed. These results provide a reference for municipal pipeline design to mitigate ground collapse.

To investigate the service performance of reinforced soil retaining wall with rigid facing in high-speed railway seismic zones, the response characteristics of facing horizontal displacement and surface settlement under seismic action were studied through vibration table tests and numerical simulations, revealing the deformation characteristics of the structure. The findings suggest that regardless of the influence of foundation deformation, rotational deformation occurs in the most parts of the facing, the permanent horizontal displacement after the earthquake shows the trend of large upward and small downward. The surface settlement of the retaining wall exhibits a bimodal distribution pattern, where differential settlement is observed near the ends of connectors and reinforcement bars, and failure initiated near the end of the reinforcement bars. The deformation of the reinforced soil retaining wall is divided into four stages to comprehensively assess the service performance of the structure by using the relationship between the horizontal displacement of the panel and the settlement of the retaining wall surface. Taking the post-construction settlement limit of high-speed railways as a control indicator, a method for determining the displacement index DI of reinforced earth retaining wall is proposed. For the case study presented in this paper, the DI threshold is determined to be 0.3% when the upper part of the reinforced earth retaining wall is a ballastless track structure, and 1.5% when the superstructure is a ballasted track with a design speed of V≥300 km/h. The findings can not only provide references and basis for the design of reinforced soil retaining walls in high-speed railway applications, but also contribute to enriching the seismic disaster prevention theory of reinforced soil retaining walls.

Accurately grasping the moisture content of shallow soil and its variation process holds significant importance in multiple fields, including geotechnical engineering and environmental engineering geology. Utilizing natural temperature information to estimate soil moisture represents a novel approach suitable for long-distance and large-scale monitoring. To address the issues of low accuracy in soil moisture estimation resulting from the limited resolution of soil temperature measurement and reconstruction in conventional methods, this study proposes a new approach based on distributed fiber-optic temperature sensing (FO-DTS) technology. By integrating an explicit finite difference algorithm and the Markov chain Monte Carlo (MCMC) method, a novel method for shallow soil temperature reconstruction and moisture inversion is proposed and validated through in-situ pit tests. The results indicate that: (1) The high spatial and temporal resolution temperatures obtained through FO-DTS allow the explicit finite difference algorithm to effectively reconstruct temperature distributions at various soil depths, with a temperature reconstruction residual error of approximately 0.2 ℃. (2) The MCMC inversion optimization algorithm accurately estimates the soil thermal diffusivity, leading to an estimation error of only 7% in soil moisture. (3) The estimated shallow soil moisture effectively reflects water migration changes induced by weather variations. This new method achieves high-precision soil moisture estimation and demonstrates broad applicability.

The fractures of rock significantly affect the efficiency and safety of rock breaking caused by tunnel boring machine (TBM) disc cutters. The present study established a discrete element model of randomly fractured rock using the Monte Carlo method, and investigated the correlation between random fractures geometry parameters (dip angle, fracture diameters and fracture density) and rock mechanical properties (strength and elastic modulus) through uniaxial compression simulation. Subsequently, the randomly fractured rock breaking by disc cutter was simulated using the discrete element method (DEM). The results demonstrated a clear linear correlation between the dip angle, diameter and density of random fractures with the strength and elastic modulus of rock, and a multiple linear regression prediction model for the mechanical properties of randomly fractured rocks was established. During construction simulation, the rock-breaking specific energy increased with an increase in fracture dip angle, while it initially decreases and then increases with increasing fracture diameter and density. Based on numerical simulation results, a correction factor for rock-breaking force was introduced into the Northeastern University rock-breaking force prediction model, thereby establishing a prediction formula that accounts for the influence of random fractures.