Geological storage of carbon dioxide (CO2), a core component of carbon capture, utilization, and storage (CCUS), is a key strategy to mitigate greenhouse gas emissions. However, the continuous expansion of storage capacity increases the risk of CO2 leakage, posing significant challenges to the safety and effectiveness of storage projects. Firstly, this study provides a comprehensive review of leakage issues and research progress in large-scale CO2 geological storage. We examine the primary leakage pathways and their underlying physical, chemical, and geological mechanisms, emphasizing wellbores, faults/fractures, and caprocks as critical conduits. We summarize the cascading effects of CO2 leakage, highlighting its potential impacts on groundwater, soil microorganisms, vegetation, and climate change. Then, we discuss recent advances in leakage monitoring and risk assessment, underscoring the roles of multi-source sensing, intelligent data analysis, and multi-scale coupled models. Furthermore, we review the progress of leakage control and remediation technologies, including cement-based materials, polymer gels, biomineralization, foam injection, and nanotechnology, while identifying limitations regarding long-term stability and large-scale applicability. Finally, we propose future research directions that focus on identifying leakage mechanisms, multi-source monitoring, intelligent early-warning systems, and rapid-response remediation strategies tailored to complex geological conditions, aiming to establish an integrated full-cycle leakage prevention and management framework.

Creep between the anchor and the soil is a critical factor in determining the prestress loss of the anchor, directly influencing the long-term stability of the slope. Unlike traditional anchors, the prestress loss calculation for anchors with grout bulb, which serve as pressure-bearing anchors, must account for the coupling effects of soil shear and compression creep. Thus, revealing the unique creep mechanism resulting from the interaction between anchors with grout bulb and the soil holds significant research value. Firstly, shear and compression creep tests on red clay were conducted to obtain clays creep parameters. Secondly, a creep characteristic test for the grout bulb anchor was performed using a self-developed model test system. Finally, a fractional-order creep model for grout bulb anchors, incorporating the coupling effects of soil shear and compression creep, was established based on fractional calculus theory. The results indicate that, compared to traditional grouting anchors, the attenuation creep stage of anchors with grout bulb lasts longer and exhibits a slower attenuation rate. In red clay, compression creep accounts for over 90% of the total creep and increases over time. The anchor with grout bulb creep model, which considers the coupling creep of soil shear and compression, more accurately describes the creep behavior of anchors with grout bulb in soil. This study not only provides a theoretical basis for the design and application of the new type of prestressed anchor with grout bulb but also contributes to the broader understanding of prestressed anchors with grout bulb.

The principal clay mineral in bentonite is montmorillonite. Its layers carry fixed negative charges arising from isomorphic substitution. The resulting layer charge is the key factor controlling bentonite’s shrinkage behavior. This study combines experimental and theoretical methods to investigate the mechanism by which layer charge affects bentonite shrinkage. Sodium bentonite was used as the starting material. A series of charge-reduced samples with progressively lower layer charges were prepared using the lithium fixation method. Shrinkage characteristic curves were obtained by digital image analysis. Soil–water characteristic curves and water distribution were measured using a dewpoint potentiometer and nuclear magnetic resonance (NMR). Results indicate that decreasing layer charge transforms bentonite from highly to weakly shrinkable and leads to the emergence of a structural shrinkage stage in the shrinkage curve. Based on the inflection point, the shrinkage curve can be divided into a capillary stage and an adsorption stage. This division agrees with the observed water distribution patterns. Reducing layer charge also decreases water retention capacity. However, after normalizing by cation exchange capacity (CEC), the soil–water characteristic curves converge at high suction, indicating that the adsorption stage is primarily governed by hydration of interlayer exchangeable cations. Drying-induced compression curves, expressed as intergranular stress, show that most shrinkage in the capillary stage is elastoplastic, whereas deformation in the adsorption stage is predominantly elastic. Overall, the boundary between the capillary and adsorption stages identified using shrinkage curves, water distribution, soil–water characteristic curves, and desiccation compression curves is consistent across these methods.

The interlocking L-shaped caisson, as a new type of caisson structure, exhibits enhanced performance under complex marine loading conditions. This structure shows significant potential for applications in marine infrastructure, including deep-water port terminals, breakwaters, and artificial islands. The feasibility of replacing the conventional L-shaped caisson (CLC) with the proposed interlocking L-shaped caisson (ILC) is investigated through indoor loading model tests. The paper investigated the effects of filling materials, foundation types, and load forms on the stability of caisson docks formed by adjacent ILCs within a hexagonal prism cavity. Compared to CLC quay wall, the ultimate bearing capacity of the ILC quay wall, when pinned by gravel or concrete blocks, increased by 15.5% and 20.1% under strip load. The ILC quay wall with concrete block interlocking reinforcement exhibits superior load-bearing performance. When the sand ground is replaced with a soft soil interlayer ground, the ultimate bearing capacity of the ILC quay wall decreases. The ultimate failure mode of the ILC quay wall shifted from overturning to overall instability failure, with the failure surface changing from arcs and straight lines to multi-segmented lines. When strip loads are replaced by concentrated loads with a smaller range of action, the integrity of the ILC quay wall deteriorates, its ultimate bearing capacity significantly decreases, and the settlement of the backfill soil surface near the caisson increases.

To investigate the collapsibility of loess in long-distance water conveyance projects in Xinjiang, comprehensive field monitoring experiments were carried out. The experiments assessed the collapsibility, moisture content, and void ratio of channel foundation loess at various burial depths, using collapsible loess from the Ili River long-distance water conveyance project in Xinjiang as the research subject. Detailed analyses of the spatial distribution patterns of loess collapsibility within the channel foundation loess were conducted. Concurrently, laboratory-based self-weight collapse tests and immersion compression tests were performed to quantitatively evaluate the collapse characteristics and pore structure of undisturbed loess across different moisture levels. By integrating scanning electron microscope (SEM) and particle and crack image recognition systems, the study explored the relationship between the collapse characteristics and the internal microscopic pore structure of undisturbed loess under varying collapse frequencies and vertical stress conditions. The results show that: (1) The collapsibility of the loess in the water transport channel is primarily controlled by the moisture content. Lower moisture content correlates with more pronounced micro-pore structure characteristics and greater collapsibility deformation, indicating a certain level of “residual” collapsibility. (2) The collapsible deformation process of loess exhibits particle softening and polymer effects, leading to a gradual decrease in pore structure and significant collapsible deformation. The characteristics of collapsibility deformation are more pronounced in a low moisture content state. (3) The collapsibility of loess in long-distance water conveyance channels gradually decreases with increasing burial depth. Additionally, the collapsibility of loess in the canal base occurs multiple times, being greater in the early stages and smaller in the later stages.

Understanding and utilizing the laws of heat and moisture migration in loess under climate change is crucial for slope engineering safety and agricultural production. A custom-designed vertical temperature-controlled heat and moisture migration test device, coupled with non-contact continuous measurement technology for temperature and moisture fields, was used to perform heating tests with varying temperature levels and initial water content conditions at the bottom of loess samples. The study investigates the vertical heat and moisture migration in loess under the combined effects of thermal potential, gravitational potential, and matric potential. The results show that: (1) At heat source temperatures ranging from 45℃ to 75℃, the temperature field of the loess samples stabilizes within approximately 24 hours. (2) Between 0 and 40 cm in height, samples with higher heat source temperatures and initial water content exhibit larger stable temperatures and thermal gradients. (3) As the heating time increases, the vertical moisture content of the soil sample shows a significant peak in the height distribution curve, with the position of the peak gradually shifting upward and the peak magnitude progressively increasing. (4) The thermal potential plays a dominant role in the upward migration of moisture in loess, with higher temperatures significantly increasing the driving force for moisture movement. (5) The upward migration of water is most pronounced when the initial moisture content is moderate.

To investigate the mechanical properties and failure characteristics of fly ash as a cementitious material, uniaxial compression, acoustic emission (AE) and scanning electron microscopy tests were carried out on the cemented tailings backfill with fly ash replacing cement at 0%, 40% and 100%. Utilizing fractal and cusp catastrophe theory, we analyzed the AE parameters and strain energy parameters obtained during the loading process. We analyzed the variation characteristics of AE fractal dimensions and the early warning intervals associated with strain energy mutations during the cementation failure process for three different fly ash dosages. The results show that the hydration products of the cemented tailings backfill for each fly ash content primarily consist of ettringite and amorphous clustered calcium silicate hydrate. As the fly ash content increases, the quantity of hydration products, compactness, and integrity decrease. The strength of the specimens exhibits a decreasing trend, while the elastic modulus initially decreases and then increases. The mutation regions in strain energy for cemented tailings backfill at each fly ash content occurred prior to the stress peak and exhibited two distinct changes. Local failure intensification in specimens with 0% and 40% fly ash content was concentrated after the stress peak. Prior to overall failure, the fractal dimension exhibited a downward trend, with the warning interval situated in the middle to later stages of the fractal dimension decrease area. Local failure in the 100% fly ash content specimens intensified and concentrated before the stress peak. The fractal dimension exhibited an upward trend prior to overall failure, with the warning interval positioned in the initial and middle sections of the fractal dimension rising zone. The early warning intervals for cements with 0% and 40% fly ash content align more closely with the precursory characteristics of AE compared to those for cemented tailings backfill with 100% fly ash content. These research findings provide a theoretical basis for early warning regarding the failure of cemented tailings backfill.

The mining works in underground coal mines induce the changes in stress state of rock mass in front of mining face, which can lead to rock mass damage, form groundwater seepage channel, and then cause disasters such as water inrush and surrounding rock collapse. In view of this situation, three stress loading paths are designed to simulate the stress state of rock mass under mining disturbance in different regions: conventional triaxial compression test(CTCT), loading axial pressure and unloading lateral pressure test(IUT), and keeping axial pressure and unloading lateral pressure test(KUT) for triaxial compression tests, and creep tests of two loading modes are designed: the creep test involving step loading and unloading confining pressure are conducted to investigate the evolutionary characteristics of rock damage and permeability and their time-dependent mechanisms. The damage to limestone during creep and creep unloading processes is characterized through theoretical analysis. The results show that:(1) Limestone exhibits significant differences in mechanical and permeability properties, such as yield characteristics and permeability, under different stress paths. However, shear failure dominates its failure mode in all cases. (2) As confining pressure gradually increases, the stress paths corresponding to the maximum permeability growth rate are CTCT, IUT, and KUT respectively. This indicates that the evolution of limestone permeability is closely related to in-situ stress levels and stress states. (3) Damage primarily occurs during axial loading and confining pressure unloading processes. The rate of damage accumulation and failure in limestone is faster under confining pressure unloading paths than under conventional loading paths. (4) A modified Nishihara model was developed, and its reliability was successfully validated. The research results can provide reference for the construction stability research in underground engineering, such as roadways and tunnels.

Rock joints may undergo damage and failure under dynamic disturbances such as earthquakes. Understanding their mechanical behavior of rock joints under pre-peak cyclic shear loading is crucial for preventing dynamic disasters in underground engineering. Current studies predominantly use analog materials , often neglecting the effects of rock matrix and in-situ stress effects, , which leads to a poor understanding of the evolution mechanisms of rock joints under cyclic shearing loads. This study innovatively generated natural rough structural surfaces through Brazilian splitting tests and reconstructed rock specimens with natural morphological features using 3D scanning and engraving technologies. Cyclic loading experiments were conducted to analyze the influences of normal stress, loading frequency, static and dynamic load amplitudes on mechanical indicators, including ultimate strength, cumulative displacement, hysteresis average stiffness, and damping ratio, etc. Random forest analysis was used to quantify the relative significance of these four controlling factors. Experimental findings reveal that with an increasing number of cyclic, the local strain on the structural surface increases, transforming initially banded low-strain zones into distinct high-strain clusters. Cumulative displacement and mean stiffness exhibit positive correlation with the number of cycles, in contrast to the reduction in the damping ratio. Increased normal stress and higher loading frequencies suppress displacement accumulation, while enhancing mean stiffness and damping. An increase in dynamic load amplitude reduces cumulative displacement and mean stiffness but amplifies the damping ratio, whereas an increase in static load reduces mean stiffness and the damping ratio while promoting cumulative displacement. The hierarchy of influencing factors is as follows: normal stress, loading frequency, dynamic amplitude, and static amplitude. These results provide a data foundation for assessing dynamic stability and preventing disasters in underground engineering.

Expanded perlite (EP) synergistically solidifies sludge with cement and other binding agents, simultaneously achieving sludge-water separation and exhibiting pozzolanic activity. To verify the pozzolanic activity effect of EP, the initial approach was to immerse EP in a saturated Ca(OH)₂ solution. The pozzolanic reaction of EP in an alkaline environment was systematically examined using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and other test methods. It is found that the main products resulting from the pozzolanic reaction of EP are calcium silicate hydrate (C-S-H) gels, and the porous architecture of EP provides a large specific surface area that promotes the growth of hydration products. The extent of pozzolanic reaction is affected by the duration of immersion. After mixing EP with sludge and using cement for solidification, an investigation would be conducted to study the changes in strength. Combined with Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) test, the microscopic mechanism by which EP enhanced the strength of solidified soil was revealed. The test results show that the pozzolanic reaction process of EP is indirectly reflected in the change of pH in solidified soil. The strength of EP-cement solidified soil derives from both the cementing effects of hydration products and the pozzolanic activity of EP. This reaction enhances frictional interactions between the cement hydration products, sludge, and EP, thus increasing the soil’s resistance to deformation. EP slowly leaches active silica and aluminum under alkaline conditions. These elements subsequently react with Ca2+ to form gel-like substances, such as C-S-H, which enhance the bonding effect among sludge particles, hydration products of cement, and EP.

Plant roots undergo a life cycle of growth, maturation, and decay, yet the effect of dynamic process of this cycle on the mechanical behavior of the root–soil composite have been largely overlooked. Long-term deterioration of root–soil mechanical properties caused by root decay is a critical consideration in assessing the durability of ecological slope-protection structures. Using Masson pine–covered slopes in Wuping County, Fujian Province as the study subject, this paper employs single-root tensile tests and large-scale direct shear tests on root–soil composites to systematically investigate the evolution of root mechanical properties during mortality dynamics and the corresponding changes in the shear strength of the root–soil composite. The results show that the tensile strength and ultimate tensile force of Masson pine roots decrease exponentially with decay duration. In the early stage of decay, tensile strength declines rapidly by 30%–50%, after which the degradation rate gradually levels off. Root decay significantly affected the shear strength of the root–soil composite: the root-conferred additional cohesion decreases progressively with decay duration, whereas the internal friction angle remains essentially unchanged. Based on the experimental data, we developed a power-law model for root tensile strength and an exponential-decay model for composite shear strength. We further modified the Wu model by introducing a cohesion-decay coefficient to quantify the decay-duration-dependent reduction in shear strength. These findings clarify the mechanism by which root decay undermines soil reinforcement and provide a theoretical basis for long-term stability assessment and maintenance planning of ecological slope-protection projects.

To elucidate the long-term deformation behavior of quasi-saturated subgrade soils under traffic loading, this study investigated the combined effects of initial saturation, wet-dry cycling, and principal stress axis rotation. The key factors considered in this study include the cyclic stress ratio (CSR), cyclic torsional shear ratio ( ), initial degree of saturation, number of wet-dry cycles, and cycle amplitude. Cyclic triaxial and torsional shear tests were conducted using a GDS hollow cylindrical torsional shear apparatus on remolded silty clay, which is representative of subgrade soils in a quasi-saturated state. The results demonstrate that the axial strain is significantly affected by initial saturation; higher saturation levels, which correspond to lower entrapped air content, lead to greater final axial strains. An increase in CSR significantly accelerates strain accumulation, with larger CSR increments resulting in larger strain increments. Similarly, axial strain increases in proportion to the torsional shear ratio, indicating a strong positive correlation. Furthermore, both the number and amplitude of wet-dry cycles contribute to greater cumulative deformation, with the number of cycles having a more dominant impact. These results highlight the critical role of stress path rotation and gas-liquid interactions in governing the deformation characteristics of quasi-saturated soils. The findings provide valuable insights for predicting long-term performance and designing subgrade structures subjected to repeated traffic loads, especially in regions where soils undergo seasonal moisture fluctuations.

Existing studies on the dynamic response of tunnel linings and surrounding soil under explosive shocks primarily treat the soil as isotropic, however, it is actually a transversely isotropic medium. To investigate the axisymmetric dynamic response of transversely isotropic soil under explosive loading, we derive the governing equations for the lining and the surrounding transversely isotropic saturated soil based on Biot’s theory and the theory of transversely isotropic elastic mechanics. The potential function was introduced and Laplace transform and Fourier transform were performed to obtain the general solution. The results indicate that as the transversely isotropic parameter  increases, both the radial displacement and the peak effective circumferential stress of the soil decrease. The peak values of radial stress, circumferential stress, and pore water pressure in transversely isotropic soil occur almost simultaneously at the moment of the explosion. In the axial direction of the tunnel, these responses decay exponentially as the distance from the explosion source increases. When the axial distance reaches six times the tunnel radius, the transient response of the soil approaches zero.

To investigate the temporal influence of thermal ageing on the thermal conductivity of bentonite buffer material under high temperature conditions, MX80 bentonite powder was pretreated at 100 ℃ and 200 ℃ for durations of 0, 15, 30, 60, 90, 120 days. The thermal conductivity of the compacted bentonite samples after pretreatment was measured using the thermal probe method, and the temporal influence was analyzed. The microscopic mechanism underlying the temporal influence on thermal conductivity  of bentonite samples was revealed through particle size analysis, X-ray diffraction and thermogravimetric analysis tests. The experimental results indicate that: 1) After high-temperature aging (100 ℃ and 200 ℃), the thermal conductivity  of bentonite samples decreased significantly with increasing thermal aging time t, demonstrating a significant temporal effect. A sharp decline was observed from 0 to 15 days, followed by stabilization after 30 days. The effect was more pronounced at 200 ℃ compared to 100 ℃. 2) High temperatures (100 °C and 200°C) result in the gradual desorption of various forms of water, thinning of the bound water film, and a reduction in the particle size of bentonite samples. Additionally, at 200°C, some montmorillonite minerals in the samples transform into sodium mica. These microstructural evolutions are consistent with the temporal influence observed in the thermal conductivity  of the samples. 3)The fundamental reason for the temporal influence of thermal aging on the thermal conductivity of bentonite materials is as follows: At 100 °C, as thermal aging time t increases, the temperature effects lead to the gradual desorption of various forms of water, thinning of the bound water film, reduction in particle size, decrease in solid volume, and increase in gas volume, while the mineral composition remains unchanged. At 200 °C, as the thermal aging time t increases, the aforementioned temperature become more pronounced, and the high temperature causes some montmorillonite minerals to transform into sodium mica, which exhibits a lower thermal conductivity .

The application of buffer layer provides an effective solution to the problem of secondary lining failure. Different buffer layer materials exhibit significant variations in mechanical properties, making it essential to establish a widely applicable theoretical model. For this purpose, this study firstly divides the nonlinear compressive stress-strain curve of buffer layer materials into n deformation stages, and the deformation characteristic of each stage is described by replacing with a straight line. Secondly, an interaction mechanical model between rheological surrounding rock and support considering the effect of the buffer layer is established. By using the deformation coordination in both the surrounding rock-buffer layer interface and the buffer layer-secondary lining interface during the whole interaction process, analytical solutions for tunnel displacement and contact pressures at different interfaces during various deformation stages of buffer layer materials are presented. Furthermore, the effectiveness of the proposed theoretical model is validated by comparison with previous studies and numerical results. Finally, a parametric analysis of the mechanical responses of tunnels with polyurethane and polyethylene foam buffer layers (with differing deformation characteristics) is carried out based on the theoretical model. The results show that the proposed model is applicable to different buffer layer materials. The division of deformation stages in buffer layer materials significantly impacts prediction outcomes. For polyurethane foam buffer layer, the prediction result of the secondary lining pressure without considering the deformation stage division is 35.2% higher than that under consideration, while for polyethylene foam buffer layer, the predicted value is even 96% higher than that considering the deformation stage division. For a given tunnel, the thickness of buffer layer has a reasonable range, with an optimal thickness of 25 cm for both polyurethane and polyethylene foam buffer layers under these conditions. Installing a buffer layer is more beneficial for tunnels subject to significant long-term deformation, as it effectively reduces secondary lining pressure and ensures long-term safety.

Freeze-thaw damage is a critical issue in engineering research in cold regions. Rock piles is a unique type of rock-soil mixture. To investigate the mechanical properties of rock piles in cold regions and the meso-scale damage induced by freeze–thaw erosion, the triaxial compression tests were conducted under varying water contents and freeze–thaw conditions. A pore damage increment model was proposed, and the particles (pores) and cracks analysis system (PCAS) method was employed to analyze the evolution of pore structure during the freeze–thaw process. Based on the fractal dimension of porosity, a freeze–thaw damage model was developed to systematically examine the relationship between freeze–thaw cycles and damage in rock piles. Combined with the variation patterns of meso- and macro-scale material parameters, the model’s rationality was verified and the damage mechanisms of rock piles under freeze–thaw action were elucidated. The results indicate that: (1) Meso-scale damage significantly affects macro-scale strength during freeze–thaw cycles. An increase in the pore increment parameter corresponds to a decrease in peak stress, indicating a negative correlation. (2) The peak stress of the rock pile decreases with increasing freeze–thaw cycles. The rate of decrease rises until approximately four cycles, after which the rate gradually declines. (3) The pore increment model, based on the fractal dimension of porosity, effectively confirms that freeze–thaw damage in rock piles increases with the number of cycles at the meso-scale. Model parameters show high consistency with measured data, and its calculations are simpler than those of traditional models.

Ground deformation caused by geological or human activities, such as tunnel excavation, landslides, and faulting, can seriously threaten the integrity of shallow-buried pipelines. However, most studies of buried pipelines rely on saturated-soil mechanics and neglect the influence of matric suction on pipe-soil interaction in unsaturated sand. This study conducted six laboratory model tests on shallow-buried pipes in sand under varying saturation conditions. Tensiometers were installed concurrently at the pipe crown and within a 45° shear band. Particle image velocimetry (PIV) was used to measure the displacement field, enabling quantification of the coupled evolution of suction, deformation, and failure during pipe uplift. Based on these observations, we propose a simplified mechanical model of pipe-soil interaction. The model assumes an inverted-trapezoidal wedge failure mode and applies limit-equilibrium theory. Equivalent suction stress is incorporated into shear strength to derive a closed-form expression for the ultimate uplift resistance. Results show that matric suction increases peak pipe-soil uplift resistance in unsaturated sand to approximately 3-4 times the value observed in dry or saturated conditions. The displacement required to reach this peak increases by about 30%. Around the pipe, soil fails as an inverted trapezoidal wedge. Under unsaturated conditions, the wedge width is approximately 6D （D is the outer diameter of pipeline）and the shear-band inclination about 40°, significantly larger than the 4D width and 25° inclination observed in dry or saturated sand. The simplified analytical model predicts both the current experimental data and published sand data with errors generally within ±15%. We establish an integrated framework linking the evolution of suction and displacement fields, identification of deformation and failure mechanisms, and simplified mechanics-based analysis. The simplified mechanical model can be used for engineering estimates and design verification of ultimate uplift resistance for shallow-buried pipelines in sand at various saturation levels.

Vertical upheaval buckling is a critical instability mode in buried pipelines and poses substantial risks to pipeline safety. Most prior studies have focused on upheaval behavior under flat terrain, with limited attention to failure mechanisms on slopes. In this study, model tests of buried-pipeline upheaval on slopes were conducted using distributed fiber-optic sensing and particle image velocimetry (PIV). We systematically analyzed soil deformation and failure mechanisms, and the mobilization of uplift resistance, under varying slope angles and burial-depth ratios. The results show that, 1) Increasing slope angle gradually reduces the soil’s peak uplift resistance, while higher burial-depth ratios significantly enhance both peak and residual uplift resistances. 2) Regardless of slope angle or burial depth, the pipeline displacement at the onset of residual resistance is approximately 0.2D, where D is the pipe outer diameter. 3) During the uplift process, the pipe cross-section undergoes ovalization, and a wedge-shaped failure zone forms in the overlying soil. Based on these findings and Mohr’s circle theory, we propose a method to calculate the peak soil resistance of pipelines under slope conditions. These findings advance understanding of soil–pipeline interaction on sloped terrain and provide theoretical and practical guidance for the design and safety assessment of buried pipelines in complex geological settings.

Soil nailing reinforcement is a widely used reinforcement method for the granite residual-soil slopes in the Guangdong-Hong Kong-Macao Greater Bay Area. The region experiences frequent rainfall, and the interface between soil nails and granite residual soil is subject to wet-dry cyclic effects, gradually weakening the interface shear strength. This weakening effect accumulates with increasing cycles, leading to reduced slope stability. However, the cumulative weakening of the interface shear strength under long-term wet-dry cycles remains unclear. To address this, a series of small and large-scale direct shear tests was conducted under high wet-dry cycling conditions (up to 100 cycles) to analyze variations in cohesion, friction angle, shear strength, and other parameters of the nail-soil interface, considering the number of wet-dry cycles and interface saturation under consistent vertical stress conditions. The cumulative weakening effect of the nail-soil interface was quantified. Experimental results indicate that the apparent cohesion of the interface weakens rapidly during the first 10 cycles, but the rate of weakening stabilizes afterward. However, the total accumulated weakening remains significant. The friction angle of the interface did not exhibit a regular pattern of change as the number of wet-dry cycles increased. A neural network model was developed to predict the cumulative weakening of the shear strength of the nail-soil interface, and its accuracy was quantitatively evaluated and validated. The analysis reveals that the overall error of the neural network model is less than 10%, with low variability in prediction accuracy. The findings of this study provide theoretical support for assessing the long-term stability and predicting slope failure in soil nail reinforcement of the granite residual soil slopes in the Guangdong-Hong Kong-Macao Greater Bay Area.

To reasonably capture the magnitude, distribution, resultant force, and action point height of lateral earth pressure with depth on retaining structures for a circular foundation pit in unsaturated soils, the inclination angle of the soil sliding surface behind retaining structures was first derived. The derivation, suitable for both uniform and linear profiles of suction stress, was based on the suction stress theory of unsaturated soils and the limit equilibrium method. Subsequently, a method for calculating lateral earth pressure on retaining structures of circular foundation pits in unsaturated soils was introduced by integrating the characteristics of vertical and circumferential soil arches to account for the spatial soil arching effect. Additionally, the proposed calculation method was validated by comparing it with existing theoretical solutions and model test data, and the influence of relevant factors was analyzed. The results show that the proposed calculation method not only demonstrates excellent consistency with existing theoretical solutions and model test data, confirming its accuracy and rationality, but also effectively addresses the comprehensive effects of unsaturated formation, spatial soil arching, and structure-soil contact parameters on the lateral earth pressure of circular foundation pits. This contributes to optimizing the design and construction of circular foundation pits. Consequently, the proposed calculation method holds theoretical significance and promising practical applications. The resultant force of lateral earth pressure for a foundation pit significantly decreases with an increase in absolute value of surface suction stress, circumferential stress coefficient, and external cohesion. However, the variation in the action point height of the resultant force remains relatively minor. Lateral earth pressure under a linear profile of suction stress is greater than under a uniform profile. However, the variation in lateral earth pressure is more pronounced under the uniform profile of suction stress

The minimum tunnel overburden thickness is a critical parameter in underwater tunnel construction. To calculate the minimum tunnel overburden thickness considering the influence of grouting, an analytical solution for the seepage field of an underwater tunnel influenced by grouting is derived using the mirror method and seepage mechanics theory. The solution is refined using the Japanese minimum seepage method. The accuracy of the theoretical solution is verified through formula simplification and laboratory simulation tests. Using this solution, this paper investigates the influence of parameters including the relative permeability coefficient of grouting, grouting range, and water depth. The findings show that, at different depth ratios, water pressure outside the tunnel lining increases linearly with head height. A lower depth ratio increases the sensitivity of external water pressure to water depth variations. Improving the permeability of the grouting ring reduces tunnel seepage more effectively than enlarging the grouting range, especially within a range of 1 m to 3 m, where the effect is most pronounced. In the absence of grouting, the tunnel overburden thickness is highly sensitive to changes in water depth, and enhancing the permeability of the grouting material can significantly mitigate the impact of water depth. For high-risk tunnels, high-permeability grouting materials with a thickness exceeding 5 m are recommended. In conventional projects, a grouting range of 1–3 m provides an optimal balance between safety and cost.

Prior to geotechnical design and construction, it is quite necessary to thoroughly understand the geological conditions of the project site to ensure the safe operation of the project during subsequent stages. Reconstructing the three-dimensional geotechnical stratigraphy provides an effective approach for accurately understanding the geological conditions of the project site. Due to the complexity of geological structure spatial characteristics and the sparsity of site exploration data, it is difficult for traditional methods to reveal the boundary patterns and spatial distribution characteristics between different strata based on a small amount of site exploration data. Reconstruction of the three-dimensional stratigraphy based on limited site exploration data still faces considerable challenges. To address this problem, a series of three-dimensional distance field features is used to characterize the potential boundary characteristics between strata. This paper introduces the feature selection process of the distance field and proposes a three-dimensional stratigraphic reconstruction method based on a boundary dictionary-random forest (BD-RF) model. The effectiveness of the proposed method is validated through two engineering cases. The results indicate that the proposed method, by employing a series of three-dimensional distance field features, can effectively capture the stratigraphic distribution patterns revealed by drilling data. Compared with other methods, the proposed method has significant advantages in predicting the boundary characteristics between different strata, providing an effective analytical tool for reconstructing three-dimensional geotechnical models based on limited drilling data in practical engineering applications.

To study the failure mechanism of deep pillars and the reinforcement effect of rockbolts, a Voronoi breakable block model (VBBM) on the basis of the combined finite-discrete element method (FDEM) was proposed to characterize rock pillars. Laboratory- and field-scale uniaxial compression tests were conducted to develop a parameter calibration method and to validate the model. Combined with the fully grouted rockbolt model, the study explored the progressive damage mechanism of the pillar and the supporting effect of rockbolts. The results show that the proposed parameter calibration method effectively utilizes laboratory data to determine the model parameters for rock pillars at different scales. Based on reasonable parameter settings, it is found that the model can effectively capture the macroscopic failure mechanisms, including initial edge spalling, shallow-surface spalling, and deep conjugate shear failure within pillars. The width-to-height ratio (W/H) is identified as the fundamental factor influencing the transition from strain-softening behavior to pseudo-ductility behavior of pillars and the deformation differences in the core zone. Passive confinement from rockbolts activates when the pillar undergoes sufficient volumetric expansion. The constraints generated by rockbolts significantly affect the post-peak deformation behavior of pillars. The deformations of pillars exhibit a gradient feature from the shallow surface toward the core. The crack aperture and kinetic-energy release rate are negatively correlated with rockbolt support pressures, which shows a strong power-law relationship. This indicates a transitional range of supporting pressure and an optimal rockbolt spacing. The study provides a powerful analytical framework for elucidating the progressive failure mechanism in deep rock mass, and offers theoretical support for disaster risk assessment and rock-support reliability evaluation in deep mining.

The heterogeneity in breccia content and geometry significantly influences the variability of the mechanical properties of sandstone containing breccia clasts. However, previous studies have often neglected the distribution of breccia geometry, resulting in inaccurate assessments of mechanical behavior. To investigate mechanical properties and determine the minimum number of samples for testing, particle-shape indices were introduced to quantify breccia geometry and its statistical distribution. Using laboratory experiments and numerical simulations, we developed a model that incorporates breccia content and the distribution of breccia geometry. The study explored the effects of breccia area, slenderness, and roughness on the mechanical properties of sandstone containing breccia clasts, along with their impact on the minimum sample number. The findings reveal a strong positive correlation between breccia content and fine length with the uniaxial compressive strength of sandstone containing breccia clasts, with Pearson correlation coefficients of 0.87 and 0.62, respectively. In contrast, breccia roughness exhibited a weaker correlation, with a Pearson coefficient of 0.31. Increasing the variability of the fine length of the breccia significantly elevated the minimum sample number, while variability in breccia roughness had no significant effect. Although the area of individual breccia particles did not alter the minimum required sample number, it contributed to an increase in the uniaxial compressive strength of the sandstone with breccia clasts. This study reveals the underlying causes of the variability in the mechanical properties of sandstone containing breccia clasts and establishes a dynamic approach to determine the minimum sample number, which was found to be 14. The proposed method achieved a relative error of less than 2% in predicting the uniaxial compressive strength. These findings provide valuable insights into evaluating mechanical properties and determining its minimum required sample number.

Deep-sea pipelines are typically laid on the seabed. Under the influence of their own weight and pipeline-laying operations, they become embedded into the seabed. The embedment depth wini significantly affects the lateral soil resistance exerted by the seabed on the pipeline. Existing research has primarily focused on pipelines with embedment ranging from 0.1 to 0.5 times the pipe diameter D. However, recent studies show that some pipelines embed deeper than 0.5D. We employed the radial point interpolation method-remeshing and interpolation technique with small strain (RPIM-RITSS) to perform large-deformation analyses of the lateral pipe-soil interaction for initial embedment from 0.1D to 1.0D. The method’s effectiveness was validated by comparisons with centrifuge tests and other numerical results. Subsequent analyses examined how initial embedment and pipe weight influence the lateral-buckling mode and soil resistance. A residual-resistance model for lateral buckling, applicable to initial embedment from 0.6D to 1.0D, was proposed to support the safe design of deep-sea pipelines.

The use of levees is one of the most prevalent and effective strategies for flood protection. However, owing to the ageing of levees, inconsistent reinforcement efforts, and complex geological conditions, hazards such as piping frequently arise during flood seasons, which lead to significant and often irreparable damage. This study investigates backward erosion piping (BEP) in the foundations of double-structured levees via a back-propagation (BP) neural network optimized by a genetic algorithm (GA). The primary contributions of this study include: 1) the construction of a training dataset through numerical simulations of BEP in heterogeneous aquifers and validation of the dataset against laboratory sandbox piping tests to verify its reliability; 2) the extraction of head H and permeability coefficient K data from Groups II, III, and IV in the BEP laboratory tests, augmentation of the dataset, and optimization of the GA–BP model to characterize test results in Group I, where the results demonstrate that the optimized model more accurately characterizes areas where the K≤1.0 cm/s; and 3) the use of the optimized GA-BP model to characterizes the development of a BEP channel. The results indicate that the model accurately captures the general trends. However, minor discrepancies remain in the characterized channel location and size compared with the actual conditions. In conclusion, this study offers an effective tool for characterizing BEP and demonstrates the potential of the GA–BP network model for practical applications in this field.

Fractures are the primary pathways for fluid flow in rock masses, and they commonly occur as interconnected networks. Rock grouting is a process in which flowing water is displaced by grout. Since rock fracture networks are formed by a large number of crossed fractures, it is of great significance to study the displacement of grouts under the action of flowing water for designing effective grouting schemes. In this study, a rough orthogonal fracture model was established using three-dimensional reconstruction, and a laboratory visualization grouting test was conducted. We developed a numerical orthogonal fracture model using COMSOL Multiphysics to investigate the effects of fracture roughness, the grout-to-water flow rate ratio, and inlet–outlet configurations on the grout–water displacement process. After validation, the experimental and simulation results suggest that grout primarily fills well-connected channels. Grouting pressure rises rapidly after injection and stabilizes once most water is displaced. Efficient mixing at intersections yields more consistent grout volume fractions across branches. Displacement efficiency is governed by the dominant flow channels. If the conventional parallel-plate model is used, which ignores fracture surface roughness, the grouting pressure may be underestimated by more than 30%.

The quartet-parameter structure generation set (QSGS) method is a commonly used modeling algorithm for porous media. The fractal dimension D and pore autocorrelation distance  of porous media are important indicators for evaluating modeling effect. There is currently a lack of research on the relationship between the parameters of the QSGS method and the fractal dimension, as well as the pore autocorrelation distance of porous media. A method for normalizing the probability distribution of the cores of growth phase is proposed, and a set of numerical simulation schemes for modeling porous media with different grid sizes N, porosities  and normalized distribution probability is designed on this basis. Then the variations of D and  with the modeling parameters N,  and P are analyzed based on the numerical simulation results, and the sensitivity of the modeling parameters is analyzed based on the orthogonal tests. Finally, the fitting relationships between the modeling parameters N, , and D,  are established. The results show that the modeling parameters N,  and P all have a certain degree of influence on D, and the degree of influence is ,  and N in descending order. The main influencing factor of  is , and the other parameters have less influence. The constructed multiple regression fitting models have high precision and can be used to guide the modeling of the QSGS method.