This study investigates the time-dependent seepage–deformation response and interfacial failure mechanisms of a pipeline-embedded earth dam under cyclic impoundment-infiltration loading. A full-scale in-situ test with controlled water-level variations recorded the spatiotemporal evolution of pore-water pressure, earth pressure, and displacement. Results revealed cumulative pore-pressure buildup near the pipe, progressive effective stress reduction, and irreversible moisture infiltration leading to nonlinear "heave–settlement" displacement cycles. Non-destructive testing identified a four-stage interfacial failure process: cavity initiation, localized seepage, erosive zone expansion, and preferential flow channel connection. Based on these findings, a transient seepage–stress coupling model was developed and validated using the experimental data. Parametric studies showed that higher impoundment levels accelerate pore-pressure rise and stress degradation, while improved backfill compaction significantly reduces failure-prone seepage paths. Furthermore, a stepwise impoundment strategy ("raise–stabilize–raise") was effective in attenuating peak pore pressures and delaying hydraulic instability. This research establishes a new framework for understanding interfacial seepage failure in pipeline-embedded embankments and offers guidance for optimizing water-level management and anti-seepage design to improve dam stability under cyclic loading.

This study develops an enhanced semi-analytical framework by coupling the scaling surface-based scaled boundary finite element method with a modified Picard iterative linearization scheme. The governing formulation is established from Richards' equation, with the Gardner-Basha model adopted to describe pressure-head-dependent hydraulic conductivity and water retention behaviour. To treat heterogeneous media, a scaling surface is constructed consistently with the near-far field interface, allowing different material zones and their interfaces to be mapped along the radial direction while preserving hydraulic continuity across heterogeneous regions. Within each Picard iteration, the nonlinear hydraulic prope hydrorties are updated locally according to the current pressure head and relaxed to improve convergence robustness. The steady-state and transient seepage matrices are obtained by eigenvalue decomposition of the Hamiltonian system and continued-fraction expansion, respectively, and the time-domain solution is then computed using the Crank-Nicolson scheme. A series of benchmark and engineering-oriented examples are conducted to assess the accuracy, robustness, and efficiency of the proposed method. The results demonstrate that the proposed formulation accurately captures transient hydraulic-head redistribution, seepage-flux evolution, interface-induced flow refraction, and attenuation behaviour in heterogeneous half-spaces. Compared with conventional full-domain discretization methods, the proposed approach achieves comparable accuracy with substantially fewer degrees of freedom and reduced computational cost.

Horizontal contact erosion at the structure-soil interface is a critical trigger for various engineering failures. However, systematic investigations into its mechanism at internal structural interfaces remain insufficient. This study focuses on the horizontal contact erosion along the pipe axis at the concrete-soil interface in dam engineering. The horizontal contact erosion tests were conducted at the interface, and established and validated a CFD-DEM coupled numerical model. The evolution of interfacial horizontal erosion was revealed through parameter analysis. Subsequently, a global sensitivity analysis of the factors was conducted based on a self-developed multi-factor rapid prediction model for erosion quality. The results indicate that fine-particle horizontal contact erosion presents four-stage evolutionary characteristics. The erosion mode gradually transforms from dispersed pore scouring to connected channel erosion. Increasing confining pressure from 16 kPa to 80 kPa reduces erosion mass by 34.21%, whereas increasing fine-particle content (20% similar to 40%), particle gradation (4.0-6.0), and concrete particle radius (0.25 mm similar to 1.25 mm) increases erosion mass by 744.23%, 278.45%, and 85.44%, respectively. Smaller concrete particle radius induces early-stage erosion, while larger radius enhances late-stage erosion mass. Rising flow velocity intensifies the competition between heterogeneous seepage driving force distribution and the pore clogging effect. Compared with both the simulation and experimental results, the proposed prediction model shows high prediction accuracy, with absolute errors controlled within 9.38%. The factor sensitivity ranks as: particle gradation > fine-particle content > concrete particle radius > confining pressure > flow velocity. Erosion mass is mainly dominated by the main effects of each parameter with negligible inter-parameter coupling effects.

Track slab concrete (TSC) and filling layer self-compacting concrete (FLSCC) are the key materials used in the China Railway Track System (CRTS) III slab ballastless track. Understanding the dynamic damage evolution of TSC and FLSCC under load is essential for assessing the stability and safety of the slab tracks. In this study, the damage characteristics of TSC and FLSCC were investigated under uniaxial compression based on the acoustic emission (AE) technique. The results showed that the AE events occurred in the failure process and were the most significant during the yielding stage. The AE analysis revealed that the damage of TSC and FLSCC specimens was predominantly tensile cracks, accounting for 70.33

The self-healing behavior of concrete is crucial for enhancing the durability of underwater concrete structures. Cementitious Capillary Crystalline Waterproofing material (CCCW) interacts with substances within the concrete to generate crystals that fill the pores and cracks, thereby improving its self-healing capacity. This study systematically investigates the self-healing behavior of cracked concrete following the incorporation of CCCW and curing in a water environment. The effects of CCCW dosage on the crack healing process for concrete with different strength and crack width were studied and analyzed. The healing performance and microscopic mechanisms were analyzed via permeability tests, surface crack monitoring, and SEM/XRD characterization. Results indicate that the incorporation of CCCW material significantly enhances the self-healing performance of cracks. At a 5% CCCW content, the self-healing rates for 0.1 mm, 0.3 mm, and 0.5 mm cracks increased by 94.7%, 65%, and 45.39%, respectively, compared to the specimen without contain CCCW. However, with 5% CCCW content, the healing performance gradually weakened as both crack width and concrete matrix strength increased. Microstructural characterization analysis revealed that CCCW promotes crack self-healing and guides the formation of C-S-H gel, leading to a dense microstructure of hardened cement hydration products. Furthermore, a multi-factor theoretical model for water permeability, based on the principle of mass conservation, was established, showing high consistency between theoretical calculations and experimental values. These findings provide crucial theoretical guidance and technical support for crack control and self-healing design in hydraulic concrete structures.

In this study, a sensing-inversion method was proposed to investigate the mechanical response mechanisms of shield tunnels under heavy rainfall conditions, integrating displacement monitoring, distributed fiber optic sensing, and a strain-displacement-internal force recursive inversion method. Physical model tests were conducted to simulate interactions between heavy rainfall, soil strata, and tunnel structures. Laser displacement sensors and distributed optical fibers were used to monitor dynamic structural deformations and strains. An inversion model based on elastic foundation curved beam theory was developed to quantitatively analyze tunnel deformation evolution, load development mechanisms, and internal force distribution characteristics. The results indicate that the proposed inversion method improved accuracy by over 80% compared to conventional models and effectively captured radial displacements and internal force distributions. Under rainfall loading, the tunnel lining exhibited elliptical deformation and settlement, accompanied by compressive stresses at the crown and invert. The region of compressive stress expanded with increasing overburden thickness, whereas tensile stress developed at the haunches. The compressive stress at the crown exceeded that at the invert. When the tunnel was deeply buried, longer rainfall infiltration paths delayed structural responses to water penetration. Furthermore, deep overburden facilitated the dispersion localized stress concentrations in the lining caused by rainfall.

Local scour around the semiconical structure of a monopile was systematically studied considering the side slope angle (alpha = 0 degrees-60 degrees), protruding height (E/d = 0-2), and flow intensity (clearwater or live-bed flow conditions). The three-dimensional scour profiles and features were meticulously explored using flow visualizations through large-eddy simulations. As the semiconical structure was buried in the seabed (E/d = 0), increasing side slope angle alpha from 0 degrees to 60 degrees reduced the maximum scour depth Smax by 53 % compared with the results of the monopile without the countermeasure. At E/d = 2, the maximum scour depth occurred at the downstream edge for alpha >= 30 degrees, while the scour upstream was significantly diminished. Smax decreased significantly with an increase in alpha. At alpha = 60 degrees, the reduction of Smax is up to 100 %. Vortex shedding also diminished owing to the semiconical structure. An increase in E led to a reduction in Smax, while the flow intensity had a limited impact. An equation for predicting scour-protection efficiency was derived from experimental results; it shows good predictive performance, with errors within 20 %.

Rapid restoration of ballastless track settlement requires grouting materials that can rapidly develop sufficient bearing capacity and maintain stable performance under repeated train loads. In this study, a novel early-strength and fatigue-resistant polymer (ESFRP) was developed and systematically investigated. Uniaxial compression tests at different curing ages and fatigue compression tests under various stress ratios were conducted on ESFRP specimens. Acoustic emission and digital image correlation techniques were used to characterize the damage evolution during compression, while computed tomography and scanning electron microscopy were employed to investigate the micro- and meso-structural characteristics and failure mechanisms. The results show that the compressive strength of ESFRP reached 43.51 MPa after 1 h and stabilized at about 63.85 MPa after 28 d, indicating excellent early-strength performance. The average peak strain reached 32.78%, reflecting pronounced ductile behavior. A constitutive model related to curing age was established. Under low stress level cyclic loading closer to train-load-induced service conditions, ESFRP maintained stable deformation behavior and a stable dynamic elastic modulus after 4 × 10⁶ cycles, with the accumulative axial strain reaching only approximately 0.051%. Microstructural analysis indicates that ESFRP is a dense multiphase composite with very low porosity, which provides the structural basis for its high early strength and deformation capacity. Under uniaxial compression, fracture of SiO2 particles is a major microstructural feature of the final failure stage, while fatigue loading mainly induces damage accumulation and lamellar tearing in the polyurea matrix. These findings provide experimental evidence supporting the potential application of ESFRP in ballastless track settlement restoration.

This study presents a semi-analytical computational framework based on the scaled boundary finite element method (SBFEM) combined with a modified Picard iteration scheme for solving transient saturated-unsaturated seepage problems. Richards' equation is adopted as the governing model, and the Gardner-Basha constitutive relationships are used to describe the pressure-head-dependent hydraulic conductivity and water retention behavior. Starting from a frequency-domain formulation and low-frequency expansion, the governing equations are derived within a unified framework based on an energy functional and the variational principle, leading to the transient Picard-SBFEM formulation. An adaptive relaxation strategy is introduced into the linearized Picard iteration to improve nonlinear convergence robustness, and the resulting system is discretized in time using the Crank-Nicolson scheme. The proposed method is validated through benchmark problems involving homogeneous and heterogeneous media, rainfall infiltration, and moving phreatic-line evolution. The results show good agreement with analytical solutions, experimental data, VEM, IGA, and FEM results. Additional mesh refinement, time-step refinement, and nonlinear convergence studies further demonstrate the spatial-temporal reliability and iterative robustness of the proposed formulation. Compared with the reference numerical methods, the proposed method achieves comparable accuracy with fewer DOFs or elements and lower CPU time, demonstrating improved computational efficiency while maintaining reliable accuracy.These findings indicate that the proposed Picard-SBFEM framework provides a reliable and efficient computational approach for nonlinear transient seepage analysis in saturated-unsaturated media.

Earth dams with embedded structures such as culverts and pipelines are essential components of modern hydraulic systems, facilitating water diversion, drainage, flood discharge, and cross-dam transport. However, these internal inclusions create material discontinuities and weak interfaces, making the dam susceptible to seepage-induced damage. This study investigates the mechanisms of contact leakage and the effectiveness of polymer grouting repair through a comprehensive framework integrating theory, full-scale physical testing, and numerical modeling. A full-scale embankment model with dual embedded pipelines was constructed to replicate seepage damage under controlled hydraulic loading. Advanced multi-sensor monitoring alongside geophysical techniques accurately captured the initiation and development of seepage and enabled precise localization of defects. Two polymer grout types—expandable and permeable—were applied for targeted remediation. Results show that by precisely controlling the rates of gas generation and curing during the polymerization process, porous foam or network gel microstructures are formed. These microstructures not only effectively densify and block seepage pathways but also significantly improve interfacial adhesion, reduce internal friction, and enhance the overall load-bearing capacity and deformation compatibility of the interface, thus realizing a synergistic sealing and flow-guiding effect. A validated 3D dam-pipeline coupled numerical model through test results was developed to simulate seepage-stress interaction and assess dam stability before and after repair using the strength reduction method. The findings highlight the critical role of interface conditions in seepage damage and demonstrate the engineering feasibility of polymer grouting repair technology for embedded pipeline dams.

Engineering construction in weak geological formations frequently confronts significant challenges related to foundation stability. This is primarily owing to the low shear strength, high compressibility, and high moisture content. These problems are particularly acute in extensively distributed problematic soils such as weathered clay. To ensure construction safety and long-term performance, weak foundations need to be strengthened. This study introduces a double yield surface constitutive model designed to simulate the mechanical response of chemically treated soils. The model couples bonding degradation and fabric hardening within a geometric damage framework, enabling a unified description of the evolving mechanical response of treated soils. Validation was conducted using drained and undrained triaxial tests on cement soil and polymer clays with varying curing agent contents. The results demonstrate that the model accurately captures the stress-strain behavior of treated soils across both brittle and ductile failure modes. To improve the computational efficiency and facilitate practical implementation, the model is embedded into ABAQUS via a mixed explicit-implicit algorithmic framework using user subroutines. The model’s applicability is demonstrated through a simulation of subgrade reinforcement for pavement lifting in a weathered red clay formation in South China. The case study highlights its potential to inform geotechnical design and decision-making in challenging soil conditions.

The scour protection performance of the conical structure under different slope angles, α, was investigated through numerical simulations. By solving the Navier–Stokes (N–S) equations, using the Renormalization Group (RNG) k–ε turbulence model and the Meyer-Peter and Müller (MPM) sediment transport formula, the scour protection performance, undermining process, and the flow field around the devices were fully analyzed at different slope angles. The findings indicate that the conical scour protection provides effective protection against scour damage. As the slope angle increases, greater scour depth is observed around the structure. A critical slope angle was identified between 30° and 40°, slope angle effects are obvious below the threshold; otherwise, it minimized. Undermining is the main cause of failure of such stiff scour protection, mainly driven by flow contraction and sand sliding. Upstream undermining beneath the structure is more pronounced, while the downstream undermining is largely related to the near-bed flow separation point. The critical undermining point (CUP) is proposed based on the undermining curve to distinguish the undermining state, which is critical in scour protection and structural stability.

Rockfall seriously threatens the construction and operation safety of karst tunnel. Obtaining the damage characteristics of tunnels under rockfall impacts is of great significance to optimize the design of protective structures, but is still unclear. In this study, a bond-based peridynamic (BBPD) method taking the strain rate influence of failure criterion into account is proposed. The accuracy and effectiveness of the proposed BBPD method was verified by comparing it with two experimental tests. Further numerical analyses using the proposed BBPD method were conducted to identify the influence of factors, including the impact velocity and impact position, on the damage characteristics of protection measures of a karst tunnel under rockfall impact. Protection measures include the composite lining, the composite lining with reinforced arch, and the composite lining with reinforced arch and buffer layer. The results show that the structural damage index follows a three-stage growth rule, including rapid growth period, slow growth period, and gradual stability period. The impact velocity and position have a significant effect on the structural damage index. The higher the impact velocity and the closer the impact position to the structural vault area, the greater the structural damage index. Under the three protection conditions, the tunnel damage index basically meets the requirements from large to small: the composite lining > the composite lining with reinforced arch > the composite lining with reinforced arch and buffer layer. The advantage for damage index reduction is not obvious for polyurethane thicknesses over 2.5 m. Finally, a composite lining with reinforced arch and buffer layer is proposed, which can resist the impact of the rockfall with a mass of 7.5 t falling freely from 105 m.

The pipe culvert embedded in the embankment is a critical structure in hydraulic engineering; its stability under unsteady seepage flow is of paramount importance. However, the mechanical responses of embankment (containing pipelines) under water level fluctuations remain insufficiently studied, and further discussion is needed. This study aims to investigate the impacts of water level fluctuations on the deformation and seepage field of embankments, as well as the strain of pipelines, through full-scale experiments. Furthermore, a finite-element model based on seepage-stress coupling theory is developed to simulate the deformation behavior of the embankment and the evolution of the internal seepage field under varying fluctuation rates. Additionally, the mechanical response of the pipelines' most critical cross section is analyzed. The results indicate that both circumferential and longitudinal pipe strains propagate downstream along the pipeline, exhibiting a nonmonotonic distribution. Moreover, the peak longitudinal strains at the pipe invert are more localized than the peak circumferential strains. The bending moment displays limited sensitivity to water level fluctuations, with a maximum variation of only 5.86% throughout the entire testing period. During the rapid water level rise phase (vh = 0.2 m/h, vh is the water level fluctuation rate), the displacement at the upstream slope monitoring point (0.2459 mm) was 2.36 times greater than that at the downstream slope monitoring point (0.1041 mm), whereas longer fluctuation durations (48 h) allowed the system to stabilize, leading to significant reductions in both pore-water pressure and overall displacement. These findings provide valuable guidance for the safe design, monitoring, and maintenance of pipeline-containing embankments in environments subject to frequent variations in reservoir levels.

Heat-related challenges in tunnel engineering, particularly in high geothermal areas, pose significant risks to both personnel and equipment. This study investigates the cooling performance of sprayed polymer thermal insulation layers (SPTIL) in tunnels under hydrothermal environments, addressing a critical gap in prior research, which has largely ignored the effects of high-temperature water. Through integrated numerical and experimental analyses, the applicability of the equivalent thermal resistance theory and the water-rock convective heat transfer coefficient was validated for evaluating the cooling effect (CE) of the SPTIL, defined as the temperature difference between the inner and outer surfaces of the insulation layer. The results demonstrate that the cooling performance of SPTIL is governed by five dominant control factors: the thermal conductivity and thickness of the SPTIL, the thermal conductivity of the surrounding rock, the temperature of the groundwater, and the location of the water-bearing fracture. Among these, only the thermal conductivity of the SPTIL is inversely correlated with the cooling effect, while the other four factors exhibit positive correlations. The evolution of the temperature field exhibits a characteristic three-stage pattern with increasing radial distance from the tunnel center. Subsequently, a regression-based predictive model was developed to quantify the cooling effect of SPTIL, with validation demonstrating excellent agreement between predicted and measured values. Suitable design parameters for the SPTIL in high-geothermal tunnels are proposed, which are applicable when the rock temperature is below 65 degrees C and the water temperature is below 80 degrees C. These parameters are namely a thermal conductivity not exceeding 0.045 W/(m & sdot;K) and a thickness ranging from 5 to 15 cm. Finally, a field-applicable technical framework was established, integrating rock temperature and water temperature to optimize SPTIL deployment. Together, the predictive model and technical framework provide a solid theoretical foundation for enhancing the protective capabilities of SPTIL in high-temperature water tunnels.

Accurately evaluating the evolution of interfacial bonding properties between track slabs and selfcompacting concrete (SCC) filling layers over time is crucial. In this study, push-out tests were conducted on track slab concrete (TSC)-SCC composite specimens at different ages, and the acoustic emission (AE) technique was used to monitor the process. The results revealed that the interfacial shear strength of the 56-day specimen reached 1.275 MPa under a test loading rate of 0.01 MPa/s. Additionally, a predictive model for the shear strength of the TSC-SCC interface was established. The TSC-SCC specimens exhibited brittle failure under shear load. The sharp increase in AE ringing counts and energy showed the rapid development of interfacial damage. Both the conventional Japanese Construction Materials Standard method and the Gaussian Mixture Model algorithm effectively revealed the evolution of crack types in TSC-SCC specimens, and their trends and magnitudes of change were nearly identical. As the curing age increased, shear cracks became more prevalent while tensile cracks diminished. This change in the failure mode of the specimens can be attributed to the increased degree of cement hydration. This study offers a valuable reference for the design, operation, and maintenance of the CRTS III slab track.

Sprayed polymer (SP) is increasingly adopted as a waterproofing spray material for underground structures in hot, water-rich environments. However, the interfacial properties and waterproofing failure mechanisms of shotcrete-sprayed polymer (SC-SP) composites under such hygrothermal conditions remain poorly understood. Through a novel integration of muti-scale experimental techniques, this study comprehensively investigates these mechanisms under hygrothermal aging (65 degrees C, 95 % Relative Humidity (RH) for 0-56 days). The research combines interfacial bonding performance tests with acoustic emission (AE) monitoring, as well as interfacial waterproof performance tests synergized with AE and infrared thermography. The results indicate that the interfacial failure modes of SC-SP composite structures can be categorized into three types, with Mode II identified as the dominant failure type. The stress-displacement curves exhibited a three-stage characteristic: an initial linear rising stage, a progressive nonlinear rising stage and a final stepwise descending stage. Additionally, the microcrack propagation evaluated using a three-stage model, namely, negligible, stable, and sharply accelerated. The propagation of finer microcracks is a typical feature of microcrack size development, while the growth of tensile microcracks is characteristics of microcrack type evolution. A key finding is the first identification and quantification of a distinct two-stage interfacial flow process (from flow to seepage) by uniquely correlating AE waveforms and infrared thermography with hydraulic pressure. Furthermore, a bilinear displacement response model was developed, and an integrated, microcrack-controlled framework was established to assess the interfacial waterproof potential. This study provides a practical micro-damage-based predictive tool for optimizing the waterproof performance of SC-SP composite in hygrothermal environments, offering significant value for durability design in underground engineering.

Loess is extensively distributed across China. Roadbeds constructed in loess regions are susceptible to water damage, leading to pathologies such as settlement and collapse that severely compromise the stability of road structures. Polymer grouting technology, as a novel trenchless repair technique, minimizes disturbances to the existing roadbed while offering rapid and effective construction. This study employs micro-scale testing, macroscale testing, and fatigue testing methodologies to investigate the enhancement effects of permeable polymer grouting on the load-bearing capacity and fatigue performance of loess roadbeds. Through microscopic examination using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and X-ray powder diffraction (XRD), this study reveals the correlation between the microstructure of polymer grout and the enhancement of loess's mechanical properties. Concurrently, mechanical and fatigue testing evaluated the performance enhancement of permeable polymer grout-reinforced loess subgrades. The results indicate that after polymer grouting, total porosity dramatically decreases from 38.64% to as low as 12.44% at 13% moisture content. The mean pore diameter reduces from 288.83 nm to 134.92 nm, the proportion of micropores increases from 13.75% to 59.96%, while macropores decrease from 33.29% to 9.31%. XRD analysis confirms no new mineral phases are formed, indicating that reinforcement occurs purely through physical pore filling and interparticle cementation. The damage constitutive model established based on the Weibull distribution accurately captures stress-strain behavior under uniaxial compression conditions. Fatigue testing demonstrates that polymer grouting significantly extends fatigue life, with specimens withstanding up to 200,000 cycles. These findings provide a detailed understanding of the multi-scale reinforcement mechanism of polymer-grouted loess, offering a theoretical basis for this material's application in sustainable subgrade engineering.

The thermal insulation and impermeability of polymer grouting material could reduce the temperature variation and the water migration of permafrost embankments in cold region. This study proposed a new heat-moisturedeformation coupling numerical model for permafrost embankments with polymer grouting layers. The model was verified by an in-situ test and the observed data from the National Cryosphere Desert Data Center (NCDC). The long-term impacts of polymer grouting layer interval and thickness on the temperature and deformation distributions were further investigated. The results reveal that the polymer grouting layer functions as a thermal barrier and an impermeable curtain, which effectively decouples the heat and moisture exchange between the upper embankment and the underlying permafrost, thereby raising the permafrost table and mitigating the extreme frost heave and thaw settlement. And the simulations demonstrate that after six years of grouting, the active layer thickness stabilizes, showing a reduction of up to 35 % compared to the ungrouted embankment (PEU). Most notably, an optimal layout was identified: when two polymer grouting layers with 3 cm thickness are set at depths of 0.75 m and 2.5 m, the long-term frost heave at the pavement center can be reduced by 69.4 %, and the freezing rate at a 2-meter depth can be slowed down by 45.2 %, resulting in a temperature 5.03 degrees C higher than PEU at the end of the test period. The research findings could provide scientific basis for assessing effect and promoting application of polymer grouting technology in the rehabilitation of permafrost embankment.