The integration of urban construction and metro-line-oriented commercial development is a growing trend in major cities. In response to extensive cracking and fracture in the segment lining of an underlying shield tunnel subjected to large-scale ground excavation and unloading, this paper adopts a real-world shield tunnel project as a case study. The underlying shield tunnel is experiencing overall heaving deformation, characterized by a decrease in its horizontal diameter and an increase in its vertical diameter. The variation laws of displacement and stress in segment lining are comprehensively analyzed from key perspectives, including geological conditions, ground excavation sequences, on-site assembly quality, and lining crack locations. The longitudinal joint at the tunnel vault transitions from opening to crushing at the intrados. This paper presents the stress behavior in the tunnel vault, which is characterized by negligible fluctuations in axial force concurrent with a pronounced decrease in bending moment. A similar stress variation behavior is detected in the tunnel invert. This indicates that the ground unloading and the increase of tunnel’s vertical diameter constitute the primary causes of the intrados crushing at longitudinal joint of tunnel vault. And the intrados crushing, in conjunction with segment misalignment observed on site, results in a transition in the interface behavior to a line-to-surface contact. Consequently, the lining stress near the intrados exceeds permissible limits, thereby resulting in subsequent cracking and fracture. The primary threats to the structural safety of segment lining arise from the increased vertical ovalization, the intrados crushing, and uneven line-to-surface contact at longitudinal joint of tunnel vault, rather than from the changes in lining stress. Consequently, a specific repair scheme is proposed, involving modified epoxy resin grouting, epoxy mortar filling, and composite fiber reinforcement. Following structural rehabitation, the load-bearing capacity of the shield lining can meet all the specified design service requirements. Several preplanned mitigation measures can be implemented for land development and construction activities adjacent to operational metro lines. This paper can lead a reference for similar project in the future.

Understanding the dynamic response of soils under low confining pressures is crucial for applications such as slope engineering and offshore foundations. In this study, triaxial tests were conducted on silty clay under a strain-rate range of 1 × 10−4 s−1 2 × 10−1 s−1. The effects of strain rate on the stress–strain response, pore pressure evolution, and failure mode were analyzed. The results show that the cohesion c and Young’s modulus E50 increase with increasing strain rate, while the internal friction angle ϕ first decreases and then remains stable. Pore pressure of saturated silty clay changes minimally at low strain rates (1 × 10−4 s−1 1 × 10−3 s−1) and decreases at higher strain rates (1 × 10−3 s−1 2 × 10−1 s−1). Therefore, the strength exhibits a U-shaped dependence on strain rate, decreasing at low strain rates and increasing at higher rates. As the water content and the confining pressure decrease, this strength reduction at low strain rates gradually diminishes. A mechanism to explain this behavior is proposed: at low strain rates, time-dependent strength recovery contributes to the strength, whereas at high strain rates, viscous resistance and reduced pore pressure are the dominant factors. A Fractional Derivative Merchant (FDM) model incorporating strain-rate-dependent parameters is proposed, which better captures the strain-softening behavior and reproduces the U-shaped variation of soil strength with strain rate. The model provides a reference approach for predicting the one-dimensional deformation of soils subjected to varying loading rates in engineering applications.

Under wet-dry cycling conditions, the structural evolution and hydromechanical behavior of magnesia-stabilized sludge exhibit significant complexity, which is critical for its engineering applications. This study conducted systematic experiments through macro- and microstructural analyses, soil-water characteristic measurements, and mechanical performance tests. The results reveal that, although magnesia materials effectively suppress crack development, the progressive dissolution of cementitious compounds (e.g., magnesium silicate hydrate, magnesium aluminate hydrate, Phase 5, and brucite) with increasing cycle numbers leads to a reduction in interparticle bonding strength. This induces a dual structural deterioration effect: at the microscale, porosity accumulates progressively, while at the macroscale, large interconnected cracks form, ultimately causing a systematic decline in the soil's water retention capacity, manifested as reduced saturated water content, diminished matric suction, and enhanced hydraulic hysteresis. This coupled degradation mechanism between bonding strength and pore structure results in a nonlinear decay of the material's initially enhanced mechanical properties (e.g., compressive strength and elastic modulus) with ongoing cycles and fluctuating moisture content. Additionally, a bimodal pore model based on fractal theory accurately predicts soil-water characteristic curves, with microstructural parameters showing strong correlations with mechanical properties. The resulting predictive model for mechanical strength, integrating microstructural parameters and soil-water characteristics, provides a quantitative basis for the durability design of sludge stabilization projects.

Undrained creep behaviors of a clay within the atmospheric influence depth are studied considering the typical low confining pressure and alternate freeze–thaw–drying–wetting (FTDW) effects. Triaxial experimental tests and numerical simulations based on the proposed material point method (MPM) algorithm are conducted to cross-validate and investigate the creep characteristics of a compacted clay after FTDW cycles. The experimental tests focus on the effects of stress states and FTDW cycles on macroscopic axial strain development. After confirming that the simulated deformation property matches the measurements, the variation of microscopic information for solid particles and water particles within specimens is analyzed from numerical simulation. The results indicate that the increase in different components of axial strain is inconsistent under FTDW effects. In particular, the proportion of creep strain rises after FTDW cycles under low-stress states. Microscopic information illustrated by axial displacement field, water pressure evolution, and solid particle spacing variation is influenced by the monitoring position, stress states, and FTDW cycles. Our research provides a comprehensive understanding of the undrained creep behaviors of a compacted clay under FTDW effects.

This paper investigates the stress-strain relationships and volumetric behaviors of expanded polystyrene (EPS) under compression and monotonic/cyclic shearing, considering the effects of vertical stress (sigma v) and EPS density (rho EPS). The experimental results demonstrate that under monotonic shearing, EPS exhibits strain hardening, and the resulting shear-induced axial strain (epsilon a) significantly exceeds the creep-induced epsilon a under sustained sigma v. The apparent shear strength (tau f) is governed by equivalent cohesion (c), which increases linearly with rho EPS, while the equivalent friction angle (phi) remains insensitive to rho EPS. Under cyclic shearing, symmetric hysteresis loops form, with secant shear stiffness (G) increasing with rho EPS and sigma v but decreasing with shear strain amplitude (gamma a), the equivalent damping ratio (D) shows opposite trends. Axial strain accumulates nonlinearly during cycling, stabilizing after about four cycles under fixed gamma a but increasing continuously under multistage loading. An extended hypoplastic model is proposed, incorporating two key advancements: the characterization of shear-induced volumetric contraction and a shear strain-dependent equivalent cohesion to describe damage accumulation. The model accurately simulates the stress-strain relationships and axial strain evolution of EPS with different densities and stress levels under both monotonic and cyclic shearing, providing a robust tool for analyzing EPS in geotechnical applications.

The dynamic response of silty clay in unpaved roads is affected by the duration of wheel loading, but the role of loading frequency remains insufficiently understood. This study investigates the effects of loading frequency on the progressive plastic deformation and the pore structure of silty clay under repeated high-amplitude loading and low confining pressure by cyclic triaxial tests and Mercury intrusion porosimetry (MIP) tests, respectively. The results show that a higher loading frequency reduces accumulated plastic strain, and the reduction from 0.1 to 1.0 Hz is more pronounced than that from 0.01 to 0.1 Hz. A higher loading frequency produces a higher resilient modulus and lower cumulative energy dissipation. The MIP results indicate that cyclic loading mainly alters macro-pores and meso-pores, whereas micro-pores remain comparatively stable. Macro-pore volume decreases with increasing accumulated plastic strain, and part of the macro-pore space is transformed into meso-pores. Lower loading frequencies prolong the duration of stress action within each cycle, thereby promoting more sufficient pore-structure rearrangement and compression. The fractal dimension results further show that cyclic loading increases the heterogeneity of macro-pores but simplifies the meso-pore and micro-pore structures. These findings provide a microstructural basis for evaluating frequency-dependent deformation of silty clay in unpaved roads.

Simple shear tests, three-dimensional morphology scanning, and fractal analysis were combined to investigate the relationship between interface morphology and shear resistance. Two granular soils with different particle characteristics were considered, and the effects of normal stress, soil relative density, EPS geofoam density, and preload duration were systematically evaluated. Results showed that increasing normal stress enhanced particle penetration into the EPS geofoam surface, producing rougher and more complex interface morphologies. The fractal dimension D of the interface morphologies increased rapidly with normal stress and then approached a stable value once EPS geofoam densified. Coarse granular soil produced larger D values and higher interface friction than finer sand due to stronger particle interlocking. Increasing soil relative density reduced both D and interface friction, whereas EPS geofoam density had only a minor effect within 15–25 kg/m3. A strong relationship was observed between the interface friction coefficient μ and D, with μ increasing approximately linearly with D and the increment in friction coefficient showing a near-linear relationship with the increment in fractal dimension. These findings indicate that interface shear behavior is governed primarily by the evolution of real contact morphology.

This study investigates and compares the evolution of the void ratio-vertical stress-lateral earth pressure (i.e., e-σV-σL) relationships and pore structure of an expansive soil following three hydromechanical paths, namely the swelling-under-load (SUL) path, constant-volume (CV) path, and swell-consolidation (SC) path. It was demonstrated that (i) the e-σV and σV-σL relationships show piecewise-linear and hysteretic characteristics when σV is less than 400 kPa. The e-σV-σL relationships obtained from different paths become identical when σV exceeds 400 kPa; (ii) the σV required to suppress the lateral swelling pressure is much higher than that required to restrain the vertical swelling strain, which indicates that simply restraining the swelling strain is not adequate to eliminate the swelling potential; (iii) the e-σV-σL relationships of different paths show consistency and can be reasonably fitted by a simple model; (iv) the pore structure of specimens following different paths becomes identical under σV of 700 kPa, which corroborates the convergence of the e-σV-σL relationships under high σV. Under σV less than 400 kPa, specimens following the SC path exhibit greater stress sensitivity in macropores, while those following the SUL path show higher stress sensitivity in micropores. These contrasting sensitivities of the macro- and micropores govern the differences in the e-σV-σL relationships.

This study proposes a sludge storage dam constructed by stacking sand-filled annular geotubes of geotextile, and investigates its design and stability via model tests and DEM simulations. Model tests on a multi-layered dam reveal non-uniform local tension distribution in the geotextile due to interface friction between sand-geotextile and geotube-geotube contacts. Interlayer friction suppresses tension in the bearing zone, while tension in the non-bearing zone exhibits a gradient distribution, peaking at the junction. Geotextile ultimate tensile strength positively correlates with bearing strength, whereas modulus and filling ratio indirectly affect tension by altering tube geometry. A DEM framework was established, calibrating mesoscopic parameters to characterize macroscopic responses of the geotextile, sand, and their interfaces. Simulations analyzed evolution of geotextile stress, displacement patterns, and the influence of key parameters on bearing behavior. The mechanism by which interface friction regulates tension distribution and gradient, thereby affecting ultimate bearing capacity, was clarified. Finally, by introducing a modified principal stress ratio function and a tension attenuation model incorporating interface friction effects, a calculation method for ultimate bearing strength based on maximum local geotextile tension is proposed, considering non-uniform tension distribution and sand strain-softening. DEM results agree well with the proposed formula, verifying its accuracy.

Silty clay in unpaved roads is often subjected to low-cycle wheel loading under relatively high dynamic stress amplitudes and low confining pressures. However, its dynamic behavior under such conditions remains insufficiently understood. In this study, cyclic triaxial tests were conducted on silty clay from unpaved roads under high dynamic stress amplitude and low confining pressure to investigate the evolution of accumulated plastic strain, resilient modulus, and dissipated energy. The results show that higher dynamic stress amplitude, lower confining pressure, and higher water content all promote the development of accumulated plastic strain. The plastic deformation behavior within 50 loading cycles can be classified into plastic shakedown, plastic creep, and incremental collapse. The initial plastic strain increment is shown to be a useful indicator for identifying the transition to incremental collapse. The resilient modulus decreases with increasing dynamic stress amplitude and water content, but increases with confining pressure. A UKTC-based resilient modulus model and a power-function accumulated plastic strain model were then established. The proposed model successfully predicts the evolution of accumulated plastic strain in the plastic shakedown and plastic creep regimes. Moreover, a method was proposed to distinguish plastic creep from incremental collapse, providing a preliminary basis for determining critical stress states in unpaved roads.

This paper investigates the interactions between wheels and soft soil terrain, focusing on the impact of soil strain rate, which is related to the forward velocity of the wheel, on the sinkage of wheels. An improved Drucker-Prager model, incorporating strain rate effects on the cohesive (c), elastic modulus (E), and strain-hardening/strainsoftening behaviors, is proposed and validated against triaxial tests in this study. Using finite element methods (FEM) with the Coupled Euler Lagrange (CEL) method, this study simulates dynamic wheel-soil interaction and analyzes the influence of soil parameters (i.e., including internal friction angle phi, cohesion c, elastic modulus E, axle load, and forward velocity) on wheel sinkage. The results show that: (i) Strain rate affects the c and E, with negligible impact on the phi; the enhanced D-P model effectively captures these characteristics; (ii) The sensitivity of the wheel sinkage to strain rate is pronounced for soils with low c and phi but diminishes in high-strength soils; (iii) Wheel sinkage nonlinearly decreases as the c, phi, E, and velocity increase while increases as the axle load increases. The sensitivity of wheel sinkage to velocity is as significant as that to c, phi, E, and axle load, with a CAM of 0.52.

Stabilization is an important approach to improve the performance of expansive soils. Conventional additives such as cement and lime may lead to environmental concerns and increased carbon emissions. In contrast, industrial wastes such as fly ash (FA) and lignin fibers (LF) are considered more sustainable and economical alternatives. However, studies on the combined effects of FA and LF on the engineering behavior of expansive soil remain limited. This study investigates the effects of FA and LF on the physical properties, mechanical behaviors, water stability, and microstructure of an expansive soil from both macroscopic and microscopic perspectives. The results indicate that LF and FA increase the optimum moisture content and slightly reduce the maximum dry density of the expansive soil. The FA has a more pronounced effect on the Atterberg limits, while the LF show a relatively limited influence. Reductions in plasticity index, swell–shrink potential, and compression index are observed with increasing FA and LF content. The unconfined compressive strength (UCS) increases with curing time and additive content, reaching a maximum at 1% LF and 6% FA within the tested range. After infiltration-induced aging, the stabilized soil retains better structural integrity, with reduced strength loss attributed to LF-related reinforcement and FA-related cementation effects. Nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM) analyses indicate a reduction in large pores in the treated soils compared with the untreated soil. Based on these observations, a possible stabilization mechanism is suggested, in which LF may form a reinforcing network, while hydration products from FA may contribute to particle bonding, potentially leading to a more integrated soil–fiber–gel structure.

This paper investigates the cyclic simple shearing behaviors of Expanded Polystyrene (EPS) geofoams considering influences of the shear strain amplitude (gamma a), number of shear cycles, shear rate, vertical stress (6n), and EPS density (rho EPS). The experimental results demonstrate that the cyclic shear stress (z)-shear strain (gamma) relationships of EPS are not sensitive to the shear rate. As the gamma exceeds 2%, the EPS yields and its z-gamma relationships and backbone curve become nonlinear. There are linear relationships between the elastic modulus E, elastic shear modulus Ge, and plastic shear modulus Gp. They increase linearly with an increase in the rho EPS. The Ge and Gp are not sensitive to the gamma a. The cyclic shear stiffness G increases while the equivalent damping ratio D of EPS decreases with an increase in the 6n and rho EPS. The G decreases while the D increases nonlinearly as the gamma a increases. Empirical models were developed to describe the variations of the Ge, Gp, G, and D with 6n, rho EPS, and gamma a. A modified Hardin-Drnevich model was proposed to describe the backbone curves and z-gamma loops upon cyclic simple shearing, which has achieved good agreement with the experimental measurements and the testing results from the literature.

Placing EPS inclusions between retaining walls and expansive soil backfill has been proven effective in reducing the lateral earth pressure on the walls, particularly during the swelling of expansive soils upon infiltration. However, two critical knowledge gaps remain: (i) case studies and field-monitored data are desired to further illustrate the performance of this technique, and (ii) the absence of specific approaches for estimating and modeling the lateral earth pressure. This study presents two case studies of retaining wall projects backfilled with expansive soils in Guangxi and Hubei, China. The distribution and evolution of lateral earth pressure of different test sections were monitored. It is demonstrated that: (i) EPS inclusions can effectively reduce the lateral earth pressure exerted by expansive soil backfills on retaining walls by more than 50 %, significantly outperforming bagged gravel inclusions; (ii) EPS inclusions induce a "homogenizing effect", producing a more uniform distribution of lateral earth pressure along the wall height. Combining field observations and laboratory test results, this study proposes theoretical and numerical approaches for estimating the lateral earth pressure for the "retaining wall-EPS inclusion-expansive soil" system. The proposed approaches were validated against the data obtained from the presented case study.

This study investigates the evolution of the dynamic characteristics of a solidified dredge sludge, including the resilient modulus (MR), accumulative plastic strain (epsilon p) and damping ratio (lambda) during long-term traffic loadings considering influences of environmental actions (dry-wet, DW, and freeze-thaw, FT cycles), stress states (confining stress sigma cand deviator stress sigma d) and loading frequency (f). The experimental results indicate that the dynamic characteristics continuously change with increasing loading cycles and the influences of environmental actions, external stress state, and loading frequency are coupled. The resistance of the solidified sludge against traffic loading decreases after both DW and FT cycles, which is manifested by the decrease in the MR and the increase in the lambda and epsilon p. DW cycles induce greater reductions in the dynamic characteristics than the FT cycles. The increasing sigma c improves the resistance of the soil against cyclic loadings, resulting in higher MR and lower epsilon p and lambda. Besides, their rates of change with loading cycles (i.e., delta MR, delta epsilon p and delta lambda) reduce. The MR, epsilon p, lambda, and delta ap increase while the delta MR and delta lambda decrease with the sigma d, indicating that the increase in the cyclic loading level contributes to the accumulation of plastic strain and energy assumption while the resultant densification effect leads to the increase in the MR and decrease in the delta MR and delta lambda. The soil dissipates less energy when loaded under higher f, resulting in higher MR and lower epsilon p and lambda. Results reported in this paper are helpful for better understanding the dynamic responses of solidified sludge under complex loading and environmental conditions.

This study investigates the pore structure, water-retention capacity, and dynamic characteristics (including the resilient modulus MR, accumulated plastic strain ep, and damping ratio A) of a clayey pavement subgrade soil that has been subjected to different moisture-temperature cycling conditions. Three distinct moisture-temperature cycling conditions are designed by combining freeze-thaw and wetting-drying processes in different sequences to simulate complex environmental actions. Experimental results reveal that (i) when the impacts of the moisture and temperature have reached equilibrium, the soil exhibits comparable pore-structural, water-retention, and dynamic characteristics across different moisture-temperature cycling conditions; (ii) moisture-temperature cycling induces significant pore structure evolutions, which are characterized by micropore contraction and macropore development. These morphological changes directly affect the soil-water characteristic curve (SWCC), manifesting as reductions in the air-entry value and decreases in the slope of the SWCC in the transition zone slope; (iii) freeze-thaw cycles increase the moisture sensitivity of the ep but impose minor impacts on that of the MR and A. Under unsaturated conditions, the ep and MR constitute consistent relationships with suction regardless of freeze-thaw histories; (iv) there are linear relationships between the ep, MR, and A during cyclic loading, which show strong dependence on the humidity and freeze-thaw conditions. For specimens under different external stress, humidity, and freeze-thaw conditions, the relationships between their ep and MR at the end of long-term cyclic loadings show consistent nonlinear relationships, which can be well described by a simple model. Ten machine-learning approaches were employed to predict the ep from the soil's stress state and moisture-temperature conditions. The Bayesian Neural Networks were found to be most capable in terms of computational precision and efficiency.

This study investigates the pullout resistance of glass fiber reinforced polymer (GFRP) screw anchors through laboratory experiments and numerical simulations, considering variations in H/D (H and D are the embedment depth and diameter of the anchor plate, respectively). A generalized unified failure surface and calculation formulas for the ultimate pullout capacity were proposed. The research findings indicate that: (i) The pullout load-displacement curve of GFRP screw anchors can be divided into three stages: elastic, localized plastic, and through-failure stages. Correspondingly, the anchored soil can be partitioned into an active zone, a transition zone, and a passive zone; (ii) The failure surface shape of the anchored soil dynamically evolves following the sequence of ''trumpet'', ''Wide-mouthed cup'', ''bulb'' configurations as H/D gradually increases. The critical embedment depth ratio (H/D)cr varies with soil type, with typical values of 7 for clay and 11 for sand, highlighting the necessity of soil-specific design criteria for GFRP screw anchors. Both ultimate pullout capacity, Qu, and ultimate displacement ratio, u/D (u refers to ultimate displacement) of GFRP screw anchors exhibit approximately linear positive correlations with H/D; (iii) Increasing slope inclination angle reduces the ultimate pullout capacity, Qu, transitioning failure surfaces shape from symmetrical vertical propagation to asymmetrical slope-oriented deviation. The differences between the measured and calculated ultimate pullout capacity, Qu of GFRP screw anchors are within 20 %, demonstrating the rationality and accuracy of the proposed formulas.

The effects of freeze-thaw-drying-wetting cycles on undrained stress relaxation behavior are studied from the perspectives of physical experiments and numerical simulations using the proposed multi-set material point method (MPM) algorithm. The effectiveness of the established MPM model is validated by comparing the simulation results with experimental data. To gain insights into the microscopic characteristics of undrained stress relaxation, the evaluation focuses on the variations in elastic Green-Lagrangian strain, water pressure, water particle velocity, and solid particle space. The deviator stress relaxation and water pressure evolution are correlated with the decrease in elastic strain and spatial variation in water velocity, respectively. The stress relaxation process breaks the interparticle bonds and results in structural weakening. Freeze-thaw-dryingwetting cycles reduce the relaxed deviator stress within different relaxation stages and promote variation in water pressure, instability in water velocity field, and adjustment of solid particles.