This study investigates the microhardness and geometric degradation mechanisms of interfacial transition zones (ITZs) in recycled aggregate concrete (RAC) exposed to saline soil attack, focusing on the influence of supplementary cementitious materials (SCMs). Ten RAC mixtures incorporating fly ash (FA), granulated blast furnace slag (GBFS), silica fume (SF), and metakaolin (MK) at 10 %, 15 %, and 20 % replacement ratios were subjected to 180 dry-wet cycles in a 7.5 %MgSO4-7.5 %Na2SO4-5 %NaCl solution. Key results reveal that ITZ's microhardness and geometric degradation decreases with exposure depth but intensifies with prolonged dry-wet cycles. The FAGBFS synergistically enhances ITZ microhardness while minimizing geometric deterioration, with ITZ's width and porosity reduced to 67.6-69.0 mu m and 25.83 %, respectively. In contrast, FA-SF and FA-MK exacerbate microhardness degradation, increasing porosity and amplifying microcrack coalescence. FA-GBFS mitigates the diffusion-leaching of aggressive/original ions and suppresses the formation of corrosion products, thereby inhibiting the initiation and propagation of microcracks. In contrast, FA-SF and FA-MK promote the formation of ettringite/gypsum and crystallization bloedite/glauberite, which facilitates the formation of trunk-limb-twig cracks.

Seismic fragility denotes the probabilities of a system exceeding some prescribed damage levels under a range of seismic intensities. Classical seismic fragility studies in slope engineering usually construct fragility functions by making some assumptions for fragility curve shape, and always neglect spatial variability of soil materials. In this study, an assumption-free method on the basis of probability density evolution theory (PDET) is proposed for seismic fragility assessment of slopes. The random input earthquakes and spatially-variable soil parameters in slope are simultaneously quantified. By the proposed method, assumption-free fragility curves of a slope are established without limiting the fragility curve shape. The obtained fragility results are also compared with those from two classic parametric fragility methods (linear regression and maximum likelihood estimation) and Monte Carlo simulation. The results demonstrate that the proposed assumption-free method has potential to gives more rigorous and accurate fragility results than classical parametric fragility analysis methods. With the proposed method, more reliable fragility results can be obtained for slope seismic risk assessment.

The hydraulic effect of plant roots reduces precipitation infiltration and enhances shallow slope stability. However, after root death and decay, soil permeability increases while water-retention capacity decreases. The time-varying mechanisms governing the hydraulic properties of root-soil composites after root decay remain unclear. This study examines the evolution of soil pore structure following root decay. A time-varying soil water retention curve (SWRC) model was developed to characterize changes in water-retention capacity. Additionally, a time-varying saturated infiltration coefficient model and a permeability coefficient prediction model were established to describe variations in hydraulic properties. A one-dimensional soil column infiltration test was conducted on root-soil composites at different stages of root decay to investigate the time-dependent changes in hydraulic properties. The reliability of the proposed models was validated using experimental results. The findings indicate the following: After root death, root biomass, diameter, length, and number decreased with increasing decay time, stabilizing after four months. Root decay led to a reduction in root volume ratio, which altered soil structure and enhanced the permeability of root-soil composites. Longer decay periods increased soil porosity, modifying the soil water characteristic curve and reducing water-retention capacity. Creeping roots decayed more significantly than fibrous roots due to their distinct morphological traits, making changes in hydraulic properties more pronounced in the topsoil. Therefore, plant root decay negatively affects soil hydraulic properties by continuously altering soil pore structure. These findings provide a crucial foundation for understanding the time-dependent mechanisms of hydraulic property variations in root-soil composites during plant root decay.

In practical engineering, earthquake-induced liquefaction can occur more than once in sandy soils. The existence of low-permeable soil layers, such as clay and silty layers in situ, may hinder the dissipation of excess pore pressure within sand (or reconsolidation) after the occurrence of liquefaction due to the mainshock and therefore weaken the reliquefaction resistance of sand under an aftershock. To gain more mesomechanical insights into the reduced reliquefaction resistance of the reconsolidated sand under aftershock, a series of discrete element simulations of undrained cyclic simple shear tests were carried out on granular specimens with different degrees of reconsolidation. During both the first (mainshock) and second (aftershock) cyclic shearing processes, the evolution of the load-bearing structure of the granular specimens was quantified through a contact-normal-based fabric tensor. The interplay between mesoscopic structure evolutions and external loadings can well explain the decrease in reliquefaction resistance during an aftershock.

Waste red layers have the potential to be used as supplementary cementitious materials after calcination, but frequent and long-term dry-wet cycling leads to deterioration of their properties, limiting their large-scale application. In this study, the feasibility of using calcined red layers as cement replacement materials under dry-wet cycling conditions was analyzed. The damage evolution and performance degradation of calcined red layer-cement composites (RCC) were systematically evaluated via the digital image correlation (DIC) technique, scanning electron microscopy (SEM) analysis and damage evolution mode. The results show that the calcined red layer replacement ratio and number of dry-wet cycles affect the hydration and pozzolanic reactions of the materials and subsequently affect their mechanical properties. Based on the experimental data, a multiple regression model was developed to quantify the combined effects of the number of dry-wet cycles and the replacement ratio of the calcined red layer on the uniaxial compressive strength. As the number of dry-wet cycles increases, microcracks propagate, the porosity increases, and damage accumulation intensifies. In particular, at a high substitution ratio, the material properties deteriorate further. The global strain evolution process of a material can be accurately tracked via DIC technology. The damage degree index is defined based on strain distribution law, and a damage evolution model was constructed. At lower dry-wet cycles, the hydration reaction has a compensatory effect on damage. The pozzolanic reaction of the calcined red layer resulted in an increase in the number of dry-wet cycles. The RCC samples with high replacement ratios show significant damage accumulation with fast damage growth rates at lower stress levels. The model reveals the nonlinear effects of dry-wet cycling and the calcined red layer replacement ratio on damage accumulation in RCC. The study findings establish a scientific foundation for the resource utilization of abandoned red layers and serve as a significant reference for the durability design of materials in practical engineering applications.

The entrance of permafrost tunnels in cold regions is particularly vulnerable to frost damage caused by complex thermal-hydro-mechanical (THM) interactions in unsaturated frozen soils. The effects of temperaturedependent volumetric strain variations across different stratum materials on heat and moisture transport are often neglected in existing THM coupling models. In this study, a novel THM coupled model for unsaturated frozen soil integrating volumetric strain correction is proposed, which addresses bidirectional interactions between thermal-hydraulic processes and mechanical responses. The model was validated through laboratory experiments and subsequently applied to the analysis of the Yuximolegai Tunnel. The results indicate that distinct layered ice-water distribution patterns are formed in shallow permafrost under freeze-thaw cycles, driven by bidirectional freezing and water migration. Critical mechanical responses were observed, including a shift in maximum principal stress from the invert (1.40 MPa, frozen state) to the crown (5.76 MPa, thawed state), and periodic lining displacements (crown > invert > sidewalls). Frost damage risks are further quantified by the spatial-temporal zoning of ice-water content-sensitive regions. These findings advance unsaturated frozen soil modeling and provide theoretical guidance for frost-resistant tunnel design in cold regions.

Laboratory experiments have shown that the proportional shearing of granular materials along arbitrary strain path directions will lead to stress states that converge asymptotically to proportional stress paths with constant stress ratios. The macro- and microscopic characteristics of this asymptotic behaviour, as well as the existence of asymptotic states exhibiting a constant stress ratio and a steady strain-rate direction, have been studied using the discrete element method (DEM). Proportional shearing along a wide range of strain-rate directions and from various initial stress/density states has been conducted. The simulation results suggest that general contractive asymptotic states (except for isotropic states) do exist but may be practically unattainable. Dilative strain path simulations, on the other hand, result in continuously changing stress ratios until static liquefaction occurs, indicating the absence of dilative asymptotic states. Despite this difference, a unique relationship between the stress increments and the current stress ratio gradually emerges from all strain path simulations, regardless of strain path direction and initial stress/density conditions. At the particle scale, the granular assembly sheared along proportional strain paths exhibits a constant partition ratio between strong and weak contacts. Although general proportional strain paths are associated with changing geometric and mechanical anisotropies, the rates of change in these anisotropies for contractive strain paths are synchronised to maintain a constant ratio of their contributions to the mobilised shear strength of the material, with a higher proportion being contributed by geometric anisotropy for more dilative strain paths.

To study the failure mechanism of high ductile coagulation (HDC) under sulfate attack in cold saline soil area, cement-based cementing material (cement: fly ash: sand: water reducing agent: water = 1:1:0.72:0.03:0.58) and 2 % polyvinyl alcohol fiber (PVA) were used to prepare HDC sample, to increase the density and ductility of concrete. a 540-day sulfate-long-term immersion test was performed on HDC specimens under two low-temperature curing environments and different sulfate solution concentrations (5 %, 10 %). Using a combination of macro and microscopic methods, according to the principle of energy dissipation, To study the relationship between the evolution of energy (total damage energy U, dissipated energy Uds, elastic strain energy Ues) and the deterioration of strength and the change of pore structure during the compression process of HDC. According to the characteristics of stress-strain curves during HDC compression, the damage evolution characteristics of characteristic stress points during HDC compression are summarized, establish energy storage indicators Kel to evaluate the degree of internal damage of HDC. The results show that during the compression damage process of HDC after long-term soaking in sulfate solution under low temperature environment, Uds and Ues of HDC at characteristic stress points both increase first and then decrease, Kel are reduced first and then increased. The development trend of elastic strain energy and dissipative energy of HDC in 10 % sulfate solution is more drastic than that in 5 % sulfate solution. Compared with the other three groups, the D group energy storage level rises and falls more violently, and the HDC has a smaller ability to resist damage under this condition. Through the study of the correlation between macro and micro changes of HDC in cold saline soil areas and energy evolution, to provide a reference for the stable operation of highly ductile concrete in cold saline soil areas.

Earthquake-induced soil liquefaction causes ground and foundation failures, and it challenges the scientific community to explore the liquefaction problem in deep deposit under strong shaking. Due to the capacity limitation of physical modelling facility, it is difficult to reproduce soil liquefaction response of deep sand ground by centrifuge shaking table test. To address this problem, a suite of centrifuge model tests were conducted with the aid of Iai's Type III generalized scaling law (i.e., GSL) to observe the liquefaction response of deep sand ground, where Models 1 and 2 were used to validate the GSL and Model 3 with the validated GSL stands for the deep sand ground with prototype depth of 80 m. The test results of Models 1 and 2 indicate that GSL generally performs well for small-strain shear modulus, nonlinear dynamic response of acceleration and the generation of excess pore water pressure, but leaves considerable errors for post-shaking dissipation process and ground settlement with large plastic strain. The test results of Model 3 indicate that liquefaction is also possible in depth of 30-40 m under shaking event of PBA = 0.4 g and Mw = 7.5. For deeper depth without triggering of liquefaction, a depthdependent power function relationship between the peak excess pore water pressure and Arias intensity has been established. The test results also revealed that consolidation and earthquake shaking history contribute to the development of soil anisotropy in a deep ground, leading to a continuous increase of anisotropy degree, which could be evaluated using the small-strain shear moduli in different stress planes under orthogonal stress conditions.

Ground subsidence is a common urban geological hazard in several regions worldwide. The settlement of loess fill foundations exhibits more complex subsidence issues under the coupled effects of geomechanical and seepage-driven processes. This study selected 21 ascending Sentinel-1 A radar images from April 2023 to October 2024 to monitor the loess fill foundation in Shaanxi, China. To minimize errors caused by the orbital phase and residual flat-earth phase, this research combined PS-InSAR technology with the three-threshold method to improve the SBAS-InSAR processing workflow, thereby exploring time-series deformation of the loess fill foundation. Compared with conventional SBAS-InSAR technology, the improved SBAS-InSAR technique provided more consistent deformation time-series results with leveling data, effectively capturing the deformation characteristics of the fill foundation. Additionally, geographic information system (GIS) spatial analysis techniques and statistical methods were employed to analyze the overall characteristics and spatiotemporal evolution of the ground surface deformation in the study area. On the other hand, the major drivers of the subsidence in the study area were also discussed based on indoor experiments and engineering geological data. The results showed gradual and temporal shifts of the subsidence center toward areas with the maximum fill depths. In addition, two directions of uneven subsidence were observed within the fill foundation study area. The differences in the fill depth and soil properties caused by the building foundation construction were the main factors contributing to the uneven settlement of the foundations. Foundation deformation was also positively and negatively affected by surface water infiltration. This study integrates remote sensing and engineering geological data to provide a scientific basis for accurately monitoring and predicting loess fill foundation settlement. It also offers practical guidance for regional infrastructure development and geological hazard prevention.