This study investigates salt weathering in the indoor, humid environment of China's Jinsha earthen site. Methods such as digital microscope, scanning electron microscopy (SEM), ion chromatography (IC), energy dispersive spectroscopy (EDS), and laser particle size analysis were employed to collect and analyze samples from four heavily weathered walls. The sampling approach took into account differences in depth and height and prioritized the extraction from various weathering layers to unveil the attributes, causes, and mechanisms of salt weathering. The findings indicate that the Jinsha site's eastern segment suffered salt-induced damage, such as powdering, salt crusts, and blistering, due to the presence of gypsum and magnesium sulfate. These salts were primarily sourced from groundwater. Groundwater ions ascended to the site's surface via capillary action, instigating various forms of salt damage. Salt damage severity has a direct link to salt and moisture content. The degradation patterns can be categorized into powder and multi-layered composite deterioration, both seems related to soil particle composition. Powder deterioration tends to occur when the sand content exceeds 40%. This research proposes preservation strategies that focus on managing groundwater and conducting environmental surveillance. These measures are designed to effectively address and mitigate the risks associated with salt damage.

Ground granulated blast furnace slag (GGBS), calcium carbide slag (CS), and phosphogypsum (PG) were combined in a mass ratio of 60:30:10 (abbreviated as GCP) to solidify dredged sludge (DS) with high water content. The long-term strength characteristics of solidified DS under varying curing agent dosage and initial water contents, as well as its durability under complex environmental conditions, were investigated via a series of mechanical and microstructural tests. The superior performance of GCP-solidified DS (SDS-G) in terms of strength and durability was demonstrated in comparison to solidified DS using ordinary Portland cement (SDS-O). The results indicated that the unconfined compressive strength (UCS) of SDS-G was approximately 3.0-4.5 times greater than that of SDS-O at the same dosage and curing ages, exhibiting a consistent increase in strength even beyond 28 days of curing. Additionally, the strength and deformation modulus (E50) of SDS-G increased initially and then decreased during wet-dry cycles, with reductions in mass, volume, and strength significantly were smaller than those observed in SDS-O. Furthermore, the reductions in UCS and E50 induced by freeze-thaw cycles were considerably smaller for SDS-G than for SDS-O, with strength losses of 50.7 % and 88.3 %, respectively, after 13 freeze-thaw cycles. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the enhancements observed in SDS-G were attributed to the formation of ettringite (AFt), which effectively fills larger pores between agglomerated soil particles, thereby creating a denser and more stable microstructure in conjunction with hydrated calcium aluminosilicate (C- (A)-S-H) gels.

Given the insufficiency in research on the mechanism of fine particle impact on gravelly soil subgrade deterioration, a series of saturated gravelly soil consolidated drained triaxial shear tests was conducted using the GDS triaxial testing system under varying fines contents and effective confining pressures to investigate the effect of fine particle contamination on the static shear characteristics of gravelly soil. The results indicate that: (1) As the fines content increases, the stress-strain curve development pattern transitions from strain softening to strain hardening, with a critical threshold at a fines content of Fc=15%. (2) The addition of fine particles leads to a decrease in the principal stress ratio, brittleness index, peak strength, cohesion, and internal friction angle of the gravelly soil, while the degradation indices increase. The relationship between the degradation indices of peak strength and cohesion and fines content can be described by quadratic functions, and the degradation index of the internal friction angle by a cubic function. (3) With increasing fines content, critical state parameters decrease. The effective stress path shows retracing behavior, becomes shorter, and shifts to the left. (4) The addition of fine particles results in a decrease in the secant modulus, and the volumetric strain-axial strain curve changes from contractive-dilative to purely contractive.

Water level fluctuations in the reservoir deteriorate soils and rocks on the bank landslides by dryingwetting (D-W) cycles, which results in a significant decrease in mechanical properties. A comprehensive understanding of deterioration mechanism of sliding-zone soils is of great significance for interpreting the deformation behavior of landslides. However, quantitative investigation on the deterioration characteristics of soils considering the structural evolution under D-W cycles is still limited. Here, we carry out a series of laboratory tests to characterize the multi-scale deterioration of sliding-zone soils and reveal the mechanism of shear strength decay under D-W cycles. Firstly, we describe the micropores into five grades by scanning electron microscope and observe a critical change in porosity after the first three cycles. We categorize the mesoscale cracks into five classes using digital photography and observe a stepwise increase in crack area ratio. Secondly, we propose a shear strength decay model based on fractal theory which is verified by the results of consolidated undrained triaxial tests. Cohesion and friction angle of sliding-zone soils are found to show different decay patterns resulting from the staged evolution of structure. Then, structural deterioration processes including cementation destruction, pores expansion, aggregations decomposition, and clusters assembly are considered to occur to decay the shear strength differently. Finally, a three-stage deterioration mechanism associated with four structural deterioration processes is revealed, which helps to better interpret the intrinsic mechanism of shear strength decay. These findings provide the theoretical basis for the further accurate evaluation of reservoir landslides stability under water level fluctuations. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

During winter construction of earthworks such as earth dams and embankments, the structural properties of the soil may deteriorate due to freeze-thaw cycles. A new measure to combat freeze-thaw damage, incorporating phase change materials (PCMs) into the soil to regulate temperature, has been verified and applied in roadbed and pavement engineering. However, the law of deterioration from freeze-thaw cycles for this novel construction material is not clear yet. This study investigated the characteristics and mechanism of deterioration of clay mixed with paraffin-based PCM (PPCM-clay) through freezing and thawing using freeze-thaw tests, unconfined compression tests, permeability tests, and macro-micro structural analysis. The results show that the freeze-thaw resistance of PPCM-clay is better than that of pure soil. The amount of PPCM added is proportional to the effect of inhibiting soil strength and permeability degradation. Under the same number of freeze-thaw cycles, the compressive strength of PPCM-clay is greater than that of pure soil. Micropore expansion and frost heave are also not significant in PPCM-clay. This indicates that the low initial water content, relatively large porosity, thermal hysteresis, frost contraction, hydrophobicity, and high viscosity of PPCMs are the main reasons for the improvement in PPCM-clay freeze-thaw resistance. These findings provide a theoretical basis for the potential application of PPCM-clay as a dam or embankment material for weakening soil frost damage in winter construction in cold regions.

A new type of asphalt pavement disease, known as arch expansion, has appeared in the saline soil regions of Northwest China. The emergence, as well as the evolution of the disease, is strongly related to the distribution of sulfate. However, the decay of Cement-stabilized gravel (CSG) mechanical properties is closely related to the onset and development of arch expansion. The relationship between CSG mechanical strength and salinity in the arch expansion area is analyzed based on field investigations to systematically study the mechanical property degradation law and mechanism of CSG. The mechanical strength and deterioration patterns of CSG with different coupling conditions were investigated. The mineral composition and micromorphology of the erosion products were analyzed. The results show that the mechanical properties of CSG in the area of the arch deteriorate more than those in the regular section. The mechanical strength of the specimens initially containing salt and partially immersed in salt solution decayed most severely. In terms of the deterioration mechanism of mechanical strength of CSG, the water-heat-salt erosion process is also divided into two parts, including the formation stage of gypsum and ettringite, the stage of C-S-H decomposition and thaumasite formation, respectively. The degradation mechanism of CSG is a combination of physical and chemical erosion.

River silt deposited by water in coastal areas is unsuitable for engineering construction. Thus, the in situ stabilization treatment of river silt as the bearing layer has been an important research area in geotechnical engineering. The strength degradation behavior and mechanism of stabilized river silt reinforced with cement and alginate fibers (AFCS) in different engineering environments are crucial for engineering applications. Therefore, freeze-thaw (F-T) cycle tests, wetting-drying (W-D) cycle tests, water immersion tests and seawater erosion tests were conducted to explore the strength attenuation of stabilized river silt reinforced with the same cement content (9% by wet weight) and different fiber contents (0%, 0.3%, 0.6% and 0.9% by weight of wet soil) and fiber lengths (3 mm, 6 mm and 9 mm). The reinforcement and damage mechanism of AFCS was analyzed by scanning electron microscopy (SEM) imaging. The results indicate that the strength of AFCS was improved from 84% to 180% at 15 F-T cycle tests, and the strength of AFCS was improved by 26% and 40% at 30 W-D cycles, which showed better stability and excellent characteristics owing to the hygroscopic characteristics of alginate fiber arousing the release of calcium and magnesium ions within the alginate. Also, the strength attenuation of AFCS was reduced with the increase in the length and content of alginate fibers. Further, the strength of specimens in the freshwater environment was higher than that in the seawater environment at the same fiber content, and the softening coefficient of AFCS in the freshwater environment was above 0.85, indicating that the AFCS had good water stability. The optimal fiber content was found to be 0.6% based on the unconfined compressive strength (UCS) reduction in specimens cured in seawater and a freshwater environment. And the strength of AFCS was improved by about 10% compared with that of cement-stabilized soil (CS) in a seawater environment. A stable spatial network structure inside the soil was formed, in which the reinforcing effect of fibers was affected by mechanical connection, friction and interfacial bonding. However, noticeable cracks developed in the immersed and F-T specimens. These microscopic characteristics contributed to decreased mechanical properties for AFCS. The results of this research provide a reference for the engineering application of AFCS.

The lack of researches on the intrinsic microstructure evolution of coarse-grained soil fillers during subgrade compaction-operation period (SCOP), resulting in a deficiency of theoretical guidance for the lifecycle health monitoring of high-speed railway subgrade. In this paper, the self-developed intelligent vibratory compaction instrument (IVCI) was used to rapidly simulate the loading action on high-speed railway gravel aggregate (HRGA) during SCOP. Additionally, two physical-mechanical indicators, dry density rho d and dynamic stiffness Krb, were used to characterize the physical-mechanical properties of HRGA fillers. Besides, the microstructure (coarse particles and voids) evolution within the HRGA fillers during SCOP were in-depth explored based on X-Ray computed tomography (X-CT) technology. The results indicate that the rho d exhibits a continuous slow increase trend, but the Krb exhibits distinct deteriorating characteristics, with a consistent gradual decline after compaction periods. The particle rearrangement is crucial in the compaction periods of HRGA fillers, and the optimal compaction level (referred to the locking point) can be determined by the particle rearrangement indicator Hr. Besides, the particle local shape indicators (angularity coefficient and contour coefficient) as well as void local shape indicator (abundances) can used to explain the deterioration characteristics of HRGA fillers during operation periods. It is important to note that under the vibratory loading, insufficient crushing occurs at the particle corners within the internal skeleton, decreasing the stability of skeleton and giving rise to the content of fine particles, which can fill up the large-sized voids and generate a significant number of morphologically flawed middle-sized and small-sized voids. The finding of this research not only provide a refined analysis and insight understanding of the construction and operation of high-speed railway subgrade, but also can contribute to establishing a solid theoretical foundation for the lifecycle health monitoring of subgrades.

Understanding the destabilization mechanisms in bedrock and overburden layer slopes influenced by both rainfall and seismic activity is of significant engineering importance. A series of large-scale shaking table model tests was conducted to investigate the instability evolution in bedrock and overburden layer slopes after rainfall and seismic events. This study identifies and assesses degradation modes based on spatial deformation characteristics and slope surface displacement patterns. It integrates soil stress-strain behavior, permeability characteristics, seismic stress distribution, and slope deformation characteristics to explore the deformation mechanisms in bedrock and overburden layer slopes after rainfall and seismic events. The results indicate: (1) During rainfall, saturation significantly increases at the slope crest and toe, leading to notable strength degradation without significant overall deformation. However, during seismic activity, the slope crest initially experiences sliding failure, evolving into multi-stage sliding instability. (2) Macroscopic damage occurs suddenly, and the spatial strain distribution within the slope better identifies the evolution of plastic zone expansion, penetration, and instability. (3) The slope's instability evolution pattern, analyzed by residual displacement ratios, aligns well with the spatial strain evolution within the soil, showing greater sensitivity in identifying the slope's damage state compared to cumulative displacement. (4) Changes in moisture content affect soil mechanical properties, and post-rainfall infiltration field distribution affects the slope's overall mechanical behavior and the transmission and spatial distribution of seismic stress. Soil mechanical properties and dynamic stress spatial characteristics determine the slope's failure modes.

Wet-dry (W-D) cycles will cause the release of toxic Cr(VI) from stabilized/solidified soils, posing a threat to the surroundings. In this research, Cr(VI)-contaminated soil treated by alkali-activated granulated blast furnace slag (GGBS) was studied. Through accelerated leaching tests and Cr spatial distribution analysis, the effects of W-D cycle and rainfall pH on Cr mobility in the solidified soil were investigated. The mechanisms of Cr release were studied by chemical form analysis and a serious of micro analyses. The results showed that the leaching characteristics varied with W-D cycles and pH. Under a neutral pH, the cumulative leaching concentration of Cr decreased after 3 W-D cycles and then increased, and the leaching mechanism transitioned from surface wash-off to dissolution. Under acidic environments, the leaching concentration increased by 1-2 orders of magnitude along with the decomposition of hydration products. During the W-D cycles, Cr(VI) content in the solidified soil decreased from top to bottom, reflecting the top-down process of degradation, release, and migration. The W-D cycles had no obvious influence on valence state of Cr. After acidic W-D cycles, the fraction of soluble state Cr(VI) and adsorbed Cr(VI) increased significantly. The CrO4-jarosite phase exhibited good chemical stability in acidic conditions, indicating that chemical substitution is an important immobilization mechanism of Cr(VI). The microscopic morphology analysis showed that W-D cycle caused irreversible damage to the microstructure, and that in an acidic condition C-A-S-H gels were more stable than Aft and C-S-H gels. Along with the W-D cycles, the proportion of macropores increased and the interlayer/gel pores became larger, which significantly facilitated the release of Cr(VI).