To investigate the coupled time effects of root reinforcement and wet-dry deterioration in herbaceous plant-loess composites, as well as their microscopic mechanisms, this study focused on alfalfa root-loess composites at different growth stages cultivated under controlled conditions. The research included measuring root morphological parameters, conducting wet-dry cycling tests, and performing triaxial compression tests and microscopic analyses (CT scanning and nuclear magnetic resonance) on both bare loess and root-loess composites under various wet-dry cycling conditions. By obtaining shear strength parameters and microstructural indices, the study analyzed the temporal evolution of the shear strength and microstructural characteristics of root-loess composites under wet-dry cycling. The findings indicated that the alfalfa root-loess composite effective cohesion was significantly higher than that of the plain soil in the same growth stage. The alfalfa root-loess composite effective cohesion increased during the growth stage in the same dry-wet cycles. The alfalfa root-loess composite effective cohesion in the same growth stage was negatively correlated with the number of dry-wet cycles. The fatigue damage of the soil's microstructure (pore coarsening, cement hydrolysis, and crack development) increased continuously with the number of dry-wet cycles. However, due to the difference in mechanical properties between roots and the soil, the root-soil composite prevented the deterioration of the soil matrix strength by the dry-wet cycles. As the herbaceous plants grow, the time effect observed in the shear strength of the root-soil composite under the action of dry-wet cycles is the result of the interaction and dynamic coordination between the soil-stabilizing function of the herbaceous plant roots and the deterioration caused by drywet cycles.

The present paper sets out a comparative analysis of carbon emission and economic benefit of different performance gradients solid waste based solidification material (SSM). The macro properties of SSM were the focus of systematic study, with the aim of gaining deeper insight into the response of the SSM to conditions such as freeze-thaw cycles, seawater erosion, dry-wet cycles and dry shrinkage. In order to facilitate this study, a range of analytical techniques were employed, including scanning electron microscopy (SEM), X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP). The findings indicate that, in comparison with cement, the carbon emissions of SSM (A1) are diminished by 77.7 %, amounting to 190 kg/t, the carbon-performance ratio (24.4 kg/ MPa), the cost-performance ratio (32.1RMB/MPa) and the carbon-cost ratio (0.76kg/RMB) are reduced by 86 %, 56 % and 68 % respectively. SSM demonstrated better performance in terms of freeze-thaw resistance, seawater erosion resistance and dry-wet resistance when compared to cement. The dry shrinkage value of SSM solidified soil was reduced by approximately 35 % at 40 days compared to cement solidified soil, due to compensatory shrinkage and a reduction in pores. In contrast to the relatively minor impact of seawater erosion and the moderate effects of the wet-dry cycle, freeze-thaw cycles have been shown to cause the most severe structural damage to the micro-structure of solidified soil. The conduction of durability tests resulted in increased porosity and the most probable aperture. The increase in pores and micro-structure leads to the attenuation of macroscopic mechanical properties of SSM solidified soil. The engineering application verified that with the content of SSM of 50 kg/m, 4.5 % and 3 %, the strength, bearing capacity and bending value of SSM modified soil were 1.9 MPa, 180 kPa and 158, respectively in deep mixing piles, shallow in-situ solidification, and roadbed modified soil field.

In the northwestern saline soils and coastal areas, cement soil (CS) materials are inevitably subjected to various factors including salt erosion, dry-wet cycle (DWC), temperature fluctuations and dynamic loading during its service life, which the coupling effect of these unfavourable factors seriously threatened the durability and engineering reliability of CS materials. Additionally, combined with the substantially extensive application prospects of rubber cementitious material, as a resource-efficient civil engineering material and fibre-reinforced composites, consequently, in order to address aforementioned issues, this investigation proposed to consider the incorporation of rubber particles composite basalt fiber (BF) to CS materials as an innovative engineering solution to effectively enhance the mechanical and durability properties of CS materials for prolonging its service life. In this study, sulphate ions were utilized to simulate external erosive environment and basalt fibre rubber cement soil (BFRCS) specimens were subjected to various DWC numbers (0, 1, 4, 7, 11 and 15) in diverse concentrations (0 g/L, 6 g/L and 18 g/L) of Na2SO4 solution, and specimens that had completed the corresponding DWC number were then conducted both unconfined and dynamic compressive strength tests simultaneously to analyze static and dynamic stress-strain curves, static and dynamic compressive strength, apparent morphological deterioration characteristics and energy absorption properties of BFRCS specimens. Furthermore, further qualitative and quantitative damage assessments of pore distribution and microscopic morphology of BFRCS specimens under various DWC sulphate erosion environments were carried out from the fine and microscopic perspectives through pore structure test and scanning electron microscopy (SEM) test, respectively. The test results indicated that the static, dynamic compressive strength and specific energy absorption (SEA) of BFRCS specimens exhibited a slight increase followed by a progressive decline as DWC number increased. Additionally, compared to 4 mm BFRCS specimens, those with 0.106 mm rubber particle size demonstrated more favorable resistance to DWC sulphate erosion. The air content, bubble spacing coefficient and average bubble chord length of BFRCS specimens all progressively grew as DWC number increased, while the specific surface area of pores gradually decreased. The effective combination of BF with CS matrix significantly diminished pores and weak areas within specimen, and its synergistic interaction with rubber particles efficiently mitigated the stresses associated with expansive, contraction, crystallization and osmosis subjected by specimen. Simultaneously, more ettringite (AFt) had been observed within BFRCS specimens in 18 g/L sulphate erosive environments. These findings will facilitate the design and construction of CS subgrade engineering in northwestern saline soils and coastal regions, promoting sustainable and durable solutions while reducing the detrimental environmental impact of waste rubber.

Red mud is a kind of solid waste, which can be used as engineering roadbed filler after proper treatment. Due to the special physical and chemical properties of red mud, such as high liquid limit and high plasticity index, it may affect the stability of soil. Therefore, red mud can be improved by adding traditional inorganic binders such as lime and fly ash to improve its road performance as roadbed filler. Red mud-based modified silty sand subgrade filler will be affected by dry-wet alternation caused by various factors in practical application, thus affecting the durability of the material. In order to study the strength degradation characteristics and microstructure changes of red mud, lime and fly ash modified silty sand subgrade filler after dry-wet cycle, the samples of different curing ages were subjected to 0 similar to 10 dry-wet cycles, and their compressive strength, microstructure and environmental control indexes were tested and analyzed. The results show that the sample cured for 90 days has the strongest toughness and the best ability to resist dry and wet deformation. With the increase of the number of dry-wet cycles, the mass loss rate of the sample is in the range of 6 similar to 7 %, and the unconfined compressive properties and tensile properties decrease first and then increase. There are continuous hydration reactions and pozzolanic reactions in the soil, but the degree of physical damage in the early stage of the dry-wet cycle is large, and the later cementitious products have a certain offsetting effect on the structural damage. The internal cracks of the sample without dry-wet cycle are less and the structure is dense. After the dry-wet cycle, the microstructure of the sample changed greatly, and the cracks increased and showed different forms. Through SEM image analysis, it was found that the pore structure of the sample changed during the dry-wet cycle, which corresponded to the change law of mechanical properties. After wetting-drying cycles, the leaching concentration of heavy metals in the modified soil increased slightly, but the overall concentration value was low, which was not a toxic substance and could be used as a roadbed material. The study reveals the influence of dry-wet cycle on the strength characteristics and microstructure of red mud, lime and fly ash synergistically improved silty sand, which provides a technical reference for the engineering application of red mud-based materials.

Ultra-high performance concrete (UHPC), due to its superior mechanical and durability properties, is extensively applied in saline soil areas. In this paper, the damage evolution process and constitutive relationship of UHPC under sulfate dry-wet cycling were investigated through mechanical property tests combined with acoustic emission (AE) technology. The results showed that With the increase in erosion cycles and SO42- content, the proportion of low-amplitude (<= 50 dB) AE events exhibited a decreasing trend. In contrast, the fraction of medium-and high-amplitude AE events gradually increased, suggesting that large-scale damage began to play a dominant role in the specimen's deterioration process. Based on AE characteristic parameters, the damage evolution model of UHPC under uniaxial compression was established, the model can effectively characterize the uniaxial compression damage evolution behavior of UHPC under sulfate dry-wet cycling, providing theoretical support for the service performance evaluation of UHPC structures in saline soil areas.

The deterioration of rock mass in the Three Gorges reservoir area results from the coupled damage effects of macro-micro cracks and dry-wet cycles, and the coupled damage progression can be characterized by energy release rate. In this study, a series of dry-wet cycle uniaxial compression tests was conducted on fractured sandstone, and a method was developed for calculating macro-micro damage (DR) and energy release rates (YR) of fractured sandstone subjected to dry-wet cycles by considering energy release rate, dry-wet damage and macro-micro damage. Therewith, the damage mechanisms and complex microcrack propagation patterns of rocks were investigated. Research indicates that sandstone degradation after a limited cycle count primarily exhibits exsolution of internal fillers, progressing to grain skeleton alteration and erosion with increased cycles. Compared with conventional methods, the DR and YR methodologies exhibit heightened sensitivity to microcrack closure during compaction and abrupt energy release at the point of failure. Based on DR and YR, the failure process of fractured sandstone can be classified into six stages: stress adjustment (I), microcracks equal closure (II), nonlinear slow closure (III), low-speed extension (IV), rapid extension (V), and macroscopic main fracture emergence (VI). The abrupt change in damage energy release rate during stage V may serve as a reliable precursor for inducing failure. The stage-based classification may enhance traditional methods by tracking damage progression and accurately identifying rock failure precursors. The findings are expected to provide a scientific basis for understanding damage mechanisms and enabling early warning of reservoir-bank slope failure. (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/).

The structural integrity of slopes in the Ili Valley is critically influenced by the inherent characteristics of loess, particularly when it is subjected to the seasonal climatic changes. In the present research, a series of triaxial shear tests were carried out to examine the mechanical behavior of the Ili loess under different dry-wet and frost-thaw cycles. In parallel, some testing methods, including scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR), were applied to investigate the progressive damage characteristics and the alterations in terms of the microstructures. Test results demonstrated a strong correlation between the macroscopic mechanical resistance and microstructural changes of the Ili loess subjected to the dry-wet and freeze-thaw cycles. The impact of the freeze-thaw cycles was more pronounced than other parameters, when the reduction in shear strength of the Ili loess under dry-wet cycles was accounted for. The results also showed that either the cohesion or the internal friction angle is very different from each other. Furthermore, changes in terms of the microstructure, such as the particle size, porosity, morphology, soil structure, and particle contact mode, exhibited distinct characteristics under varying climates. The research outcomes obtained from this research offer valuable data reference and theoretical guidelines to prevent or postpone the occurrence of the landslide in the Ili Valley under critical environmental conditions.

Complex adverse weather conditions such as rain erosion and frost are frequently encountered in practical construction projects, particularly in the Inner Mongolian region of China. In this study, a new biopolymer (GGPAM) with an interpenetrating crosslinked network structure was developed by chemically modifying GG to address the poor resistance of soil to rainwater erosion, frost, and other complex environmental conditions in open-air construction buildings. First, GG-PAM was synthesized by chemically modifying guar gum (GG) through graft copolymerization, and thermogravimetric (TG) analysis confirmed its favorable thermal stability. Subsequently, experiments were conducted to investigate the mechanical properties and microstructural characteristics of GG-PAM-solidified soil. Then, using GG as a control, dry-wet cycle and freeze-thaw cycling tests were performed to compare the changes in unconfined compressive strength (UCS) of GG- and GG-PAM-solidified soil. Finally, water erosion, crack propagation, and permeability tests were conducted to evaluate the resistance of GG-PAM-solidified soil to external forces. The results indicated that the mechanical strength, durability, and erosion resistance of the GG-PAM-solidified soil were significantly superior to those of GG. When the GG-PAM content reaches 1 %, both the mechanical strength and erosion resistance of the solidified soil are significantly improved. These findings provide a theoretical basis for the construction and maintenance of roadbeds.

The development of cracks and deterioration of mechanical properties in aeolian deposits are common phenomena during dry-wet cycles. The redistribution of soil particles and the change of clay mineral aggregates are some of the reasons for the change in soil properties in this process. In this paper, the physical and mechanical properties, apparent digital images, and scanning electron microscopy (SEM) were used jointly to analyze the properties of silty clays (Xiashu loess) during the dry-wet cycle. The amplitude design of the dry-wet cycle is 2.52%-28.39%, and the number of cycles was designed to be 2,4,6,8and 10 times. The results show that the shrinkage and breakage of clay minerals and the release of pore water stress are caused by the change in water content leading to the redistribution of aggregate particles. The permeability and swelling ability of soil tend to be stable, indicating the stable trend of particle redistribution. The soil cohesion and internal friction angle have an exponential relationship with the number of dry-wet cycles, and the exponential relationship parameters are related to the soil type. Based on the analysis of particle migration, it can better explain the reasons for the deterioration of soil mechanical properties.

The solidification effect of contaminated soil degrades under wet-dry (W-D) cycles and acid rain. Acidic dry-wet cycle tests for Cr-contaminated soil solidified by alkali-activated granulated blast furnace slag (GGBS) are carried out. Toxic leaching test and accelerated leaching test are performed to study the leaching characteristic and mechanism. Scanning electron microscopy and energy spectrum analysis are used to investigate the microscopic mechanism. The long-term stability is evaluated through the apparent diffusion coefficient. The results show that a few W-D cycles at pH=7 will cause additional hydraulic reaction of GGBS and thus reduce the leaching concentration of total Cr and Cr(VI). Along with W-D cycles more AFt is generated. The expansion of AFt results in micro-fracture and thus more Cr leaching. In acidic W-D cycles, AFt dissolves first, releasing Cr immobilized by ion exchange. With the increasing acidity, C-S-H gels dissolve and more gypsum is generated, resulting in more micro-fractures. Consequently, the encapsulation effect weakens, resulting in more Cr leaching. However, the C-A-S-H gels remain stable. The slopes of the logarithmic curves of cumulative leached fraction versus time range from 0.373 to 0.675. The errors of fitting by a pure-diffusion analytical solution are mainly below 0.5%, indicating that diffusion is the dominant leaching mechanism. However, after 18 W-D cycles at pH=3, the effect of dissolution increases and the diffusion-dominated criteria are not satisfied. The mobility of Cr under neutral, weak acidic, and strong acidic W-D cycles is low, moderate, and high, respectively. It is necessary to take measures to reduce acid rain infiltration and W-D cycles when utilizing solidified soil. This research provides a reference for evaluating the long-term stability of solidified contaminated soil.