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 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.

This study explores the application of calcium carbide residue, desulfurization gypsum, and ground granulated blast slag as curing agents to solidify sludge. Through indoor experiments simulating dry-wet cycles and sulfate erosion, using unconfined compressive strength (UCS), X-ray diffraction, and scanning electron microscope as testing methods, the durability of solidified sludge against dry-wet cycles and sulfate erosion was studied. The objective is to provide technical support for the application of solidified sludge in engineering projects and promote the resource utilization of industrial solid waste. The results indicate that solidified sludge exhibits excellent durability against dry-wet cycles and sulfate erosion, with improved durability as the dosage of curing agent increases. In terms of dry-wet cycles, UCS initially increases but experiences a certain degree of decline as the number of dry-wet cycles increases, with the strength change rate exceeding - 35%, and failure strain gradually increases. As for sulfate erosion, UCS initially decreases following 1 day of erosion and subsequently shows a gradual improvement as the erosion time progresses. Higher sulfate concentrations lead to higher UCS, with strengths reaching up to 2.102 MPa, and failure strain gradually decreases. Microscopic tests revealed that, although dry-wet cycles initially weaken the structure and network of solidified sludge, increasing dry-wet cycles numbers leads to enhanced hydration reactions, resulting in higher content of hydration products and a denser microstructure. Experimental results indicate that using calcium carbide residue, desulfurization gypsum, and ground granulated blast slag as curing agents for sludge results in excellent resistance against dry-wet cycles and sulfate erosion.

Currently, utilization of hydrophilic polyurethane (W-OH) materials for slope protection in arid areas has proved to be a cost-effective protocol. The treatment effect highly depends on the interfacial performance between the W-OH treated and the original sandstone. This study aims to investigate the corresponding shear strength and its long-term performance under dry-wet cycles under the arid environment. The results from the direct shear test indicate the interface shear strength increases with W-OH solution concentration and decreases with the increase of water content of the Pisha sandstone. Further investigations under dry-wet cycles indicate the interface cohesion is obviously weakened by the dry-wet cycles, while the influence on the internal friction angle is not obvious. The correlation between the degradation level and the dry-wet cycles can be well fitted with the inverted Scurve using two combined exponential functions. Furthermore, the ethylene-vinyl acetate (EVA) content is utilized to enhance the durability performance under dry-wet cycles. It is found the EVA can obviously improve the bonding property and the resistance to dry-wet cycles. This study's results can serve as a solid base for the application of W-OH materials to resolve the soil erosion in the arid region.

To improve the mechanical and durability properties of low liquid limit soil, an eco-friendly, all-solid, waste-based stabilizer (GSCFC) was proposed using five different industrial solid wastes: ground granulated blast-furnace slag (GGBS), steel slag (SS), coal fly ash (CFA), flue-gas desulfurization (FGD) gypsum, and carbide slag (CS). The mechanical and durability performance of GSCFC-stabilized soil were evaluated using unconfined compressive strength (UCS), California bearing ratio (CBR), and freeze-thaw and wet-dry cycles. The Rietveld method was employed to analyze the mineral phases in the GSCFC-stabilized soil. The optimal composition of the GSCFC stabilizer was determined as 15% SS, 12% GGBS, 16% FGD gypsum, 36% CS, and 12% CFA. The GSCFC-stabilized soil exhibited higher CBR values, with results of 31.38%, 77.13%, and 94.58% for 30, 50, and 98 blows, respectively, compared to 27.23%, 68.34%, and 85.03% for OPC. Additionally, GSCFC-stabilized soil demonstrated superior durability under dry-wet and freeze-thaw cycles, maintaining a 50% higher UCS (1.5 MPa) and a 58.6% lower expansion rate (3.16%) after 15 dry-wet cycles and achieving a BDR of 86.86% after 5 freeze-thaw cycles, compared to 65% for OPC. Rietveld analysis showed increased hydration products (ettringite by 2.63 times, C-S-H by 2.51 times), significantly enhancing soil strength. These findings highlight the potential of GSCFC-stabilized soil for durable road sub-base applications. This research provides theoretical and technical support for the development of sustainable, cost-effective, and eco-friendly soil stabilizers as alternatives to traditional cement-based stabilizers while also promoting the synergistic utilization of multiple solid wastes.

The selection of structural strength indicators is of utmost importance for slope engineering safety. This paper, with the backdrop of the destruction of high liquid limit clay layers in the Huai River slope, aims to investigate the influence of dry-wet (D-W) cycles on the structural and mechanical properties of undisturbed high liquid limit clay. Through unconfined compression tests, scanning electron microscopy (SEM) tests, and triaxial shear tests, the structural behavior, stress-strain curves, porewater pressure-strain curves, and effective stress paths of undisturbed samples taken at three different angles and reconstituted samples were analyzed under the condition of maximum drying stress with 0 and 1 D-W cycle. Based on the impact of D-W cycles on the effective stress path, the shear failure mode of structurally high liquid limit clay under the influence of D-W cycles was identified. A method for evaluating the anisotropic level of structural clay after experiencing D-W cycles was proposed. The test results show that compared with reconstructed soil, the undisturbed high liquid limit clay with structure is more significantly affected by the D-W cycle. After D-W cycles, the CU shear strength of high liquid limit clay increased significantly. The failure mode transitioned from a hardening-shear dilation mode to a softening-partial shear contraction-partial shear dilation mode. The appearance of the phase transition state (PTS) point may be attributed to the partial action of effective stress on cracks inside the sample, resulting in shear contraction. D-W cycles weakened the structural properties (anisotropy) of high liquid limit clay.

The protection of the ecological environment and the scarcity of renewable resources are increasingly concerning global issues. To address these challenges, efforts have been made to use desert sand and fly ash in the preparation of building materials. This study attempts to replace river sand with desert sand and cement with fly ash to create an environmentally friendly and economical building material-desert sand dry-mixed mortar (DSDM). Through preliminary mix ratio experiments, five grades of DSDM were developed, and their durability in the saline soil regions of northwest China was studied. The study conducted macro-performance tests on the five strength grades of DSDM after sulfate dry-wet cycles (DWCs), analyzing changes in appearance, mass loss rate, compressive strength loss rate, and flexural strength loss rate. Using SEM, XRD, and NMR testing methods, the degradation mechanisms of the DSDM samples were analyzed. Results indicate that sulfate ions react with hydration products to form ettringite and gypsum, leading to sulfate crystallization. In the initial stages of DWCs, these erosion products fill the pores, increasing density and positively impacting the mortar's performance. However, as the number of cycles increases, excessive accumulation of erosion products leads to further expansion of pores and cracks within the DSDM, increasing the proportion of harmful and more harmful pores, degrading performance, and ultimately causing erosion damage to the mortar. Among the samples, DM5 exhibited the poorest erosion resistance, fracturing after 30 cycles with a mass loss of 43.57%. DM10 experienced failure after 60 cycles, with its compressive strength retention dropping to 78.86%. In contrast, DM15, DM20, and DM25 showed the best erosion resistance, with compressive strength retention above 75% after 120 cycles. Finally, the Wiener random probability distribution was used to predict the remaining life of DSDM samples under different degradation indicators, with flexural strength being the most sensitive indicator. Based on the flexural strength loss rate, the maximum sulfate DWCs for DM5, DM10, DM15, DM20, and DM25 were 132, 118, 78, 52, and 35 cycles, respectively. This study provides a theoretical basis for the promotion and use of DSDM in desert fringe areas.

The quality of the railway subgrade is directly related to the fill soil structure, which, in turn, is determined by the local physical and chemical environment. A karst environment, with its frequent rainfall, promotes the dissolution of soluble rocks and underground transportation of solutes, altering the soil structure and performance. To investigate these alterations, we analyzed the properties of underground soil from highly developed karst areas. Fine breccia soil from karst regions was tested to assess its macroscopic mechanical properties and microstructural features, for differing initial water contents and compaction levels. Samples were subjected to simulated rainfall conditions through dry-wet cycles, and then underwent triaxial shear and electron microscopy tests. From these data, a micro-to-macro correlation model and a normalization model were developed. The findings suggest that the resistance of fine angular breccia soil to degradation during dry-wet cycles can be enhanced through high-pressure compaction and by maintaining a moisture content close to 15.6%. Increasing the degree of compaction improves the particle size distribution and the density of the soil skeleton. This is advantageous for minimizing soil particle erosion, thereby ensuring the strong performance of railway subgrades in karst areas with frequent rainfall.

Understanding the mechanical response of Q2 loess subjected to dry-wet cycles (DWCs) is the premise for the rational design of a hydraulic tunnel. Taking the Hanjiang-to-Weihe south line project in China as the research background, the microstructure evolution, strength degradation and compression characteristics of Q2 loess under different DWCs were investigated, and the fluid-solid coupling analysis of the hydraulic tunnel was carried out using the FLAC3D software. The amplification effect of tunnel surrounding soil pressure (SSP) and its influence on the long-term stability of the tunnel under different DWCs were obtained. The results showed that the pore microstructure parameters of the undisturbed and remolded loess basically tend to be stable after the number of DWCs exceeds 3. The porosity of Q2 loess is increased by 26%. The internal friction angle and cohesion of Q2 loess are decreased by 35% and 31%, respectively. The vertical strain of Q2 loess is increased by 55% after considering the DWCs. After the DWCs stabilized, the SSP ratio is increased between 10% and 25%. With the increase in buried depth of the tunnel, the SSP ratio is increased by 8%-10%. The SSP is reduced from 8% to 16% by the rise in groundwater level. As the number of DWCs increases and the burial depth of the tunnel decreases, the distribution of SSP becomes progressively more non-uniform. Based on the amplification factor and the modified compressive arch theory, the SSP distribution model of loess tunnel was proposed, which can be preliminarily applied to the design of supporting structures considering DWCs. (c) 2024 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/).