In this paper, the effect of salt (Na2SO4, NaCl) on the clay Atterberg limits and shear strength is revealed by using volumetric flask test and triaxial shear test, and the macroscopic mechanical performance results of the Atterberg limits and triaxial shear test reveal the mechanism of salt solution's effect on the evolution of the deterioration of the microscopic pore structure of the soil body based on the perspective of microscopic pore characterization by using nuclear magnetic resonance (NMR) scanning and scanning electron microscopy (SEM) techniques. The results show that in Na2SO4 solution and NaCl solution, the decrease of double layer thickness and the increase of PH value caused by the increase of cation concentration are the main reasons for the gradual decrease of soil Atterberg limits, adsorbed bound water (ABW) content and shear strength. In addition, when the cation concentration is the same, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{SO}_{4}{2-}$$\end{document} has a greater barrier effect like semi-permeable film than Cl-, which makes the double layer thickness of Na2SO4 solution thinner than NaCl solution, the Atterberg limits and ABW content is further reduced; Meanwhile, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text{SO}_{4}{2-}$$\end{document} has greater intergranular repulsion on the particle surface compared to Cl-, forming a larger pore structure further deteriorating the soil structure and reducing the soil shear strength. It provides more support for studying the effect of salt on the physical and mechanical properties of clay.

Foam concrete boasts widespread applications in backfill engineering, energy -efficient insulation components, and road infrastructure. However, the foam concrete with lower density tends to possess the lower stability. The unstable characteristics of foam concrete restricts its application. In this study, the feasibility of employing biochars to increase stability of foamed concrete is investigated. The rheological properties of base mix are carried out to analyze the foam concrete stability. The analysis of water state, interparticle distance and ion concentration are tested to analyze the stabilization mechanisms. Our findings demonstrate that the introduction of corn husk biochar (CHBC) within the base mix expedites flocculation formation, reducing interparticle distance and subsequently elevating the yield stress. Conversely, the inclusion of rice husk biochar (RHBC) diminishes ion concentration, heightening repulsion forces between particles and thereby reducing yield stress of base mix. Higher yield stress exert the higher constraining force and frictional force to the bubbles, thereby decreasing bubble size in fresh foamed concrete, bettering pore structure, compressive strength and foam stability of foamed concrete. Additionally, the increase in CHBC content enhances pore sphericity, potentially attributed to decreased bubble deformation parameters Ca eta.

Microbially induced calcite precipitation (MICP) stands as an environmentally friendly and promising technique for enhancing the performance of soil. Bacteria catalyze the hydrolysis of urea, prompting calcium ions to react with carbonate ions, ultimately forming calcium carbonate precipitation as a cement within soil grains. However, studies of using MICP to enhance granite residual soil (GRS) that is recognized as a problematic soil because of its wide grain size distribution are relatively rare. In this present study, bio-cemented GRS samples were prepared through grouting with Sporosarcina pasteurii as the colony and a mixture of urea and calcium chloride as the cementation solution. The effect of cementation-solution concentrations on the mechanical properties of the bio-cemented samples was analyzed through unconfined compression and triaxial shear tests. Furthermore, X-ray computerized tomography, scanning electron microscopy, and X-ray diffraction experiments were performed to reveal the mechanism of MICP from a microscopic perspective. The experimental results indicate that an optimal concentration of 2 mol/L achieved the highest level of cementation, resulting in an impressive 47.15% increase in the unconfined compressive strength of the GRS samples. The triaxial shear strength and stress paths of bio-cemented samples were affected by the cementation level. The variation of porosity indicated that CaCO3 precipitation improves soil densification by filling the macropores among the soil grains. The CaCO3 precipitates from the MICP treatment predominantly exist in the form of calcite crystals, serving to fill, wrap, and cement within the soil structure, thereby enhancing the cohesive and frictional forces exerted by the bio-cemented grains.

Analysis of environmental significance and hydrochemical characteristics of river water in mountainous regions is vital for ensuring water security. In this study, we collected a total of 164 water samples in the western region of the Altay Mountains, China, in 2021. We used principal component analysis and enrichment factor analysis to examine the chemical properties and spatiotemporal variations of major ions (including F-, Cl-, NO3-, SO42-, Li+, Na+, NH4+, K+, Mg2+, and Ca2+) present in river water, as well as to identify the factors influencing these variations. Additionally, we assessed the suitability of river water for drinking and irrigation purposes based on the total dissolved solids, soluble sodium percentage, sodium adsorption ratio, and total hardness. Results revealed that river water had an alkaline aquatic environment with a mean pH value of 8.00. The mean ion concentration was ranked as follows: Ca2+>SO42->Na+>NO3->Mg2+>K+>Cl->F->NH4+>Li+. Ca2+, SO42-, Na+, and NO3- occupied 83% of the total ion concentration. In addition, compared with other seasons, the spatial variation of the ion concentration in spring was obvious. An analysis of the sources of major ions revealed that these ions originated mainly from carbonate dissolution and silicate weathering. The recharge impact of precipitation and snowmelt merely influenced the concentration of Cl-, NO3-, SO42-, Ca2+, and Na+. Overall, river water was in pristine condition in terms of quality and was suitable for both irrigation and drinking. This study provides a scientific basis for sustainable management of water quality in rivers of the Altay Mountains.