Dispersive saline soil is a type of water sensitive special soil with the characteristic of instability when encountering water, and its engineering properties are unstable. Therefore, this research proposes the use of environmentally friendly biopolymer guar gum to improve soil dispersivity and explores the feasibility of guar gum in improvement of dispersive saline soil. The mechanical properties of the improved dispersive saline soil were determined through unconfined compressive strength tests and direct shear tests. The influence of guar gum on the dispersivity and physical properties of the soil were investigated by crumb tests, pinhole tests, liquid plastic limit tests and particle size distribution tests. The microstructure and mineral composition of the improved soil were analyzed by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy tests. Experimental results indicate that 1.5 % guar gum can transform highly dispersive soil into non-dispersive soil after curing 28 days. When the guar gum content increases from 0 % to 4 %, the unconfined compressive strength increases by 81.30 %, and the cohesion and internal friction angle increase by 117.02 % and 32.69 %, respectively. Guar gum is enriched with hydroxyl groups, which form hydrogels in contact with water, and form a cationic bridge with the surface cations of clay particles, the two aspects work together to cement the soil particles, dense soil structure. Guar gum can effectively improve the dispersivity and mechanical properties of dispersive saline soil, and can be used as an environmentally friendly soil modification material.

Cement-stabilized soil in coastal soft soil regions is essential for infrastructure construction. However, under the combined effects of seawater erosion and cyclic loading, cement-stabilized soil often faces issues such as strength degradation, reduced durability, and stiffness softening. To enhance the engineering properties of cement soil, this study utilized nano-Al2O3 as a modifier. The effects of nano-Al2O3 on the dynamic properties of cement soil under various erosion environments were assessed using the GDS dynamic triaxial system. Furthermore, scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests were performed to study the microstructural changes in cement-stabilized soil modified with nano-Al2O3 subjected to seawater erosion. The results indicate that nano-Al2O3 significantly improves the resistance of soil to deformation. As the content of nano-Al2O3 increases, the dynamic strain of cement-stabilized soil initially decreases and then increases, while the dynamic shear modulus first increases and then decreases, showing optimal performance at a 0.25% content. Seawater erosion severely weakens the strength and stiffness of cement-stabilized soil; as erosion concentration increases, dynamic strain increases, and dynamic shear modulus decreases. Nano-Al2O3 improves the strength of cement-stabilized soil and mitigates the negative impacts of seawater erosion through pozzolanic reactions and filler effects.

Dispersive soils are frequently employed as construction materials in projects such as drains and dams in western Jilin, China. However, their propensity to disperse upon contact with water presents a grave threat to construction projects if left unaddressed. Therefore, following the identification of the fundamental physical and chemical properties, as well as the dispersivity of soils in the western region of Jilin Province, Sporosarcina pasteurii was chosen to conduct laboratory experiments and mechanistic studies aimed at improving dispersive soils in the area through MICP. The treatment effect of the soil samples was quantitatively assessed through tests including comprehensive dispersivity identification, unconfined compressive strength (UCS) measurement, and determination of calcium carbonate content. Furthermore, scanning electron microscope (SEM) tests were conducted to examine the microstructural alterations of the soil samples before and after microbial treatment. The experimental results showed that soil dispersion can be significantly reduced under various conditions, and increase the soil strength under certain condition. MICP facilitates the replacement of exchangeable Na+ in soil and induces the formation of calcium carbonate, which fills pores and acts as a cementing agent. Treating dispersive soil in western Jilin is crucial to ensuring the safe and normal operation of its water conservancy projects.

The engineering problems caused by dispersive soil are of worldwide concern. Traditional high carbon emission soil amendments such as cement and lime cause several environmental problems, including pollution and soil alkalization. Inorganic polymers are considered to be an economical, effective, and environmentally friendly soil amendment. Therefore, this paper proposes the use of the polymeric coagulant polyaluminum chloride (PAC) to improve soil dispersivity. PAC was added to the dispersive soils at different dry mass ratios of 0%, 0.5%, 1%, 1.5%, 2.5%, 4%, 5%, 6%, 7%, 8%, and 10%. The soil samples were then cured for 1, 4, 7, 14, and 28 days. Soil dispersivity was determined by crumb tests, pinhole tests, and exchangeable sodium ion percentage tests. Soil mechanical strength was assessed through unconfined compressive strength tests and unconsolidated undrained triaxial tests. Particle size distribution, pH, resistivity, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy tests were conducted to investigate soil improvement mechanisms. Experimental results indicate that 1.5% PAC can transform highly dispersive soil into non-dispersive soil after 1 day of curing. When the PAC content increases from 0% to 7%, the unconfined compressive strength of the soil increases by 110.1%, and the internal friction angle and cohesion increase by 61.1% and 24.2%, respectively. The changes in the physicochemical properties and microstructure of the soil indicate the high-valence cations produced by PAC hydrolysis can effectively replace Na+ in the soil, while significantly reducing the pH value of the soil. Simultaneously, the coagulation effect generated markedly reduces soil porosity, resulting in a more compact soil structure. In summary, PAC demonstrates excellent potential in improving soil dispersivity and mechanical properties. Compared to traditional high carbon emission amendments such as cement and lime, PAC can effectively reduce soil alkalinity, mitigate environmental issues associated with these materials, and offer new possibilities for improving dispersive soils.

To achieve value-added recycling of slurry -like mud (MS) and resolve the shortage issue of construction fill materials, physicochemical combined methods (PCCMs), which integrate flocculation, solidification, and vacuum preloading (optional), have been proposed to enhance the engineering properties of MS. The optimization of chemical admixtures, which consist of solidification and flocculation components, is crucial in ensuring the effectiveness and cost -efficiency of PCCM in practical application. In this study, a number of solidification model tests are performed to optimize the solidification components for PCCM via determining the optimal mixing ratio in each of the two GGBS-based binders. Subsequently, surcharge preloading deposition tests and vacuum preloading model tests, with different types/dosages of flocculant, are conducted to determine the appropriate flocculation components. The results indicate that OPC-GGBS exhibits remarkable effectiveness in strength improvement, and the use of a combination of organic and inorganic flocculant, particularly CaO-PAM, can significantly enhance the efficiency of PCCM. Moreover, increasing the dosage of the composite flocculants enhances the dewatering process, but the benefit becomes less significant when the dosage exceeds a threshold value of 0.16%. Additionally, this study provides a preliminary understanding of the key mechanism involved in synergizing flocculation, solidification and preloading to enhance the performance of MS. These findings contribute to the optimal design and application of PCCM for the treatment of MS.