This investigation focused on the cementation mechanisms and mechanical properties of soil-rock mixtures-slurry cement (SRM-SC) to ensure the safety of tunnels during operation. SRM-SC specimens were prepared with different types of slurry and rock contents based on an actual slurry injection ratio. The macroscopic level analysis involved measuring the specimens' uniaxial compressive strength and shear strength, determining the strength parameters, and analyzing the damage forms. At the microscopic level, the surface morphology and composition of the specimens were examined using scanning electron microscope imaging. This allowed for a comparative analysis of the cementation ability and mechanism of the slurry under different control conditions, providing a basis for determining the mechanical properties of SRM-SC. The results indicated that the rock content significantly impacts the macromechanical properties of SRM-SC. The compressive strength and stiffness of SRM-SC initially increase and then decrease with the increasing rock content, with an inflection point observed between a 20% and 60% rock content. On the other hand, the shear strength and stiffness both increase with the increasing rock content. Additionally, the macroscopic mechanical properties of SRM-SC formed by different types of grout exhibit noticeable differences. These findings serve as a reference for regulating the mechanical properties of SRM-SC.

Acid contamination has a notable influence on the geotechnical properties of soil and this influence is strongly dependent on contamination concentration (pH) and contamination duration. To fully investigate the effect of acid contamination on the microscopic and strength properties of natural clay, a series of micro- and macrolaboratory tests were performed in this study, and the mechanism of this effect was comprehensively revealed. Microscopic analysis indicates that acid contamination could lead to some mineral transformations in clay, such as illite-smectite transforming into chlorite and illite transforming into kaolinite. Besides, more large pores and a looser structure can be observed in the clay due to the erosional effects of acid contamination, which could effectively weaken the strength properties of natural clay. The experimental results also indicated that, when subjected to acid contamination, the lower contamination pH could lead to a notable decrease in clay's shear strength, while the clay's shear strength increased initially and then decreased as contamination duration increased. In addition, gray correlation analysis results demonstrated that calcite has a significant effect on cohesion, while also indicating a strong correlation between illite and the internal friction angle.

For construction quality control, the compaction delay referred to as mellowing time (MT) is crucial for achieving the desired outcomes of the chemical soil stabilization process in the field. In the current study, fly ash-based geopolymer (GFA) is used as a chemical stabilizer for expansive clay because of its significance in resource utilization and waste repurposing for soil stabilization through an enhanced process. The MT-influenced macroscopic physicomechanical properties and microstructural and mineralogical properties of expansive clay treated with varying GFA and curing period (CP) were investigated. The significant amelioration of strength and compression properties is observed through the unconfined compression test, California bearing ratio test, and one-dimensional (1D) consolidation test with an increase in GFA content and CP. This improvement is caused by the formation of cementitious [(N, C)-A-S-H] compounds as confirmed by SEM, EDAX, and XRD analyses. Meanwhile, as the MT increases, a decline in both the strength and compression characteristics of the GFA-treated specimens is observed. However, these specimens exhibit a reversal in deformability and brittleness with an increase in MT, which can be attributed to the development of a porous aggregated soil structure resulting from initial hydration before densification. In addition, a generalized mathematical modeling framework was established based on three-dimensional (3D) response surface modeling to quantify the MT-influenced strength and brittleness-related characteristics using MT, GFA, and CP as predictors. The established mathematical framework showed generality and reasonable accuracy in the prediction based on the experimental data. This article outlines the implications for practitioners and researchers of using GFA for the stabilization of expansive clay considering MT-influenced mechanical characteristics in the field.

With the advancement of ecological and environmental protection construction, the research on the modification of expansive soil using environmentally friendly polymers can make up for the harm to the ecological environment caused by traditional modification. Mechanical and microscopic properties of modified expansive soils were analyzed through indoor tests. The results showed that the liquid limit and plasticity index decreased by 52.14% and 77.36%, respectively, and the plastic limit increased by 20.83%. Maximum dry density decreased by 5.11% and optimum moisture content increased by 28.47%. The compressive and shear strength increases and then decreases with the increase of dosage, and the strength reaches the maximum when the dosage is 4%, and the vertical and lateral deformation of the specimen is the smallest. Modified soil swelling was reduced by 54.57% and swelling forces were reduced by 15-57%. The modified soil cracks developed slowly and the width of the cracks was reduced by 61.68% after the modification. Microscopy showed that no new minerals were generated after doping modifier, while hydrophilic minerals were reduced by 43.14%, and the gel film formed by hydration made the pores smaller and the structure tighter by filling and wrapping on the surface of the particles.