The effects of basalt fiber incorporation on the mechanical properties of red clay soils were investigated. Through the direct shear test, unconfined compressive strength test, and microstructure test, the shear strength curves and stress–strain curves of basalt fiber-modified red clay soils were obtained under different basalt fiber incorporation rates and different soil dry density conditions. The results showed that: (1) the shear strength and compressive strength of the soil were significantly increased after the incorporation of basalt fiber; (2) the strength increase was greatest at 0.3% of basalt fiber incorporation, which was the optimum incorporation level; (3) the damage form of the soil changed, and the red clay soil incorporated with basalt fiber changed from brittle damage to ductile damage; and (4) the microscopic electron microscope pictures showed that, at the appropriate amount of fiber incorporation conditions, the fiber bond with the soil particles and form a fiber‒soil column. When subjected to external forces, the discrete fiber‒soil columns interact with each other to form an approximate three-dimensional fiber‒soil network, which acts to restrain the displacement and deformation of the soil particles, which is the main reason for the improved mechanical properties of the improved soil. The experimental research on the improvement of red clay soil with basalt fiber can provide a theoretical basis for engineering practice and help provide an environmentally friendly and efficient method of road base treatment in engineering.

Temperature is one of the important factors affecting the mechanical properties of geotechnical soils, and its role in engineering construction in China cannot be underestimated. In order to study the effects of temperature and zinc contamination concentration on the mechanical properties of Guilin local red clay, a temperature-controlled triaxial shear test was conducted on Guilin red clay under three variables of temperature, zinc contamination concentration and surrounding pressure. The test findings revealed that there are significant differences in the effects of temperature, zinc contamination concentration and surrounding pressure on the mechanical properties of Guilin red clay. The stress–strain curves of the red clay at various temperatures, contamination concentrations and envelope pressures are of the strain-hardening type, and the deformation modulus showed a tendency to increase rapidly with increasing strain, then decrease rapidly, and finally, decrease slowly. With the increase of temperature, the cohesion of Zn-contaminated red clay increases, while the angle of internal friction increases and then decreases, both of which increase the shear strength of red clay. As the concentration of Zn contamination grows, the shear strength of the red clay increases, while the internal friction angle increases and then decreases, and the shear strength of the soil increases and then decreases. The shear strength of the Zn-contaminated red clay improved as the surrounding pressure increased.

With the continuous improvement of the construction of the ecological economic system in the new era, the problem of heavy metal pollution has become an important issue in urban construction. In this paper, Zn²⁺ contaminated red clay is used as the research object, and calcium superphosphate and calcium oxide are used as curing agents to conduct the simultaneous test of unconfined compressive strength-resistivity. The mechanical properties and resistivity of the contaminated soil under different test conditions were analyzed to investigate their effects on the cured red clay. The results showed that different contamination concentrations showed different weakening effects on the unconfined compressive strength of red clay soils, and the unconfined compressive strength of cured soils increased significantly. The age of maintenance affects the unconfined compressive strength of cured soil, and the growth of unconfined compressive strength is most obvious in the age of 0–7 day. After that, it tends to be stable with the growth of age. The deformation modulus of contaminated soil before and after curing was reduced to different degrees. Before and after curing, the resistivity of contaminated soil decreased with the increase of ion concentration, and the resistivity of cured soil increased with the increase of curing agent incorporation rate under the same contamination concentration. The research results can enrich the soil treatment problem of heavy metal contaminated sites and provide theoretical support for the application of this type of curing agent in the field engineering of Zn²⁺ contaminated red clay soil.

The heavy metal contamination of red clay in Guilin is a serious problem. Lead ions pollute red clay and have a series of effects, which affect the macroscopic properties of red clay. However, fundamentally, the effects occur because the internal microstructure of red clay is eroded by Pb²⁺, which results in the change in the macroscopic properties of red clay. Therefore, we adopted a mercury injection experiment and used electronic microscope Pb²⁺ to explore the microscopic mechanism through which red clay is internally influenced. From the mercury injection experiment, we found that an increase in the concentration of Pb²⁺ increased soil pore diameter and volume, and that a higher heavy metal content of Pb²⁺ had a greater effect on red clay cementation. Using scanning electron microscopy, we found that when the micro-image magnification was 500 and 20,000 times, the inside of the red clay pore increased with the increase in the concentration of Pb²⁺, showing that the heavy metal within the microstructure damaged the red clay. The above two experiments showed that heavy metal ions increase the intergranular fractures of red clay, and the thickness of the double layer reduces, which results in the weakening of the interaction force between particles.