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The exploitation of underground space is accompanied by complex geotechnical problems. The development of electromagnetic exploration technology provides a new perspective for preventing and avoiding these problems. In this work, electrochemical impedance spectroscopy (EIS) was used to test the single-phase and mixed-phase medium. Based on the unsaturated soil theory and the dual-water conductivity theory, an equivalent circuit model to describe the electrochemical characteristics and microstructure of silty soil with temperature changes through comparative research. The results indicate that the resistance of near-water layer is not affected by temperature, the resistance of silty soil increases mainly results from the influence of the far-water layer until which increases significantly after freezing. The capacitance change of silty soil is mainly affected by the slowing down of the orientation movement of polar molecules in the far-water layer. Based on the fitting data, a mathematical model for calculating the unfrozen water content of frozen soil was proposed, which reasonably verified the relationship between the unfrozen water content and electrical resistance. By improving the testing conditions of electrochemical impedance spectroscopy, this method may provide new insights for future research of soil electromagnetic testing technology.

In this paper, the solidification of Cu2+-contaminated kaolin by high belite sulphoaluminate cement (HBSC) combined with red mud (RM) and fly ash (FA) was investigated. The effects of solidification/stabilization (S/S) and its electrochemical responses were experimentally explored by mixing RM and FA as the main raw materials with small amounts of low-energy HBSC and quicklime serving as solidifiers of heavy metal contaminated soil. The solidification mechanism of the solidifier on Cu2+ and its solidification effect were then systematically investigated by analyzing the unconfined compressive strength (UCS) of the solidified body, toxic leaching, permeation characteristics, and surfaces morphologies. The study of the electrochemical response of the solidified body during the solidifying and remediation process allowed the development of an evaluation method for repairing the effect of Cu2+-contaminated kaolin based on electrochemical impedance spectroscopy (EIS). The results showed that the strength, impermeability, and leaching toxicity of solid waste co-HBSC solidifying of contaminated soil met industrial requirements. The incorporation of low energy consumption HBSC generated a mass ratio of RM to FA of 8:2 with the best solidification effect. Heavy metals can be absorbed by chemical precipitation, displacement reactions, and encapsulation by hydration gels. In addition, the electrochemical impedance characteristics of the solidified bodies were found consistent with the conventional evaluation of the solidification effect. In sum, HBSC synergistic solid waste solidifier looks very promising for use in the S/S remediation of Cu2+-contaminated soil.

The main purpose of this work was to study a new method for evaluating the solidification of contaminated soil based on electrochemical impedance spectroscopy (EIS). To explore how the EIS parameters were affected by the pore structure and mesostructure of the cured system, the physical and mechanical properties, leaching toxicity, microstructure, and EIS of the stabilized contaminated soil were tested after 7, 28, 60, and 90 days of curing. Based on the EIS results, a physical and equivalent circuit model of the stabilized contaminated soil's impedance response was established to reveal the mechanism of binder-heavy metal ion-soil interaction. The results showed that as the red mud (RM)-fly ash (FA) mass ratio and curing age increased, the strength and structural compactness of the solidified body also increased. The best curing effect was achieved with an RM-FA mass ratio of 7:3 after curing for 90 days. The equivalent circuit model of the solidified body obtained by EIS was Rs (Q1 (Rct1W) Q2Rct2). The pore solution resistance Rs, solid-liquid interface ion transfer resistance Rct 1, and unconfined compressive strength (UCS) qu all showed an increasing trend with increasing RM-FA mass ratio and increasing curing time. Fitting the model demonstrated that both Rs and Rct1 were closely correlated with the strength of the solidified bodies. These conclusions were further verified by scanning electron microscope (SEM) experiments. Overall, this work demonstrates that the strength characteristics of solidified bodies can be evaluated by EIS and reveals the microscopic mechanism of the solidification of Cu2+-contaminated soil.

In this study, the effects of high-sulphur fly ash on the properties of lightweight cement-treated materials (LCMs) immersed in sodium sulphate solutions were studied. The unconfined compressive strength of LCMs corroded by sulphate was tested. The microscopic properties were characterised by X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). The results show that high-sulphur fly ash has an adverse effect on the structural strength of LCMs after corrosion, but when the content of fly ash is less than 75%, the effect of fly ash on the strength is small. A small amount of high-sulphur fly ash can improve the density of the material structure; the internal pore structure of LCMs provides space for the growth of ettringite and other corrosive substances and relieves the expansion pressure. LCMs mixed with high-sulphur fly ash have a certain resistance to sodium sulphate corrosion.

The size of soil particles can change the conducting channels through which an electrolyte solution flows in a soil mass, which has an influence on the tortuosity of pores in soil mass, thus further changing the conductivity of the soil mass. By carrying out laboratory tests, the influences of moisture and particle size of sandy soil on the resistivity of sandy soil polluted with sodium chloride were evaluated. Furthermore, the models for analyzing relationships linking the resistivity of sandy soil polluted with sodium chloride with moisture and particle size of sandy soil under experimental conditions were separately established. The test results showed that the resistivity of sandy soil polluted with sodium chloride at different moisture contents linearly decreases with increasing particle size. Based on the Archie resistivity model, the influence of particle size on the resistivity of polluted sandy soil was explored by carrying out laboratory tests. On this basis, the formula (ρ = [(3 - 2ω)(3ω - 35)][(ω + 3) + g]) for predicting the resistivity of polluted sandy soil with changes in moisture content and the particle size of the system of sandy soil is established, where ω, g, and ρ separately refer to the moisture content, particle size, and resistivity of the system, respectively. Finally, by analyzing the influence of particle size on tortuosity, a resistivity model (ρ=Aρωτe(θ)θ) for analyzing the influence of tortuosity on the resistivity of sandy soil is established, where τe(θ), θ, and ρω separately refer to tortuosity, porosity, and resistivity of pore water, respectively. [ABSTRACT FROM AUTHOR]