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Adopting more efficient and sustainable remediation materials is of great importance for the development of solidification and stabilization (S/S) technology. Among them, soda residue could be considered as a desirable binder due to its strong adsorption for heavy metals. For understanding of the performance of Cr-contaminated soils treated by cement/soda residue, the strength, leaching and microstructural characteristics, and the long-term effectiveness under wetting-drying cycles were comprehensively investigated in this study. The results showed that the unconfined compressive strength (UCS) increased and the leached Cr3+ concentration decreased with curing time, binder content, and binder ratio. Increasing the soda residue from C6S14 to C6S24 could improve soil strength and reduce leachability of Cr3+, while a reverse trend was presented with increasing initial Cr3+ concentration. With subsequent wetting-drying cycles, the UCS further increased and then decreased; inversely, the leached Cr3+ decreased, followed by an increase of Cr-contaminated soils. For the specimens of C6S14 and C6S24, the maximum UCS of 6.04 MPa and 6.48 MPa was reached; correspondingly, the minimum leached Cr3+ concentration of 2.78 mg/L and 1.93 mg/L was reached after 3 wetting-drying cycles, respectively. Microstructure analysis results found that reaction products like calcium silicate hydrate (C-S-H) and ettringite (AFt) increasingly occupied the soil pore space and caused a denser soil structure after 3 wetting-drying cycles, which indicated the long-term effectiveness of contaminated soils treated by cement/soda residue.

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As one of the extensively used gasoline additives, MTBE can leak into the subsurface, which will not only deteriorate the ecological environment, but also affect the geotechnical characteristics of the soil. In this study, the geotechnical properties of MTBE-contaminated soil consisting of the basic physical properties, strength, compressibility, hydraulic conductivity, leachability, electrical resistivity and microstructural characteristics are comprehensively investigated. The results show that the Atterberg limits consistently decrease with increasing MTBE content in the soil. As the MTBE content increases from 0% to 10%, the specific surface area of the soil decreases by 28%, the sand content increases by 22%, the clay and silt contents decreases by 3% and 18%, respectively. The soil compression index, hydraulic conductivity, leached MTBE concentration and electrical resistivity increase, while the UCS decreases with increasing the MTBE content. Microstructural analysis shows that increasing MTBE content would result in mineralogical alterations that decrease the illite and kaolinite content in the soil. The aggregation and flocculated structures could be detected with an increase in the number and size of the inter-aggregate pores. Additionally, electrical resistivity of the contaminated soil is adopted to assess the geotechnical properties of MTBE-contaminated soil based on the well-established empirical relations.