Abstract
The effect of the attack by chemical contaminants on the microstructure of loess and the resultant changes in shear strength properties threaten the safety of engineering projects in Northwest (NW) China. The aim of this study was to investigate the microscopic mechanisms of the variation in shear strength of acid- and alkali-contaminated loess. Intact loess samples were immersed in acid and alkali solutions of various concentrations, and triaxial shear, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) measurements were then conducted to assess the effects of acid and alkali contamination on the shear strength and microstructure of loess. The results indicated that the shear properties (stress‒strain behavior, failure strength and cohesion) of loess deteriorated under acid contamination but were improved under alkali contamination. The structural damage (particle fragmentation, cement dissolution, and pore expansion) in acid-contaminated loess intensified with increasing acid concentration. In contrast, structural improvement occurred in alkali-contaminated loess because new cementation balanced local damage and enhanced the degree of structural connection. In acid-contaminated loess, the diffuse double layer (DDL) thinned, the calcium carbonate content rapidly decreased, and the liquid limit (LL) and plastic limit (PL) declined, while in alkali-contaminated loess, these parameters were improved. A series of physicochemical reactions (mineral dissolution, ion exchange, and particle and pore structure adjustment) in the presence of acid and alkali contamination drove the observed structural variation in loess. This comprehensive effect resulted in either loess shear strength enhancement or reduction, depending on whether damage to the original structure or formation of a new structure dominated, respectively. These findings contribute to a deeper understanding of the response of intact loess under various hydrochemical conditions, which has important practical significance for elucidating the disaster mechanism of loess slopes and facilitating ecological environment protection in acid–alkali-polluted areas.
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The authors thank the editor and four anonymous reviewers for their constructive comments, which greatly enhanced the quality of the manuscript.
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This work was supported by the National Natural Science Foundation of China (Grant No. 42072319) and the Postdoctoral Research Projects of Shaanxi Province, China (No. 2023BSHEDZZ309).
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KL proposed the original idea; KL and WY designed the experiments; KL conducted the main tests and analyzed the data; WY and PL helped conduct the mechanical tests and analyzed the data; WY supported the project and discussed the results; KL prepared the manuscript. All authors have reviewed the manuscript.
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Liu, K., Ye, W. & Long, P. Microscopic mechanisms of shear strength variation in acid- and alkali-contaminated loess. Environ Earth Sci 82, 547 (2023). https://doi.org/10.1007/s12665-023-11252-z
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DOI: https://doi.org/10.1007/s12665-023-11252-z