Yeyang Chun ^1,2,3,4 Zhengquan Liu ^5,6 Yong He ^2,3,4* He Wei ^2,3,4 Dongpo Su ⁷

• ¹ Central South University, Changsha, China
• ² Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Central South University, Changsha, Hunan Province, China
• ³ Hunan Key Laboratory of Nonferrous Resources and Geological Hazard Exploration, Central South University, Changsha, Anhui Province, China
• ⁴ School of Geosciences and Info Physics, Central South University, Changsha, Hunan Province, China
• ⁵ Universiti Sains Malaysia Engineering Campus, Nibong Tebal, Malaysia
• ⁶ Guangxi Water Conservancy and Electric Power Vocational and Technical College, Nanning, Guangxi Zhuang Region, China
• ⁷ College of Civil Engineering and Architecture, Guangxi University, Nanning, Guangxi Zhuang Region, China

To elucidate the time-dependent swelling behavior of landfill sand-bentonite mixture liners under the effect of organic pollutants, an no loading swelling ratio test was conducted on mixtures with varying sand and diesel content. The evolution characteristics of the swelling time curve morphology were investigated. The micro-mechanisms underlying the swelling time effect evolution were explored. The results indicated that the sand-diesel interaction significantly altered the swelling time curve morphological characteristics of the mixture. As the sand content increased, the swelling coefficient at the stable state decreased. However, during the rapid swell phase, diesel-contaminated mixed soil does not exhibit the increase-then-decrease pattern in swell coefficient seen in unpolluted mixed soil. The duration of both the slow swelling phase and the time to reach a stable state were longer. Mechanistic analysis revealed that cation exchange capacity is insufficient to effectively analyze the evolution characteristics of the swelling time curve. Instead, the initial swelling potential of bentonite is the true indicator of the mixture's swelling properties. The particle size distribution influences the changes in the swelling coefficient during the rapid swelling phase, but diesel alters the particle size distribution, mitigating its impact. The oil sealing effect within intra-aggregate and inter-aggregate pores not only weakened the swelling characteristics of the mixture at all stages but also increased the permeability resistance, thereby reducing the duration of the rapid swelling phase and extending the slow swelling and stable swelling phases.