Investigation on the Mechanical Properties of Low Plasticity Clay Contaminated with Engine Oil Khalid Riyadh Omar (B ) , Behzad Fatahi, and Lam Dinh Nguyen School of Civil and Environmental Engineering, University of Technology Sydney (UTS), Sydney, Australia khalid.r.omar@student.uts.edu.au Abstract. Oil contamination presents a challenge for geotechnical engineers to remedy and improve the properties of the contaminated ground. Many researchers have shown that the behaviour of granular soil is highly affected by the level of oil contamination. However, studies on the mechanical properties of the oil- contaminated clay remain limited. Hence, this paper aims to investigate the effect of engine oil on the behaviour of clayey soil, particularly its impacts on the level of oil contamination are investigated and discussed. Extensive laboratory experi- ments are conducted on Kaolin clay mixed with various amounts of engine oil up to 16% and experimental results in terms of Atterberg limits, unconfined compres- sion strength and small strain shear modulus (G max ) are reported. It is observed that the liquid limit and plastic limit of the oil-contaminated clay initially increases with the oil content up to an optimum value where further addition of oil results in a decrease in the liquid limit. In addition, the presence of oil within the clay structure results in a reduction of the shear strength and the shear modulus of the contaminated clay. Hence, this paper concludes that the engineering properties of the oil-contaminated clay can be adversely impacted by a considerable level of contamination. Keywords: Oil contamination · Kaolin clay · Atterberg limits · Unconfined compression strength · Shear modulus 1 Introduction The leakage of engine oil in the vicinity of storage tanks, industrial engines, and during transportation are accidental and can be significant, imposing an ecological threat to the environment. Engine oil contains base oil and other additives which are toxic when released to the environment and can contaminate the surrounding soil with significant adverse effects. The base oil consists mainly of petroleum-based hydrocarbons which is one of the frequently used organic chemicals in the petrochemical industry. Indeed, hydrocarbons are obtained by drilling, stored in tanks, and often transferred by ships and pipelines (Routh et al. 1969). © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 A. Tapase et al. (Eds.): GeoChina 2021, SUCI, pp. 21–32, 2021. https://doi.org/10.1007/978-3-030-79644-0_3