Leachate formed due to the decomposition of municipal solid waste is a major cause of soil contamination. Geotechnical properties of the soil found in the surroundings of waste dumpsites need to be crucially assessed for strength and stability. It is needed to prevent the contamination of soil caused by migration of leachate. A conventional slurry trench cutoff wall is cost-effective but was found weak, against the exposure to heavy metals abundantly found in municipal solid waste. Although the cutoff walls possess low permeability, by adding bentonite, the walls are still weak when come in contact with organic components and heavy metals of waste. The present study investigates the effect of the addition of lime and bentonite on the geotechnical characteristics of the slurry cutoff wall. Hydration occurs due to the addition of lime to soil–bentonite. Compaction, consistency limits, permeability, free swell, unconfined compressive strength, and pH tests were conducted on the mixtures of soil–lime–bentonite, to determine the geotechnical characteristics of the mixture. The soil was amended with bentonite and lime in 4, 7, and 10%. The results showed that with the application of bentonite and lime to the contaminated soil, an increase in liquid and plastic limit was found. Improvement in the maximum dry density from 14.62 to 14.91 kN/m3 due to the addition of lime and bentonite. A decrease in the permeability from 0.075 × 10–7 to 0.056 × 10–7 m/s, whereas, for the natural soil, it was found to be 0.0286 × 10–7 m/s. The unconfined compression strength increased from 15.04 to 16.24 kPa. The present study identifies the addition of lime-treated bentonite to soil may improve its geotechnical properties.