<p>The present research seeks to comprehend and evaluate the impact of varying concentrations of HCl acid solution on the compressibility and shear strength of silty clay. The compression test and the unconfined compressive strength test were conducted, and the SEM test was performed to analyze the microstructure of the soil with and without contamination. The results indicate that the contamination of silty clay soil with HCl acid caused a reduction in strength and an increase in the compression index and coefficient of consolidation; the more significant change in compressibility and strength was seen when the acid solution became more acidic. Concerning the SEM test, the images demonstrate the formation of macro pores between soil particles due to soil contamination. As the HCl acid solution concentration increased, more pores were formed and irregularly distributed across the whole soil surface. HCl acid solution contamination of soil causes the soil characteristics to degrade generally. Construction on this soil would consequently need to take into account the environment. Preparing the soil before building on it is suggested by adding materials that can increase the acid resistance of the soil.</p>