Experimental Investigation of Chemical Effects on the Swelling Properties and Shear Strength of Expansive Clay

Abstract

The volumetric instability of expansive soils caused by moisture variations often leads to catastrophic consequences, including geohazards, structural damage, and high repair costs. The situation becomes more intricate when expansive soils are subjected to the chemical composition present in the fluid. This study investigates the chemical effects on the swelling and mechanical properties of expansive soil through comprehensive experiments. The results indicate that chemical effects inhibit swelling deformation and pressure, while saline solutions enhance effective stress and shear strength, evidenced by upward shifts in the strength envelope. Notably, the chemical influence on bentonite exhibits a threshold around 0.5 mol/L NaCl solution; below this threshold, soil properties change significantly with increasing solution concentration, whereas beyond it, the impact diminishes. Additionally, this study considers the effects of infiltration methods, initial moisture content, and shearing rate on shear strength. Different infiltration methods result in similar maximum volume variation and swelling pressure despite varied duration curves, with double infiltration reacting the fastest, top infiltration reacting slower, and bottom infiltration reacting the slowest. For soil samples with identical solutions, low initial moisture content causes notable strain softening and peak shear strength, while higher moisture reduces strain softening and peak strength. Under the same conditions, rapid shearing leads to higher shear strength. This study investigates how the chemical composition of pore fluids affects the swelling behavior and shear strength of expansive soils, which can cause structural damage and high maintenance costs. The experiments reveal that saline solutions effectively reduce swelling deformation and pressure, while enhancing shear strength, especially up to a concentration of about 0.5 mol/L NaCl; beyond this, additional salt has less effect. The research also examines different water infiltration methods (top, bottom, double-sided) and finds that they influence the rate at which soils reach equilibrium but not the final swelling properties. Additionally, lower initial moisture content in the soil leads to higher peak shear strength but more pronounced strain softening, whereas higher moisture content results in more ductile behavior with lower peak strength. Faster shear rates also increase soil strength. These findings can improve the design and maintenance of foundations, roads, and other structures in regions with expansive soils, leading to more durable and cost-effective solutions. The knowledge gained in this study is also crucial for engineering or soil science related to expansive soils.