Effects of surfactant on the consolidation and shear strength of synthetic clay soils

Surfactants are introduced into the ground either through leakage or a spill, or intentionally for soil remediation. However, their effects on the compressibility and strength characteristics of the ground are largely unknown. This paper examines the effects of reduced surface tension of pore fluid on the liquid and plastic limits, gradation, compressibility, and shear strength of reconstituted clay samples. Clay samples were prepared by mixing kaolin and bentonite with water. The surface tension of the pore fluid was reduced by adding different percentages of a commercial detergent to the pore fluid. The Atterberg limits demonstrated progressively decreasing liquid limits (from 220 to 140) and plasticity indices in clay samples prepared with increasing amounts of surfactant. The SEM images showed a dispersed fabric of face-to-edge and edge-to-edge particle contacts in the original clay soil, while those mixed with surfactant were highly flocculated with clusters of stacked clay particles. Shear strength and compressibility of clay samples were also measured in a series of direct shear and ring shear tests. In the presence of up to 10% detergent, the peak and the residual strengths measured in these experiments increased by about 98–96% and 78–65%, respectively. Nevertheless, the specimens became more brittle with added surfactant during both the direct shear and the ring shear tests. The addition of the detergent to the clay specimens also increased the compression indices from 0.64 to 0.89, as well as the initial void ratio from 2.76 to 2.85.