Effect of Pore Fluid Concentration on Shear Strength of Soft Clay

Abstract

Consolidated quick direct shear tests were conducted on bentonite and mixed bentonitekaolin soils with different concentrations of sodium chloride solution. The physical mechanism of the pore fluid concentration effect was explained at the micro level on the basis of micro forces among particles. The test results indicated that the shear strength of bentonite and bentonite-kaolin noticeably varied with increase in sodium chloride solution concentration, especially under high vertical stress. The friction angle increased with the pore fluid concentration, but the cohesion decreased. With increase in pore fluid concentration, the electric double-layer repulsion among soil particles decreased, thereby increasing the effective contact stress at the mineral-mineral contact and leading to increased consolidation settlement and a lower water content under vertical stress. This means a larger shearing resistance at the mineral-mineral contact point and a thinner absorbed water layer at the mineral-water-mineral contact point, leading to a greater friction angle and a lower cohesion.