Effect of pore water salinity on the coefficient of earth pressure at rest and friction angle of three selected fine-grained materials

This study investigates the effects of pore fluid salinity on the shear strength and earth pressure coefficient at rest (K0) of three fine-grained soils: kaolin, bentonite and a marine clay found in Hong Kong. The K0 coefficient and critical state friction angle (ϕ ') are evaluated from triaxial stress path testing of remolded normally consolidated samples. The pore fluid salinity has little effect on the K0 and ϕ ' of kaolin and the studied marine clay, whereas an increase in pore fluid salinity noticeably increases ϕ ' and decreases the K0 of bentonite. These phenomena are explained by the microstructure of the fundamental minerals of the materials. The K0 of each of the studied materials is estimated by two commonly used empirical formulas in which the internal friction angle (Jaky's formula) or Atterberg limits are used, respectively. Jaky's formula satisfactorily predicts K0 for kaolin regardless of its salinity, whereas it slightly but consistently underestimates that of the studied marine clay. Moreover, Jaky's formula gives a reasonable prediction of K0 for bentonite at higher salinity. Prediction using the Atterberg limits fails in all cases, particularly for bentonite at low salinity.