Influence of Salinity of Pore Fluid on the Undrained Shear Strength of Clays

摘要

Due to the inherent nature of the deposition process of soils in costal and marine environments, the stability of clayey slopes requires accounting for the shear strength parameters when sodium chloride (NaCl) is present in the pore fluid. To examine the influence of the salinity on the undrained shear strength of clayey soils, seven soils, as mixtures of montmorillonite with quartz and kaolinite with quartz, were prepared in the laboratory with saline water of 0.5 M NaCl concentration, as the pore fluid. The soils were subjected to constant volume, strain-controlled static simple shear testing to obtain the undrained and fully softened shear strengths. Similar tests were conducted on soils with the same mineralogical compositions, but with distilled water as the pore fluid. The results from this study demonstrate that the undrained and fully softened shear strength of these soils will be greater when NaCl is present in the pore fluid, but a reduction in the shear strength can be expected when the NaCl is leached out from the soil samples. The experimental results suggest that the difference in both the total and effective fully softened friction angles will increase with an increase in plasticity index up to plasticity indices of 100. For soils with plasticity indices greater than 100, the difference remains constant at 9° for the total fully softened friction angle and 15° for the effective fully softened friction angle.