Variation in Residual Shear Strength of the Soil with the Salinity of Pore Fluid

Abstract

Slope stabilization procedures for seven landslides in the Niigata Prefecture of Japan had provided an excellent and rare opportunity to examine the composition of ground water, and residual shear strength of the sliding surface soil, as well as unsheared mudstone. Ring shear tests were conducted on the soil samples collected from sliding surface soil, revealed during the installation of 3 m diameter drainage galleries. Shear strength and index properties of the soil were measured by mixing the soil with distilled water and sea water, and after leaching the NaCl from the pore water. The residual shear strength of the soil sample with distilled water was 3–5° lower than that with the sea water. The residual shear strength of the intact rock powder after leaching the dissolved salt was close to that of the soil from sliding surface, and the residual shear strength of the soil from sliding surface after mixing with sea water was close to that of the intact rock powder. The increase in residual shear strength had a parabolic increment with the specific surface area. This research finding has very important practical implications on the postfailure stability analysis of the landslides having saline pore water.