Stress Dependence of Shear Strength in Fine-Grained Soils and Correlations with Liquid Limit

Abstract

The undrained strengths and friction angles of a variety of natural fine-grained soils are investigated over an effective stress range of 0.1 to 10 MPa. The resedimentation technique was used to produce identical saturated samples for laboratory shear testing. The majority of the results presented are derived from Ko-consolidated undrained triaxial compression tests, although behavior under direct simple shear and triaxial extension modes of shear is also presented for a single soil. Normalized shear stress-strain responses, undrained strength ratios, and critical state friction angles are found to vary considerably and consistently at each overconsolidation ratio when viewed over a significant effective stress range. Correlations are developed that allow the undrained strength and friction angle of a fine-grained soil, as well as the variation in these properties with stress level, to be estimated effectively from liquid limit, together with an evaluation of the in situ stress history of the sediment. Liquid limit is an easily measured index property that reflects the clay mineralogy and clay fraction of a soil.