On the Nonlinearity of Shear Strength of Unsaturated Soils


Pei-yong Li

School of Civil and Safety Engineering,
Dalian Jiaotong University, Dalian, China
e-mail: eobserverlpy@gmail.com



Shear strength theory is one of important theories in unsaturated soil mechanics. The purpose of this paper is to research the nonlinear relationship between shear strength and matrix suction. By analyzing nonlinearity in total cohesion versus matrix suction, a nonlinear equation is presented. The equation uses nonlinear coefficient to connect total cohesion with effective cohesion and matrix suction. Then a new shear strength equation for unsaturated soils is derived from it. The reliability and practicability of two equations are verified, using four sets of test data on different unsaturated soils. The results show that nonlinear coefficient is a significant parameter of an unsaturated soil, and can indicate the nonlinearity in the shear strength versus matrix suction failure envelope. Different soils can take different values of nonlinear coefficient, which do not vary with matrix suction. The new shear strength equation exhibits a smooth transition towards the shear strength equation of unsaturated soils presented by Fredlund et al. (1978), when the value of nonlinear coefficient is equal to 1.

Keywords: Unsaturated soils; Shear strength; Nonlinear coefficient; Total cohesion; matrix suction

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