Simplified Model for Interpretation of Undrained Shear-Strength from Field-Vane Tests in Transient Soils

Abstract

Interpretation of field vane tests in transient soils requires assessing partial drainage effects within the soil surrounding the vane. This subject is investigated in this paper using a nonlinear poroelastic model to simulate the rotation of a rigid cylinder in a nonlinear poroelastic medium. This simplified approach of a vane test yields analytical expressions that help to explore rate effects in silty materials. Analytical expressions were validated against experimental results in low permeability soils under undrained conditions as well as field vane tests performed on silty tailings. The dimensionless velocity v/k is proposed for normalization of testing data allowing to assess the effects of normalized strength, stiffness, and extent of the influence zone. It is concluded that the ratio of the drained to undrained resistance is generally lower than 3. As further considerations of practical importance, the standard velocity of 0.1 deg/s is not suitable to reach undrained conditions in silts. A solution is then established to account for possible errors induced by pore pressure dissipation, yielding a practical criterion for determining the undrained shear strength.