Direct measurement of shear stress and shear strain in soil: getting more out of simple shear testing

Data from simple shear testing can be significantly enhanced through implementation of local, in-soil measurement of shear stress and shear strain. Use of such tools circumvents difficulties in dealing with data collected through measurements made at the specimen boundaries. This paper illustrates how data from sensors embedded within simple shear specimens has been used to measure small strains in the determination of stiffness degradation over the entire range of relevant shear strains. Local, in-soil measurement of shear stress has allowed for the measurement of complementary shear on a vertical plane within the specimen and its comparison to shear stress, which develops on the horizontal plane of the specimen. Test data illustrate that within the small-strain regime the locally measured shear strain is significantly smaller than that determined through measurement of deflection at the specimen’s boundary. The most significant outcome from this study is the understanding that from a single simple shear test the entire shear stiffness degradation curve can be compiled and the maximum shear stiffness quantified. Determination of shear stiffness from small-strain measurement probes results in stiffness values very close to those determined through bender element experiments.