Influence of shear rate on the soil's shear strength

One of the most important mechanical properties is shear strength. It is conditioned by the value of the maximum shear stress that the soil can withstand before failure. Exceeding the shear strength causes one particle to slide next to another, causing the failure of soil. The shear strength of the soil for effective stresses is1 a combination of drained strength parameters: internal friction angle (φ) and cohesion (c) defined by the Mohr-Coulomb failure criterion. It is determined “in situ” and by laboratory experiments. Direct shear is the oldest and the simplest laboratory experiment to determine the shear strength of the soil. The first phase of experiment is specimen consolidation under specific vertical stress, and in the second phase specimens are sheared at a given shear rate, depending on the consolidation properties of the soil. Cohesionless soils are sheared at up to 100 times higher shear rate compared to cohesive soils. Shear rate and drainage conditions affect the magnitude of soil strength parameters. The paper is based on the comparison and demonstration of the influence of different shear rates on the peak and residual shear strength in the direct shear device. The tests were performed on two samples of low plasticity clay (CL) and one sample of high plasticity clay (CH).