Cyclic Shear Behaviour of High Plasticity Cohesive Soil Subjected to Variation of Frequency and Amplitude

In many instances, saturated cohesive soils are subjected to various types of cyclic/dynamic loading conditions such as earthquake loading, blast loading, oceanic wave storms, machine vibrations and traffic loading, etc. All of these loadings are different based on the rate and magnitude of loading cycles. Hence, the aim of the current study is to evaluate the undrained cyclic shear behaviour of saturated Nagpur soil subjected to various loading conditions. A series of strain-controlled cyclic simple shear tests were carried out on the compacted specimens of Nagpur soil at varying shear strain amplitudes (γ_s = 0.25, 0.5, 1.5, 2.5, 3.75, and 5%) and loading frequencies (f = 0.1, 0.5, 1, and 2 Hz). The hysteresis response was analysed in terms of shear modulus and damping ratio variation along with cyclic stiffness degradation and cumulative strain energy dissipation. Shear modulus and damping ratio were found highest for specimens loaded at the highest frequency with the lowest excess pore pressure generation. Rate and magnitude of stiffness degradation were reduced with a decrease in shear strain amplitude. Dissipated cumulative strain energy was observed to be maximum for higher shear strain amplitude and rate of loading. The results indicated that the frequency and amplitude variation greatly influenced the hysteresis response of saturated Nagpur soil.