Cyclic deformation of a clay

Abstract

Dynamic loading tests consisting of one hundred sinusoidal strain-controlled cycles at 0.2 cps. followed by a compression test to failure were conducted on remoulded, fully saturated clay triaxial specimens. Electrical transducers coupled with automatic recording equipment were used to measure pore-pressure, axial load and deformation. The effects of strain amplitude and stress history on the peak shear stresses, the mean effective stress and the specific damping energy were investigated.

Mean effective stress, which showed negligible cyclic variation, decreased progressively during dynamic loading except that for over-consolidated soils it increased during the first cycle only. Progressive reduction of peak shear stress and specific damping energy was closely related to the reduction of mean effective stress. After 100 cycles the strength and structure of the clay was dependent on the void ratio and the dynamic strain amplitude. All effects were more marked with increasing strain amplitude.

A descriptive model was proposed to account for the development of unusual ‘S’-shaped loops.