Dynamic Moduli and Damping Ratios for a Soft Clay

Abstract

Cyclic, simple shear, and free vibration tests were performed on 12-in × 12-in × 6-in block samples of a remolded 3:1 kaolinite-bentonite clay mixture of various water contents. The simple shear tests were performed by using predetermined sinusoidal displacements at frequencies ranging from 1 cps to 10 cps. A free-vibration damping factor was obtained from the logarithmic decrement of the free-vibration decay curve. By using the theory of the transverse vibration of shear beams, it was possible to obtain the shear modulus from a known period of free vibration. The shear moduli, established by simple shear and free-vibration tests, were in good agreement. The modulus for a given strain decreased as the shear strain increased and as the number of cycles increased. The damping value, which is also strain-dependent, increased with increasing strain. The value of free-vibration damping was always higher than the value of hysteretic damping for a given strain value.