Shear Modulus and Damping of Peat Subjected to Overconsolidation Stress History

Abstract

This paper describes how overconsolidation affects the shear modulus at small strain (G0) for peat, as well as the strain dependence of the shear modulus (G) and the damping ratio (h) of overconsolidated peat. Hayashi et al. (Soils Found 52(2):299–311, 2012) pointed out that peat deposits tend to be overconsolidated as a result of seasonal changes in ground water levels, even when they have not been subjected to artificial stress. Therefore, it is necessary to carefully examine how overconsolidation affects G0 and the strain dependence of G and h in order to determine these dynamic characteristics for peat under in-situ stress. In this study, cyclic torsional shear tests were conducted on peat samples with a stress history of overconsolidation in order to study the effect of overconsolidation in detail. Peat samples with a wide range of physical properties were collected in Hokkaido, Japan. This paper presents the relationship between the G0 and the overconsolidation ratio (OCR), and proposes an experimental equation that expresses G0 as a function of the ignition loss of peat and the OCR. The paper finds that the overconsolidation stress history does not significantly affect the strain dependence of G or h for peat.