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ORIGINAL PAPER

Shear Modulus and Damping of Peat Subjected to Overconsolidation Stress History Hirochika Hayashi Masahiko Yamaki

. Osamu Hatakeyama . Hijiri Hashimoto .

Received: 24 September 2019 / Accepted: 28 June 2020 Ó Springer Nature Switzerland AG 2020

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.

H. Hayashi (&)  O. Hatakeyama  H. Hashimoto  M. Yamaki Civil Engineering Research Institute for Cold Region (CERI), Sapporo, Japan e-mail: [email protected]

Keywords Peat  Dynamic property  Overconsolidation  Shear modulus  Damping ratio  Cyclic torsional shear test  Experimental formulation

1 Introduction Peat soil has a high content of organic matter that derives from the undecomposed remains of dead plants that have grown in wetlands. The lack of decomposition is due to low temperatures and/or wet conditions. Large areas of peatland are found in North America, Europe and Asia (Lappalainen 1996). In Japan, peat is widely distributed in Hokkaido (CERI 2017). Peat soil is known to be a soft soil that has peculiar engineering properties (Noto 1991; Mesri and Ajlouni 2007; Huat et al. 2014). When embankments (e.g., for roads or river dikes) or other structures are constructed on peaty soft ground, the peculiar engineering properties cause geotechnical engineering problems, such as bearing capacity failure and large consolidation settlement (den Haan 1993; Kurihara et al. 1993). In addition to those problems of static behavior, dynamic issues of peat should be considered as essential geotechnical engineering problems. This is because peatlands are found on the West Coast of North America and in the Russian Far East, Indonesia, Japan and elsewhere, which are areas where severe earthquakes frequently occur, and serious damage to

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Geotech Geol Eng

embankments and other struc