A Case Study on the Microstructure of Fibrous Peat (West Lake, China)

Abstract

The classification of peat soils involves a very large number of different types. From a descriptive perspective this is useful, however such a system generates too many options for engineering purposes. The behaviour of organic soils varies based on the quantity and type of organic material present within the soil. The effects of fibre content are particularly important. The West Lake in Hangzhou has been dredged many times during its history to maintain its beauty. During the most recent dredging the sludge from the lake was transported via a 4 km pipeline and deposited inside the Jiangyangfan Reservoir. The organic soil situated in Jiangyangfan Ecopark is a particularly interesting peaty material. The organic sludge was mixed and homogenised during the transportation process, and then settled out within the reservoir. This resulted in a more than 20 m thick peat layer deposited with an uneven surface. The Ecopark buildings were then constructed on top of this in 2008. A combined electron microscope and mechanical study of the microstructure and behaviour of the peat has been used to identify the engineering impact of the presence of relatively small number of fibres within the soil matrix. The fibres within the peat modify its behaviour such that it can no longer be understood within the typical critical state framework for soils. The peat starts to deform plastically under very small levels of applied stress. In addition, it does not display a tension cut-off failure and, ultimately, fails in shear.