Malfunction of Irrigation Pipelines Associated with Peat Subsidence

Abstract

In lowland peat areas of Hokkaido, the number of malfunctions on rice paddy irrigation pipelines, such as misalignment and leakage, has recently been increasing due to peat subsidence. However, the quantitative evaluations of the behaviour of the pipeline after construction have not been well explored. In this study, focusing on irrigation pipelines placed in Shinotsu Peatland, central Hokkaido, changes in the vertical alignment of pipelines after a couple of decades from the construction and their cause were examined. The average amount of subsidence of the pipelines was ca.20 cm after approximately 20 years of the initial construction. The subsidence was relatively uniform in the section without any special construction conditions such as intersection with road or junction to aqueduct bridge. On the other hand, the subsidence of the pipelines occurred unevenly at the intersection with the road where the vertical load was high and at the junction to the aqueduct bridge where the pipeline was fixed to a firm pile foundation. Uneven subsidence may damage the joints of the pipes and some of the observed misalignment excessed the allowance designated by the design criteria. Thus, the risk of incidence such as leakage may increase at those sections. Therefore, continuous observation and measures against uneven subsidence of pipelines are strongly required.