Development of geosynthetic-reinforced soil embankment resistant to severe earthquakes and prolonged overflows due to tsunamis
Kenji Watanabe, Susumu Nakajima, Kimihiro Fujii, Kosuke Matsuura, Atsuhiro Kudo, Takahiro Nonaka, Yudai Aoyagi
Abstract
Many railway embankments sustained extensive damage due to the tsunami triggered by the 2011 off the Pacific Coast of Tohoku Earthquake, and the operations of several railway lines were suspended for an extended period of time. Numerous studies have been conducted on enhancing the earthquake resistance of embankments, and this has led to the wide application of geosynthetic-reinforced soil (GRS) structures. However, only a few studies have been conducted on enhancing the tsunami resistance of embankments. Based on onsite surveys and wave model experiments, the authors concluded that the damage to embankments was mainly caused by the large-scale earthquake occurring prior to the onset of the tsunami, and by the prolonged tsunami overflows that eroded the embankment bodies and the supporting ground. In this study, therefore, two types of model tests were performed in order to propose a sturdy tsunami-resistant soil structure that exhibits ductile behavior against an earthquake prior to the onset of a tsunami as well as against prolonged overflowing. It was confirmed that conventional embankments with sufficient seismic stability can be rapidly eroded by overflowing. On the other hand, the GRS method was found to be very effective for resisting the erosion of embankments due to overflowing. Furthermore, given that the collapse of river dikes and levees due to overflows is often reported during heavy rainfall events, the findings obtained in the study are considered applicable to embankments as well as to river dikes and levees.