Influence of cyclic loading on the secondary consolidation behavior of peats

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Peat ground is a soft, highly organic soil with high water content, of which long-term settlement continuing after the start of superstructure service is often a problem. When constructing river embankments on peat, it is therefore necessary to design them by predicting long-term settlement to meet the height requirements. Recent research indicates that the settlement behavior can be successfully described by using the Isotach law, which assumes that the compression curve is uniquely determined for a given strain rate. However, some settlement data of embankments built on peat ground showed that the settlement rate was accelerated or maintained after the 2018 Hokkaido Eastern Iburi Earthquake, Japan, even after the apparent densification due to the dissipation of excess pore water pressure induced by the cyclic loading. This observation suggests that when cyclic loading, such as from an earthquake, is applied to peat ground, the Isotaches undergo an apparent parallel shift, indicating a phenomenon that cannot be explained by the conventional Isotach law. In this study, therefore, cyclic triaxial tests were conducted on several types of peat specimens to investigate the secondary consolidation behavior before and after the cyclic loading and to discuss the applicability of the Isotach law. The experimental results showed behavior similar to the in-situ settlement data, where the Isotaches appeared to shift in parallel due to cyclic loading. Consequently, caution should be exercised when using the Isotach law to predict the long-term settlement of peat ground subjected to cyclic loading from such events as earthquakes.

International Conference on Advances and Innovations in Soft Soil Engineering (ICAISSE2026)

Multiphysics Behaviour