An Integrated Experimental and Numerical Approach for Assessing the Hydro-mechanical Response of Flood Embankments

Extreme geohazards, such as flood events, are becoming increasingly frequent due to the major impact of climate change, with severe consequences in terms of economic damage and loss of human. Water retaining earthworks play a key role in the preservation of the built and rural environment, thus a reliable assessment of river embankment safety conditions represents an essential task to enhance the resilience of these critical infrastructures. In current engineering practice, the design and validation of flood embankments is still performed under the simplistic hypothesis of steady-state groundwater flow and generally disregarding – or possibly oversimplifying - unsaturated soil issues, mainly due to the difficulties in estimating the actual suction distribution and shear strength. In this paper, a methodological approach for accurately predicting the hydro-mechanical response of flood embankments to high water events, based on the complementary use of laboratory testing and numerical modelling, is proposed. An extensive experimental campaign, including standard and advanced suction-controlled tests, has been carried out to investigate the effect of suction changes on the shear strength and compressibility of a silty sand mixture, representative for the riverbank systems of the main river Po tributaries (Italy). Then laboratory test results have been considered to perform finite element (FE) transient seepage and stability analyses by Strength Reduction Method, finalized to the assessment of an embankment model performance, under a set of possible hydrometric peaks. Factor of safety variations over time have been estimated, in connection with the changeable water level imposed, providing some useful insights for flood risk assessment of river embankments.