Infiltration behaviour of dike covers made of dredged material on the Rostock Research dike

Abstract

The knowledge about the infiltration behaviour of a dike body is an important issue in dike design and flood risk assessment. To reduce the risk of stability failures during flood events, the infiltration rate of a dike should be kept low and the elapsing time to reach the saturated steady state should be long. A number of full-scale physical flood simulation experiments on the Rostock research dike, on which different processed dredged materials were applied in the dike body (cover layers in particular) showed that the infiltration time and rate is much higher as can be expected from comprehensive laboratory test data. To obtain information about the unsaturated/saturated hydraulic soil properties of the installed dredged materials in situ, an automatic multi-objective model calibration method for a minimizing problem is used to reduce the residuals between simulated and observed time series (hydraulic head pressure, suction pressure and rate budget). The measured suction pressure time series of these physical experiments lets us suppose, that it is not possible to simulate the suction pressure behaviour of the installed dredged material using RICHARD’s unsaturated flow equation with a proper water retention function and unsaturated flow conductivity. It seems that the hysteresis effects are negligibly small and the hydraulic behaviour is governed by the inter-aggregate pore structure. In the paper, different back-calculation methods to fit the soil hydraulic parameters to the full-scale measurements are discussed and compared a proposal for the evaluation of the data is provided.