Matthias Kudella

INTERACTION OF WAVE OVERTOPPING AND CLAY PROPERTIES FOR SEADIKES

The interaction of wave overtopping and the soil properties of a seadike is responsible for the initiation of dike failures and the breaching process. Unfortunately, the present design of seadikes is based on the separate determination of hydraulic and geotechnical design parameters. Therefore, large scale hydraulic model tests were set-up on the basis of a detailed failure analysis for seadikes to investigate the infiltration and erosion process due to wave overtopping. Results are presented in this paper. INTRODUCTION Dike failures are often initiated by wave overtopping (Fig. 1). If a broken wave overtops a dike crest, the overtopping water is eroding the dike surface and water is infiltrating the soil. Therefore, the knowledge about the interaction between the hydraulic processes due to wave overtopping and the soil properties is required to predict the failure of a seadike. Unfortunately, the design of seadikes is performed in two separate ways in present design. First, the crest level is determined by a design water level and the resulting wave run-up height. Sometimes, an average overtopping rate is regarded and compared to critical 1 Dipl.-Ing., Leichtweiss-Institute for Hydraulics. Beethovenstr. 51a. 38106 Braunschweig. Germany. E-Mail: Ja.Moeller@tu-bs.de 2 Dipl.-Ing., Institute of Soil Mechanics and Foundation Engineering. University of Essen. Universitatsstr. 15. 45117 Essen. Germany. E-Mail: Roland.Weissmann@uni-essen.de 3 Dr.-Ing., Federal Waterways Engineering and Research Station. Wedeler Landstr. 157. 22559 Hamburg. E-Mail: schuettrumpf@hamburg.baw.de 4 Dipl.-Ing., Coastal Research Centre. Merkurstr. 11. 30419 Hannover. Germany. E-Mail: gruene@fzk.uni-hannover.de 5 Prof. Dr.-Ing., Leichtweiss-Institute for Hydraulics. Beethovenstr. 51a. 38106 Braunschweig. Germany. E-Mail: H.Oumeraci@tu-bs.de 6 Prof. Dr.-Ing., Institute of Soil Mechanics and Foundation Engineering. University of Essen. Universitatsstr. 15. 45117 Essen. Germany. E-Mail: Werner.Richwien@uni-essen.de 7 Dipl.-Ing., Leichtweiss-Institute for Hydraulics. Beethovenstr. 51a. 38106 Braunschweig. Germany. E-Mail: M.Kudella@tu-bs.de

DEVELOPMENT OF RESIDUAL PORE PRESSURE IN THE SAND BED BENEATH A CAISSON BREAKWATER

Soil liquefaction has been suggested as one of the causes of failure of monolithic breakwaters and further marine structures. This phenomenon is generally defined as the state of the soil where the effective stress completely vanishes causing the soilwater mixture to behave like a liquid; i.e. the shear strength of the soil becomes zero as a result of the pore pressure build-up reaching the value of the initial effective stress. If the effective stress is only reduced without completely vanishing, the term “partial liquefaction” is often used. Especially the gradual increase in mean pore water pressure becomes a crucial phenomenon as it may considerably affect the stability of the foundation over a long period.

EXPERIMENTAL AND NUMERICAL STUDY OF THE RESPONSE OF A SANDBED BENEATH A CAISSON BREAKWATER SUBJECT TO CYCLIC WAVE LOAD

The foundation design of marine structures is one of the most demanding tasks for coastal or geotechnical engineers. Due to the dynamic and cyclic loading conditions a variety of governing processes have to be considered, some of them beeing difficult to assess. Furthermore, the determination of relevant loading parameters and dynamic response parameters of the structures and their foundations is often imprecise. The quality of the results is also determined by the soil model used to describe the response of the subsoil. All these will affect an adequate assessment of the overall stability. In view of the considerable costs of breakwaters, it is obvious to optimize the design process. For this purpose, it is important to improve the knowledge of the processes involved, to assess more precisely the quantitative influence of crucial parameters and to select an appropriate constitutive law for the calculations.