Wellen-Bauwerks-Interaktion bei mörtelvergossenen Schüttsteindeckwerken

  • Wave-structure-interaction of mortar-grouted riprap revetments

Kreyenschulte, Moritz; Schüttrumpf, Holger (Thesis advisor); Goseberg, Nils (Thesis advisor)

Aachen (2020)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Abstract

Revetments protect dikes from erosion caused by waves and currents and thus are an essential element of flood and storm surge protection. Due to a limited understanding of the wave-structure-interaction, the design of the frequently build mortar-grouted riprap revetment on the North Sea coast is yet solely based on empirical knowledge. This procedure involves the danger of a potential undersizing or uneconomical oversizing of the revetments and in particular cannot take into account the effect of changing wave loads on structural safety. The aim of the present work is therefore to establish process-based models for the decisive damage mechanisms of mortar-grouted riprap revetments with regard to the structural integrity under wave loading. For this purpose, the boundary state equations of the decisive damage mechanisms "crack formation in the toplayer" and "erosion of an individual stone" are established. The models presented in this thesis for the first time describe the loads and resistances in the boundary state equations and thus create the basis for a process-based design of mortar-grouted riprap revetments. Consequently, this design procedure is based on the physical processes under wave loading and takes into account both the wave parameters and the structural, hydraulic, mechanical and fracture-mechanical properties of the revetments. Since the permeability is one of the essential hydraulic parameters that determine the wave-structure-interaction, permeability tests are carried out on toplayers of mortar-grouted riprap revetments. Due to the lower porosity and higher tortuosity, the results show significantly lower permeabilities of these toplayers compared to non-grouted riprap. With the results of the permeability tests, for the first time an equation for estimating the permeability of mortar-grouted riprap revetments as a function of porosity is established. For the limit state "crack formation in the toplayer", the toplayer is modelled as a beam on an elastic foundation. The pressures on and beneath the toplayer that were recorded in full-scale model tests in the Large Wave Flume in Hannover are applied as boundary conditions and thus the tensile stresses in the toplayer are calculated. An analysis of the decisive load cases shows that the sole consideration of the impact load to determine the maximum bending tensile stress is not sufficient for all wave parameters, but that the load resulting from the wave run-down must also be taken into account. For the first time, the decisive load cases are parameterized with semi-empirical equations as load shapes depending on the wave parameters and the structural properties of the revetment. As resistance, the adhesive bending tensile strength between mortar and riprap determined in fracture mechanical tests is used. For the boundary condition "erosion of an individual stone" the equilibrium of forces due to loadings and resistances on the individual stone is established under wave load. The wave run-up velocity and the pressure difference at the individual stone are used as loading parameters. They are modelled with semi-empirical equations on the basis of results of the full-scale model tests in the Large Wave Flume. With laboratory tests and in-situ tests carried out for the first time, the data base for determining the force when pulling an individual stone from the toplayer is enlarged. Based on these results an existing semi-empirical model for the description of the bonding force is validated and used as resistance in the limit state equation. A possible procedure for the statistical description of the bonding force and thus for the assessment of the resistance under consideration of the prediction accuracy is presented.

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