Die Entmischung bei der Schüttung von Wellenbrecherkernen mit Hinterkippern

Abstract

Rubble mound breakwaters are built since centuries to protect harbours and coastlines. Very basic construction methods were commonly used. The designed structure is mostly a resut of long-term non-scientific experience. Storm events are repeatedly leading to failure of these structures resulting in costly rehabilitation measures. The focus of this thesis is on the land-based buildup of the core of a rubble mound breakwater by dumping truck. Using this common method, rock size separation (segregation) is expected but the resulting distribution within the structure is unknown. Experimental research on rock separation has been conducted in the hydraulic laboratory of the Institut für Wasserbau und Wasserwirtschafl of Technische Universität Berlin. The resulting core structure of broken rock dumped in a still water basin has been studied on three model scales. The resulting core structure is substantially graded by size. The segregation prevails over the complete core structure trom coarse material at the base to fine material in the upper sections. Measures to diminish this segregation by variation of the dumping process parameters (e.g. dumping depth) showed no improvement on the structure's composition. As a preliminary result it can be stated, that the segregation is inevitable and now weil known. A force model is used for the theoretical approach of single rocks of different sizes. The calculated velocities of single rocks on an underwater slope displayed a high degree of accuracy. This theoretical approach contributes to a beller understanding of the physical process. The presented conclusions are applied to define a breakwater's filter layers: core/base and core/armour as weil as to check out the structure's overall hydraulic stability. It is shown, that the common general assumption of a homogeno"usgrain size distribution in the core is unjustified and results in reduced usability and possible damages. The presented results prove the relevance of rock size segregation and contribute to the beller understanding of the physical process. Based on these results, the design of breakwaters can be improved.