Theoretical and Experimental study on the placement of Xbloc

Abstract

Single layer armouring is a state-of-the-art protection for rubble mound breakwaters. The quality of placement affects interlocking of the armour units, which is essential for the hydraulic stability of the entire armour layer. The main objective of this study is to make a detailed design of an Xbloc placement, this includes grid design, placement accuracy and quality control. The study is based on a theoretical placement analysis which is verified by large scale model tests. Single layer armour units are placed on a predefined staggered grid in order to achieve good interlocking, this creates a stable armour layer. The distance between armour units is essential for proper functioning of the armour layer. Therefore, single layer armour units shall be placed if possible with a constant horizontal and upslope placement distance, which results in a diamond-shaped placement pattern. However, the placement pattern will be distorted if the seabed level varies or if a section of breakwater is curved (bended trunk sections or roundhead). To design a placement grid for a head a theoretical model has been built, which is capable to design a grid on irregular breakwater profiles. This model is been tested in an experimental study. The proposed placement model proved to predict stable unit positions even for breakwater heads. The placement model has been recently applied for the design of a breakwater, which is currently under construction in Ireland.