The stability of synthetic gabions in waves

Abstract

Gabion mattresses consist out of a steel wire grid in which fill material is retained. The advantage of these constructions is that the individual particle stability is no longer of importance. The containing function of the grid results in the effect that the fill material starts to behave as a group. Next to that the mattresses are all interconnected to each other. Loads are divided over the length of the revetment. The grid is protected with zinc to prevent corrosion. The problem is that when gabions are applied in waves, vibration of the particles can damage the protective layer. Next to that, zinc gives an environmental objective, due to slow dissolving of particles. By applying a synthetic geogrid these problemes are eliminated. From the material demands it comes forward that certain types of geogrid are suitable. The general fear of applying synthetics in gabions is the sensitivity to deformation. Scale model experiments are performed in a wave flume to study the process of deformation. From these tests it came forward that the development of deformation depends on the filling degree of the compartment. The material will always settle in a bulging shape, which results in tension on the grid. Therefore it is recommended to close compartments under tension in the bulging shape. Second objective is the improvement of the stability relation. Aspects as mattress length, friction and permeability are not taken into account in the current design formula. Scale model experiments are performed to determine the stability relation of different revetment designs. With the results a start is made for an improved stability relation. Based on a ratio that represents the tension force absorbation capacity and a relative length parameter, influence of these parameters are implemented. The permeability is implemented by creating three different filter groups, which have a different mutual relation. Further research is necessary to confirm and improve the stability relation.