Design and Re-Use of Placed Block Revetments

Abstract

Flood defences in the Netherlands are mainly covered with grass. Hard revetments are applied in places where the grass can't provide sufficient resistance against the attack of waves and current. Since centuries these revetments consist of placed block revetments. In the old days natural stones such as basalt were used. Initially the basalt was placed directly on the clay, but this clay appeared to erode beneath the blocks. Consequently, a filter layer beneath the basalt was applied: a straw mattress with above that a layer of rubble. After the flooding disaster of 1953, natural material was scarce, so it was replaced by concrete blocks, which were placed directly on the clay. The idea was, that these concrete blocks could be placed close to each other, resulting in a relatively impermeable layer, through which the clay would not erode. The very neatly look was another advantage of this type of structure. The height of the concrete blocks was dimensioned based on experience. The design criterion was not too much damage during yearly circumstances. If the damage appeared to be too much, the concrete elements were being replaced by heavier ones.