Stability of pattern placed revetment elements

Abstract

A revetment of pattern placed elements, or a so called pitching, is used worldwide to protect shorelines and embankments. Also in The Netherlands more than 500 km of river, lake and sea dikes is protected by pitchings. Until the 60’s the design and construction of pitchings was based on experience. After the first damages on pitchings and the negative assessment results, an intensive investigation program on pitchings was carried out. The results are commonly used nowadays in the Dutch dike reinforcement works. When comparing pattern placed block revetments with other revetments, the remarkable difference is that the amount of material to be used is significantly less than when using loose riprap. However placing blocks is more labour intensive. This is a specific advantage for countries with a large inexpensive labour force. In China, Vietnam and Bangladesh these are very common constructions. The leakage length L, describing the relationship between top layer elements and sublayer properties, is the most important design parameter; a small leakage length is favourable for the stability of the pitching. The maritime commission of PIANC has in 2007 decided to start a working group to make a small document on the design of pattern placed revetment elements. This PIANC MARCOM working group 57 report is now available (PIANC report 114, 2011). This paper presents an outline of this new knowledge of pattern placed block revetments, required for assessment and design purposes usable all over the world. It follows more or less the contents of the new PIANC report.