The deviatoric behaviour of peat: a route between past empiricism and future perspectives

The geotechnical description of peats represents one of the main challenges in the Netherlands to assure the required safety standard and performance of the flood defence infrastructure. Almost a third of the country is situated below the sea and the rivers level with about 60% to 70% of the population and economic assets concentrated in low-laying areas prone to flooding. Flood protection in the Netherlands is assured by a vast system of primary and secondary dykes, of which 14000 km are regional dykes. Design and assessment procedure of these dykes is not straightforward, especially when peats layers are encountered. Adequate geotechnical description of the behaviour of peats at the engineering scale represents one of the biggest concerns that public water authorities and geotechnical engineers are currently facing. The majority of the previous investigations have regarded the volumetric and time dependent behaviour of peat, both from the experimental and the modelling viewpoints. However, the information on the deviatoric counterpart is still scarce and contradictory. This has contributed to generate geotechnical uncertainties on the deviatoric behaviour of peats with severe overly conservative approaches in the current engineering practice and diffuse misconceptions within the research community on traditional experimental tests.