Effective stress strength testing of peat

Abstract

It has been approximately 80 years since the first effective stress strength testing of peat was performed using triaxial apparatus. In light of recent unexpected failures of embankments, dykes, foundations and slopes in peat deposits, it is timely to review current laboratory practice and also provoke discussion about the best way forward for understanding and determining the effective stress strength properties of peat. Compared with fine-grained mineral soils, significant fabric and structural differences (including the porous, compressible nature of the organic solids themselves) make the direct application of classical soil mechanics strength models doubtful for peat. Uncertainties and difficulties of effective stress testing of peat using standard strength apparatus are discussed. Compared with triaxial compression, direct simple shear testing appears to provide conservative estimates of the strength parameter values, and the specimen deformation (failure) mode more closely represents that occurring in translational planar slides. It is recommended that the geotechnical profession investigates alternative theoretical frameworks to explain and predict peat strength (and compression) behaviour along with the development of new apparatus and methodologies for determining appropriate parameter values.