Erosivity of natural intact structured clay: Evaluation

Previous studies on erodibility of cohesive soil are briefly reviewed and it is concluded that experimental observations have been mainly concerned with remolded and reconsolidated or weathered clays. The structure effect, which is considered important in the behaviour of natural intact clay, especially for Eastern Canadian clays, has not up to now been really considered in the evaluation of clay erodibility. This paper proposes a new laboratory technique for the study of the erodibility of natural intact clays and presents results of a testing program on three Canadian clays. The results indicate that Canadian structured clays are very resistant to erosion if intact and unweathered. Erosion is not taking place at the clay particle level but rather by the pulling out of larger elements composed of sand or silt grains or of clay aggregates. The pulling out of clay aggregates appears related to defects in the clay matrix, such as microfissures or planes of weakness associated with bedding. Key words: erosivity, intact clay, rate of erosion, tractive force, erosivity test, microstructure, macrostructure.