Degradation of marls; two case studies from the Iberian Peninsula

Abstract

The strength degradation of two marl formations (Pamplona marls in Spain and Abadia marls in Portugal) is analysed in the paper. In the case of Pamplona marls, a number of large-scale direct shear tests on natural and saturated specimens of the undisturbed material were performed. Tests on marl-concrete interfaces were performed and are also presented. Both cases analysed show that the saturation of the marl leads to a strong reduction of friction and effective cohesion. Negative effects of suction changes on the mechanical behaviour of the marls were investigated in more detail in suction controlled tests on Abadia marls, a more plastic material. A numerical simulation of wetting effects on a marl fragment of finite size helps to identify the nature of degradation mechanisms, which are associated with the development of tensile surfaces inside the marl matrix. They, in turn, are due to the expansive behaviour of the clay fraction of the marl relative to suction changes. © The Geological Society of London 2010.