A constitutive model for compacted expansive and bonded marls

Abstract

This paper focuses on understanding the mechanical response of non-saturated compacted marls used to build some motorway embankments in Portugal. The compacted material consists of crushed marls, which can be assumed to be a set of fragments with relatively large dimensions. Experimental studies on the hydromechanical behaviour of this compacted, evolving material show that it behaves as a material in the transition between rockfill (when the fragments can be considered approximately intact) and a clayey soil (when a large number of fragments show strong physical disaggregation). Existing models for compacted rockfill and compacted clayey materials are not adequate to reproduce this complex behaviour. Constitutive models able to reproduce this behaviour are required for predicting the behaviour of earth structures such as these embankments. A model is proposed for the prediction of volumetric deformations for stress and strain boundary conditions corresponding to the oedometric test. It consists of an elasto-plastic unsaturated, double-structure, constitutive model in which the compacted material is assumed to be the macrostructure, and the microstructure is the fragment itself. Owing to the fundamental role of the loss of structure of the marl fragments in global behaviour, a constitutive equation for soft rocks is given, which includes a rule for bond loss depending on suction. Good results are obtained when the model is used to reproduce experimental tests performed on samples of compacted marls to which stress and suction cycles are applied. Other than the model proposed in this paper, attempts to reproduce the behaviour of compacted soft rocks are unknown.