Modelling the mechanical behaviour of expansive clays

摘要

A simple formalism is presented to model thebehaviour of expansive clays. Two levels of structure areconsidered. The behaviour of the macrostructure follows themodel developed for unsaturated materials by Alonso et al.[Geotechnique 40 (3) (1990) 405250L?30]. The behaviour of themicrostructure is adapted from the work of Gens and Alonso[Gan. Geotech. J. 29 (1992) 1013—1032] in order to include thepossibility of he micropores being partially saturated. Mechanicalcoupling between both levels of structure are defined throughtwo functions, one for wetting and the other for drying. Theyexpress the change in microstructural void ratio due to a changein microstructural void ratio, and their value depends on the stateof compaction of the macrostructure. The general shape of thesecurves is discussed on the basis of experimental evidence.Phenomena such as the dependency of strain on stress-suctionpath, accumulation of expansion strain during suction cycles atlow confining stress, accumulation of compression strain duringsuction cycles at high confining stress, strain fatigue duringdrying-wetting cycles, macropore invasion by expandedmicrostructure and development of macroporosity during strongdrying can be represented. A mathematical formulation of themodel is described and its performance finally assessed bycomparison with laboratory tests.