INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS Int. J. Numer. Anal. Meth. Geomech., 2005; 29:751–787 Published online 26 April 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/nag.434 A double structure generalized plasticity model for expansive materials Marcelo Sa´nchez 1,z , Antonio Gens 1,} , Leonardo do Nascimento Guimara˜es 2 and Sebastia´n Olivella 1,n,y 1 Department of Geotechnical Engineering and Geosciences, Universitat Polite ´cnica de Catalunya (UPC), Barcelona, Spain 2 Universidade Federal de Pernambuco, Recife, Brazil SUMMARY The constitutive model presented in this work is built on a conceptual approach for unsaturated expansive soils in which the fundamental characteristic is the explicit consideration of two pore levels. The distinction between the macro- and microstructure provides the opportunity to take into account the dominant phenomena that affect the behaviour of each structural level and the main interactions between them. The microstructure is associated with the active clay minerals, while the macrostructure accounts for the larger- scale structure of the material. The model has been formulated considering concepts of classical and generalized plasticity theories. The generalized stress–strain rate equations are derived within a framework of multidissipative materials, which provides a consistent and formal approach when there are several sources of energy dissipation. The model is formulated in the space of stresses, suction and temperature; and has been implemented in a finite element code. The approach has been applied to explaining and reproducing the behaviour of expansive soils in a variety of problems for which experimental data are available. Three application cases are presented in this paper. Of particular interest is the modelling of an accidental overheating, that took place in a large-scale heating test. This test allows the capabilities of the model to be checked when a complex thermo-hydro-mechanical (THM) path is followed. Copyright # 2005 John Wiley & Sons, Ltd. KEY WORDS: constitutive modelling; expansive soils; unsaturated porous medium; fabric/structure of soils; suction 1. INTRODUCTION The study of expansive soils has been a subject of increasing interest in recent research [1–6]. A major motivation is the possible use of those materials as engineered barriers and seals Received January 2004 Accepted December 2004 Copyright # 2005 John Wiley & Sons, Ltd. y E-mail: sebastia.olivella@upc.es z E-mail: marcelo.sanchez@upc.es } E-mail: antonio.gens@upc.es Contract/grant sponsor: ENRESA Contract/grant sponsor: European Commission Contract/grant sponsor: CAPES Contract/grant sponsor: Ministerio de Ciencia y Tecnologı´a; contract/grant number: BTE 2001-2227 n Correspondence to: Sebastia´ n Olivella, Departamento de Ingenierı´a del Terreno, Universidad Polite´cnica de Catalunya, Jordi Girona 1-3, Edificio D-2, 08034 Barcelona, Spain.