Expansive bentonite–sand mixtures in cyclic controlled-suction drying and wetting E.E. Alonso, E. Romero * , C. Hoffmann, E. Garcı ´a-Escudero Department of Geotechnical Engineering and Geosciences, Universitat Polite `cnica de Catalunya, UPC, c/ Jordi Girona 1-3, Building D-2, 08034 Barcelona, Spain Available online 11 August 2005 Abstract Expansive clay buffers in radioactive waste disposal designs experience cyclic drying and wetting paths during different stages of their design life. Clayey soils subjected to these processes develop swelling and shrinkage deformations, which give rise to the accumulation of compression or expansion strains during suction cycles. Experimental studies were undertaken using oedometer tests on an artificially prepared bentonite–sand mixture (80% bentonite by dry mass). In order to study these processes and to identify the most important features controlling soil behaviour, several wetting–drying cycles with suctions ranging between 130 and 4 MPa were applied using vapour equilibrium technique and covering a wide range of over- consolidation ratios (OCR). The tested samples showed cumulative shrinkage strains along the successive cycles, which became more significant at increasing vertical net stresses (low OCR values). However, no accumulation of expansion strains was detected at elevated OCR values. Test results were interpreted and predicted within the context of an elastoplastic model proposed by Alonso et al., 1999, [Alonso, E.E., Vaunat, J., Gens, A., (1999). Modelling the mechanical behaviour of expansive clays. Engineering Geology, 54, 173–183.] which takes into account the accumulation of strains. A good correspondence between measured soil response and model predictions was observed. The paper also presents the methodology to derive the constitutive parameters. D 2005 Elsevier B.V. All rights reserved. Keywords: Swelling; Shrinkage; Suction; Expansive clay; Model 1. Introduction Soils are naturally subjected to cyclic and strong drying and wetting paths due to natural environmental fluctuations. Buffers constructed using clays of expan- sive nature in radioactive waste disposal designs also experience stress and suction cycles during different stages of their design life. In a general case, stress and suction paths are far from being a simple monotonic 0013-7952/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.enggeo.2005.06.009 * Corresponding author. Geotechnical Laboratory, Departamento de Ingenierı ´a del Terreno, Jordi Girona 1-3, Edificio D-2, Universi- tat Polite `cnica de Catalunya, 08034 Barcelona, Spain. Tel.: +34 93 4016888; fax: +34 93 4017251. E-mail address: enrique.romero-morales@upc.edu (E. Romero). Engineering Geology 81 (2005) 213 – 226 www.elsevier.com/locate/enggeo