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Abstract:
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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 overconsolidation
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. |
