Reactive plasticity for clays: application to a natural analog of long- term geomechanical effects of nuclear waste disposal

Long-term changes in mechanical properties of clays induced by heating are investigated based on findings at Orciatico site of natural analog of nuclear waste disposal. To quantify the extent of such changes, a chemo–thermo-plastic model for illitization and re-smectitization of clays [Int. J. Plast. (2000)] is used. The model is an extension of Cam-clay model. Identification of parameters is presented for the material from one peripheral borehole where temperatures developed in clay near the contact were in the analogy range. Short-term heating experiments on previously thermally unaffected specimens were used to identify thermal softening characteristics. Apparent maximum past precompression stress was determined throughout the borehole. Hypothetical history of the clay in the borehole including pre-loading, heating, cooling and mineralogical reaction was reconstructed, and the apparent maximum past precompression stress data were used to identify the characteristics of chemical softening function describing the long-term clay transformations. D 2002 Elsevier Science B.V. All rights reserved