Published online by Cambridge University Press: 15 February 2011
Heating to temperatures up to 500°C, gives a reduction in Young's modulus and increase in permeability of granitic rocks and it is likely that a major reason is grain boundary cracking. The cracking of grain boundary facets in polycrystalline multiphase materials showing anisotropic thermal expansion behaviour is controlled by several microstructural factors in addition to the intrinsic thermal and elastic properties. Of specific interest are the relative orientations of the two grains meeting at the facet, and the size of the facet; these factors thus introduce two statistical aspects to the problem and these are introduced to give quantitative data on crack density versus temperature. The theory is compared with experimental measurements of Young's modulus and permeability for various rocks as a function of temperature. There is good qualitative agreement, and the additional (mainly microstructural) data required for a quantitative comparison are defined.
This work has been funded by the UK Department of the Environment and by the Commission of the European Community as part of the U.K. radioactive waste management research programme. The results will be used in the formulation of U.K. government policy, but at this stage they do not necessarily represent government policy.