Indenter studies of the swelling, creep and pressure solution of Bure argillite

Experimental deformation of Bure argillites was performed by indenter techniques in order to investigate the kinetics of pressure solution processes. Various parameters included in pressure solution laws were tested: solubility of the mineral in solution (calcite), diameter of the indenter, temperature and stress. None of the observed effects confirm the contribution of pressure solution. In long duration experiments, a stabilized linear relation was found between displacement rate and stress, at least after 2 months. However, wide scattering of the data was observed, associated with unstable microfracturing around the indenter that may be linked to the swelling that always occurs before the indenting and that weakens the strength of the rocks (especially when using water). Argillite deformation is likely to be linked to the deformation of clay minerals acting as potential weak zones. The study does not exclude the possibility that pressure solution mechanisms may be of some importance for the long-term behavior of the natural barrier. This work just underlines the difficulty of studying this mechanism in weak rocks where several mechanism of deformation may competes and the faster strain rate hide the slower one at human time scale, whereas the slower one may be predominant on long-term duration.