This research was performed on coupled effects between mechanical behaviour and mass transfer properties of salt. The work was carried out in support of the long term safety analysis of underground storage facilities in salt, especially radioactive waste repositories. It consists of three parts.
In situ tests were carried out in a salt layer in the "Mines de Potasse d''Alsace" (MDPA, France). Theoretical and experimental studies on design, instrumentation and interpretation of the field tests were also performed. One original aspect of the field tests is the experimental set up specially developped. It allowed accurate measurements of fluid percolation in salt. The results of the field experiments confirm that the investigated rock salt is permeable to gas and to brine, even far enough from underground openings. The results of the tests with brine are interpreted in a satisfactory way using a model based on the Darcy''s law and characterized by a permeability value of 2.10–21 m2 and an initial pore pressure value of 1 MPa. The experiments were performed without jacket, in order to allow percolation of fluids (brine and oil) in the samples taken from the field test site. The mechanical behaviour is characterized by a brittle failure, whatever the mean stress is. The compressive strength and the damage initiation related to wet condition are systematically lower than those of dry condition. These results are explained by the permeability effect and consequently by the pore pressure build-up in the sample directly subject to fluid. Moreover, relaxation and creep tests performed on the samples without jacket show that viscoplastic behaviour is affected by the the fluid percolation and damage.
Damaged rock salt is considered to be a porous medium, eventually subjected to the chemical reaction between brine and salt.
