Damage and sealing of clay rocks detected by measurements of gas permeability

Various damage and sealing experiments have been performed on samples of the Callovo-Oxfordian argillite and the Opalinus clay in order to enhance the knowledge about the development of the excavation damaged zone around nuclear waste repositories in clay formations. Stress-induced damage and permeability changes were examined in triaxial compression tests. Preliminary criteria were derived for the detection of dilatancy, percolation, and failure boundaries. By measuring the gas permeability changes due to re-compaction and re-saturation, the self-sealing behaviour of strongly damaged clay samples was investigated. Short-term re-compaction by increasing the confining stress up to 15 MPa reduced the permeability by several orders of magnitude to 10−19–10−20 m2. After water re-saturation, the permeability of the damaged samples decreased significantly to 10−21 m2. All laboratory observations suggest a high self-sealing capacity of the studied clay rocks.