Paper 2B 40 — SINOROCK2004 Symposium Int. J. Rock Mech. Min. Sci. Vol. 41, No. 3, CD-ROM, © 2004 Elsevier Ltd. 1 A NEW COUPLING CONCEPT FOR THE HYDRO-MECHANICAL INTERACTION OF CLAY STONE AND ROCK SALT IN UNDERGROUND WASTE REPOSITORIES Z. Hou¹, K.-H. Lux² ¹) Disposal Technology and Geomechanics, TU Clausthal, Germany zhengmeng.hou@tu-clausthal.de ²) Disposal Technology and Geomechanics, TU Clausthal, Germany lux@tu-clausthal.de Abstract: For the simulation of the hydraulic and mechanical behaviour of clay stone and rock salt as well as the hydro-mechanical interaction in the excavation disturbed zone (EDZ) around sealing systems in under- ground radioactive or toxic waste repositories, a new hydro-mechanical coupling concept has been developed, which includes the Hou/Lux constitutive model formulated with effective stresses, the Darcy flow model as well as several coupling models. An exemplary drift in clay stone and an exemplary drift sealing in rock salt have been investigated. Following the calculation results, the construction of a drift dam can noticeably reduce or even heal the EDZ of ∆ r≈1.5m in a 1000m deep drift over a period of approx. 20 years, due to the creep behaviour of rock salt and the supporting effect of the dam. To improve the design for the construction of sealing systems, the drift should be expanded shortly before constructing the dam, and the dam should be constructed as early as possible in order to heal damage in time and in order to reduce the permeability and porosity in the EDZ around the dam prior to a possible brine entry. Keywords: Hydro-mechanical coupling, radioactive waste repository, rock salt, clay stone, excavation disturbed zone (EDZ), sealing system. 1. INTRODUCTION Through sealing systems, e.g. drift or shaft sealing systems, direct influx of brine or water in disposal cavities of the underground radioactive or toxic waste repositories is initially ruled out. However, secondary micro cracks in the EDZ around the sealing systems build networked hydraulic pathways, which make axial seepage flow along the sealing direction possible. The hydraulic pathways in the EDZ have additional impacts through the present pore pressure as well as hydrodynamic and hydrostatic forces with the development of further secondary micro cracks as a result in case of flooding. This process can continue itself progressively: Micro cracks build-up ⇒ Additional creep deformations ⇒ Deterioration of the load bearing capacity ⇒ Intensification of the strain softening and loosening ⇒ Increase of the porosity and permeability ⇒ Intensification of the seepage flow ⇒ Increase of the hydraulic impacts induced by seepage flow and so on. This accumulated damage and dilatancy of the EDZ can be removed, if the healing boundary is undershot as a result of convergence and the redistribution of stresses around the sealing systems (passive or active contact pressure). Then the opposing process is activated: Closing and healing of the micro cracks and pores ⇒ Regression of the creep deformation ⇒ Improvement of the load bearing capacity ⇒ Reduction of the strain softening and loosening ⇒ Reduction of the porosity and permeability ⇒ Decrease of the seepage flow ⇒ Reduction of the hydraulic impacts induced by seepage flow and so on. Figure 1. Hou/Lux hydro-mechanical coupling concept for rock salt and clay stone. The above description illustrates the interactions between the mechanical and hydraulic fields in the