Mechanical and hydraulic behavior of rock salt in the excavation disturbed zone around underground facilities

The mechanical and hydraulic behavior of rock salt in the excavation disturbed zone (EDZ) around sealing systems in underground repositories is relevant for the assessment of the safety function of these geotechnical barriers. It has been determined through laboratory tests that the development of the EDZ, and thus, the hydraulic pathways, is closely related to the corresponding damage boundary and the associated damage. By integrating short- and long-term strength considerations, dilatancy, damage and healing into the newly extended Hou/Lux constitutive model for rock salt, it is possible to treat the tertiary creep in order to identify the EDZ around underground facilities. This leads to prediction of the time-dependent development of the EDZ and, together with a permeability model, calculation the permeability of rock salt in the EDZ. With the Hou/Lux model, several phenomena, such as EDZ, spalling, dilatancy and radial deformation into the axial bore observed in laboratory tests on axially perforated cylinder samples are simulated qualitatively and quantitatively. Under in situ conditions, the EDZ of a 37-year-old drift at the Sondershausen mine, the prototype cavity at the Asse mine, as well as a 1,000,000 m(3) salt cavity, are examined. The results are then compared with the stress and permeability measurements at the Sondershausen mine. The calculations show the various capabilities of the Hou/Lux model, including tertiary creep and creep rupture, identification and development of the EDZ, development of dilatancy, of permeability, of damage and of healing, and finally, stress rearrangements from the contour into the center of the rock mass formation. (C) 2003 Elsevier Ltd. All rights reserved.