Coupled processes in geomechanics

The safe operation of an underground repository for the disposal of nuclear wastes, and the isolation of these wastes form the accessible environment, may be affected adversely by the formation of new fractures in the rock close to these excavations or by movements across pre-existing fractures. Both phenomena may so enhance the permeability of the rock as to allow possibly contaminated groundwater to reach the accessible environment. For hard rocks, the formation of new fractures in the regions of high stress concentration adjacent to excavations is analyzed in terms of breakouts or spalling. In rocksalt, creep may allow the stress adjacent to excavations to decrease below the hydrostatic pressure so that hydraulic fractures may form, or the extension of layers other than salt may produce new hydraulic conduits. The deformation of fractures in response to changes in stress pore pressure and temperature are analyzed for pre-existing fractures, as is also the shear stability of the fractures. Experience and in situ testing are seen to be of the greatest importance in identifying and understanding coupled phenomenon in geomechanics