Stress relaxation during creep of rocks around deep boreholes

The variation of stress during creep convergence of a deep borehole excavat ed in rock salt is examined. A non-associated elasto/viscoplastic constitut ive equation is used to describe both compressibility and/or dilatancy duri ng transient and steady-state creep, as well as evolutive damage possibly l eading to failure. An in-house FEM numerical method is used for this purpos e. The variation in time of radial convergence of the borehole walls and of the stress state (at various distances from the borehole surface) is illus trated by several figures. The significance of these variations for long-te rm stability is discussed. (C) 2001 Elsevier Science Ltd. All rights reserv ed.