THERMOELASTIC AND THERMOPLASTIC RESPONSE OF A DOUBLE-LAYER POROUS SPACE CONTAINING A DECAYING HEAT-SOURCE

Solutions are presented for the behaviour of a layered porous space wh ich contains a decaying heat source. Such a problem arises-when high-l evel nuclear waste is placed in deep underground depositories in deep clayey formations of sedimentary basins. The geometry of the problem i s one dimensional and the porous space is constituted by two layers: a deep low permeability layer which contains the nuclear waste disposal and a superficial layer, The solution is used to examine the effects of contrasts of permeability, thermal conductivity and specific heat c apacities between the two layers on the large-scale behaviour of the p orous space. Results are presented, using realistic data, for the pore pressure and temperature evolution at the heat source centre; and for the vertical displacement of the ground level. The superficial layer has no significant effects on pore pressure, temperature and stress ev olution near the heat source centre. The vertical displacement of the ground level is mainly due to the thermal dilatation of the pore water , so it decreases with an increasing of permeability of the superficia l layer. The solution of the time-dependent problem is carried out by applying Laplace transforms to the field variables, obtaining solution s and then using numerical methods to invert the transformed solutions . Comparisons with numerical simulations taking into account the non-l inear and non-reversible behaviour of the rock mass are presented. (C) 1998 by John Wiley & Sons, Ltd.