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Characterization of drained and undrained response of thermally loaded repository rocks
Author(s) -
Palciauskas V. V.,
Domenico P. A.
Publication year - 1982
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/wr018i002p00281
Subject(s) - porosity , isothermal process , permeability (electromagnetism) , materials science , geotechnical engineering , pore water pressure , porous medium , consolidation (business) , thermal conductivity , fluid dynamics , effective stress , geology , composite material , mechanics , thermodynamics , chemistry , biochemistry , physics , membrane , business , accounting
The fluid pressure and mechanical response of a potential repository rock to heating is shown to be characterized by the isothermal parameters of the classic stress‐strain theory for a porous medium, in combination with some nonisothermal parameters describing the fluid, solid, and pore volume expansivities. The isothermal coefficients are described in terms of easily interpretable parameters by noting that the fluid response can be formulated within the limits of drained and undrained behavior. The low permeability‐high thermal conductivity environment generally considered to be ideal for nuclear waste storage would appear to favor an undrained response, at least within the isolated pores and cracks of a fractured rock medium. Several cases are presented that provide a qualitatively correct demonstration of the effects of heating in this environment. These include fluid pressure increases in excess of temperature‐induced increases in in situ stress, elastic strain and the potential for inelastic crack propagation, and porosity‐permeability augmentation. If the rocks are dry, or of a high permeability such that fluid flow takes place at constant fluid pressure, similar rock material alterations are possible. This follows from the fact that when the temperature is raised to some high value, say 80° or 90°C, and then decreased to its ambient value, the final volume of a polycrystalline substance will generally be greater than the initial one. Hence the effect of temperature is irreversible because of the differential thermal expansion of the composite mineral grains and the generation of new grain boundaries. The increase in porosity during such a heating episode is calculable and empirically related to increases in permeability.