INTRODUCTION
The safe disposal of high level radioactive waste in mined cavities, geothermal energy production, and thermally driven in situ resource recovery methods all require knowledge of the mechanical, thermal, and fluid flow characteristics of rock at shallow depths as perturbed by a thermal pulse. In order to accurately predict the response of the rock to the thermal and mechanical loading, numerical models based on the physicochemical processes are needed along with input data on rock properties. These properties must be determined at the expected conditions at depth and include thermal expansion, elastic moduli, and permeability.
In the case of radioactive waste disposal, mined repositories to 2 km in depth are being considered. Crystalline igneous rocks are among the candidates for the location of such a repository, and effective pressures at a depth of 2 km would be about 50-60 MPa in dry rock or 30-40 MPa in water-saturated rock. Current design criteria yield a maximum temperature rise in the rock of about 200°C above ambient. Other mass or energy production schemes from depth can involve even higher temperatures.
In this paper we present new Young's modulus, bulk modulus, and thermal linear expansion measurements on two diverse igneous rocks, Sudbury gabbro and Climax quartz monzonite, at 6.9-55.2 MPa and 19-500°C. In addition, we calculate the permeability of each rock as a function of pressure and temperature. At the conditions covered in this work, opening and closing of cracks have a strong influence on the rock response. The nonlinear behavior suggests that this type of model input data cannot be estimated with sufficient accuracy a priori, and thus actual measurements are necessary.
STARTING MATERIAL AND EXPERIMENTAL TECHNIQUE
All types of igneous rocks are being considered as hosts for nuclear waste repositories. The Sudbury gabbro and the Climax quartz monzonite were chosen for this study because both come from sites where field experiments are planned or in progress to determine the consequences of emplacing spent nuclear fuel in the shallow crust (Laroque, 1978; Ramspott, 1979a; Carlson et al., 1980).
The Sudbury gabbro starting material was taken from a 0.15-m diameter unoriented drill core from the in situ heater test site at the 700-m level in the Creighton Mine, Sudbury, Ontario (Larocque et al., 1978). The rock varies en masse between a gabbro and a norite, depending upon the local ratio of clino- to orthopyroxenes. We will refer to the rock as Sudbury gabbro. This quartz biotite gabbro is medium to coarse grained (1-5 mm) phaneritic, composed of 50-60% pyroxene plus biotite and 40-50% plagioclase plus quartz, with quartz less than 5%and biotite varying between 5 and 10% (Miles, 1976). The plagioclase is approximately Ab45An55.
The Climax quartz monzonite used in this study was taken from a 0.56-m diameter unoriented vertical drill core from the site of Heater Test No. 1 at the 420-m level in the SFT-C mine (Ramspott, 1979b). Maldonado (1977) provides a petrographic description of the Climax monzonite that has been verified by our observations. The quartz monzonite is medium-grained (1-2 mm) porphyritic, containing approximately 5% potassium feldspar phenocrysts from 5-150 mm in length and 5-10% quartz phenocrysts averaging 4 mm in length.
