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The Need for High Pressure Rock Tests for a Geological Survey at Great Depths |
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The Need for High Pressure Rock Tests for a Geological Survey at Great Depths Author: J. Pininska
This paper presents the results of high-pressure and high-temperature laboratory testing of rocks
for modelling rock behaviour mechanisms at depths not directly accessible. The uniaxial and triaxial
strength tests under controlled pressure and temperature were performed on various rocks: a Kośmin
syenite, a Górażdże limestone and a Blue Cloud granite-gneiss from Canada. Samples confi ned in the
thermo-compression chamber were tested using an MTS-815 machine at temperatures (T) 24 and 100°C
under uniaxial conditions, and at confi ning pressures (p) of 30 and 60 MPa. Generally, all the rock types
showed a signifi cant increase in compressive strength with an increase of confi ning pressure while the
thermal impact is variable. The strength of granite and granite-gneiss increased under uniaxial compression
with an increase of temperature from 24 to 100°C, while the strength of the limestone decreased. Under
triaxial compression conditions, an increase in temperature caused a decrease in the strength of granitic
rocks and an increase in the strength of the limestone (Fig. 4).
Combined pressure and temperature-induced deformation processes result in a variability of rock bulk
density (ρ) changes (Fig. 9). Therefore, under the combined impact of pressure and temperature at greater
depths, rock density depends on the balance between thermal and mechanical stresses. Thus the rock
parameters determined under surface conditions without modelling the impact of great depth conditions
cannot be used as a criterion for determining rock properties at greater depths. The simple extrapolation
of rock properties from surface conditions to those at a greater depth will be inaccurate. |
2011