ABSTRACT: Increase in subsurface temperature causes changes in physical & mechanical properties of rocks thereby causing instability in the strata which results in rock failure & surface subsidence. In this study, sandstone rock samples were collected from the Damodar River Valley of Dhanbad, India and have been subjected to laboratory experiments to evaluate the temperature effects on sandstone rock. Individual rock samples were given a heat treatment at a specified temperature. The temperature range of 200degC to 1200 degC is considered with the upper limit following the highest reported temperatures in the region. Under this heat treatment, the sandstone samples were first heated at a specified temperature for continuous 6 hours a day and 7 days. After this process, their physical properties (mineralogy, grain size and spontaneous imbibition by water and mechanical properties (Uniaxial compressive strength-UCS, tensile strength, ultrasonic wave velocities etc.) were determined in the laboratory.

The result obtained shows that the temperature has a significant effect on the measured rock properties an attempt has been made to explain these changes using thin-section analysis. For example, the trend observed on UCS versus temperature crossplot suggest an increase in strength up to 400DegC and then decrease upto 1200 DegC. The initial increasing trend is attributed to the removal of moisture and change in compactness whereas the decreasing UCS trend is the result of the development of multiple fractures. These fractures enhance the secondary porosity and are evident in the thin sections heated to 600 degC,800 degC,1000 degC and 1200 degC. Because of the changes at the granular level, most of the physical and mechanical properties of the sandstone rock are influenced.

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