Elastic modulus evolution of triaxially stressed mudstone at high temperature up to 400°C

The elastic modulus is a key parameter in the constitutive equation of rock material, which changes with exterior conditions, including temperature. To study the evolution of the elastic modulus of the surrounding rock in some high-temperature underground engineering works (eg, underground coal gasification, in situ pyrolysis of oil shale), a servo-controlled rock testing machine was used in a study of the variation in elastic modulus of Jimsar mudstone (the roof stratum of Jimsar oil shale) when subjected to triaxial compression at high temperatures. The elastic modulus exhibited nonmonotonal variation when heated to 400 degrees C while subjected to triaxial compression. This occurred in three stages. An empirical model involving piecewise linear function was used to quantitatively describe the relationship between elastic modulus and temperature. Elasticity increased between room temperature and 265 degrees C, then weakened between 265 and 341 degrees C, then increased at 341-400 degrees C, in accordance with the calculated result from the empirical model. Thermal expansion, thermal cracking, water loss, and structure reconstruction had a combined effect on the elastic modulus of the mudstone. The results will be helpful for understanding the mechanism of strata movement in some underground high-temperature engineering operations.