Experimental study of the influence of temperature and cooling method on mechanical properties of granite: Implication for geothermal mining

In geothermal mining, the mechanical properties and micro-structure of the rock under different temperature or cooling modes are highly relevant to the stability of the artificial reservoir. For reflect the actual working conditions, an experimental study is carried out on high-temperature granite that has been cooled both naturally and rapidly with water. The following conclusions are reached. (a) The wave velocity, elastic modulus, and uniaxial compressive strength of the test specimen decrease with an increase in its heating temperature under both cooling modes. (b) The characteristics of the stress-strain curve of granite are different after different temperatures and cooling modes. With natural cooling, the stress-strain curve features double peaks in the range of 200-300 degrees C, whereas such phenomenon occurs at temperatures greater than 300 degrees C with water cooling. (c) When the temperature is less than 300 degrees C, no obvious change occurs in the crystal structure of the sample. When the temperature is more than 300 degrees C, the original micro-cracks gradually expand and eventually develop into larger cracks.