Evaluation and analysis of sandstone brittleness under the influence of temperature

Abstract

Abstract: The influence of temperature on rock brittleness is one of the key problems that must be considered in geothermal exploitation. To effectively evaluate and analyse the brittleness of sandstone following high-temperature treatment, a new method for calculating the brittleness index was constructed based on the volumetric stress–strain curve. Uniaxial compression tests were performed on sandstone after treatment at different temperatures, and acoustic emission (AE) signals were monitored during the test. According to the test results, the relationship between the brittleness index and temperature involves a quadratic function; brittleness is first enhanced and then weakens with rising temperature, and there is a critical value of 400 °C. AE presents a three-stage distribution during rock failure. The analysis of the accumulated AE energy of stage III shows that the AE energy intensity is highly consistent with the brittleness index trend as the temperature increases, which further suggests that temperature affects rock brittleness and reflects the applicability of the method established for calculating the brittleness index. Using the scanning test, the box dimension of the section crack at different positions of the damaged sample was calculated, which indicated that the distributions of rock fracture cracks were obviously different due to the differences in brittleness. Finally, the microstructural characteristics of different rock surfaces were analysed, and the reliability of the brittleness index obtained by the new method was verified by AE, macroscopic failure and the microstructure of the samples. The results provide a reference for engineering design and construction accounting for the effects of temperature. Article Highlights: (1)Uniaxial compression tests were carried out on temperature-heated sandstone.(2)A new method for calculating the brittleness index was proposed.(3)Differences in sandstone brittleness after temperature treatment were analysed.