Mechanical properties and brittleness characteristics of sandstone from different burial depths

The variation in rock mechanical properties with burial depth has always been a cutting-edge research topic worldwide. However, due to the difficulty in sampling from different burial depths, few studies have examined the change in rock mechanical properties with burial depth, especially in terms of the brittleness index. In this paper, 45 sandstone samples were acquired from depths of 101.6, 203.2, 317.3, 406.4, 509.8 and 589.3 m in the Buertai coal mine, and uniaxial compression experiments were conducted on the samples. An energy evolution method has been adopted based on the positive and negative correlation of stress–strain. Furthermore, a new brittleness index of the samples for different depths is proposed based on the energy release rate and then verified. The reasons for the difference in mechanical properties at different depths are explained. The results show that the stress–strain curves of sandstone from various burial depths can be classified into four types. The quantitative correlations between the peak stress, elastic modulus, secant modulus and depth obey a quadratic formula, while the changes in the peak strain and total strain are irregular with increasing depth. The patterns of the energy release rate at different burial depths can be grouped into five general patterns. The brittleness index and maximum energy release rate of sandstone generally increase with increasing depth. Furthermore, the brittleness index shows no clear tendency to change with other mechanical parameters, including the elastic modulus, secant modulus, peak strain, and total strain. Highlights The variations in mechanical properties and brittleness characteristics of sandstone from different burial depths were investigated. An energy analysis method was established, and a new brittleness index was proposed based on the energy release rate on this basis. The reasons for the difference in mechanical properties at different depths were explained.