Study on Energy Evolution Law of Rocks With Different Lithologies and Sizes

ABSTRACT Investigating the actual patterns of energy accumulation and release in roof rock, particularly with varying stiffnesses in mining environments, is crucial. By conducting cyclic loading and unloading tests on rock samples of different lithologies, different sizes, and consistent stiffness, how lithology, size, and stiffness affect the evolution and distribution of rock energy were explored. Furthermore, the practical applications of stiffness theory in engineering contexts were discussed. This paper finds that, for samples of the same size but different lithologies, in loading, the rate of elastic energy growth accelerates with load and decreases with stiffness, whereas the peak proportion of elastic energy rises with stiffness. In unloading, lower stiffness leads to higher, prolonged elastic energy release. For samples of the same lithology but varying sizes, energy growth increases as stiffness decreases, with minimal peak proportion of elastic energy variation. In unloading, lower stiffness leads to higher, prolonged elastic energy release. Among samples with identical stiffness but different lithologies and sizes, little difference is seen in loading energy growth or unloading release rates, but elastic energy proportion varies mainly due to lithology. Higher Young's modulus and larger sizes result in greater elastic energy storage. Lab tests show that low‐stiffness machines will cause dynamic damage to the coal specimen, whereas hard rocks are more prone to coal bursts due to higher energy storage and release compared to soft rocks. The main reason for the deviation between the two is that the energy storage capacity of hard rock is greater than that of soft rock, and the storage‐release elastic energy of hard rock is greater than that of soft rock.