Abstract: The freezing method is adopted in Xinzhuang coal mine, and during the process of shaft excavation lateral, unloading leads to the unloading deformation of surrounding rock. The cretaceous media-grain sandstone is collected from Xinzhuang coal mine, and the samples are processed into saturated states. Then, the constant-axial compression and unloading confining pressure triaxial tests are carried out under freezing (-10 ℃) conditions using GCTS servo-controlled high-low temperature and high-pressure triaxial rock testing system. The stress change path of surrounding rock is simulated in the process of shaft excavation, and the deformation characteristics of frozen sandstone are explored. The results show that under the condition of lateral unloading, the frozen sandstone shows obvious elastic-brittle characteristics. There has compression deformation in the axial direction, but expansion deformation in the radial direction. Moreover, the radial deformation is approximately two times larger than the axial deformation. With the same unloading rate, the unloading deformation of rock specimens increases with the increase of initial unloading confining pressure, and especially the radial deformation is the most significant. This may be related to the unloading rebound deformation and the amount of energy accumulates within the sample. When the confining pressure is unloaded to the same stress level, the unloading deformation of rock specimens is small, and the deformation rate is greater under high unloading rate. The deformation modulus of rock samples decrease in the unloading process, but the ratio of lateral strain to longitudinal strain change increases. The smaller the unloading rate is, the larger the initial unloading confining pressure is, and the greater the variation of deformation modulus is.

Key words: frozen sandy, lateral unloading, initial unloading confining pressure, unloading rate, deformation properties