Abstract: In this study, uniaxial cyclic loading and unloading experiments were conducted on dry and saturated sandstones from Xiaojihan coal mine in Shaanxi province, respectively. The strength and deformation characteristics of rock and its corresponding energy evolution and distribution during the process were analyzed. It is found that the peak strength of dry specimens under cyclic loading and unloading condition was 19.47% lower than that under uniaxial compression condition. The results demonstrate that the saturation affects both the strength and deformation of sandstone specimens. Compared with dry specimens, the average peak strength of saturated specimens was 39.55% lower, meanwhile, the saturated specimens present more obvious compaction stage. The loading elastic modulus and unloading elastic modulus tend to increase for dry and saturated sandstones. However, the elastic modulus of saturated specimens was lower than that of dry ones. When the peak strength was normalized, the elastic strain energy Ue and the dissipation energy Ud of dry specimens were larger than those of saturated specimens at different stages of stress loading. During the loading process, the proportion of elastic strain energy Ud of saturated specimens was greater than that of dry one. In addition, the Ud proportion of saturated specimens declined gradually during the loading process. The Ue proportions of dry and saturated specimens achieved an appropriate level prior to failure.

Key words: cyclic loading and unloading, saturated specimen, elastic modulus, energy evolution, proportion of elastic strain energy