Abstract: The uniaxial step loading and unloading creep experiments were conducted on the sandstone samples from Shaanxi Province to analyse the law of energy evolution of the samples during the process of deformation and failure. The results show that with the increase of cyclic series, the dissipation energy of each grade exhibits a nonlinear increase and the plastic strain energy of each grade is relatively stable. The dissipation energy exceeding plastic strain energy can be regarded as a precursor energy characteristic of the sample failure. By defining the correlation coefficient and establishing the relationship between energy and deformation, it can be found that with increasing cyclic series, there is a positive correlation between the plastic strain energy and the new adding plastic strain of each grade, and the dissipation energy of each grade is positively correlated with the plastic strain accumulation. According to the calculation of the energy of loading, creep, unloading and recovery stages, the evolution rate of energy in each grade increases with the increase of cyclic series. When the rates of loading and unloading are constant, the change rate of energy at the loading stage is larger than that at the unloading stage, and the change rate of energy at the creep stage is greater than that at the recovery stage under the same grade. Finally, by analysing the change law of energy at each cyclic loading stage, an energy attenuation coefficient is proposed, which decreases as a power function with increasing stress level. Thus, an effective method is introduced for predicting failure stress.

Key words: creep, sandstone, energy evolution, plastic strain energy, dissipation energy