Energy evolution and macro-micro failure mechanisms of frozen weakly cemented sandstone under uniaxial cyclic loading and unloading

Further research is needed on the deformation behaviour and the macro-micro failure mechanisms of frozen soft rock driven by energy under cyclic loading and unloading conditions. Combined with specific engineering projects of freeze shaft construction, taking frozen weakly cemented sandstone (−10 °C) as the research object, uniaxial cyclic loading and unloading (UCLU) tests at different rates and microscopic observations of the fracture surface by scanning electron microscopy (SEM) were conducted. Then the failure mechanisms of frozen weakly cemented sandstone during UCLU were driven by energy, which was revealed by the proposed method for calculating rock damage based on damage energy. The results showed that the peak strength of sandstone was much smaller under UCLU conditions than the uniaxial compression test, proving that the mechanical properties of the frozen sandstone were affected by UCLU. The dissipation energy and damage energy of sandstone grew with increasing rates of loading and unloading, but the elastic energy and damping energy showed opposite trends. The energy evolution eventually shifted from being dominated by damping energy to being dominated by damage energy as the loading and unloading rates increased. The cumulative damage of sandstone grew logarithmically with increasing loading and unloading rates, and tensile cracking considerably increased at fast loading and unloading rates. Hence, the fast loading and unloading rates caused the rock dissipation energy and damage energy to be larger, which was the main reason why damage was more significant at fast than slow rates.