Abstract: According to the results of limestone samples under uniaxial compression test, conventional triaxial test and unloading test, energy evolution characteristics of limestone during the whole-process deformation are analyzed. Results show that rock failure laws of energy evolution are different between loading and unloading. The confining pressure restrains the internal crack growth. The absorbed total energy U and elastic energy U e in conventional triaxial compression test are larger than that of uniaxial compression test. The elastic energy U e continues increasing before peak strength. However, it remains the same during the unloading stage. The elastic energy U e with release availability mainly accumulates in the loading process prior to the unloading process. The geostress state before engineering excavation determines the releasing amount of elastic energy. The dissipated energy U d increases quickly near the peak strength. But the increasing velocity of dissipated energy under unloading stress path is faster than that under loading stress path. The rapid increase of dissipated energy indicates the occurrence of rock failure in loading and unloading stress paths. The absorbed total energy U and elastic energy U e increase with the confining pressure increasing. The absorbed total energy U, elastic energy U e and dissipated energy U d decrease with the unloading velocity increasing.

Key words: loading, unloading, limestone, energy evolution