Experimental study of energy features of sandstone under loading and unloading

In order to get the features of energy absorption and dissipation of sandstone under loading and unloading,the tests of uniaxial compression,triaxial compression and post-peak unloading confining pressure have been performed on sandstone with the MTS81.5 servo-controlled test machine.The results show that the dissipated energy of sandstone increases from uniaxial compression test through post-peak unloading test to triaxial compression test.The dissipated energy in triaxial compression and post-peak unloading confining pressure tests increases linearly with the confining pressure.Under uniaxial compression,the sandstone presents abrupt brittle failure and the elastic strain energy initially stored in the sandstone is instantly transformed into dissipated energy which is the power source of all phenomena of the rock failure.Under triaxial compression,the sandstone demonstrates progressive failure,i.e.the failure of sandstone is the process of from local cracking to global destruction in which the dissipated energy gradually increases with deformation.When the deformation reaches a critical level,the residual energy stored in sandstone will be rapidly released and the sandstone globally destructed.