Experimental Study on Energy Evolution Process of Fracture Propagation of Marble under Different Stress Paths

The deformation and fracture of rock mass are processes along with procedural evolution of energy dissipation and energy release. With an aim to explore the principles of evolution process, the loading and unloading tests are carried out of the marble specimens under complex stress path for analysis of evolution principles of axial energy and actual absorbed energy as the strain changes. The present results show (1) under complex stress paths, the axial energy rises nonlinearly as the strain increases; the rate of rise remains low at the initial stage; with the rate growing gradually to critical damage, the rate will turn to an abrupt inflection point and tends to stabiliz;. (2) under complex stress paths, the axial energy, the strain curves and the gross energy all have abrupt inflection points of rate; the point of the axial energy is at the critical damage of corresponding stress-strain curves while the point of the gross energy at the corresponding peak; (3) the change of the confining pressure fails to change the axial energy of the specimen under complex stress paths; however, under different confining pressures, the gross energy-strain curves of the loading axial pressure and unloading confining pressure present differing forms; (4) the rate of the unloading confining pressure does not change the curve form of the axial energy and the gross energy, only to alter the changing rate of the curves under different stages; and (5) under complex stress paths, the increase of the confining stress comes with the increase of the gap between axial energy and gross energy whereas the effect on the unloading rate is just the contrary.