Dilatancy and energy properties of marble under triaxial unloading condition

Dilatancy is an important feature of rock during deformation and failure processes. By means of the MTS815 servo-controlled test machine, laboratory triaxial unloading experiments and plasticity theory analysis are made to obtain the characteristics of dilatancy and energy change of marble under unloading condition. The results show that the characteristic stress of rock samples increase and the dilatancy characteristics decrease with the increase of the confining pressure. The dilatancy parameters of rock samples, dilatancy index and dilatancy angle, have obvious effects of confining pressure. The dilatancy index and confining pressure have good exponential distribution, and the relationship between dilatancy angle and stress ratio is linearly distributed. The energy characteristics of rock samples under unloading destruction process are that the main energy is releasable strain energy at the initial stage and dissipation energy at the failure stage, and the turning point between these two stages is the initial damage dilatancy point. Meanwhile the characteristic energy value and confining pressure under unloading condition have a good exponential relationship. Both at the peak point and the residual point, the relationship both between the energy damage amount and the dilatancy angle and between the energy eigenvalues and the dilatancy index has a good exponential distribution.