A STUDY ON MICRO-MACRO MECHANISMS OF CRACK NUCLEATION DURING CREEP IN BRITTLE ROCKS

The creep behaviours influenced by the growth, coalescence and nucleation of microcracks in brittle rocks have an essential meaning for evaluating the microseismicity and rock bursts of the surrounding rocks in deep underground engineering. However, the micro-macro mechanisms of the damage catastrophe from the crack nucleation effect on the total creep behaviour of brittle rocks are rarely studied. In this study, based on the subcritical crack growth model, the damage model relating to the crack, strain and acoustic emission events, and the function of the damage path influenced by crack nucleation, a micro-macro model is proposed to explain the effect of crack nucleation on creep of brittle rocks. The function of the damage path influenced by crack nucleation is defined by the parameters of the size of damage catastrophe (i.e., \Delta D_CN) and the time difference (i.e., \Delta t) between the adjacent crack nucleations. The damage and time parameters in this proposed function of the damage path can be determined by the use of the experimental data of acoustic missions. The rationality of this proposed micro-macro model is verified by comparing the experimental results. The effects of the damage catastrophe size from crack nucleation, the happened time of crack nucleation, and the number of crack nucleation on the crack length, crack velocity, axial strain, and axial strain rate are discussed during creep of brittle rocks. The suggested model provides a certain theoretical help for the more reasonable, economical, and efficient construction of deep underground engineering.