Abstract: According to the theory of subcritical expansion of cracks, we know that the breakage is caused by the extension of micro-cracks in rockfill particle. Based on the long-term deformation characteristics of rockfill particle proposed by predecessors, we study the influences on the stress intensity factor and extension of crack by discussing the stress on the crack surface, geometrical characters of particles and cracks, relative humidity, etc. The analysis results show that, ratio of the initial crack length to particle radius (α) and the stress (σ^*_i ) which acts across the surface of a crack, are the main influencing factors of crack expansion. The longer the length of initial crack is, the larger the stress on crack surface is, and the shorter the time from propagation till breakage of crack is. Big relative humidity is in favour of speeding crack propagation. However, the effect of relative humidity is limited when α and σ^*_i are large enough. The time interval from start of loading to particle breakage ranges from 1 minute to 100 years, which indicates that the particle breakage happens in the whole process of loading.

Key words: rockfill particle, sub-critical model of crack expansion, particle breakage, stress intensity factor, relative humidity