Fracture path of cracks emigrating from two circular holes under blasting load

Abstract

In rock excavating and mining, blasting a row of circular holes is a common practice. It is often observed that cracks emanating from two adjacent holes tend to avoid each other when closely approached and form a hooked or butterfly-shaped loops. Five crack models were designed in this paper to study the propensity of forming the hook pattern. The five models are to simulate geometric imperfection in the field or laboratory for the two borehole case. Using the T-stress at the crack tip, the incremental crack growth method is adopted to simulate the crack propagation paths. The results showed that: (1) the T-stress values calculated from the first two models are negative, indicating curving (or hooking) cannot occur, (2) the T-stress at the crack tip is positive in the third model, and therefore crack curving (or hooking) may occur, (3) unlike the first three models, the fourth and fifth models are mixed mode I/II crack geometries and the mode II stress intensity factor dictates the crack curving direction, (4) the hook pattern would indeed happen under certain conditions.