Investigation on Rock Fracturing in Presplit Blasting Under Various Initial Stresses

The evolution characteristics of rock fracturing in presplit blasts are generally affected by in situ stress resulting from tectonic forces in the Earth’s crust and from gravity. In this study, rock fracturing under coupled static stress and presplit blasting conditions is comprehensively investigated by combining experimental, theoretical and numerical methods. Model tests of two-borehole presplitting on 200 × 200 × 50 mm granite samples are carried out using a biaxial hydrostatic loading system, and blast-induced rock fracture is identified using high-speed digital image correlation. The postblast granite samples are further image processed using ImageJ to show the detailed rock fragmentation and fracture networks. The rock fracturing behaviours and fractal characteristics in presplitting under various biaxial and uniaxial stresses, and under constant uniaxial stress with different β values (angle between the orientation of uniaxial stress and the line connecting blastholes), are examined. Blast tests show that the number and length of blast-created fractures in presplitting decrease with increasing static stress, and thus, presplit crack formation gradually fails, producing a rock crack pattern with relatively low fractal dimension and fractal damage levels. Moreover, the formation of crack coalescence fails between presplit holes, and the damage to the remaining rock significantly increases when β is larger than 15°. Then, the variations in crack patterns in recent presplitting tests are analysed based on elastic mechanics by calculating the transmission and superimposition of detonation stress waves and the static stress distribution near presplit holes. Later, after performing numerical verification, the rock fracturing processes in presplitting are numerically modelled in LS-DYNA. The influences of boundary conditions on presplitting test results and the implications of the recent findings for practical presplitting are discussed accordingly.