Influences of the burden on the fracture behaviour of rocks by using electric explosion of wires

The burden is one of the most important parameters in the blasting operation of rock engineering, so it is essential to evaluate its influences on the fracture behaviours of rocks. In this work, blasting experiments on cement mortar samples were conducted with different burdens by taking the electric explosion of wires as the explosion source. Then, the fracture process of samples was revealed based on images captured by an ultra-highspeed camera. Changes in the scope of the fractured zone with the burden were quantitatively evaluated. Experimental results indicate that fractures on the free face are composed of transverse, longitudinal, oblique, and circular cracks. As the burden increases, the initiation time of cracks on the surface delays, accompanied by a decreased degree of fracturing on the free face. Meanwhile, the explosive load causes formation of a cratershaped fractured zone in the samples. With the increase of the burden, the short axis, perimeter, and volume of the fractured zone all tend to increase, then decrease. The finite element program ANSYS/LSDYNA was used to perform numerical simulations. The simulation results were compared with the fracture mode of the free face and the fractured zone in samples in the experiments. Besides, the damage and fracturing patterns inside the samples were further investigated based on the numerical simulation results.