The size of the damage zone in relation to the linear charge concentration

To evaluate the relation between the linear charge concentration (LCC) and the damage zone a project was initiated where six different charges and explosives were tested, ranging in LCC from 80 g/m to 3.7 kg/m. Test blasts were performed in a Swedish aggregate quarry consisting of hard crystalline rock (granitic gneiss). After the test blasts one rock core for each explosive was drilled, in a horizontal direction, starting at the remaining half cast on the rock face. A number of test methods were used in order to log the extension of blast damage along the rock core. As a first step, conventional fracture mapping was performed on the cores to detect visible damage. The cores were then split into approx 10 cm long rock samples. On each sample ultrasonic velocity, porosity and density were measured. The methods were used to show variations in material properties. Reliable estimates of the damage zone from each explosive could be made using the combined results from these methods. The determined depth of the damage zone varied from 0.14 m to 2.42 m and a good correlation between the LCC and the depth of the damage zone was found and could be expressed by an empirical formula. The measured results compared favourably with two other empirical formulas taken from literature (Sjöberg et al. 1977, SRA 1991)