Explosive Testing by Single Hole Blasting in Model SHB-MS and Full-Scale SHB-FS

摘要

The selection of the correct explosive properties for a certain kind of rock mass is still today a difficult task. By tradition it was said by experience that explosives with low detonation velocity and high gas production should be used in soft rocks and explosives with high detonation velocity and low gas production should be used in hard rocks. A scientific well proofed explanation was lacking. The goal was therefore to find a method to study how the explosive properties should be matched to the rock mass properties. The method, developed in 1983 at Lulea University of Technology LTU, was named the single hole blasting method in model SHB-MS. The single hole burden is varied in blocks 100mm x 300mm x 300mm in size from very small burdens up to the critical burden (the smallest burden without breakage). Totally 6 different rock or rocklike materials were tested. All possible result parameters were studied at each burden like fragmentation (sieve analysis), back break depth, crater size at the top and bottom of the block etc. The result shows that the specific charge is the most important parameter for the fragmentation but also the burden and spacing and the acoustic impedance plays a significant role. Other important fragmentation factors are also the number of joint sets and there orientation compared to the blast direction. This influence was studied in other model blasts not reported here. The SHB-MS method was expanded to full-scale tests, SHB-FS, in Stomgns limestone quarry on Gotland in Sweden and was followed later on by SHB-FS in Turkey, in Divrigi hematite and later also in Tamtas Limestone both reported by Bilgin. In the SHB-FS tests in the Storugns limestone quarry the blast direction for 4 burdens had to be changed by 62° due to the limited space in the quarry for the SHB-FS tests. The fragmentation gradient n and critical burden Bc were best correlated to the acoustic impedance Z both in model and full-scale but a good correlation was also achieved between critical burden and tensile strength of rock σt in the LTU SHB-MS tests. The angle of breakage was best correlated to the burden both in SHB-MS and SHB-FS in Sweden but also in the SHB-FS blasts made in Turkey. This paper is a summary of the following three papers Rustan et al 1983, Rustan and Nie 1987 and Rustan and Kumar 1999. The suggested test procedure for SHB-FS blasts is given in the Appendix. For a nation to be leading in rock blasting it is necessary to perform SHB-FS tests to learn more about the transmission of energy between explosive and the rock mass and also to get basic data for calibration of computer fragmentation models. At the end of the paper several recommendations are made for future research where a new mismatch impedance theory has to be developed for supersonic velocities used in blasting. Acollaboration with detonation physicists and military researchers for measurement technology will be necessary.