Blasting technologies for tunnelling and underground construction

Abstract

The methods of forming excavations, tunnels or underground chambers in rock rely on either blasting or mechanical boring machines. In both cases, the aim is to create the excavation rapidly while ensuring the remaining rock incurs minimum damage in terms of its ability to maintain the desired excavation shape, but also to restrict the extent of support requirements. Advances in the technology of mechanical excavation methods have developed in tandem with various aspects of material science and mechanical design of machine components. Advances have also occurred in blasting technologies which sometimes go unnoticed. The present paper elaborates on blasting technologies that deliver significant benefits in hard rock excavations. In particular, the advent of new, purpose-designed explosives and loading systems have demonstrated benefits in logistics, fume control, safety, fragmentation and blast-induced damage control. Explosives are now loaded in blastholes using sophisticated remote control techniques which keep operators away from regions of potential concern. Once the explosives are loaded, revolutionary electronic delay detonator systems provide unique opportunities to release the explosive energy in a controlled and engineered manner. Such approaches have the potential to yield lower blast-induced damage, lower ground vibrations - either through extended timing approaches or in spectral content control, and improved excavation shape control. A number of case studies will be presented to demonstrate the types of improvements and success offered by the blasting technologies. The benefits are identified and delivered as cost savings in excavation, support and lining as well as improvements in safety and project risk management, reduction in nuisance and increased community utility. In some cases, these areas of specific interest have been benchmarked using packaged explosives and then reviewed after conversion to bulk emulsion technology and the changes are quantified in the case studies. In this paper the authors seek to indicate where further significant improvements can be realised in construction over traditional drill and blast methods. Whilst there is a limit to the amount of experimentation and measurement that can take place in a construction project without starting to adversely impact on progress, it appears there is still more scope to improve performance and reduce costs. This paper demonstrates how suppliers are working with contractors to improve overall performance as well as focus specific requirements. The application of new technologies coupled with greater knowledge of explosives/ground interaction have reduced or eliminated many of the undesirable side effects experienced in the past, and will continue to deliver improvements. (A) Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.