Analysis of the impacts due to Drill and Blast excavation

Drill and Blast is one of the most used techniques for rock excavation, especially in the mining industry. If compared to mechanical excavation, it has the advantage of being more versatile and more cost-effective on the point of view of the specific energy spent, since a large amount of the excavated volume is directly fragmented through the energy released by the explosives. The explosives adopted in the blast are high explosives, being able to react, upon detonation, with the contribution of a high shock wave energy and the expansion work of the gas released. However, the use of explosives, associated to the other activities involved in the drill and blast technique can have negative consequences on the environment surrounding the construction sites, bot open-cast or underground. The main issues to be addressed are: blast induced vibrations, flyrock, airblast, dust and toxic fumes. In this thesis, the main problems caused by drill and blast are presented, and for each of them the main effects and the possible mitigation measures are provided. More specifically, blast induced vibrations and flyrock were studied more in detail since they represent the biggest challenges . Ground vibrations are always produced after a blast and can have a direct impact on the population and structures near the excavation areas or the tunnel under construction. The vibrations induce dynamic stresses into the rock mass and can cause damages to the nearby structures. The typical approach to predict the induced vibrations was presented from a theoretical point of view and from a practical perspective, by the analysis of a monitoring campaign performed in a limestone quarry located in Tuscany. The flyrock phenomenon is another unwanted consequence of the drill and blast process and it consists of rock fragments that are thrown great distances from the blast site. It represents one of the most undesired phenomena, since even a single rock fragment can cause a possible death. The phenomenon is presented from a theoretical point of view with details on the possible causes and mitigation measures. The theoretical considerations are then applied to a flyrock accident occurred in a limestone quarry located in Lombardy, with a detailed analysis on the possible causes and with proposals for practical solutions to the problem. This study provides useful insights for minimizing the potential impacts caused by drill and blast activities and underlines the concept that a well-designed blast always serves as the first preventive measure.