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Top1. Introduction
Blasting is the most popular means of excavation for tunnels despite the rapid developments in the mechanical excavators, namely, tunnel boring machines, road headers, continuous miners. Faster drivage rates are possible with the recent developments in explosives (emulsion), initiating systems (NONEL, electronic detonator) and drilling (automation) systems. However, longer pulls, associated with high concentration of explosives, often lead to overbreak due to excess ground vibrations. Overbreak can become an expensive phenomenon in terms of extra concrete backfilling and may also give rise to additional mucking time. Most of the existing controlled blasting techniques, to reduce the blast-induced overbreak, need extra drilling, in turn, adding to drilling and blasting cost and time. Blasting in tunnels aims at the following objectives:
Thus, it is rational to assess blast-induced overbreak in production blasting and control the same by modifying the blast design.
Top2. Previous Work
Overbreak is largely affected by a host of rock, blast design and explosive parameters. Several researchers have attempted to study overbreak/blast-induced rock damage either based on experimental studies or relating some of the above influencing parameters. A brief discussion on the previous works is provided in the following section.
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