Abstract
Blasting with longer advance per round leaves an impact both visible (in the form of overbreak) and invisible (cracks) in the surrounding rockmass, however, a number of controlled-blasting techniques, that is line drilling, pre-splitting, and smooth blasting, have been developed to minimise this problem. These techniques require additional drilling, controlled charging, and detonation, and thus, are not preferred in regular development activities. Investigations have been carried out in five different horizontal development drivages of metal mines to assess the blasting impact using burn cut and arrive at the blast-induced rock damage (BIRD) model. Vibration monitoring close to the blast was carried out using accelerometers for the first time in India to develop vibration predictors and overbreak threshold levels for individual sites. This paper reports the development of the overbreak predictive model (BIRD) for burn cut blasting in hard rock drivages by combining the relevant rock, blast design, and explosive parameters. A multivariate statistical model has been developed and validated and the same can find ready application in tunnels and mines for exercising suitable engineering controls both in blast design and explosive selection for reduced basting impacts.
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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