Optimization of the blasting design in the excavation of tunnels in rock

摘要

The design of blasting operations was based for decades on the adjustment of older successful schemes to the geometric conditions of the new excavation and to the local rock mass characteristics, applying a process of cut and try that is very much dependent of the executive technician's personal expertise. In this case it is very difficult to proceed with simulations of the blasting operation in order to analysze cost and rock break optimization, because there is not applied a well defined calculation method that takes in sense the rock and explosive characteristics. The common practice in drilling and blasting operations in tunnels and galleries, is to use drilling patterns with equal diameter blast holes, except for the central cut hole which has bigger diameter in order to act as a free surface to the detonation, in accordance to the particular cut configuration. This makes the operations easier, reduction bit changes to once and reducing the need of drill steels (bits) storing to only two types. Some researches in drilling patterns with multiple diameters to blast floor and contour holes, shows that it is possible to obtain better rock fragmentation and productivity at lower costs. In this paper a computational methodology is presented that allows blasting design using information like excavation geometry, rock mass geomechanical parameters, explosive technical properties, hole size, type of cut, cost parameters, plasting vibrations re-strictions and smooth blasting at the excavation contour. This paper also discusses operational aspects of the two methods and analyzes blasting operation performance parameters like: specific and total charge, specific and total drilling meters, ratio (rock blasted volume)/(meters advanced) and ratio (charge)/(drilling meters).