Correlation of Q System with Underground Excavation by Drill and Blasting

Abstract

Rock excavation of underground spaces is extensively used in developing countries to construct hydroelectric-power plants, pumping stations, waterways, railway, and traffic tunnels, and many more of such projects. Rock excavation is mostly carried out either by tunnel boring machine (TBM) or by drill and blast method. Excavation of large volume of rock by drill and blast method produces Excavation Damaged Zone (EDZ) around the periphery of the tunnel or shaft. It is necessary to calculate the extent of blasting damage for accurately designing the support works. This study presents the influence of EDZ on rock mass classification and support system during shaft construction in dolerite rock. The vibration wave characteristics and parameters for evaluating the blasting impacts and subsequent changes in stress conditions were numerically simulated in FLAC3D. Field excavation data was used to modify the Q-system for EDZ determination. The extent of EDZ was calculated with the help of software as well as analytical solution and the minimum of the two was used as the zone from which the core was extracted for the evaluation of modified value of rock quality designation (RQD). The borehole investigation data before the actual excavation exhibits the RQD as 40% which was observed to get reduced to 30% after blasting. The results show the Q-value decrease up to 25% in the EDZ of dolerite rock due to blasting effects.