Modeling of Blast Induced Damage Distance for Underground Tunnels

One of the terminology which quantifies the amount of damage to the tunnel face, invert, crown, and sidewall is damage distance. It is the minimum distance where blast provoked discontinuities are formed beyond the periphery of newly excavated face. This distance mostly contains the unnatural discontinuities developed due to blasting. In order to cater to the uncertainties and prediction of large numbers of outcomes for different combinations of controllable and uncontrollable parameters, probabilistic analysis has been carried out in this study. As input for probabilistic analysis, the controllable parameters taken into considerations are maximum charge per delay (W), perimeter charge factor (P), specific charge (q), and as uncontrollable parameters rock quality index (Q). Data has been compiled from the literature pertaining to three different underground tunnels. The relationship between damage distance and the input parameters have been determined by drawing scatter plots implementing simple regression. These input have then been used to develop a deterministic model for prediction of damage distance. Following this, the probabilistic analysis employing Monte-Carlo (MC) simulation has been carried out. The existing blast design has been found to have 100% probability of occurrence for damage distance greater than 1 m. The occurrence of 1 and 2 m damage distance has been found to be inevitable. In order to mitigate the intensity of damage distance, a proper blast design can be chosen by trial methods implementing probabilistic analysis.