Abstract
This study presents the formulation of an optimum design of smooth blasting using a manual drilling machine in hard-rock tunnelling and the cost estimation of overbreaking and underbreaking. The proposed design method aims to minimize the total expense of the extra concrete cost in the region of overbreaking and of the labour cost required to remove the unbroken rock in the region of underbreaking. The design variables is the collaring radius ΔR only. The calculated results indicate that the drilling precision of the look-out angle is the most important factor in the optimum design of smooth blasting in tunnelling, in the case of using a manual drilling machine. The results also indicate that 40% of the total expense can be saved by the improvement of drilling precision and the application of an optimum design.
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