Two-dimensional theoretical model for design of burn-cut pattern

Excavation methods for underground drivage should be cost effective and minimise damage to the periphery rock wall. Among the various methods of excavating systems the ‘drill and blast’ method is the most commonly used because of the low capital investment required, its easy manoeuvring and excavating capability and the flexibility of changing the excavation profile if ground conditions necessitate. The burn-cut method of blasting is cost effective and has a good advance rate compared to other conventional drilling patterns. This paper investigates how errors in the burn-cut method can be minimised and how the parameters influencing the progress per round of blast can be optimised. The importance of drilling accuracy, low burden and heavy charge concentration for the initial holes of the burn-cut method of blasting is discussed. This paper proposes a conceptual mathematical model to enable a better understanding of the burn-cut method of blasting. The model assumes that the process of breakage for the initial holes is a slabbing action and uses the concept of the deflection of a cantilevered beam (rock strata between charge and relief hole) to explain the importance of deeper relief holes. The results of an experimental study conducted in one of the tunnels in the Dul Hasti hydroelectric project in the Himalayan region are also discussed.