Abstract

Drilling of rocks through the conventional techniques of percussion, rotation, or combined percussive rotational loading methods consumes a huge amount of energy and time to obtain the required hole length for a definite application. Controlled blasting could be one of such techniques to drill holes through rocks which have been seldom explored in the literature. The present work focuses to study the effect of the application of shockwaves for drilling purposes. First, the drilling efficiencies for both percussive and rotational drilling techniques were studied numerically by varying the drill rod diameters and by keeping the velocity of the drill rod constant. The geometry of the rods taken for the present study is cylindrical in shape. The extent of damage in the rock domain was assessed and compared for both percussive and rotational drilling techniques with cylindrical drill rods of the same diameters. It was seen that the extent of damage increases with increase in the drill rod diameters for both percussive and rotary drilling techniques keeping the velocity of the drill rod constant. The numerical model was developed in the finite element package, ABAQUS 2017. The Mohr-coulomb constitutive model is used for the rock domain and the Johnson-Cook model was used for the drill rod. A comparative analysis was done between the stresses and deformations generated in both rotary and percussive drilling techniques for a particular drill bit diameter. Thereafter, the loading rate was increased to 25 m/s for percussive drilling only with one diameter of drill rod, i.e., 0.25 m and the results were compared with drill bit velocity of 1 m/s. The extent of damage was studied under shockwave loading and compared with the results obtained for the percussive drilling with nominal drill bit velocity of 1 m/s. The suitability of the shockwave that could be imparted to a rod for drilling a hole in terms of stress and deformation yielded in the rock is also numerically assessed.

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