Safe dismantling of unstable boulder using controlled blasting in the historical Town of Gaya, India

A torrential rain caused displacement of a big size boulder in Brahmayoni Hills which was situated in the historical town of Gaya in India, posing serious threat to many residential houses located below the boulder. The district administration had evacuated more than 70 families who were resided below the unstable boulder. A concrete support was constructed at the base of the boulder for temporary preventive measure and for the permanent solution, it was decided to dismantle the whole boulder using controlled blasting. The boulder was of gneiss granite rock somewhat pyramid in shape with irregular trapezium at the base having 16 m circumference and 8 m height. It was located in very congested area on the hill slope and the nearest residential house was situated at 2.3 m only. No machinery could be deployed for removal of any blasted materials due to unapproachability of the area. The dismantling work of the boulder was carried out in three stages using controlled blasting from top to bottom. Double-layered wire-mesh covering, anchoring with wire rope, double layer fencing below the boulder, conveyor belts and sand bags were used to control flyrock and possible rolling down of the blasted material. The blasthole diameter used was 32 mm drilled with jackhammer and depth of holes in the different stages of dismantling work varied from 1.2 to 1.75 m. The spacing of holes varied from 0.30 to 0.45 m and the explosive charges were distributed in the hole using decked charging to obtain smaller fragment sizes for manual removal of the blasted materials. This paper discusses detailed planning of the dismantling work, protective arrangements made, design of the blast and successful dismantling works of the unstable boulder without causing any harm and damage to the nearby habitant