Excavation of pilot hole of pressure shaft by raise boring machine in Dhauliganga H.E. project, stage-Ⅰ

摘要

Excavation of deep shafts is a challenging task specially in the Himalayan media comprising heterogeneous rock mass and adverse jointing pattern giving rise to the difficult situation in construction. Further construction of shaft by conventional methods is time consuming and due to the presence of weaker rock, it is sometimes impossible to deploy the raise climbing equipment for raising shafts for safety consideration. To cater to the need of faster and safer construction of shafts, raise boring machines are widely used world over. In the construction of shaft, a pilot hole is of great importance which facilitates further widening of pilot hole to the required size as excavated muck will fall in the bottom of the shaft and same can be removed by deploying loader and tippers as against sinking of shaft in which excavated material is to be lifted up against gravity. In construction of shaft by raise boring machine, first a pilot hole of 10″ or 12″ dia is drilled from the top which is reamed subsequently to the designated dia by raising from bottom to top through pilot hole (10″ or 12″) by the reamer head attached to the drill rod of RBM in the bottom of the pilot hole.