Patent ID: 6431075
Filing Date: 2002-08-13
Classification: F42D

Abstract:
A center-cut blasting method for tunnel excavation, comprising the steps of:drilling a single central center-cut hole at the center of a center-cut region, drilling a plurality of auxiliary center-cut holes comprised of large unloaded auxiliary holes and loaded auxiliary holes that are alternately arranged around said central center-cut hole to be situated in a circle having a predetermined diameter, and drilling a plurality of spreader center-cut holes outside said auxiliary center-cut holes to be situated in concentric circles centered by said central center-cut hole; loading said center-cut holes with delay detonators and explosives and stemming said center-cut holes with stemming material at their entrances; blasting the loaded auxiliary holes of said auxiliary center-cut holes so as to create a circular pre-split; blasting said central center-cut hole so as to create initial dual free surfaces; and sequentially blasting said spreader center-cut holes with a time delay so as to create final dual free surfaces.