METHOD OF TUNNEL CENTER CUTTING BY LARGE EMPTY HOLES AND PRE-SPLITTING

摘要

PURPOSE: A method is provided to easily maintain two free surfaces through relieving an initial base rock constraining force by a pre-splitting blasting of large empty-and discharge holes in a concentric circle as a center cut subsidiary function of a center cutting area. CONSTITUTION: A method comprises a step of forming the center cut holes of a single center cut hole(7) as a discharge hole at the center of a center cut area, large empty holes(5) in a concentric circle with a radius centering around the single center cut -sub drilling(8) arranged alternately at regular intervals, discharge holes(6) arranged at regular intervals per stage in a plurality of concentric circles with each fixed radius respectively in sequence order from the center cut sub drilling(8) outwards, a step of pre-splitting blasting in a circular form of the center cut sub drilling(8) in a concentric circle formed of large empty holes(5) and discharge holes(6) functioning a man made small free surface during blasting, a step of maintaining an initial surface(F2) by forming a circular center cut after a single center cut hole(7) at the true center of a center cut area is blasted, and a step of blasting of center cut enlarged holes(9) in concentric circle per stage with a time lag in sequence order. So the tunnel center cut method is achieved by large empty holes and pre-splitting.