Vertical Retreat Mining of Drop Shafts Saves Time and Money on Atlanta's West End Combined Sewer Overflow Tunnel Project

摘要

Initial planning called for three separate drop shafts and three separate vent shafts to be pulled back from the excavated tunnel with a large diameter raise bore machine. With time constraints and the raise bore machine already in high demand on other shafts, a more "traditional" drill and blast approach was taken on a few of the larger drop shafts. This decision proved to be not only cost effective, but also time-saving as the shafts were excavated simultaneously with the other raise bores.