Board of Water Supply. City Water Tunnel No. 1. Illustration of tunnel excavation by drill and blast method. To advance the tunnel excavation, holes are drilled in the rock face then filled with explosives. Shooting is the activity of blasting the explosives to break apart the rock. Muck is the rock and mud debris that must be cleared from the tunnel after each blast. This operation was repeated in sequence until the tunnel was fully excavated. April 1914.