Estimated 30 LF of cover to the top of the tunnel, then 20’ from the top of the tunnel to the floor of the tunnel. Estimated the tunnel to be 20’ wide. Drilling of 8 boreholes at 6" diameter for filling in the void of the tunnel. Each hole to be 50 ft deep (run the drill rods to the floor of the tunnel to the bottom which would equal 50 LF deep) * X 50 = 400 LF of grout hole drilling type 1 drilling (to include a contingency of 150 LF is added in case a few more holes would be required). Use 10' of casing per borehole as a safety factor to prevent cave-in of soft overburden - to be included in above item. Cofferdam boreholes will be required on each end of the tunnel to contain the grout. Drill 3 holes on each end of the roadway , either an 18" or 24" diameter size. These holes would only be 30 LF deep or thru the top of the tunnel, thus a total of 6 holes at approximately 30 ft (+6' contingency) deep each totaling 180 LF (216 LF total with contingency). We estimate approximately 180 tons of #4 stone to be used on each end to build the grout containment dam.
