Chicago : Engineering and Contracting Pub. Co. · leaf 390
heshaft bottom and was bored in an easterlydirection at an elevation of 25°. The maximumrate of boring was 4.3 ft. in one hour and theaverage rate was 1 ft. in one hour. The workwas begun Sept. 26 and completed Oct. 15,boring double shift to a depth of 318.75 ft.The material encountered consisted… … EngHContg Figs. 1 to 3—Sketches Showing Use of LoneColumn Arms for Drills in Tunnel Work. Another hole bored from the same locationas the one just recorded was drilled at an ele-vation 45°. The fastest rate of boring was 4ft. 2 ins. in one hour and the average rate was1 ft. per hour. Drilling…
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Internet Archive · University of Illinois Urbana-Champaign · Public Domain Mark 1.0. Free to use for anything.
