Niagara Falls 100.000-Hp. Development

Niagara Falls 100,000 Hr. Development [31 First a drift A approxi- mately 7 ft. x 9 ft. was driven through to the upper portal, then the ribs and about 50 per cent of the bench B, and lastly the remainder of the bench C. Excavation of the drift was naturally the most difficult op- eration, as the drilling and shooting of portions B and C more nearly approximated that of open excavation and were quite rapid. During ex- cavation of the drift the work was carried on in two shifts of eleven hours each, working seven days a week. For the lower two-thirds of the 45° tunnel, each shift was able to drill and shoot a heading, averaging about 7 ft. each shot. Above that the prog- ress slowed down owing to the difficulty of getting the heavy equipment of the 45° slope and also to the wet working conditions. The drills, columns, and other equipment were hauled up the long slope by a rope passing through a block attached to an eyebolt in F1G the roof. The planking and 8 x 8-in. timbers for staging were first hauled up and placed and the heading was then scaled, after which the columns and drills were hauled up and set up in place. The electricians and pipefitters went in as soon as possible after the rounds had been shot to make any repairs that had to be made to the lighting circuit and to the air and water lines. After about 100 ft. up on the incline the air became so bad that an exhaust fan had to be installed and an 8-in. suction pipe attached to the roof of the tunnel. An auxiliary pump also had to be installed to keep up the water pressure. The field party consisted of a chief, a transitman, and two chainmen. They gave two headings in each of the three tunnels every day as a rule, checked their lines and bases, estimated quantities, etc. As a rule they laid out the grade and roof line while the drillers were getting their material together. Grades as well as line were given with a transit using the vertical arc and correcting for distance of set-up above center line, which on a 45° slope was normal distance times the secant of 45° (1.414) equals the vertical distance. On the lower curve the horizontal and vertical pro- jections were both parabolas owing to the circular curve being on an inclined plane. About five points on the curve were calculated for their projections and were then plotted up on cross-section paper and the curves were then drawn through them, prints made and fur- nished to the field party. In laying out the heading on the curve, the field party could always tell how far to the right and above the center of the horizontal section the center line was at the heading by picking the points of the curve without any long calculations of parabolic 43—BEHIND THE FOREBAY COFFERDAM formulæ. They could also tell the heading foreman just how much he had to point his drills up for the next round of holes. The rock on the lower horizontal section was hard Medina sandstone. Above this, at the upper end of the curve, was a thin layer of shale overlaid by about 12 ft. of the Clinton ledge of limestone. A small amount of seepage was encountered in this shale in each of the three tunnels, while in the first one a drill opened up a water pocket which flowed for about twenty minutes and had a very strong sulphur smell. Above the Clin- ton limestone the tunnel went through approximately 100 ft. of shale, which was soft and stratified at the lower end and which shaded into an unstratified slate just under the limestone at the top. For the remainder of the distance limestone was encountered, varying from hard blue limestone just above the slate to well- seamed limestone near the top. The slate formation underneath the limestone was so hard that the drillers insisted that they were in the limestone heading before they really reached it. The seepage in the upper part of the shale and lower portions of the limestone was such that it resembled a rainstorm, while considerablo seepage was again encountered in the upper end. The concreting of the lining was carried on in sev- eral independent operations in order to co-ordinate with the other work above and below the bank. On the lower curve a 15-in. concrete invert section was first built with slots and pipe for the reinforcing. The wooden ribs were then set up and lined and then the wooden lagging placed. Two rows of circular rein- forcing bars were then placed and the concreting done through chutes from the upper end of the tunnel. This