Niagara Falls 100.000-Hp. Development

32 J Niagara Falls 100,000 Hp. Development FIG. 44—TUNNEL HEADING OF PENSTOCK—OUTSIDE CUT ABOUT 20 FT. DIAMETER section was the only one on which reinforcing bars were used. The seepage was taken care of by an 8-in. wrought- iron pipe emptying into the tailrace. A T was placed at the end of every 20-ft. section and a short length of 4-in. pipe and elbow attached to each side. Just below each elbow a dam was built out of sacks of concrete and just before the concrete reached the top of them they were covered with a piece of canvas and a few more sacks of concrete, thus leaving a permanent drain. The bell-mouth section was concreted around wooden forms with a bulkhead between each tunnel. Concrete was carried to a height of 25 ft. above the bottom in a solid mass. The first pour was about a foot above the bottom so that the forms would not float, the second pour to slightly above center line, and the last pour to about 4 ft. above the highest part. The steel guides for the gates, anchor bolts for the racks, etc., were all set in places before concreting. It was the original intention to concrete from the top of the lower curve to the top of underground por- tion with steel forms and then to connect the tunnel concrete with the bell-mouth section with wooden forms on the upper curve. However, as it was deemed advis- able to rush the steelwork of the gatehouse in order to be able to use the crane, it was decided to concrete in the entire upper curve before doing that of the 45° slope. This necessitated making the joining at the top of the slope entirely underground. Pipes were placed along the roof of the curved section so that the slope below could be concreted at the connection. On the 45° slope Blaw-Knox steel forms were used, having a diameter of 15 ft. 6 in. and a length of 5 ft. Twelve complete sections of forms and five extra invert sections were used. Concrete in this section was con- tinuous from bottom to top, never being less than four batches per hour or just enough so that the top con- crete had not set up when a new batch was poured. It was found that by having the men walk around and stir- ring up the top that so-called mud seams or seepage rings were prevented from forming. Forms were only moved during the day shift and iron workers were employed for this work. After the first two days in getting acquainted with their equipment and making a few minor changes in the traveler, they averaged four sections or 20 ft. each day. The traveler was moved by a hoist at the top. Besides the. crew of five iron workers on the forms, there was a concrete crew of three men taking care of the concrete as it came through the chutes from the top. Lastly the steel lining was placed and concreted around. The steel plates were assembled under the crane in the Johnson valve chamber and when riveted were skidded back and new sections attacked. This steel lining extended 68 ft. in from the edge of the cliff. The diameter was 15 ft. 6 in. except where con- necting to the Johnson valve, at which point it was 17 ft. With the steel penstock in place the Johnson valve was next assembled and connected to the steel lining and the wheel case. Riveting was then completed, burnt rivets being cut out and replaced by new ones., In the majority of cases, however, it was found that the elec- tric weld on the rivet gave excellent results and made a tight' job. After the riveting was completed and all connections made, the portion under-ground was concreted in, grout pipes being placed along the roof through which grout was afterward forced under air pressure to fill any cavities along the roof which could not be concreted. At the lower end of the curve, where the joints in the concrete were made, a small keyway was left which was painted with soft asphaltum to prevent leakage in case of contraction. Several boxes were also placed at the joint with f-in. pipe leading from them into the open at the testing chamber so that any leakage froin contraction at the joint would show. FIG. 45—FORM FOR CONCRETING PENSTOCK TUNNEL. CLEAR DIAMETER 15J FT.