METHOD OF MIXING AND PLACING CONCRETE FOR A TUNNEL LINING.—The tunnel known as the Burton tunnel is located on the Jasper-French Lick extension of the Southern Ry., and about 4 miles from French Lick, Ind. It is a single track tunnel 2,200 ft. long with 300 ft. at one end on a 4°-30' curve and 1,900 ft. on tangent. The material penetrated was slate and loose rock, requiring solid timbering throughout. This timbering is shown by Fig. 138, which also shows the concrete lining; the timbering was embedded in the concrete lining.
Fig. 138.—Sections Showing Concrete Lining for Burton Tunnel.
The original timber lining was composed as follows: Posts 10×12 ins. and spaced 3 ft. apart were set on 3×12-in. sills and carried 10×12-in. wall plates which supported 10×12-in. segmental arch ribs spaced 3 ft. apart. The lagging behind the posts was 3×6-in. stuff and the lagging over the arch ribs was 4×6-in. stuff. The section of the concrete lining is shown by Fig. 138, it required 4,132 cu. yds. of concrete and 161.43 lbs. of reinforcement per lin. ft. The concrete was a 1-2½-5 crushed stone—between 2 in. and ¼ in. size—mixture; it required 1.16 bbls. of cement, 0.52 cu. yds. sand and 0.92 cu. yds. of stone per cubic yard of concrete. The amount of reinforcement per cubic yard of concrete was 39.1 lbs.
Fig. 139.—View of Mixer Plant Showing Car Tracks, Burton Tunnel.
Fig. 140.—View of Mixer Plant Showing Method of Unloading Materials, Burton Tunnel.
All the concrete was mixed and handled from one end of the tunnel. The mixing plant was located in the approach cut at one end. A standard gage main track ran through the cut. About 20 ft. in the clear to one side of this track a trestle 500 ft. long was built, carrying an 18-ft. gage derrick track and a narrow gage 3-cu. yd. dump car track. A stiff leg derrick operating a 1 cu. yd. orange peel or a 1½ cu. yd. clam-shell Hayward bucket was mounted on a carriage traveling on the 18-ft. gage track. The side of the trestle nearest the railway track was sheeted vertically and the space between this sheeting and the track was floored over at track level for stock piles. Near the end of the trestle toward the tunnel and on the same side of the track was the mixer plant. This consisted of two 85 cu. yd. bins, one for sand and one for stone, carried by a tower so that their bottoms were 25 ft. above track level. Below the bins was a charging platform pierced by a measuring hopper. Below the measuring hopper was a 1½ cu. yd. cubical mixer and below the mixer was a 3-ft. gage track for 1½ cu. yd. Koppel side dump cars. To the rear of the tower at ground level there was a 20-cu. yd. sand bin and a 20-cu. yd. stone bin set side by side with a continuous bucket elevator leading from each to the corresponding bin on the tower. The cement house was located directly across the railway track from the tower. At the side of the cement house nearest the track there was an inclined bag elevator leading up to a bridge spanning the railway track at the level of the charging floor of the mixer plant. On this bridge ran a car for carrying bags of cement. The plant as described is shown by Figs. 139 and 140.
In operation the derrick unloaded the stone and sand cars by means of the Hayward buckets either into the bins at the feet of the bucket elevators or onto stock piles on the flooring beside the trestle. When put into stock piles the materials had to be reloaded by derrick into the 3 cu. yd. cars on the trestle narrow gage track and carried by these cars to the elevator boots. The sand and stone were chuted from the tower bins directly into the charging hopper below. Here the cement bags, brought across the bridge on the car into which they were loaded directly by the bag elevator, were opened and the cement added to the sand and stone. The charge was then dropped into the mixer and from the mixer the batch dropped into the Koppel concrete cars.