Engineering and Contracting . reinforced with two plates. Xo manholes were built and no lateral con-nections were made, but 24-in. tile were setin the arch at intervals for future contract specified a concrete composedof 1 part Portland cement, 3 parts sand, and•5 parts crushed stone or gravel; the engineer,under the specifications, having the right tovary the proportions of fine and coarse ag-gregate, but maintaining the proportion of 1part cement and 8 parts aggregate. Gravelproved very satisfactory. The mix was fairlywet, except on the crown of the arch, wherea dry mix was n
Engineering and Contracting . reinforced with two plates. Xo manholes were built and no lateral con-nections were made, but 24-in. tile were setin the arch at intervals for future contract specified a concrete composedof 1 part Portland cement, 3 parts sand, and•5 parts crushed stone or gravel; the engineer,under the specifications, having the right tovary the proportions of fine and coarse ag-gregate, but maintaining the proportion of 1part cement and 8 parts aggregate. Gravelproved very satisfactory. The mix was fairlywet, except on the crown of the arch, wherea dry mix was necessary to prevent the con-crete running. The average progress per day of 0 hourswas 30 ft. for both shovel and mixer, for theplain section. This means 420 cu. yds. of ex-cavation, with disposal in backfill or spoilbank. The actual cost of excavation, backfill,and spoiling can be seen by reference to Table1. The concrete averages 2% cu. yds. per ft. £* 10 , , , ,. ..^EyfensionScrew ^-^-^^«=^«^:.«...,?x4 Loose BrickidSupport Center Fig. 4. Tunnel Section of So. 52nd Ave. Sewer Showing Invert Built, Timbering Removed and Centers Set for Arch. A daily average of 7-) cu. yds. was average progress per day on the rein-forced section was 24 ft. per day, the .slowingup being due to the time used in placing thereinforcing steel. On the same platform with the mixer wasmounted a small lioom derrick and hoistingengine. This facilitated the renioval otstringers and braces, and pulled the mixerplatform back and forth. The material forconcrete was delivered to a platform laid onthe ground alongside of the mixer, beinghauled in 4-cu. yd. dump cars by dinky en-gines an average distance of % mile. Reinforced Section.—This section is of thesame dimensions as the plain, but was rein-forced to strengthen the conduit where itpassed under railroad property. The samemethods of construction were used as on theplain section. The reinforcing steel averaged44 lbs. to th
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