On straight arch work they placed 24.1 cu. yd. daily at a cost of $0.74 per cu. yd. In three days' work on a curve, the same gang placed 26.37 cu. yd. daily at a cost of $0.675 per cu. yd.
On centering and steel for arch, three men kept up with the regular progress of the arch-concreting gang. The cost, therefore, is:
| 1 man | $3.50 |
| 2 men at $1.75 | 3.50 |
| —— | |
| $7.00 |
They averaged 13 ft. daily, or at a total cost of about $0.54 per lin. ft. of sewer.
Two-thirds of this labor was on the centering or $0.36 per lin. ft. of arch; $0.18 per lin. ft. placed the steel ready for embedding, or about 55.5 lb. per ft. of arch, at a cost of 0.32 of a cent per lb.
For the double ring brick lining at the bottom, the regular daily rate of progress was 28 ft. or 11.15 cu. yd. with:
| 2 bricklayers | $11.20 |
| 5 men at $1.75 | 8.75 |
| 1 man at $2.25 | 2.25 |
| —— | |
| $22.20 |
or at a cost of $1.98 per cu. yd. This is given only because it is of interest in connection with the cost of the concrete.
Other observations on cost of placing steel skeleton and concrete did not vary materially from the figures given. It will be observed that no charge for superintendence or anything for the general expenses is included in the estimates of cost. These charges were, of course, impossible to obtain. On another contract with machine mixing, as high as 36 lin. ft. of 13 ft. 6 in. arch were built in a day, but no data as to cost were taken, though it was evidently less than for the work with hand-mixed concrete.
REINFORCED CONCRETE SEWER AT WILMINGTON, DEL.—Records of a notable job of sewer construction at Wilmington, Del., in 1903, are furnished by Mr. T. Chalkley Hatton. The sewer was built by day labor for the city; its cross-section at various points is shown by Fig. 265. The cross-section of sewers in trenches deep enough to cover the arch are marked "deep cutting"; the sections where the arch projects above the ground surface are marked "light cutting." The section through the marsh was 700 ft. long, the cutting being 8 ft. deep, and at high tide the marsh was flooded 1 to 4 ft. The material was a soft mud that would pull a tight rubber boot from a workman's foot. The cost of this marsh excavation including cofferdams, underdraining, pumping, etc., was $4.60 per cu. yd. For 1,100 ft. the 9¼ ft. sewer was through a cut 22 to 34 ft. deep, the material being clay underlaid by granite. A Carson-Lidgerwood cableway was used. Although the crown of the arch was but 8 ins. thick, it withstood the shock of dumping 1 cu. yd. buckets of earth and rock from heights of 3 to 10 ft.; and the weight of 25 ft. of loose filling caused no cracks in the concrete.