Of this, 1726 feet was 9 feet 3 inches in diameter, 2426 feet, 6 feet 6 inches in diameter, 1374 feet, 6 feet in diameter, 804 feet, 5 feet in diameter, and 64 feet, 4 feet 9 inches in diameter. The accompanying drawings, Fig. 56, show the cross-sections of the different sizes. The engineer, Mr. Hatton, calls attention to the thin crown, only 8 inches for 9 feet 3 inches diameter, and to the fact that it proved strong enough to withstand the shock resulting from dumping a cubic yard of dirt and rock from the cable buckets from heights of from 3 to 10 feet, and the weight of 25 feet of loose filling, without any apparent fracture. In construction, both inner and outer forms, and lagging, were used, the latter being movable and placed consecutively from the invert up, as the concrete was deposited. The concrete consisted of 11⁄2-inch stones mixed with stone dust and cement in proportion of 1 cement, 2 dust, and 6 stone. The reinforcements for the largest size consisted of expanded steel 6 inches No. 6 gauge, lapped 1 inch. The other sizes were reinforced with a woven-wire fabric, mesh 6 inches X 4 inches, the wire being No. 8 gauge. The Paxton Creek intercepting sewer at Harrisburg, Pa.,1 was built in 1903 to take the sewage out of Paxton Creek and at the same time carry creek water enough to give a self-cleaning velocity on the necessarily small grade. The invert of this sewer is a short arc of a circle with tangents on each side which have an inclination of 3 to 1 as shown in Fig. 57. The larger section, shown in the figure, is 5 feet high by 6 feet wide, the arch being a parabola to the invert. The reinforcement is 3-inch No. 10 gauge expanded metal. The concrete was 1:2:42, and the invert was finished to the lines of templates set 12 feet apart. The arch centers were 2 X 2 X-inch steel angle bent to proper shape, spaced 3 feet 4 inches apart, the lagging being 2-inch pine plank 10 feet long. The thin arch was subjected to a severe test when a coal train was derailed on to the ground directly over the trench with only about 5 feet of filling, but no damage resulted. The following examples are given to show the construction where longitudinal and transverse rods have been used. Fig. 58 shows a section of reinforced concrete conduit used by the Jersey City Water Supply Company. The construction was of Portland cement concrete, reinforced with Ransome steel rods. The thickness of the sections, the size of the rods and their spacing, were modified according to the character of the soil and the depth of the cutting. Ninety per cent of the conduit, however, had the arch 5 inches thick, the haunches II inches thick, and the base 6 inches thick. The reinforcement consisted of cold twisted -inch square steel rods bent to the 1 Eng. Rec., Vol. 50, p. 444. 2 Eng. Rec., Vol. 49, p. 73. form shown in the drawings, spaced 1 foot apart, and of 1-inch longitudinal rods spaced 2 feet apart and wired to the transverse rods. The transverse rods were made of such lengths as to extend I foot below the bottom of the outside forms, below which the concrete was built against the hard earth or rock sides of the trench. TABLE OF SIZES AND REINFORCEMENT. Fig. 59 shows the cross-section of a large reinforced concrete sewer built (1907) in the borough of Queens, New York City. This sewer, nearly two miles long, varies in size from 2 to 15 feet in diameter. The drawing shows the 10-foot section, larger sizes having a double reinforcement, one row at the extrados and one row at the intrados. In the section shown the transverse rods are 11-inch Johnson corrugated bars spaced 12 inches center to center. The longitudinal bars are 3-inch and are spaced 18 inches center to center. The thickness of the crown in the section shown is 12 inches, of the springing line 24 inches, and of the base 15 inches, the minimum thickness of crown for the smallest size being 6 inches. Fig. 60 shows a storm-water sewer, 7 feet in diameter, built in Des Moines, Iowa, in 1906, and known as the Ingersoll Run Sewer. In construction the trench was dug to the form of the outside of the invert, and transverse 1-inch steel bars were then placed 1 foot |