187. Rate of Progress.—In a general way it can be assumed that the laying of 1,000 bricks will require 3⅓ hours of the time of one mason, 10 man-hours for helpers and laborers, 2 barrels of cement, 0.6 cubic yard of sand, and about 10 feet board measure of centering. One thousand bricks will make about 2 cubic yards of brickwork. To the costs, as estimated on the basis of materials and labor, must be added about 15 per cent for overhead and an additional amount for the contractor’s profit. The number of bricks required in various size sewers is shown in Table 67. A mason can lay more bricks per hour in a large sewer than in a small one as there is a smaller percentage of face work, there is more room to work, and it is easier to lay the bricks radially. The number of bricks laid and the rate of progress on various jobs are shown in Table 68.
| TABLE 67 | ||||
|---|---|---|---|---|
| Brick Masonry in Circular Sewers. Cubic Yards per Linear Foot | ||||
| (From H. P. Gillette) | ||||
| Diameter, Feet and Inches | One Ring (4½ Inches) | Two Ring (9 Inches) | Three ring (13½ Inches) | |
| 2 | 0 | 0.103 | 0.240 | |
| 2 | 6 | 0.125 | 0.280 | |
| 3 | 0 | 0.147 | 0.327 | |
| 3 | 6 | 0.169 | 0.371 | |
| 4 | 0 | 0.191 | 0.415 | |
| 4 | 6 | 0.213 | 0.458 | |
| 5 | 0 | 0.234 | 0.501 | 0.802 |
| 5 | 6 | 0.256 | 0.545 | 0.867 |
| 6 | 0 | 0.278 | 0.589 | 0.933 |
| 6 | 6 | 0.633 | 1.000 | |
| 7 | 0 | 0.677 | 1.063 | |
| 7 | 6 | 0.720 | 1.128 | |
| 8 | 0 | 0.763 | 1.193 | |
| 8 | 6 | 0.807 | 1.260 | |
| 9 | 0 | 0.851 | 1.325 | |
| 9 | 6 | 0.895 | 1.390 | |
| 10 | 0 | 0.938 | 1.456 | |
Concrete Sewers
188. Construction in Open Cut.—In the construction of sewer pipe of cement and concrete one of two methods may be employed; 1st, to manufacture the pipe in a plant at some distance from the place of final use, or 2nd, to manufacture the pipe in place. The methods of the manufacture of cement and concrete pipe which are to be transported to the place of use are treated in Chapter VIII. The process of constructing the pipes in place is ordinarily used for pipes 48 inches or more in diameter. For smaller sizes, brick, vitrified clay, and precast cement pipes are usually more economical.
The preparation of the foundation of a concrete sewer is similar to that for a brick sewer. If the ground is suitable the trench is shaped to the outside form of the sewer and the concrete poured directly on it. In soft material which would give poor support to a sewer with a rounded exterior, the bottom of the trench is cut horizontal and a concrete cradle of poorer quality than that in the finished sewer is poured on the soft ground, on a board platform, on piles, or on cribbing supported on piles.
If the invert of the sewer is so flat that the concrete will stand without an inside form the shape of the invert is obtained by a screed or straight-edge which is passed over the surface of the concrete and guided on two centers, or on one center and the face of the finished work. The construction of a flat invert sewer at Baltimore is shown in Fig. 1. The center for the concrete is shown in the foreground. When the concrete for the next section is poured it will be smoothed to shape by a screed or straight-edge resting on the face of the finished concrete and the center. The center is shaped to conform to that of the finished concrete. It is firmly staked in position and acts as a bulkhead for the concrete as it is poured, as well as a guide for the screed.
| TABLE 68 | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Rate of Progress on Brick Sewer Construction | |||||||||
| (Based on 8–hour day) | |||||||||
| Diameter of Sewer | Shape | Number Rings, Brick | Number Masons | Bricks per Mason per Day | Number Laborers | Feet Progress per Day | Location | Authority | Remarks |
| 7′ 0″ 8′ 11″ | Circular and Oval | 2½ | 6 | 4710 | 39 | 60 | Gary | Gillette | 9–hour day |
| 4′ 0″ | Circular | 2 | 3 | 2500 | 36 | Metcalf and Eddy | General average | ||
| 6′ 8″ | Circular | 3 arch 1 invert | 18 | 62 | Denver | Gillette | Concrete invert | ||
| 2′ 9″ | Egg | 1 arch 2 invert | 2 | 3 | Springfield, Mass. | Eng. Con., Jan. 16, 1907 | |||
| 5′ 6″ | Circular | 2 | 6 | 4570 | 35 | 110 | Gary | Gillette | |
| 6′ 6″ | Circular | 4 | 4800 | Gillette | Exceptional speed | ||||
| 2′ 9″ | Circular | 2 | 2 | 2080 | 5 | 13.9 | Syracuse | Gillette | Tunnel 12–hour day |
| 16′ 0″ | Circular | 5 | 8 | 5 cu. yd. | 22 | Chicago | Gillette | First year | |
| 16′ 0″ | Circular | 5 | 12 | 70–75 | 35 | Chicago | Gillette | Second year | |
| 3′ 6″ | Egg | 2300 | St. Louis | Gillette | |||||
| 9′ 6″ | Circular | 3000 | 12.5 | Chicago | H. R. Abbott | ||||
| 3′ 6″ | Circular | blocks | 2 | 13 | 30 | Lock joint and tile. 10–hour day | |||
If inside forms are to be used they are made as units in lengths of 12 or 16 feet for wooden forms, and 5 feet for steel forms. The inside form is supported by precast concrete blocks placed under it and which are concreted into the sewer. It is held in position by cleats nailed to the outside form, to the sheeting, or wedged against the outside of the trench. In some cases, particularly where steel forms are used, the inside form is hung by chains from braces across the trench as is shown in Fig. 129. The form is easily brought to proper grade by adjustment of the turnbuckles and is then wedged into position to prevent movement either sideways or upwards during the pouring of the concrete. It may be necessary to weight the forms down to prevent flotation. Cross bracing in the trench which interferes with the placing of the form is removed and the braces are placed against the form until the concrete is poured. They are removed immediately in advance of the rising concrete.
Fig. 129.—Blaw Standard Half Round Sewer Form, Suspended from Overhead Support.
Courtesy, Blaw Steel Form Co.