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to the time payment is made for it; demurrage, and possibly other items also; and finally a fair profit.

Of these, rate of interest on plant cost and other money advanced, and labor insurance are fairly constant; some materials like pipe, cement, etc., change in price slowly in ordinary times, and can be calculated very closely for a given piece of work; while other materials such as broken stone, sand, and other local products vary several hundred per cent in different localities. Wages also change slowly, but vary considerably in different sections, and the amount of actual work that is obtained for a dollar varies with the character of local labor, the ability of the foreman to get work out of the men, and that of the contractor to plan the work to the best advantage.

The engineer's estimate should not be too low, as this often gives rise to suspicion of intentional deception by the city, and if made the basis of an appropriation of funds for construction, may lead to a forced curtailment of the amount of work done. On the other hand, an unduly high estimate may discourage any appropriation whatever.

In the figures for cost that follow, the cost given does not include superintendence, use of tools, profits, or any of the general expenses of management, but is thought to be liberal and sufficient to include them under good management.

Sewer-pipe. The list prices of vitrified clay sewer-pipe and specials were given in Table 17, page 178.

Concrete Materials. According to figures collected by 'Municipal Journal" in 1916 in nearly 1000 municipalities, the cost of sand varied from $.20 to $3 per cubic yard, averaging $1; that of broken stone varied from $.40 to $3.75 per cubic yard, averaging $1.00. Cement cost about $1.25 per barrel. Labor for feeding mixers by wheelbarrow, mixing and delivering concrete direct from mixer by chute or beam and bucket, cost from $3 to $4 per cubic yard. The cost of forms will vary with their elaborateness, convenience of handling and size of sewer, but may run as high as $2 or more per cubic yard.

Trenching for pipe by hand, sheathing if necessary, and backfilling cost about as given in Table No. 18, for easy digging-

loam, sandy clay, etc. Sand and gravel are included as " easy,” but must be sheathed. Hardpan may cost about double these figures. Rock excavated in the trench will cost from $2 to $10 per cubic yard-the latter when only 2 or 3 inches depth are to be removed, and the rock does not shatter readily.

TABLE NO. 18

COST OF EXCAVATING AND BACK-FILLING, AND OF SHEATHING TRENCHES, CENTS PER LINEAL FOOT

Most favorable conditions: Compact loam, no ground water, no obstructions.

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Labor taken at $2.25 a day, lumber at $25 a M.

*Three-fourths used the second time, one-half the third time, one-fourth the fourth time. With care good sheathing, may be used an average of three to five times where driving is easy.

Quicksand may cost from two to ten times the above. No estimate can be given for it.

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Unloading, hauling, and distributing*.

Laying and calking, and cost of jute.

1.01.21.52.22.53.03.7

18 20 24 27 30 36

5.2 6.7 8.2 10.5 13.5 16.5 23.0 4.5 5.2 6.0. 7.0 8.0 9.0 12.0 Cement mortar for joints. 0.8 0.9 1.0 1.0 1.1 1.2 1.6 2.0 2.4 2.7 3.6 4.2 5.0 8.3

2.2 2.2 2.2 2.2 2.5 2.8 3.7

Total..

4.04.34.75.46.17.09.011.714.3 16.9 21.125.7 30.5 43.3

*Teams hauling 2500 to 3000 pounds per load, average haul one mile. Labor taken at $2.25 a day; teams at $5.00.

Concrete Sewers, if designed according to the formula t=1+

d

12

(all dimension in inches), will require a theoretical amount of concrete represented by the formula,

Q=0.007295d2+0.09427d+0.0808,

in which Q is the cubic yards of concrete required for 100 feet of sewer, and d is the inside diameter, in inches. From 5 to 10 per cent should be added for waste, expanding of forms, etc. In estimating cost, be sure to allow sufficient for setting up and taking down forms. Where collapsible sheet steel forms are used, this cost is about 5 to 10 cents per lineal foot for diameters up to 5 feet.

Manholes. The approximate cost of manholes, 3 feet by 4 feet 6 inches on the bottom, is given in the following table. A 4-foot circular manhole will cost about 4 per cent more. The brickwork is taken as 8 inches thick down to a depth of 12 feet, and below this as 12 inches thick. This table does not include the cost of excavation, moving of materials from one manhole to another, or overhead charges.

TABLE NO. 20

COST OF MANHOLES, 3 FEET BY 4 FEET 6 INCHES

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CHAPTER XI

SUPERVISION OF CONSTRUCTION

ART. 52. WORK PRELIMINARY TO CONSTRUCTION

As soon as possible after the signing of the contract the contractor should submit samples of the material he wishes to use, and these should be carefully examined by the engineer, and if accepted should be retained and marked for future identification and compared from time to time with the material actually furnished.

The contractor should be notified some days in advance of the point or points at which he is to begin work. Reasonable deference should be made to his wishes in this matter, since it is his privilege and duty to so organize the work as to secure the greatest efficiency at the least cost to himself. If, for instance, part of the work lies through wet ground and sub-drains are to be used it is ordinarily to his interest, and indirectly to the city's also, that the work begin at an outlet to which all ground water will drain, or at a point at which a pump, once set up, can drain the work for long distances without moving its location, as at the junction of two mains. It is also usually desired by the contractor that, if two or three small gangs are to work at as many places, they may be within a few blocks of each other for convenience of oversight. It will ordinarily be to the interests of both contractor and city to work in as dry ground as possible, and hence to leave until summer droughts construction through low, soggy land. Construction across or near streams should not be carried on when there is a possibility of floods or freshets, if it can be avoided. Both trench- and masonry-work should be avoided in winter weather, if possible, for it is then costly to the contractor, and it is impossible

to be sure that the mortar is uninjured, or to restore the streets to good condition with frozen earth.

Ordinarily the contractor will desire to place upon the street, along the line of the work, pipe, brick, sand, lumber, etc. This cannot be denied him, but he should be compelled to place and pile this material so as to interfere with travel as little as possible, and along only those stretches of street in which construction is to be begun within a week, or ten days at the outside. This material should be inspected as it is delivered, and that condemned removed at once.

Just before the work begins it is well to run levels carefully over all bench marks to see that they have not been disturbed and to check previous levelling; also to establish new ones if necessary. It is desirable to so place these that one of them can be seen from the instrument when set up for giving grades to any part of the work. They should be accurate within at least .003 of a foot.

Final arrangements should now be made for the oversight of the work, the proper instruments obtained, engineering and inspecting assistants engaged, an office or other headquarters arranged for, notebooks and blanks obtained for making and preserving records, final arrangements made as to right-of-way across private property and along county roads or others not controlled by the city or village. Arrangements should be made also for locating the branches for house-connections at the points desired by the property owners. For this purpose it is well to publish in the paper or otherwise make known to the citizens that each is desired to drive, at his fence-line or curb, a stake indicating the point at which he wishes his houseconnection to enter his property, and that in case no such stake is driven the engineer or inspector will use his judgment in locating such branches.

Counsel for the city should pass upon the sufficiency and correctness of the contracts signed, of the bonds given and of their signers, and all other legal matters in connection therewith, before the contractor is permitted to begin work.

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