Concreting in tank work is expensive. The reasons are two. The work has to be done in a narrow space, commonly pretty well filled with a network of steel rods or bars. Again the work has to be done uniformly well, not only for appearance sake but because of the necessity of watertightness. Making a reservoir watertight is, when all things are said, the one difficult constructional task in tank work and the contractor who accepts the task lightly courts trouble. Exceptionally good concreting is essential in tank work if watertightness is to be secured.

The illustration of these general admonitions will be found in the specific examples of tank and reservoir work which follow.

SMALL COVERED RESERVOIR.—The reservoir was designed to hold 75,000 gallons of water for fire purposes. As it is of a type which is certain to be frequently constructed and as we have personal knowledge of the costs recorded we describe the work in some detail. The specifications stipulated that the reservoir must be absolutely watertight and that the roof should be capable of sustaining a load of 300 tons evenly distributed and a live load of 5,000 lbs. on two wheels. Figure 273 shows a plan, Fig. 274 a longitudinal section, Fig. 275 a transverse section and Fig. 276 the column construction.

Fig. 273.—Sectional Plan of 75,000-Gallon Reservoir.

Quantities of Work.—The excavation called for the removal of 579 cu. yds. of earth. There were 83 cu. yds. of concrete in the structure, although the plans called for less, the additional amount being used in increasing the two 4-in. walls to 6-in. and increasing the bottom and top, on one end, so as to give perfect drainage. The yardage was divided as follows:

Cu. yds.
Footings3.5
Columns6.8
Sides22.6
Girders11.0
Top20.0
Floor19.1
——
Total83.0

Fig. 274.—Longitudinal Section of 75,000-Gallon Reservoir.

A manhole had to be put in the top and a sump in the bottom. Several pipes also had to be placed in the concrete. None of these details is shown on the plan. The structure had to be waterproofed.