TANK FOUNDATIONS

Considerable care should be taken in constructing the GRADE or finished foundation on which the tank is to be erected. Concrete foundations are ordinarily not necessary if the ground is reasonably hard. When the grade is properly prepared and perfectly level, the tank can be joined on an even surface, and, therefore, it is easier to fit up and erect the tank Also, with proper support, the completed tank will be less likely to leak.

Grading

The earth grade should be constructed approximately 1 foot greater in diameter than the diameter of the tank which is to occupy it. The earth must be well-tamped to a firm and smooth surface. Never fill the area for a tank foundation because erosion will, in time, result in a faulty foundation.

Foundation Construction

The tank foundation should be dry, level, and well-drained. A layer of clean gravel or sand on the grade is ideal for this purpose. Tar paper may be spread under the tank as a corrosion-resistant carpet.

When a layer of gravel or sand is used on a grade of firm earth, follow these steps:

1. Drive a peg in the exact center.

2. Mark this center peg at a point 6 inches from the top) and drive it down in the grade to this mark.

3. Use a wooden straightedge with a carpenter's level attached to set grade stakes about 10 feet apart. Note that, set in this manner, they will protrude 6 inches above the earthen grade.

4. Distribute sand over the whole grade, using shovels and rakes. When the sand just covers the top of each of the stakes and the center peg, the proper level has been reached.

5. Drive the stakes and the center peg all the way down into the earth under the sand. When the tank is filled, the sand will compact, and if the stakes are not driven down, they may cause leaks. Mark the position of the center peg with a temporary pin so that you will be able to position the center of the tank bottom later.

6. To make the surface smooth, use a sweep with a carpenter's level attached. Pin the sweep to the center peg and drag it over the sand, filling in any hollows and smoothing out humps. The sand pad should be at least 4 inches thick and should have a crown of about 1 inch in 10 feet of tank radius; however, the crown should not exceed 6 inches.

When a foundation is properly prepared, many unnecessary problems do not occur during construction of the tank. Just imagine the problems that might occur, both in erection and in subsequent maintenance of a tank, if the' foundation were to settle unevenly, throwing the steel plates on one side of the tank slightly out of line. Remember that the walls of the tank-consisting merely of steel plates bolted together-must act as bearing walls to support the roof. So, make sure you have a good foundation before starting to assemble a tank.

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