277. The weight of the different earths and stones are shown in the following table.
| Name of material. | Weight per cubic foot. |
|---|---|
| Brick, common | 97 to 125 |
| Brick, stock | 115 to 135 |
| Brickwork, (average,) | 90 to 95 |
| Chalk, | 144 to 166 |
| Granite, | 164 to 187 |
| Marble, | 111 to 117 |
| Mortar, (hair,) dry | 80 to 86 |
| Puzzolano, | 160 to 178 |
| Slate, | 157 to 180 |
| Stone, (average,) | 140 to 150 |
| Clay, (common,) | 110 to 125 |
| Clay and gravel, | 150 to 170 |
| Earth, common, | 95 to 126 |
| Gravel, | 100 to 110 |
| Quick-lime, | 50 to 55 |
| Quartz sand, | 170 to 175 |
| Common sand, | 88 to 93 |
| Shingle, | 88 to 92 |
| Earth, loose | 90 to 95 |
| Stone work, (hewn,) in wall, | 160 to 175 |
| Stone work, (unhewn,) in wall, | 125 to 140 |
CHAPTER XII.
FOUNDATIONS.
278. Foundations may be divided into four classes.
Those on firm, dry land.
Those on unfirm dry land.
Those on solid bottom, under water.
Those on unfirm bottom, under water.
Foundations upon firm dry land require only to be placed at a sufficient depth to be out of the way of frost; varying from one foot in the Southern, to two and three feet in the Middle, and four and five feet in the Northern States. The first course should consist of small, flat stones placed dry, but well packed by hand, upon the bottom; upon the top of this layer, the mortared or cement masonry should be commenced. The object of the first course of small stones is to apply the weight of the superincumbent masonry as equally as possible to the ground. All boulders and rounded stones should be carefully kept out of the foundation.
Unfirm soils are prepared by driving piles, upon which a platform holding the masonry is placed; or by placing the lower courses directly upon the heads of the piles. Sand piles are made either by driving and withdrawing a wooden pile and filling the hole thus made with sand; or by digging trenches and filling such with sand. The applied weight is thus spread over the entire surface of the sides and bottom, instead of being placed upon the bottom only. When the weight of a heavy structure is thrown upon a few small points of support, they may be made the piers and abutments of a series of inverted arches, by which the whole surface beneath the structure is made to assist in bearing the load. Foundations upon yielding or sandy and wet soils may be secured by piling around the whole structure; by which the earth is kept from spreading. Foundations upon dry land do not generally give much trouble to the engineer; but operations carried on under water require all the science and patience that he is master of.