This section is from the "Modern Machine Shop Construction, Equipment, And Management" book, by Oscar E. Perrigo. Also see Amazon: Modern Machine Shop Construction, Equipment, And Management.
The proper bed for a foundation. Care necessary in its preparation. Sounding. The various types of foundation. Timber support for heavy buildings on alluvial soil. Timber support for foundations. Piling support for foundations. Timber and concrete supports for foundations. Laying stone foundations. Mortar for foundation work. Foundations for machinery in general. Engine foundations. Planer foundation. Special foundation for testing lathes or other machines. Drop hammer foundations. Steam hammer foundations. Timber foundation for heavy machines on soft ground. Example in experience.
It is but quoting an old maxim to say that if we are to build a good house we must have a good foundation to build it on. And we may just as pertinently say that if we are to build a good and substantial foundation, we must have something solid to lay it upon.
Otherwise we shall be like the man who built his house upon the sands. The diversity of the ground, at the surface and down through the stratifications of material of various densities and strengths, from the solid nature of rock to the almost fluid condition of alluvial soil, must be considered. Each of these conditions requires special treatment according to its nature.
To properly secure a firm bed for the foundation of a building, we must either excavate down to firm and solid ground, technically called "hard pan," or we must by artificial means produce a substantial surface upon which to begin the masonry. It is quite impossible for the architect, the mason or the contracting builder to tell us by a superficial examination of the ground how deep we must go to reach solid ground, or "hard pan".
To some extent this may be ascertained by "sounding"; that is, by making small excavations at various points, to obtain the necessary information upon which to determine not only the depth to which the foundation must extend, but whether the nature of the ground renders such artificial support as piles necessary.
It may be found that at some points in the foundation of extensive buildings we need excavate only a few feet, while at others, very deeply; and still at other points the ground may be of such a yielding nature that piles must be driven. Or we may find that the use of piles would be a much more economical method than very deep masonry.
But whatever the depth we may be obliged to go to, or the process by which we produce our bed for the foundation, all parts of it must be, not only firm and practically unyielding, but level. Hence, when we excavate to varying depths the earth must be "benched out," as it is called, as shown in Fig. 31.
Great care should be taken to have all parts of the bottom of the excavation of as equal density and resisting power as possible, that they may equally support the great weight of the wall to be built. This condition becomes all the more important as the walls of the building are higher and the consequent weights and strains correspondingly increased.
It is, of course, true that no ground can be found so absolutely solid as not to yield somewhat when the weight of the building is put upon it, and therefore we must not expect to wholly prevent a certain amount of settling; but we should use all possible care to have this settling as equal as possible over the whole area of the foundation.
Having ascertained the nature of the ground as far as possible, we may determine the kind or kinds of foundation necessary. If the ground is so soft and yielding that excavation to solid earth will have to be very deep, making a stone foundation excessively expensive, piles should be driven as deep down as possible - say two feet apart from center to center - and cut off level at the top, and be down low enough to remain always wet.
Fig. 28. Piling and Timber Support for Foundation Wall.
Upon these piles timbers of sufficient size are placed, being laid across each row of piles; then upon these another course of timbers, at right angles to the first. These may be laid close together or two or three inches apart, the size of the timbers being determined by the weight of the wall they are to support. For instance, for the walls of the machine shop proposed in these articles, the timbers may be 10 × 12 inches laid on edge.
Fig. 27 gives a plan view of this method and Fig. 28 shows a cross-section of the same. It is not always necessary to arrange the piles in three lines, with those in the center row in line with those of the two outer rows, as shown. Where the weight of the superstructure is not excessive it is often preferable to begin by setting three piles in a row, then two so they will come opposite the intervals of the first row; then the next row of three in line with the first; then another row of two piles and so on.
Where there is considerable depth from the top of the piles without side support it is necessary to drive "sheet piling." Set planks three inches thick, or thicker, with their edges close together so as to enclose the work on both sides, and afterward fill in the spaces between these planks and the solid earth with tightly rammed gravel, and if necessary fill the spaces between the piles with stones or concrete. This will give them quite sufficient support to make a very firm foundation bed and prevent any lateral movement which might result from the bending of the piles.
Timber should not be used under a foundation unless it is in a position to be kept continuously wet by the surrounding soil, for the reason that if always wet enough to exclude the air it will endure for a very long time, but if so situated as to be sometimes wet and again dry, it will soon decay.