Foundation

are either natural, or artificial: natural, as when we build on a rock, or very solid earth; in which case we need not seek for any other strengthening; for these, without digging, or other artificial helps, are of themselves excellent foundations, and most fit to uphold the greatest buildings. But if the ground be sandy or marshy, or have lately been dug, in such case recourse must be had to art. In the former case, the engineer must adjust the depth of the foundation by the height, weight, . of the building: ¹⁄₆th part of the whole height is looked upon as a medium; and as to the thickne , double that of the width of a wall is a good rule. If you build upon mo y and loose earth, then you must dig until you find sound ground. This sound ground, fit to support a building, is of divers kinds: in some places so hard, as scarcely to be cut with iron; in other places very stiff; in other places blackish, which is accounted the weakest; in others like chalk, and in others sandy: but of all these, that is the best which requires most labor in cutting or digging, and when wet, does not di olve into dirt. If the earth to be built upon is very soft, as in moorish grounds, or such that the natural foundation cannot be trusted, then you must get good pieces of oak, whose length should be the breadth of the trench or about 2 feet longer than the wall; these must be laid acro the foundation about 2 feet asunder, and being well rammed down, lay long planks upon them; which planks need not lie so broad as the pieces are long, but only about four inches on a side wider than the basis, or foot of the wall is to be. But if the ground be so very bad, that this will not do, then you must provide good piles of oak of such a length as will reach the good ground, and whose diameter must be about ¹⁄₁₂th part of their length. These piles must be driven down by an engine for that purpose, and must be placed as close as one can stand by another; then lay planks upon them, and pin them fast. But if the ground be faulty in some parts, and firm in others, you may turn arches over those loose places, which will discharge them of the weight. You must not forget to place the piles under the inner, as well as the outer walls; for if these should sink, it would be a means to make the outer walls crack, and so ruin the whole building. Having thus far considered the bed of the earth on which the building is to be erected, we shall next consider the substruction, as it was called by the ancients; but our modern engineers call it the foundation . This is the ground-work of the whole edifice, which must sustain the walls, and may be termed artificial, as the other was natural; with regard to which, the following things are most nece ary to be observed: 1. That the bottom be exactly level; therefore lay a platform of good boards. 2. That the lowest ledge or row be all of stone, the broader the better, laid closely without mortar; which is a general caution for all parts of a building that are contiguous to board or timber, because lime and wood are utter enemies to one another, and, if unfit confiners any where, they are more especially so in the foundation. 3. That the breadth of the foundation be at least double the breadth of the wall which is to be raised upon it: but even in this case art should give way to discretion: and the foundation may be made either broader, or narrower, according as the ground and the ponderosity of the edifice require. 4. That the foundation be made to diminish as it rises, but yet so that there may be as much left on the one side as on the other; so that the middle of that above may be perpendicularly over the middle of that below, which should in like manner be observed in diminishing the walls above ground; for by this means the building will become much stronger than it would be if the diminution were made by any other way. 5. That you should never build on the ruins of an old foundation, unle you are well a ured of its depth, and that its strength is sufficient to bear the building. The stones in the foundation should be laid as they naturally lay in the quarry, for they have the most strength in their natural position. This should be observed in all parts of a building, because all stones have a cleaving grain; consequently, if the horizontal position of the stones in the quarry should be placed vertically in the building, the superincumbent weight would be apt to cleave them, and so render the building ruinous.