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.
Therefore, if the use of timber, as above described, is not feasible we must use stone and so arrange the piles, regarding the distances from center to center, as to allow the use of such stones as are available, cutting off the tops of the piles below the water line if possible, or at least so low as to have them always wet. This arrangement is shown in Fig. 29.
Fig. 29. Piling and Stone Support for Foundation Wall.
Fig. 30. Timber and Concrete Support lor Foundation Wall.
Sometimes fairly solid earth may be reached within a reasonable depth, but it requires digging quite a considerable depth beyond this before reaching really solid ground or "hard pan." In such a case it may be advisable to lay down, first, a course of concrete four to six inches thick, then a layer of timber and another course of concrete, which will furnish an excellent bed for the foundation.
The second course of timber may be replaced by a course of 3-inch planks if the wall is not a very heavy one. Circumstances might also warrant three courses of timber. The width of the timber work should be from two to three times the thickness of the wall. Fig. 30 shows such an arrangement.
A prominent public building has stood for many years on very soft and yielding alluvial soil, upon which such a foundation as that described above was laid over the entire area to be covered by the structure, and many feet deep. Then the stone foundation proper was built upon it, after which the very heavy and massive stone building was erected.
Where excavations vary in depth at different points of the same wall the ground should be cut out in steps, or "benches," so that the bed whereon the foundation is built may be perfectly level. The lower steps should be built in with as large stones as possible and brought up to the level of the more shallow parts. It will be readily appreciated that the larger stones require a smaller number of cement joints and will settle less, and consequently arc less liable to disturb the work by yielding unequally. See Fig. 31. In all cases the excavation should be made below the reach of frost.
Fig. 31. Benching out Ground for Foundation.
In building up a foundation of stones they should be laid with as near horizontal joints as possible so as to prevent the lateral movement of the stones by the weight put upon them. They should also be laid as far as possible in courses, and each course leveled off before commencing the next, the thickness of the courses necessarily depending on the thickness of the largest stones. These points are all the more important at corners, where tendencies to disintegrate are the most liable.
The foundation is laid considerably wider at the base than at the top, either in a wall gradually decreasing in thickness (that is, technically, with a "batter" of so much per foot, as in Fig. 32) or more commonly by a wide footing of one or more courses of larger stones. Above that it is built with regular vertical faces as shown in Fig. 33.
However the foundation wall may be built, the space between it and the sides of the excavation should be filled in, either by tightly rammed earth or gravel, or better still by "puddling," that is, by flooding the space with water, throwing in the earth or gravel and allowing it to settle, ramming only from six inches to a foot of the top. The foundation of stone should be carried up above the level of the ground, from one to two feet according to circumstances. If the main floor of a building is to be raised several feet above the ground level, it is usual to build the foundation high enough to rest the floor timbers upon it, filling in the spaces between them with brick and leveling up ready for the brick wall.
Fig. 32. Battered Foundation Wall.
Fig. 33. Straight Foundation Wall.
The importance of using strong mortar in foundation work seems to demand that particular attention be paid to the proportions of its ingredients which will make the best compound of its kind. Use two parts of Portland cement, one part of slaked lime, and about three parts of clean, sharp sand.
The quantity of sand must be varied according to its fineness, sharpness, and freedom from dirt. A larger quantity of fine sand will be needed than of coarse. Some sand has a more rounded grain instead of the sharp angles of the better quality. Of such sand more must also be used.
Foundations are generally laid in mortar having a greater or lesser proportion of cement. They should also be stronger in this respect for the lower or underground courses than for the upper ones so as to better resist the action of water. In fact much of a foundation is frequently laid in mortar composed of only cement and sand, omitting lime altogether.
Thus far only the foundations for buildings have been considered. These have for their principal object to sustain the weights of the superstructure erected upon them.
In the case of the foundations for machinery it is quite different. Here not only the weight must be sustained but the question is complicated by the jars, strains, and shocks due to the operation of the machines; and this must also be considered. These vary largely in different cases, as for instance, the steady revolutions of a large lathe, the reciprocating motion of an engine, and the vertical concussions of the steam hammer or drop press.
Foundations for engines, large lathes, planers, boring mills and so on, are built in a manner somewhat similar to that for the foundation of a building, except that they are usually much broader at the base, conforming in a general way to that shown in end elevation in Fig. 34 and a portion of the side elevation in Fig. 35.