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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 are 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.
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
Foundation Wall. 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.
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.
Only a good quality of hard bricks should be used, and the entire work should be laid in strong cement mortar.
The holding-down bolts, when it is necessary to use such fastenings, are made long enough to reach well down in the foundation, if not entirely through it, and are provided with large washers or plates at their lower ends. These
are put in place as the foundation is built up and their top ends are held in position by a templet made of boards in the form of a frame, and representing the base of the machine.
In a large foundation of this character, blocks of dressed stone should be worked into the finishing courses of bricks so as to bring them level with the top. These are usually placed crosswise, one at each end; and others at such points as to furnish firm support for the cylinder, crank shaft, pillow block, and guides of an engine; for the headstock of a lathe, and for suitable points along the length of the bed; under the uprights or housings of planers and at each pair of legs, or at proper intervals where the entire bed rests on foundations without the use of legs.
FIG. 34. – End Elevation of Engine
- Partial Side Elevation of Engine Foundation.
Foundation. Usually, in the case of a planer, and often of a large lathe, the foundation is composed of a series of piers built up separately at the points to be supported, each pier being capped by a stone of sufficient size to cover it.
In laying out the foundation for a planer of, say, 36 x 36 inches or larger, a pit should be provided under the center; that is, from a point one to two feet back of the face of the uprights to a point three to five feet in front of the uprights, and five to six feet deep. It should be broad enough for the building of narrow steps leading down into it.
This pit will receive a great portion of the chips produced, and in it, resting on large and firmly set stones, should be two cast iron columns, with strong jack screws tapped into their tops, and coming up into contact with the under side of the bed at a point near the face of the uprights. Thus arranged, they are very
FIG. 36. -- Special Pier for a Machine useful in maintaining the proper alignment of Testing Foundation. the planer.
A foundation now in use, upon which large lathes are erected and tested, was built as shown in Fig. 36. Solid ground was found about five feet below
the floor level, and a course of concrete was first laid, then three courses of stones, and upon these hard bricks, cement being used throughout.
Upon the top of each pier a cast iron plate i} inches thick was placed. This plate had downwardly projecting flanges all around it, deep enough to cover three courses of bricks. In the top of these plates was a hole six inches in diameter.
When the brickwork was finished these plates were put in place and leveled up so as to leave about half an inch space between the plate and the top of the bricks. Around the lower edges of the flanges the space was carefully closed with cement. Then cement was mixed thin enough to flow easily, and was poured into the hole at the top until the entire space at the top and sides was completely filled, and the whole was allowed to “set.” The tops of the
of the plates were about į inch above the top of the floor, which was built up closely around them. Very heavy lathes are moved on and off these piers almost daily for several years without injury, and the piers have not settled to any appreciable extent, or so as to cause any difficulty in leveling up machines to be tested.
In placing high-speed engines or planers, which are liable to lateral shocks, it may be advisable to provide cast iron plates as described above, with the downwardly projecting flanges to cover the upper courses of brickwork, and also with upwardly projecting flanges enclosing sufficient space for the base, cabinets or legs, as the case may be. After leveling up the machine with steel wedges, say a 1 to a 1 inch, the space is filled with melted lead or brimstone, which when cool will form a very secure, serviceable, and durable arrangement.
Foundations for machines subject to considerable vertical shocks, such as steam hammers, drop presses, and the like, must be treated in an entirely · different manner. From the nature of the work a solid foundation of stone and brick is not usually considered as best adapted to the conditions.
Such a foundation, unless formed of one solid block of stone, would soon be spoiled by cracks and disintegration from the shocks, and serious consequences to the machine might ensue, the parts broken, for instance, or the dies ruined. For such cases many experienced men prefer foundations that may be elastic enough to relieve the machines somewhat of the sudden strains and shocks of heavy and oft-repeated blows. In these cases the foundations are composed of timbers.
There are two common types of these foundations. The first one, for small or medium sizes of drop presses or hammers, are built with timbers set on end and firmly bolted together in sufficient numbers to form a foundation of the required size, as shown in Fig. 37, the bolts going entirely through the mass. Timbers 10 x 10 inches or 12 X 12 inches are
a convenient size, and hard pine is found by experience to be best adapted to the work.
The excavation is first made to solid ground, then a foot or so of hard gravel is tightly rammed down in the bottom, to form the bed. The timbers are cut of a proper length to reach the surface, but should not be less than 5 feet long. They are bolted together, lowered into place, and leveled up, and good hard gravel is tightly rammed in around the timbers, filling the space between them and the sides of the excavation.
This form of foundation is adapted for drop presses and small hammers in which the anvil is a part of the machine itself. In case a hammer is of such size as to have the anvil detached from the main frame, the latter is supported upon a stone foundation, or on one partly of stone and partly of brick (built in two piers for a double hammer), as shown in cross-section in FIG. 37. — Drop Hammer Fig. 38 and in side elevation in Fig. 39. The foundation for the anvil is built of timbers laid horizontally, the base being spread over as large an area as practicable, in order to resist the force of the blows of the hammer.
In a double hammer the anvil foundation must be restricted in width, but may be extended in length at the base so as to present the form shown in the engraving
The size of the foundation is necessarily proportioned to the size of the hammer, but approximately as follows: Supposing the width between the upright parts of the main frame to be 6 feet, the width of the timber work will be about 4 feet, the length on top 8 feet and at the base 12 feet — assuming the necessary depth to be 4 feet. If solid ground is not found at this