It is a well-known fact that there exist different kinds of soil. It is also a well-known fact that the structure of the upper stratum of the soil is of great importance for excavation. The foundation of a building should never be placed on organic soils because soils of this kind are easily decomposed. They are decomposed because water and wind change their structure. So, if the upper stratum of soil is organic, it must be removed from the construction area in order to guard the foundation of the building against water and wind erosion. Further excavation may take place only after the upper organic stratum has been removed. In colder climates the foundations of buildings should be placed below the level to which the ground freezes in winter.
Natural Foundations. The soils comprised under this head may be divided into two classes. (1) Those whose stability is not affected by water, and which are firm enough to support the structure, such as rock, compact gravels, and hard clay, and (2) soils which are firm enough to support the weight of the structure, but whose stability is affected by water, such as loose gravels, sand, clay and loam.
Foundations on Rock. To prepare a rock foundation, all that is generally necessary is to cut away the loose and decayed portions and to dress the surface so exposed to a plane as nearly perpendicular to the direction of the pressure as practicable; or, if the rock forms an inclined plane, to cut a series of plane surfaces, like those of steps, for the walls to rest upon. If there are any fissures in the rock they should be filled with concrete.
Foundations on Gravel, etc. In dealing with soils of this kind usually nothing more is required than to cover them with a layer of concrete of width and depth sufficient to distribute the weight properly.
Foundations on Sand. Sand is almost incompressible so long as it is not allowed to spread out laterally, but as it has no cohesion, and acts like a fluid when exposed to running water, it must be treated with great caution.
Foundations on Clay. Clay is much affected by the action of water, and hence the ground should be well drained before the work is begun, and the trenches so arranged that water does not remain in them. In general, the less a soil of this kind is exposed to the action of the air, and the sooner it is protected from exposure, the letter for the work. The top of the footings must be carried below the frost line to prevent heaving, and for the same reason the outside face of the wall should be built with a slight batter and perfectly smooth. The frost line attains a depth of six feet in some of the northern states.
The tearing power of clay and loamy soils may be greatly increased:
(1) By increasing the depth.
(2) By drainage. This may be accomplished by a covering of gravel or sand, the thickness depending upon the plasticity of the soil, and by surrounding the foundation walls with a tile drain. If springs are encountered the water may be excluded by sheet pilings, puddling or plugging the spring with concrete.
(3) By consolidating the soil. This may be done by driving short piles close together, or by driving piles, then withdrawing them and filling the space immediately with damp sand well rammed. If the soil is very loose and wet, sand will not be effective, and concrete will be found more satisfactory.
Artificial Foundations. When the ground in its natural state is too soft to bear the weight of the proposed structure, recourse must be had to artificial means of support, and, in doing this, whatever mode of construction is adopted, the principle must always be that of extending the bearing surface as much as possible.
Foundations on Mud, silt, marshy or compressible soils are generally formed in one of three ways: (1) By driving piles in which the footings are supported.
(2) By spreading the footings either by-layers of timber, steel beams, or concrete, or a combination of either.
(3) By sinking caissons of iron or steel, excavating the soil from the interior, and filling with concrete.
b) Read the text again and make a list of additional topical vocabulary (10 to 15 words and word-combinations). Consult a dictionary to finalise the choice of the Russian equivalents. Memorise the new vocabulary.
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