A foundation is the part of the structure that is in contact with the surface and its function is to transmit the loads of it to the ground. These loads reach the foundations through the columns or screens depending on the type of structure. For the design of the foundations, it is necessary to determine the maximum load capacity that the soil can support. Some types of soils fail to offer enough resistance in their upper layers, or the loads coming from the structure are very high; This type of problem cannot be solved with directly supported footings, but rather the alternative is to distribute the load by means of piles driven into firmer deep strata, or to achieve a sufficiently large contact area to dissipate the load by friction.

There are the following types of foundations:

• Shallow or direct foundations (footings).
• Deep or shaft foundations.
• Indirect or pile foundations.
• Hydraulic foundations.
• Foundations by consolidation.

The spread footing

The spread footing corresponds to the extension of the lower part of a wall, whose purpose is to adequately distribute the load on the foundation soil. Spread footings are used in the contour of a building and sometimes under the interior walls. This spread footing receives the linear load, and eventually a bending moment transmitted by the wall.

The isolated footing

The isolated footing fulfills the function of supporting load coming from only one column or pillar. This type of footing is commonly used when working with light loads and the columns have greater estrangement.

Foundation slab

A foundation slab is a concrete plate resting on the ground, which distributes the loads of the building over the entire support surface. The foundation slab covers the maximum support surface available under the building, that is, it can cover the entire area under a structure. The use of a foundation slab is especially indicated when the foundation surface through isolated or continuous footings exceeds 50% of the construction floor, in which case it could be more economical to use a foundation slab. These foundations are also used when the admissible ground pressure is low, it is recommended in structures greater than eight stories.

These are a good choice when:

• The construction has a small surface in relation to the volume (buildings).
• The calculated foundation base is such that the load transmission at 45º represents an excessive depth.
• The terrain has uneven stratification and irregular settlements are expected.
• The foundation terrain is loose and very thick and the piles to be placed would be excessively long.
• When the loads are very large, such that the continuous footings occupy about 50% of the projected area of the building, it is more economical to use slabs that cover the entire foundation area. The total load in this case can be considered uniformly distributed over the entire area.