Foundation is a structure which transfers the loads from the superstructure to the ground, while footing is the foundation which is in contact with the earth. A foundation can be shallow and deep, while a footing is a type of a shallow foundation. so, all footings are foundations but all foundations cannot be footings.
There are five main foundation types and a handful of important variations.
- Basement Foundation.
- Crawlspace Stem Walls.
- Concrete Slab Foundations.
- Wood Foundations.
- Pier and Beam Foundations.
minimum depth of foundation:– minimum depth of foundation is around 5 feet for a small residential building from ground level or at least 1.50 times the width of footing. In cold climates the depth of footing is Kept at a minimum of 1.50m below surface because of possible frost action.
A porch is a covered, single-storey structure that can be enclosed, and projects out from a house or other building. It will require foundations, and the junctions between the walls of the porch and those of the existing building will need to be properly sealed.
A Strip Footing is a relatively small strip of concrete placed into a trench and reinforced with steel. The footing supports the load of the exterior walls and any interior wall that is load bearing or supports a slab such as for a bathroom. Strip footings can be used for both traditional timber and concrete floors.
Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils.
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- Isolated Spread Footing. Also known as Pad or, simply, Spread footings, isolated footings are one of the most common shallow foundation types used to spread the weight of concentrated loads.
- Wall Footing.
- Combined footing.
- Cantilever or Strap Footing.
- Raft or Mat Foundation.
Slab-on-grade or floating slab foundations are a structural engineering practice whereby the concrete slab that is to serve as the foundation for the structure is formed from a mold set into the ground. The concrete is then placed into the mold, leaving no space between the ground and the structure.
As such, a shallow foundation is used for projects that are small or lighter-weight buildings, and deep foundations for larger or hillside developments, or those on poor soil. Shallow foundations are usually located less than six feet below the lowest finished floor of a structure.
Deep foundations are generally more expensive than shallow foundations. Shallow foundations are easier to construct. Foundation can be provided at a greater depth, Provides lateral support and resists uplift, effective when foundation at shallow depth is not possible, can carry a huge load, etc.
A shallow foundation is the one whose width is greater than depth. A deep foundation is the one whose depth is greater than width of the footing.
Above the soil surface, a base is created of any thickness, it is just done to create a base for Raft Foundation. On that base, this raft foundation is constructed. When bearing capacity of a soil is less than, raft or mat footing is used.
Shallow Foundation | Advantages and Disadvantages of Shallow Foundation
- Shallow foundation is convenient for foundations having depth is equal or less than the foundation width.
- It is used if bearing capacity of soil is high at shallow depth.
- For compressive soils, it helps to reduce settlement.
- No piling is required.
Explanation: The shallow foundations are of the following types: spread footing (or simple footing), strap footing, combined footing, and mat footing or raft footing.
There are many reasons that a geotechnical engineer would recommend a deep foundation over a shallow foundation, such as for a skyscraper. Some of the common reasons are very large design loads, a poor soil at shallow depth, or site constraints like property lines.
Shallow foundations might include; pad foundations, strip foundations, trench fill foundations, raft foundations and so on. They are typically shallower if they are on sites with rocky/stony ground, whereas it is normal in 'shrinkable' soils such as clay for foundations to require a depth of at least 1 m.
