A deep foundation is a foundation that distributes building weights to the soil deeper from the surface than a shallow foundation does to a subsurface layer or range of depths. A pile, also known as a piling, is a vertical structural part of a deep foundation that is pushed or drilled deep into the earth at the construction site. Piles can be made of wood, steel, or concrete and serve to distribute weight away from the building and up into the ground.
Deep foundations are used in areas where shallow foundations would not be stable, such as solid rock or highly erodible soil. They can also be used if the building load requires more stability than a shallow foundation provides. Deep foundations include gravity bases, pilings, pre-cast panels, and poured-in-place concrete.
In gravity base systems, the foundation is made of empty boxes called cells, which are assembled on site into a grid under the building structure. The weight of the building forces the cells into the ground, creating an underground room that acts as a basement for the house. This system is inexpensive and easy to construct but requires special design guidelines for best performance. Pilings are often used together with gravity basements to increase their stability and durability. In this case, piles are driven into the ground near the outer edges of the basement floor to create a buffer zone between the basement and the ground.
Piling is a sort of deep foundation that is used to carry weight to a deeper level than a standard shallow foundation can. Vertical columns of concrete, steel, or wood, or a mix of these materials, are pushed deep into the ground to provide additional support to the building on top. The depth that these pilings are driven into the ground depends on how much weight they will be asked to bear.
There are two types of piling foundations: open and closed-cell. In an open-cell system, the space between the piling is filled with earth or gravel. This allows water to drain away from the foundation and reduces erosion. Open-cell systems are most commonly used for small buildings such as sheds and gazebos.
Closed-cell piling foundations consist of vertical metal bars that are placed in a trench and covered with soil. The bars do not touch each other but do reach down to the bottom of the trench where they are connected by horizontal members. These connections are also made of metal and serve to hold the bars in place while the soil around them hardens. Closed-cell systems are most commonly used for larger buildings such as houses. They provide extra strength and stability for the foundation and allow water to drain away from the house.
People often think of houses as being built on solid ground, but this isn't true. A house's foundation is what supports it above ground level.
A shallow foundation is a form of building foundation that distributes building weights to the soil extremely close to the surface, as opposed to a subterranean layer or a variety of depths, as a deep foundation does. The purpose of this type of foundation is so that the building itself does not have to bear the weight of the ground above it. This allows for lighter materials to be used in construction and reduces the risk of damage due to earthquake activity.
There are two types of shallow foundations: concrete and dirt. Concrete shallow foundations are made by creating an area of compacted gravel or crushed rock below the level of the finished floor or baseboard, which will support the weight of any buildings that are placed on top of them. These bases can be as small as one ton or as large as several thousand tons. The depth of a concrete shallow foundation depends on how much load it has to sustain. If it is going to bear the weight of just a single room, then the base should be at least as deep as the wall it supports. If it is going to bear the weight of a house, then the base should be at least as deep as the height of the roof above it. Loose gravel under high traffic areas may require deeper foundations than rock underneath less active parts of the yard. The size of the rocks used to create the base should be selected based on how much pressure they are expected to withstand without failing.
A shallow foundation is one that is located near the earth's surface or transmits loads at a shallow depth. A "deep foundation" is one that is placed at a higher depth or transmits loads to deeper strata. In general, deep foundations are more costly than shallow foundations. Loads from buildings or other structures can cause damage to shallow foundations by causing them to heave or crack.
Shallow foundations are usually made of concrete or rock, while deep foundations may be composed of steel or reinforced concrete.
The depth of a foundation relates to its load-bearing capacity. The deeper the foundation, the greater its capacity to bear weight. The height of a building also affects its stability: the taller it is, the more likely it is to experience instability. This is because the weight of the building creates a tension in the structure which can only be relieved by settling under its own weight.
Buildings with shallow foundations are generally less expensive to construct and occupy less space on the land. They are therefore suitable for most small-scale projects. Deep foundations are needed only when the structure being built is high (i.e., greater than 10 meters) or subject to heavy loading. Examples of deep foundations include basements, underground floors, and skyscrapers.
The type of foundation used for a building project depends on how much stress it is expected to face during construction and use.
When the carrying capability of the earth is very poor, a deep foundation is employed. The weight from the superstructure is transferred vertically to the soil. Deep foundations are classified into three categories, and their applications in building are explained further below.
Category 1 foundations are those that reach down to bedrock or some other stable stratum. These include footings, shafts, and trenches. Footings are the most common type of deep foundation and are used for small, light structures such as bridges, walkways, and buildings with shallow basements. They usually consist of a flat slab of concrete that is poured at grade and allowed to cure in place. The depth of a footing should be sufficient to prevent damage due to seasonal freezing and thawing. If the structure is not removed each year, ice can build up inside the footings during cold weather periods and cause damage to the foundation itself and to any items located underneath it.
Shafts are similar to footings but are generally deeper (1-3 feet). They are commonly used under light load-bearing structures such as signs, trees, and large shrubs. Shallow trenches are also used as category 1 foundations and are typically 3-10 feet deep. They are placed near the base of the structure where they will support most of the weight. Trenches are often filled with gravel or stone to provide additional stability and to help drain water away from the foundation.