Foundation Systems in Building
Building foundations can be broken down into two categories: shallow and deep. Shallow foundations are the more common type. The depth of the soil in which the foundation is created is the primary consideration for these classifications. The depth at which a shallow foundation is built can be as little as one foot, but the depth at which a deep foundation is formed can range anywhere from ten to three hundred feet. As a result, a shallow foundation is utilized for projects that are smaller or lighter-weight buildings, and deep foundations are utilized for developments that are larger, on steep terrain, or on soil that is of poor quality.
Foundations that are considered shallow are often situated at a depth of fewer than six feet below the lowest finished floor of a building. These systems are utilized in situations in which the soil close to the ground surface possesses an adequate bearing capacity, and the underlying weaker strata do not result in an excessive amount of settlement. These are the types of foundation systems that are most frequently utilized for the construction of residential and timber constructions on a small scale. As a direct consequence of this, a number of distinct kinds of shallow foundations are used in buildings. Because they disperse the weight of significant loads across a broader area of earth, these footings are frequently referred to as spread footings.
In situations when shallow foundations cannot be used, it is important to use deep foundations instead. Deep foundations are structural elements that are used to transfer loads from weak and compressible soils to a stronger layer that is typically positioned at a large depth below the earth. This stronger layer is where deep foundations are typically located. These foundations have an additional support option available in the form of the friction created by the dirt immediately adjacent to them. Surface-level concrete members, such as grade beams or pile caps, are used to transfer the weight from the structure that is located above to the elements that are located here. When there are substantial design loads (four stories or more), or when the soil quality is inadequate at a short depth, it is advisable to use deep foundations.
Types of Shallow Foundations
In areas with difficult soil, particularly those near construction sites, shallow foundations, also known as footings, are an important component of the foundation of the building. The structural parts that transfer loads of soil from columns, walls, or lateral loads from earth retaining structures are called footings. Footings can also transfer lateral loads. The design of the footings must take into account the need to avoid and limit foundation settling, protect against overturning and sliding, and offer safety. The nature of the structure and its overall dimensions will determine the dimensions of the footings. To guarantee that the foundations are correctly supported and structured, it is essential to employ professionals in the building and placement of the footings. Please get in touch with us so that we may assign a qualified engineer to work on your foundation.
One of the most typical varieties of foundations that are utilized in construction is known as an isolated spread or pad footing. These are placed below separate columns or other load points, and each one has its own footing. The footings can take the form of a square or a rectangular pad made of concrete; the size of the footings is determined by the load that is being supported by the column in addition to the safe bearing capacity of the soil.
When there are two or more columns that are located in close proximity to one another and their foundations would otherwise overlap, combined footings are utilized to provide support for the columns. The name “combined” originates from a combination of isolated footings; yet, the structural design of the foundation is different from one another. The combined footing shape is typically rectangular, and its use is required only when the load points are located in close proximity to one another.
Underlines that are loaded throughout their entirety, either strip or continuous footings are employed. This happens most frequently under bearing walls or shearwalls, which are typically formed like an upside-down “T” or an “L.” These kinds of footings are also able to sustain individual columns that are arranged along these lines; however, if the load is significant, there may be additional width at these locations.
When there are numerous different loads acting across a region, which causes a number of individual foundations to overlap, mat foundations are necessary to support the structure. When constructing basements, it is usual practice to employ this sort of foundation because the basement floor slab will serve as the foundation for the structure. These are also prevalent in locations with poor soil, and their purpose is to prevent the concrete floor from cracking as a result of the settlement. Mat foundations are often more than twelve inches deep, as opposed to four to five inches deep for a standard concrete floor slab. This is because mat foundations are designed to handle the significant structural loads that are imposed on the building by its columns and walls. After that, the weight of the structure is distributed uniformly across the ground below it. This particular sort of foundation is typically less expensive and simpler to put into place than a large number of individual footings, particularly in situations where the load points on the upper level are not yet completed.
Types of Deep Foundations
Pile foundations are a sort of deep foundation that takes the form of a thin column or cylinder and can be constructed out of either concrete or steel. A pile foundation is a type of foundation that is used to transfer large loads from a structure to solid rock strata that are located several feet below the surface of the earth. They are constructed to provide support for the structure and to transfer the load at a particular depth, which is typically three times greater than its breadth . Large constructions and areas with shallow soil that cannot withstand settlement or uplift are perfect candidates for foundations made of piles. The following are some other categories that can be applied to pile foundations:
- Sheet Piles, which are employed for the purpose of providing lateral support
- Load Bearing Piles: These are the piles that are used to carry the vertical loads from the structure to the ground below.
- End Bearing Piles: These piles have a bearing surface at their bottom end, which can be a layer of solid ground or rock. The pile sits on a layer of dirt that acts as a transition between weak and strong.
- Friction Piles: These piles transfer a load of a building to the surrounding soil using the frictional force that exists between the surface of the pile and the soil in its immediate vicinity.
Another sort of deep foundation with a high-capacity, cast-in-place part that is constructed using an auger is called a drilled shaft. Caissons are another name for drilled shafts. In addition to offering structural support, drill shafts also contribute to the retention of earth. To make a hole with the specified diameter and depth, a drill is typically utilized. At this stage, casing or drilling fluid may be utilized if it is determined that the hole needs more support in order to remain open. After that, a piece of reinforcing steel that is the full length of the hole is lowered into it, and then the hole is filled with concrete. Shaft resistance, toe resistance, or a combination of the two may be utilized by the finished foundation in order to provide resistance to loads imposed by the structure. Drill shafts can transfer column loads that are greater than what can be transferred by pile foundations.
Cost implications of shallow and deep foundations
Because everything else is going to be constructed on top of the foundation, it is fair to say that the foundation is one of the most vital components of a building. There are a great number of indicators that will decide the kind of foundation that is required for a building. When evaluating the cost of the foundation, some key aspects to take into consideration are as follows:
- Tests of the soil, drainage, and moisture: Prior to beginning any design or building, it is advisable to contact a professional geotechnical engineer to test the soil on the site. This can be done before any design or construction begins. This will guarantee that the appropriate method is selected in accordance with the composition of the soil. After the concrete has been set, the foundation slabs and crawl spaces will need to be sealed so that they are protected from dampness and water.
- Depth: Foundations built on slopes typically need to be deeper in order to prevent the additional weight from contributing to a landslide. It may be necessary to build deeper foundations in areas with colder climates and soil that is damp in order to prevent damage caused by freezing and thawing. The cost of the structure will increase proportionately with the depth of the foundation.
- Type: The price of a concrete slab foundation can range anywhere from $4,500 to $21,000, depending on the scope of the job. – Because only a single layer of concrete is poured, monolithic slab foundations are more cost-effective. – Due to the fact that builders need to dig holes, fill them with concrete, and then connect these to the structure above, the cost of shallow foundations falls somewhere in the middle of the pricing spectrum. – The cost of constructing a retaining wall and deep foundations are among the highest of any type of foundation. This is due to the fact that these foundations are typically more difficult to build and require additional digging, equipment, and supplies.
- Building laws, permits, and local fees: It is crucial to evaluate how local restrictions may affect the cost of a project. It is also necessary to pay attention to any costs that may be imposed by the local government. Pricing will be based on the size and area of the project. Adding components to a project and obtaining the requisite permissions in order to comply with the regional building code can both result in additional costs.
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