Foundation is the part of building or structure upon which every successful building or other structure stands. The functions of foundation are to bear the weight of the structure, distribute the loads evenly to the ground, and provide stability against various forces such as gravity, wind, and seismic activity. Shallow foundations and deep foundations are the main foundation type which are used in the construction of various structures like home, building, bridges, retaining walls and such types of load bearing structures.
Types of Foundation for Your Building Construction
Mainly shallow foundations as individual footing, combined footing, strip foundation, raft or mat foundation, and deep foundations as pile foundation, caissons or drilled shaft foundation are used for home construction as per designer's suggestion. Selection of foundation type for a structure is recommended by considering the bearing capacity of soil in the worst condition and the total loads acting on the foundation of the structure along with structural needs. The depth of the foundation is an important factor which cannot be ignored while foundation design, it is also set by the designer.
Main Types of Foundations in Building Construction
The main types of foundations for building construction, homes, bridges or other structure construction are given below with their types.
1. Shallow Foundation
- Individual Footing or Isolated Footing or Pad Foundation,
- Combined Footing,
- Strip Foundation, and
- Raft or Mat Foundation.
2. Deep Foundation
- Pile Foundation
- Caissons or Drilled Shaft Foundation
Types of Foundation with Recommendation Condition
Table for types of foundation and their common recommendation conditions:
| Types of Foundation | Common Recommendation Condition |
|---|---|
| Individual, Isolated or Pad Foundation | Suitable for small, single-column loads or point loads. |
| Combined Footing | Suitable when two or more columns are closely spaced, or when loads are irregularly distributed between them. |
| Strip Foundation | Appropriate for long and continuous walls, distributing loads uniformly along their length. |
| Raft or Mat Foundation | Ideal for heavily loaded structures, where the entire building's weight is distributed across a broad area, and the soil condition is weak or loose. |
| Pile Foundation | Used when the soil near the surface is weak or unstable, and loads need to be transferred to deeper, more stable strata. |
| Caissons or Drilled Shaft | Suitable for situations with deep or waterlogged soil conditions, requiring excavation and drilling to reach stable load-bearing layers. |
Shallow Foundation
Shallow foundation is a type of foundation used in construction to support and distribute the load of a building or structure near the surface of the ground. These foundations are constructed closer to the ground's surface and rely on the bearing capacity of the soil directly beneath them. Shallow foundations are generally used in residential, commercial, and smaller construction projects where the soil conditions are favorable as per load of the structure.
1. Individual Footing or Isolated Footing or Pad Foundation
Individual footing, also known as isolated footing or pad foundation, is a type of shallow foundation used in construction to support and distribute the loads of a single column or a concentrated load from a structural element. It is one of the most common types of shallow foundations used in building construction.
Individual footings are typically rectangular, square or circle in shape and are designed to transfer the structural loads to the underlying soil or bedrock in a manner that prevents excessive settlement or tilting of the supported structure.
The size and shape of the footing are determined based on the applied loads and the bearing capacity of the soil. If the soil bearing capacity is 10 ton/m² and the load on column is 40 ton, then the size of square footing would be [(40 ton)/(10 ton/m²)]= 4 m² or 2 m × 2 m.
Types of Individual Footing or Isolated Footing with Their Function
Square Footings: (Uniform Load Distribution). Square footings distribute loads evenly in all directions. They are well-suited for columns or structural elements that exert symmetrical loads in both the X and Y directions.
Rectangular Footings: (Asymmetric Load Distribution). Rectangular footings are ideal when the load from the column or structural element is significantly heavier in one direction. They allow for a better distribution of loads in cases where the applied forces are not balanced.
Circular Footings: (Uniform Load Distribution). Circular footings evenly distribute loads in all directions, similar to square footings. They are particularly suitable for columns with circular cross-sections or when the structural design requires a circular layout. Circular shapes do not have corners, which can be stress concentration points. This can be advantageous in minimizing the risk of cracking or failure at corners.
2. Combined Footing
Combined footing is a type of foundation used in construction to support multiple columns or loads that are so closely spaced that individual footings would overlap or be too close to each other. It is essentially a single, continuous footing that supports two or more columns, thus "combining" their loads into a common foundation element. Combined footings are designed to distribute the loads from multiple columns while ensuring stability and preventing excessive settlement.
The shape and size of a combined footing depend on the locations of the columns, their loads, and the soil bearing capacity. Combined footings can have various shapes, such as rectangular, trapezoidal, or T-shaped, depending on the specific layout and load distribution requirements.
Types of Combined Footing
Rectangular Combined Footing: A rectangular combined footing is a common choice when columns are closely spaced and aligned in a straight line. It has a rectangular shape with a uniform thickness, and it extends beneath all the supported columns. This type is suitable when the load distribution is relatively uniform, and the columns are aligned without any irregularities.
Trapezoidal Combined Footing: A trapezoidal combined footing is similar to a rectangular one but has a trapezoidal shape. It is used when the columns are not evenly spaced or when the loads from different columns are not equal. The trapezoidal shape allows for better load distribution in situations where the columns are arranged asymmetrically.
Strap Combined Footing: A strap combined footing includes a connecting beam (strap) that links two rectangular or trapezoidal footings. It is employed when columns are not in a straight line and need to be supported on different footings. The strap transfers the load from one footing to the other and ensures stability and load distribution.
3. Strip Foundation
Spread foundation, also known as continuous footing, strip footing or wall footings, have a broader base compared to typical load-bearing wall foundations. The increased width of these footings serves to distribute the load of the building structure across a larger area, significantly enhancing stability. Spread footings and wall footings find application in supporting individual columns, walls, and bridge piers when the underlying soil layer capable of bearing the load is situated within a shallow depth of approximately 3 meters (10 feet) from the ground surface.
It is crucial that the bearing capacity of soil is adequate to sustain the structure's weight distributed across the footing's base area. However, these footings should be avoided in areas with the potential for groundwater flow above the bearing soil layer, as it may lead to issues like scour or liquefaction.
4. Raft or Mat Foundation
Raft foundation also known as mat foundation, is the types of foundation which is spread across the entire area of the building or the structure to support heavy structural loads from columns and walls. Mat foundations are specifically employed when the loads imposed by the structure on these elements are exceptionally high. The purpose of mat foundation is to prevent the differential settlement of individual footings, thus designed as a single mat (or combined footing) of all the load-bearing elements of the structure.
Mat foundation is particularly well-suited for use in expansive soils with lower bearing capacities, where the suitability of individual spread footings or wall footings is limited. It is economical when one-half area of the structure is covered with individual footings and wall footings are provided.
It is important to note that mat foundations should not be employed in situations where the groundwater table rises above the bearing surface of the soil. In such conditions, the foundation's use could lead to issues like scour and liquefaction, potentially compromising its stability and the overall structural integrity of the building.
Deep Foundation- Types and Functions of Deep Foundation
Deep foundation is a type of foundation used in construction to support heavy loads or transfer structural loads to deeper, more stable layers of soil or bedrock below the ground's surface. Unlike shallow foundations, which rely on the bearing capacity of the soil near the surface, deep foundations are designed to penetrate deeper into the ground to reach more competent and load-bearing strata. Deep foundations are commonly employed for large buildings, bridges, industrial facilities, and other structures where the upper layers of soil are not suitable for supporting the applied loads.
1. Pile Foundation
A pile foundation is a type of deep foundation system used to support structures, such as buildings, bridges, and other heavy structures, by transferring their load to a deeper and more stable layer of soil or rock below the surface. Pile foundations are commonly used when the shallow foundation is unable to support the weight of the structure, or when the structure needs to be anchored in an area with unstable or weak soil conditions.
Pile foundations serve as robust supports for structures, effectively countering the loads they bear through a combination of skin friction and end bearing. Their implementation is instrumental in averting uneven settling of foundations. Typically, pile foundations find their purpose in soils where surface conditions are inadequate to withstand substantial loads. In such cases, the depth to reach hard rock strata can range from 5 meters to 50 meters below the ground surface.
Pile foundations can be categorized based on their function or specific use in a construction project.
Types of Pile Foundations Based on Their Function
Load-Bearing Piles: These piles primarily serve the purpose of supporting and transferring vertical loads from a structure to deeper, more stable soil or rock layers. Load-bearing piles can be further classified based on their material (e.g., concrete piles, steel piles, timber piles) and construction method (e.g., driven piles, drilled piles).
End-Bearing Piles: End-bearing piles are designed to transfer loads to a firm stratum or rock layer located beneath weaker or less stable soil layers. They derive their capacity mainly from the resistance at their bottom tip, which rests on the stronger soil or rock.
Friction Piles: Friction piles primarily rely on the skin friction or adhesion along their length to support vertical loads. These piles are often used in situations where end-bearing capacity is limited or where the load is distributed over a larger area.
Tension Piles: Tension piles, also known as uplift piles or anchor piles, are used to resist uplift forces or tension loads. They are commonly employed in applications where structures need to be anchored to prevent uplift or overturning.
Combination Piles: Combination piles are designed to handle both vertical and lateral loads. These piles are versatile and can be used in situations where a variety of load types need to be supported or resisted.
Sheet Pile Walls: Sheet pile walls consist of interlocking sheet piles made of materials like steel or vinyl. They are used as retaining structures to resist lateral soil or water pressure and can serve both load-bearing and retaining functions.
2. Caissons or Drilled Shaft Foundation
Caissons are large, watertight structures, typically cylindrical or rectangular in shape, that are open at the top and closed at the bottom. They are constructed above ground and then submerged into the ground or water, creating a dry workspace for construction activities.
It is typically built in dry docks or onshore facilities and then transported to the construction site. Caissons are floated or sunk into place, allowing workers to excavate soil or rock from within the caisson while keeping water out.
It is commonly used in marine environments, such as for the construction of bridge piers, wharves, docks, and other waterfront structures. They are also used in the construction of some types of deep foundations for buildings.
Some Extra Points:
- Drilled shaft foundations, also known as drilled piers or bored piles, are cylindrical, deep foundation elements that are created by drilling a hole into the ground and then filling it with concrete or another suitable material. They can transfer column loads larger than pile foundations. It is used where the depth of hard strata below ground level is located within 10 m to 100 m.
- Drilled shafts are created using drilling equipment, such as a rotary drill or an auger, to excavate the soil or rock and create a borehole. After the hole is cleaned and inspected, it is filled with concrete and reinforced with steel reinforcing bars (rebar).
- Drilled shaft foundations are versatile and are used in a wide range of applications, including for the support of bridges, high-rise buildings, transmission towers, and other structures. They are especially suitable for areas with varying soil conditions.
FAQs 👉
How to Choose Type of Foundation for a Structure?
Choosing the appropriate foundation type involves a comprehensive assessment of soil, structural, environmental, regulatory, and logistical factors. Engineers and architects work together to determine the best foundation solution that ensures the safety, stability, and longevity of the construction project.
1. Soil Conditions
The properties of the soil at the construction site play a significant role in foundation selection. Engineers assess the soil's bearing capacity, composition, and depth to determine if it can support the structural loads. Weak or unstable soil may require deep foundations like piles or caissons.
2. Structural Loads
The total load imposed by the building or structure is a fundamental consideration. A foundation must be capable of safely distributing these loads to the underlying soil. Heavier or taller structures often require more robust foundations.
3. Geological Factors
Geological conditions, such as the presence of bedrock, rock layers, or groundwater, can influence foundation design. Foundations may need to be adapted to accommodate these geological features.
4. Water Table and Hydrology
The proximity of the water table and the site's hydrological characteristics can affect foundation design. High water tables may necessitate special considerations, such as water-resistant foundation materials or increased foundation depth.
5. Environmental Impact
The environmental impact of the foundation type is a critical concern. Certain foundation methods, like driven piles, can produce noise and vibration that may be detrimental to the surrounding environment. Projects in sensitive areas may require less disruptive foundation options.
6. Construction Timeline
Project timelines and construction schedules can impact foundation selection. Some foundation types can be installed more quickly than others, which can be crucial for meeting project deadlines.
7. Budget and Cost Considerations
The budget available for the project is a significant factor. Different foundation types vary in cost, with deep foundations typically being more expensive than shallow foundations. The available budget may dictate the choice of foundation.
8. Accessibility and Space Constraints
The accessibility of the construction site and any space constraints can influence foundation choices. Tight or congested sites may require specialized foundation solutions that can be installed in limited space.
9. Building Codes and Regulations
Local building codes and regulations often dictate the type of foundation that can be used for a specific project. Compliance with these codes is mandatory for safety and legal reasons.
10. Environmental Conditions
Environmental factors such as seismic activity, wind loads, and frost depth can impact foundation design. Foundations must be designed to withstand these conditions to ensure the safety and longevity of the structure.
11. Architectural Design
The architectural design and layout of the structure can also influence foundation selection. The foundation must align with the building's footprint, layout, and structural system.
12. Future Expansion
Consideration of potential future expansion or additional loads is essential. The foundation should be designed to accommodate these future needs without compromising structural integrity.
Declaimer: This post is written for educational purpose only and we do not suggest to use for professional purpose.
