What are the foundation techniques?

A foundation is a component of a structural system that supports and sustains a building's superstructure while somehow transferring its loads to the ground. To minimize damage through repeated freeze-thaw cycles, the foundation's bottom will be below the frost level. Spread footings, which are wide concrete bases that support walls or piers and disperse the weight over a greater area, are nearly typically used to support low-rise residential building foundations. The grade concrete beam sustained by isolated footings, piers, or piles might well be built near ground level to promote the exterior wall footing, particularly if the project does not have a basement. Spread footings are used much more with some for high-rise constructions.

           Other methods for sustaining heavyweights include pilings, concrete caisson columns, and building directly on exposed rock. As of release soil, a floating foundation made up of rigid, box-like structures installed at a depth in which the weight of the soil required to establish it equals the weight of the structure sustained can be utilized. Usually, foundations are classified as shallow or deep. The application of geotechnical engineering, including soil mechanics and rock mechanics, to the design of foundation components of structures, is known as foundation engineering.

Need of stability of the structure by the foundations

Foundations are required for all load-bearing constructions for establishing the stability of the structure is ensured by the foundations for the following reasons.

• To prevent losing the underlying soil, the structure's weight should be distributed across a broad region.
• To protect the building against natural disasters such as frost heaves, earthquakes, floods, tornadoes, and wind.
• To create a level construction surface.
• To secure the structure firmly in place, improving its stability and reducing overloading.
• To keep the supporting structure from moving to the side

Functions of foundation in construction

Based on the functions of the foundation in building, the following are the primary responsibilities of the foundation:

1. Ensure the structure's entire lateral stability.

2. The foundation's purpose is to provide a level platform for the building of the substructure.

3. Load distribution is done in an even approach.

4. The load intensity is decreased to remain within the soil's safe bearing capability.

5. The influence of soil movement is controlled and avoided.

6. The building of foundations solves the concerns of scouring and seeking to undermine.

Requirements of a good foundation

Several key conditions must be met in the design and construction of a high-performing foundation. The following are the details:

• The foundation is planned and constructed to sustain as well as transmit dead and imposed loads to the soil. This transfer must be completed without causing any settling that might compromise the structure's structural stability. Using a foundation with a firm basis helps avoid varying settlements. These problems are worsened when the superimposed loads are not evenly distributed.
• Due to the soil and area, a deeper foundation is recommended to safeguard against any damage or strain. Temperature fluctuations, which induce shrinking and swelling, cause the bulk of them. The foundation must be built in a location that is not impacted or influenced by future works or circumstances

Deep foundations' techniques

The following are the many types of deep foundations that are often used:

1. Basement foundation

These are hollow substructures that provide below-ground working or storage crawl space. Rather than considering the most effective means of resisting external earth and hydrostatic pressures, the structural design is guided by their functional needs.

2. Buoyancy rafts (Hollow box foundations)

Buoyancy rafts are hollow substructures that offer a buoyant or semi-buoyant substructure whereby net soil loading is decreased to low intensity. As transmit stresses from a structure towards stronger, deeper, and less compressible soils as well as rocks, and for other functional purposes, deep foundations are necessary. Deep foundations were constructed too deep under the completed ground surface, allowing surface conditions to affect its base payload capacity; depths of greater than 3 m under the finished floor are typical. If inappropriate soils are available near the surface, a deep foundation could be utilized to transmit the weight to a deeper, more capable stratum at depth.

3. Cylinders 

Cylinders are small single-cell caissons.

4. Drilled shaft foundations

Shaft foundations are built within deep excavations and are supported by in-place lining before being filled by concrete or other prefabricated load-bearing components.

5. Pile foundations

Pile foundations are long, slender members built by trying to drive preformed units to the desired founding level, either by driving or drilling-in tubes to a required depth the tubes becoming filled to concrete either during withdrawal or through drilling unlined or partially lined boreholes that are then made of concrete. 

Historical types of foundation techniques

The simplest foundation is a padstone. Wood in touch with the earth has long been used to construct buildings and constructions. Technically, post-in-ground construction does not require a foundation. Even beneath stone or brick walls, timber pilings were employed on soft or damp ground. Grillage is a crisscross of timbers or steel beams in concrete used in maritime and bridge construction.

Padstones: The padstone, a single stone that both spreads the weight on the ground and elevates the lumber above the ground, is perhaps the most basic foundation. Padstones known as saddle stones are a kind of padstone.

Stone foundations: Many regions of the world use dry stone and stones placed in mortar to create foundations. After construction, dry placed stone foundations may have been coated with mortar. Hewn, quarried stones are sometimes used for the visible course of stone.  Stones can be used in a gabion instead of mortar.  One drawback is that the gabion would endure a considerably shorter time if normal steel rebars were used instead of mortar (due to rusting). This disadvantage might be mitigated by using weathering steel rebars.

Rubble trench foundations: The foundation of a rubble trench is a shallow trench filled with rubble or stones. These foundations extend below the frost line and may include a drainpipe to aid in the drainage of groundwater. They're best for soils having a capacity of more than 10 tonnes per sq. meter.

Modern types of foundation techniques

Deep foundations

Used to transfer a load of a structure down through the upper weak layer of topsoil to the stronger layer of subsoil below. There are different types of deep footings including impact-driven piles, drilled shafts, caissons, helical piles, geo-piers and earth-stabilized columns. Various engineers have different naming standards for different types of footings. Piles have been made of wood, steel, reinforced concrete, and pre-tensioned concrete in the past.

Shallow foundations

Footings are usually a meter or so deep in the ground. The spread footing, for example, comprises concrete strips and pads that stretch well below the frost line and transmit weight between walls and columns towards the soil as well as bedrock. The slab-on-grade foundation is another popular form of shallow foundation, in which the structure's weight is transmitted to the earth by a concrete slab placed at the surface. Reinforced mat slabs, which range in thickness from 25 cm to several meters depending on the size of the building, or post-tensioned slabs, which are generally at least 20 cm thick for dwellings and thicker for heavier buildings, can be used for slab-on-grade foundations.

Monopile foundation

A type of deep foundation in which a single, generally large-diameter structural element is implanted through into soil to sustain all the loads of a large above-surface structure. During recent times, several monopile foundations have indeed been utilized to build fixed-bottom offshore wind at shallow-water subsea sites. A geotechnical engineer designs foundation to have a sufficient load capacity based on the kind of subsoil/rock supporting the foundation, while a structural engineer may design the footing itself. Settlement and bearing capacity are the two most important design considerations. Total settlement and differential settlement are usually considered while deciding on a settlement. When one portion of a foundation settles more than another, this is known as differential settlement. This might cause issues with the structure that the foundation supports. Clay soils with a lot of crawl space might also be problematic. 

Context and Application

This topic is useful for the students who undertake the following courses:

• Bachelor in Technology in Civil engineering

• Master in Technology in Civil engineering

• Bachelor in Science in Physics

• Masters in Science in Physics
• Architecture engineering

Practice Problems

1. Which of the following is a historical type of foundation?

1. Monopile foundation
2. Shallow foundations
3. Stone foundations
4. None of these

Ans. Option (c)

Explanation: Stone foundations are one of the historical types of foundations.

2. Which of the following is a modern type of foundation?

1. Padstones foundation
2. Shallow foundations
3. Stone foundations:
4. None of these

Ans. Option (b)

Explanation: Shallow foundations are one of the historical types of foundations.

3. In which portion of the building structure a foundation is used?

1. Lower
2. Above
3. Middle
4. None of the above

Ans. Option (a)

Explanation:  The foundation is used in lower portion of the building structure.

4. What is the other name of Caisson foundation?

1. Pier foundation
2. Padstones foundation
3. Shallow foundations
4. Stone foundations:

Ans. Option (a)

Explanation: Pier foundation is also called the Caisson foundation.

5. Which foundation type is mostly used for building construction?

1. Combined Footing
2. Isolated footing
3. Individual footing
4. Both b and c

Ans. Option (d)

Explanation: The foundation type mostly used both Isolated footing and Individual footing for building construction. 

Related Concepts

• Basic Foundation techniques 
• Purpose, requirement condition and function of Foundation process
• Type of the Foundation techniques based on the historic and modern applications