Deep Foundation: Importance And Types

The deep foundation’s principal duty is to transport various sorts of loads from the structure to the ground soil. A deep foundation is one in which the depth of the foundation is larger than the width of the foundation. If the necessary foundation depth exceeds 3m, the foundation must be planned as a deep foundation.

Deep foundation: Why utilise it?

There are various reasons why a deep foundation is desirable for structural stability. The major explanations, however, would be weak soils, damaged soils, unreported fills, and liquefaction.

• Weak soils: Weak soils are essentially a word used when the present soils may fail if a shallow foundation is employed.
• Compressible soils: These are soils that can shrink in volume due to soil densification. When a structure is built on compressible soil without substantial foundations, the soil will compress and pull down over time.
• Undocumented soil: This word is used when we don’t know the soil’s stability.
• Soil liquefaction happens when saturated soil loses strength, typically after an earthquake. In essence, what was solid becomes liquid.

Deep foundation: Types

The following are the most common forms of deep foundations:

• Pier foundation

A pier is a vertical column with a larger cross-section than a pile. A pier is built in a dry environment by digging a large diameter cylindrical hole to the required depth and then backfilling it with concrete.

The distinction between a pier and a cast-in-place pile is arbitrary. A pier is a cast-in-place piling larger than 0.6 m in diameter. The method of building distinguishes a pile foundation from a pier foundation. Pier foundations only transmit load through bearing, whereas pile foundations transfer load through friction and bearing.

Pier foundations are generally deeper than pile foundations. A pier foundation is suitable when the top layers consist of decomposed rock underlying strata of sound rocks. In this condition, driving bearing piles into the decomposed rock becomes problematic. A pier foundation is easily constructed in stiff clays that provide substantial resistance to the driving of a bearing pile.

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• Buoyancy rafts (Hollow box foundations)

Buoyancy rafts, also known as hollow box foundations, are designed to provide a semi-buoyant or buoyant substructure beneath that loads the soil at a reasonable frequency. They might be erected in open excavations or buried like caissons. Conventional foundations are significantly more expensive than buoyancy rafts. As a result, their use is mostly restricted to places with silt, soft sands, and other alluvial deposits, and where loads can be kept concentric. There are several plans that call for subsurface tanks or make it cost-effective to integrate deep basements into the design.

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• Caisson foundation

Caissons are hollow substructures that are built on or near the surface and then buried as a single unit to the desired depth. A caisson is a foundation in the shape of a hollow prismatic box built above ground level and then buried in one piece to the appropriate depth.

It is a water-light chamber used to build underwater foundations such as rivers, lakes, and ports. This is a section of the well’s foundation. It is a waterproof chamber used to build underwater foundations in rivers, ports, and lakes.

The caisson can be divided into three kinds:

1. The pen cassion‘s top and bottom are both open, and the caissons are hollow chambers. The bottom of the caisson has a sharp edge.
2. A pneumatic caisson is necessary when the soil within an open Caisson cannot be dug effectively. The shaft was damaged during the sinking process.
3. A floating caisson is made out of large hollow boxes that are open at the top and closed at the bottom. They float to the final place where the caissons will be built. They were sunk and filled with sand, ballast, dry concrete, and gravel.

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• Pile foundations

Load is carried to a lower level using vertical elements called piles in this foundation.

A pile is a thin structural component made of steel, concrete, or wood. A pile rammed into the piles might be constructed of wood, concrete, or steel. When hard strata are accessible at significant depth and the bedding is uneven, or the topsoil has a limited bearing capacity, or there are major fluctuations in subsoil water level, or the topsoil is expansive, this type of foundation is usually utilised. Load is carried to a pile foundation via friction and bearing.

Pile foundations are foundations that use vertical pieces known as piles to carry the load to a lower level. A pile is a thin structural component made of steel, concrete, or wood. A pile can be created in place or driven into the ground by digging a hole and filling it with concrete. These piles can be constructed from wood, concrete, or steel. When hard strata are accessible at significant depth and the bedding is uneven, or the topsoil has a limited bearing capacity, or there are major fluctuations in subsoil water level, or the topsoil is expansive, this type of foundation is usually utilised. Load is carried to a pile foundation via friction and bearing.

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