Table of Contents

Pile Foundations

This type of foundation can be made of reinforced concrete, steel, or wood. They are large columns that reach into deep layers of the soil which act as fixed ends for the structures that they support [6].

They are used when there is a layer of weak soil at the surface. Since the layer of soil cannot support the weight of the structure, the loads of the structure bypass this layer and are transferred to the layer of stronger soil or rock that is below the weak layer. They are also used when the building has very heavy, concentrated loads (e.g. high rise structure). Pile foundations can take higher loads than spread footings [1].

End Bearing Pile

The bottom end of the pile rests on a strong layer of soil or rock. The pile acts as a column as the load of the structure is transferred through the pile onto the strong layer. The important thing is that the bottom ends rests on the surface which is the intersection of a weak and strong layer so the load can bypass the weak layer and is safely transferred to the strong layer [1].

Friction Pile

The load of the building is transferred to the soil through the full height of the pile by friction. For visualization, imagine pushing a solid 4mm metal rod into a frozen tub of ice cream. Once the rod is pushed in far enough, it is strong enough to support some of the load. The deeper the rod is placed into the tub of ice cream, the more load it can support. The amount of load that a friction pile can support is directly proportionate to its length [1].

Diagram of End Bearing Pile and Friction Pile [1]

Caissons

These are hollow substructures that can be constructed near or on the ground surface which are sunk to the desired level as a single unit. They can carry enormous loads and are commonly used for bridges [7].

Cylinders

These are small caissons with only a single cell [7].

Caisson Foundation [2]

Basement Foundations

The hollow substructure provides storage or working space below the ground level. The usage of the space controls the structural design. They’re constructed in open excavations [7].

Basement Foundation [3]

Buoyancy Rafts

“Buoyancy rafts, also known as hollow box foundations, are designed to create a semi-buoyant or buoyant substructure below which the loading on the soil is decreased to the required low intensity.” [7]. They are more expensive than other foundations so they are mainly used on sites that are on silts, soft sands and other sedimentary deposits that are very deep, or where loads can be kept concentric [7].

Buoyancy Raft [4]

Shaft Foundation

Shaft foundations are good for numerous seismic retrofit projects as they are under low overhead conditions and can be constructed near existing structures. This foundation is constructed by drilling a cylindrical hole within a deep excavation and subsequently placing a concrete or another prefabricated load-earing unit in it. It is difficult to install them under certain conditions such as soils with boulders, soft soil, loose sand, and sand underwater [7].

Dry method of construction: (a) drill the hole, (b) clean the base, (c) place reinforcement, and (d) place concrete [5]

Additional Reading

Foundation Building Code

House Foundations

Shallow Foundations

Underpinning

References

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