FOUNDATION
Pile foundations and their pros and cons explained
Piles are often in the shape of a tree trunk- either made of wood, concrete or steel. All piles are either driven into the ground by force or are cast in place. This casting in place is often done by driving a thin, round and hollow metal tube to the right depth into the soil. All soil inside the metal tube is taken out of the ground and the casting material is poured into the hole to create the pile.
The most famous pile construction is the city of Venice in Italy, which is entirely built on piles.
Pile foundation design:
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Pile foundations are usually carefully designed by an engineer to ensure the right depth, quantity, and distance between each pile. Good design leads to an even weight distribution by the soil underneath the building. Pile foundations are very much suited to sites where the soil at the depth for a different foundation is too weak (2).
Types of piles:
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The transfer of the building weight into the soil can be done in two ways:
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The end-bearing pile, where the pile is driven to the solid soil and transfers the entire weight down.
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The friction pile, where the pile transfers the weight across its entire length in the soil. Here, the pile does not need to be driven down as far as the end-bearing pile.
Advantages of pile foundations:
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Wiring and plumbing work under the house is easier accessible
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Pile foundations add higher protection during earthquakes (1)
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Pile foundations lower the risk of flooding as water can go underneath the house and drain naturally
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Less disturbance created for the soil underneath the structure
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Inspection underneath the house for termites or any other work is easier
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Easier installation on hilly sites as the ground does not require to be flattened
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Disadvantages of pile foundations:
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Less energy-efficient as there is a large gap between the soil and the building
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Potentially more expensive depending on the soil and the extra insulation required
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Construction takes often longer than a slab foundation and can be more expensive
Environmental effects:
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Wooden piles are usually treated to the H5 hazard category- with copper, chromium and arsenic. While the mixture is relatively inert once it is in the wood, it is not recommended to utilize this type of treated wood for as example play areas (3).
Concrete and steel piles are also an environmentally friendlier version than a slab foundation as they use less material.
Sources:
(1) Computers and Geotechnics, Volume 55, January 2014, Pages 172 - 186; Authors: Aslan S. Hokmabadi, Behzad Fatahi, Bijan Samali, 'Assessment of soil–pile–structure interaction influencing seismic response of mid-rise buildings sitting on floating pile foundations'
(2)' Foundation Engineering', Publisher: Wiley, 1974, Chapter 12, Page 203, Authors: Ralph B. Peck, Walter E. Hanson, Thomas H. Thornburn
(3) www.level.org.nz, 'Working with treated timber', 16.12.2014