This document discusses different types of foundations for buildings. It describes three main types: strip foundations, which involve digging a trench and pouring concrete; raft foundations, which distribute weight over a larger area for poor soil; and piled foundations, which are used for large, heavy buildings on poor ground. The type of foundation depends on factors like the structure's weight, purpose, soil composition, and costs. Raft foundations are suitable for poor soil because they spread the load over a greater area, unlike individual piles that can sink into soft ground.

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PowerPointpresentation
Presentation 3: Types of foundations
Unit 101: Principles of building construction,
information and communication

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Aim
Introduce learners to foundations and their uses.
Objectives
• List at least two types of foundations.
• Explain one method on how foundations work.
• Link at least two buildings to the foundations they will require.
• State and explain a foundation that can be used on poor ground.

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Foundation types
Before foundation types are decided, a number of factors regarding the
structure and the site it is to be constructed on will have to be
considered. These include the:
• weight of the proposed structure
• purpose of the proposed structure
• soil composition of the proposed site (soil mechanics)
• history of the proposed site
• feasibility of costs.

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Weight of the structure
The weight and distribution of loads of the proposed structure will have
a direct impact on the loads undertaken by the sub-strata.
For example, a six-storey building will apply a greater pressure than a
two-storey building.

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Purpose of structure
The applied weights of the structure will also be affected by the
proposed use of the structure.
For example, the foundations at the Nissan car plant would be under
more load than that of a office building. However, many buildings have
mixed-use requirements. Some structures, for example, have an office
block attached to a factory which may house heavy machinery.

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Soil on site
Aspects that determine the soil type are:
• greenfield site
• brownfield site
• water table.

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Greenfield sites
Greenfield sites are areas which have never been developed (built on).
They are highly sought after by developers as they are often easier and
cheaper to construct on than brownfield.
There may be planning restrictions on greenfield sites.

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Brownfield sites
Brownfield involves land that has either been developed or is currently
in use. The redevelopment of previously developed land often incurs
higher build costs due to:
• demolition
• decontamination
• site clearance
• proximity of adjacent structures
• traffic problems.

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Make-up of subsoil material
Different soil structures have differing loading-bearing abilities.
For example, when you walk on a beach you will sink partially into the
sand.
If you are walking on a footpath, the slab is able to bear your weight.
The same principal applies when putting structures on different soil
types.

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Types of foundations
There are three main types of foundations commonly used within the
construction industry:
• strip foundation
• raft foundation
• piled foundation.

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Task
Sketch and label each foundation.

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Strip foundation
Strip foundations are arguably the
cheapest form of foundation available
to designers and constructors.
Strip foundations involve the removal
of a strip of land to a set depth and width.
Concrete is then poured into the
strip/trench and tampered level.
Strip foundations can only be used on
firm, good load-bearing strata, and
economically to a depth of no more
than 1.5–2.0 metres.
Traditional strip foundation
Trench fill

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Raft foundations
Raft foundations are often used where the ground has poor load-
bearing capacity.
Again, using sand for example, if you were to poke your fingers into
sand they would sink to a certain depth. However, if you were to hold
your hand flat across the same sand, the sand would offer more
resistance due to the load being applied across a greater area.
This is the principal of a raft foundation.

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Piled foundations
Piled foundations are frequently used on large, heavy buildings, or
where the ground has poor load-bearing capabilities.
However, piled foundations are more expensive than both strip and raft
foundations.

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Tasks
List at least two types of buildings and the foundations they will require.
State and explain a foundation that can be used on poor ground.

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Any questions?