Power point foundations L1

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City & Guilds Construction

PowerPoint presentationPresentation 3: Types of foundations

Unit 101: Principles of building construction,

information and communication



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.



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.



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.



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.



Soil on site

Aspects that determine the soil type are:

• greenfield site

• brownfield site

• water table.



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.



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.



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.



Types of foundations

There are three main types of foundations commonly used within the

construction industry:

• strip foundation

• raft foundation

• piled foundation.



Task

Sketch and label each foundation.



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



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.



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.



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.



Any questions?

Documents

Power point foundations L1