BUILDING METHODSBUILDING METHODSFoundations and Soil typesFoundations and Soil types

Main types of foundationMain types of foundation

Foundations or ‘footings’ come under two Foundations or ‘footings’ come under two main categories:main categories:

SHALLOW and DEEPSHALLOW and DEEP

Shallow foundations or ‘spread footings’ Shallow foundations or ‘spread footings’ include pads, strip footings and rafts.include pads, strip footings and rafts.

Shallow foundationsShallow foundations

The guidelines for a shallow foundation The guidelines for a shallow foundation are :are :

They are founded near to the finished They are founded near to the finished ground surface.ground surface.

The depth is generally less than the width The depth is generally less than the width of the footing and less than 3m.of the footing and less than 3m.

They are used when the surface soils are They are used when the surface soils are strong enough to support the load strong enough to support the load imposed upon it.imposed upon it.

Deep foundationsDeep foundations

Shallow foundations are unsuitable in Shallow foundations are unsuitable in weak or highly compressible soils.weak or highly compressible soils.

DEEP foundations include piles, pile walls DEEP foundations include piles, pile walls and piers.and piers.

Deep foundations are usually at depths Deep foundations are usually at depths deeper than 3m.deeper than 3m.

Deep foundations are used to transmit the Deep foundations are used to transmit the loading to a deeper, more competent loading to a deeper, more competent stratastrata

Strip foundationsStrip foundations

These are use to These are use to support a line of loads support a line of loads such as a load such as a load bearing wall.bearing wall.

They could also be They could also be used where the line of used where the line of column positions are column positions are so close that so close that individual pad individual pad foundations would be foundations would be pointless.pointless.

Raft FoundationsRaft Foundations

These are used to These are used to spread the load from spread the load from a structure over a a structure over a large area.large area.

This would normally This would normally be the entire area of be the entire area of the structure.the structure.

Raft foundationsRaft foundations

Raft foundations are Raft foundations are often needed on soft often needed on soft or loose soils which or loose soils which have a low load have a low load bearing capacity.bearing capacity.

Pads and pile foundationsPads and pile foundations

Pad foundations support Pad foundations support an individual point of an individual point of load.load.

Piles are used to support Piles are used to support buildings in poor soil buildings in poor soil conditions.conditions.

A basic pile foundation is A basic pile foundation is a series of stilts which a series of stilts which rest on a solid load rest on a solid load bearing layer.bearing layer.

SOIL TYPESSOIL TYPES

The make up of the soil has a major The make up of the soil has a major influence on the choice of foundation.influence on the choice of foundation.

A good soil type needs to be able to cope A good soil type needs to be able to cope with loadings.with loadings.

A good soil needs to drain water well.A good soil needs to drain water well. A poor soil type will shrink, swell or move A poor soil type will shrink, swell or move

depending on the loads or conditions depending on the loads or conditions placed upon it.placed upon it.

SILTSILT

Silty soil is found in flood plains or around Silty soil is found in flood plains or around lakes.lakes.

Silt holds water well and is soft when wet.Silt holds water well and is soft when wet. Silty soil is not a very good foundation Silty soil is not a very good foundation

material unless it has been compressed material unless it has been compressed and hardened, or has been dried out.and hardened, or has been dried out.

SANDY SOILSANDY SOIL

Sand is usually considered favourable Sand is usually considered favourable from the standpoint of foundation support.from the standpoint of foundation support.

It can be a problem though usually due to It can be a problem though usually due to water.water.

Water raising through a sand deposit can Water raising through a sand deposit can create an unstable condition.create an unstable condition.

Sandy soils can hold water.Sandy soils can hold water.

CLAYCLAY

Clay is composed rock particles ground Clay is composed rock particles ground extremely fine or reduced by weathering.extremely fine or reduced by weathering.

Clay soils normally contain water.Clay soils normally contain water. Clay drains slowly and compresses when Clay drains slowly and compresses when

foundations are placed upon them.foundations are placed upon them. Clay has a tendency to absorb water and Clay has a tendency to absorb water and

swell.swell.

GRAVELGRAVEL

Gravel can be well compacted and allows Gravel can be well compacted and allows water to drain freely.water to drain freely.

Gravel soils do not hold water.Gravel soils do not hold water. The variety in particle sizes in gravel The variety in particle sizes in gravel

means that even when closely packed it means that even when closely packed it still contains voids and drains well.still contains voids and drains well.

Gravel is least likely to be affected by Gravel is least likely to be affected by drying out.drying out.

Forming foundationsForming foundations

Profile boards.Profile boards. Profiles are used to set Profiles are used to set

out foundations.out foundations. These are established These are established

outside the limit of the of outside the limit of the of the excavation and the excavation and always in pairs.always in pairs.

These can be use as These can be use as ‘sight rails’ with the aid of ‘sight rails’ with the aid of a ‘traveller’ to check on a ‘traveller’ to check on excavation depth.excavation depth.

Profile boardsProfile boards

Profile boards are Profile boards are used by the used by the groundworker to groundworker to establish foundation establish foundation width.width.

Bricklayers will use Bricklayers will use them when they start them when they start to lay the damp proof to lay the damp proof course of engineering course of engineering bricks.bricks.

Using profile boards.Using profile boards.

A number of nails are A number of nails are knocked into the top of knocked into the top of the profile directly upon the profile directly upon the relevant line to which the relevant line to which it relates.it relates.

The groundworker will The groundworker will use the centre line and use the centre line and the foundation limits to the foundation limits to guide the line of the guide the line of the excavation along with the excavation along with the ‘traveller’ board to check ‘traveller’ board to check the depth.the depth.

Using profile boards.Using profile boards.

The bricklayers rely on The bricklayers rely on the Building Line nails to the Building Line nails to guide their setting out.guide their setting out.

Lines will be set using the Lines will be set using the nails to indicate the face nails to indicate the face of the brickwork.of the brickwork.

From this line the position From this line the position of the brickwork can be of the brickwork can be marked on the foundation marked on the foundation using a spirit level off the using a spirit level off the lineline

Engineering bricksEngineering bricks

Engineering bricks Engineering bricks are used below are used below ground and are strong ground and are strong and impervious to and impervious to water.water.

They are used where They are used where the strength of the the strength of the brick and the need for brick and the need for a low level of water a low level of water absorption is absorption is paramount.paramount.

Engineering bricksEngineering bricks

Engineering bricks are not susceptible to frost.Engineering bricks are not susceptible to frost. They are load bearing and have a high They are load bearing and have a high

compression strength.compression strength. They are used up to d.p.c where they will be They are used up to d.p.c where they will be

exposed to wet and freezing conditions.exposed to wet and freezing conditions. They are used below ground because they are They are used below ground because they are

strong and impervious to water.strong and impervious to water. They are usually used where appearance is not They are usually used where appearance is not

a factor.a factor. Engineering bricks form a barrier against the Engineering bricks form a barrier against the

movement of moisture.movement of moisture.