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close this book Appropriate building materials
close this folder Examples of foundation materials
View the document Natural stone foundations
View the document RAMMED EARTH FOUNDATIONS
View the document Burnt brick foundations
View the document Concrete foundations
View the document Split-bamboo piles
View the document Wooden post foundation

Examples of foundation materials

 

Natural stone foundations

KEYWORDS:

Special properties

Suitable where concrete is expansive

Economical aspects

Low cost

Stability

Good

Skills required

Skilled labour

Equipment required

Masonry equipment

Resistance to earthquake

Medium to good; depends on overall design

Resistance to hurricane

Good

Resistance to rain

Good

Resistance to insects

Very good

Climatic suitability

All climates

Stage of experience

Widely used

SHORT DESCRIPTION:

• Stone foundations are made of rubble (undressed stone) or squared stone; similar construction is possible with broken brick and concrete from demolished buildings.

• The quality of mortar is of importance to achieve good strength. An example of a good mix is:

- 4 parts cement

- 1 part lime

- 12 parts clean sand

- sufficient water to make a workable mix.

• Construction should start on firm, uniform strong subsoil. It should not be started on grass, black fertile soil, filled up materials or mud.

• Under the foundation there should be a layer of lean concrete (min. 5 cm) or tamped sand; minimum depth 40 cm.

• In earthquake areas, reinforcement with wire mesh or steel rods is required, but professional advice should be sought. Further information: Bibl. 01.01, 01.05, 01.06, 20.05.


Stone in Earth Mortar (from Vorhauer, Bibl. 20.05); Stone in Cement Mortar (Bibl. 20.05)

RAMMED EARTH FOUNDATIONS

KEYWORDS:

Special properties

Only used for earth constructions on dry sites

Economical aspects

Low cost

Stability

Poor to medium

Skills required

Semi-skilled labour

Equipment required

Excavation and tamping equipment

Resistance to earthquake

Low

Resistance to hurricane

Low

Resistance to rain

Low

Resistance to insects

Low

Climatic suitability

Only very dry climates

Stage of experience

Traditional method

SHORT DESCRIPTION:

• Rammed earth foundations are made of well graded soil, preferably wig a stabiliser for water resistance and higher strength.

• The site must be well drained and great care is needed to protect the foundation from ground moisture, especially with a plastic foil or bitumen felt. Bitumen paint, or a facing of rubble stone or burnt bricks are alternatives.

• When in doubt about suitability of rammed earth foundations, they should not be used. Stabilized soil blocks can be used instead, but similar protective measures are necessary.

• Wherever possible, the earth foundation should be placed on a concrete footing.

• The foundation is made in formwork, in the same way as the walls: layers of 10 cm soil are tamped down to 6 - 7 cm, before the next layer is filled up.

Further information: Bibl. 02.06, 02.08, 02.19, 02.32, 20.05.


Procedure of Constructing a Rammed Earth Foundation (Bibl. 20.05)

Burnt brick foundations

KEYWORDS:

Special properties

Good alternative to concrete foundation

Economical aspects

Medium costs

Stability

Medium to good

Skills required

Masonry skills

Equipment required

Masonry equipment

Resistance to earthquake

Medium to good

Resistance to hurricane

Medium to good

Resistance to rain

Good

Resistance to insects

Good

Climatic suitability

Most climates, except consistently wet areas

Stage of experience

Widely used

SHORT DESCRIPTION:

• Burnt brick foundations are principally the same as masonry wall constructions, but begun under the ground, either directly on a bed of tamped sand or lean concrete, or on a concrete footing.

• A widened base is preferable to distribute the weight of the walls.

• Care must be taken to lay the bricks in perfectly level courses, and measures for waterproofing are important.

• A good mortar for masonry foundations is:

- 4 parts cement

- 1 part lime

- 12 parts clean sand

- sufficient water to make a workable mix.

• In earthquake areas, masonry foundations should be reinforced with wire mesh or thin rods. Professional advice should be sought. Further information: Bibl. 20.04, 20.05.


Burnt Bricks in Cement Mortar (Bibl. 20.05)

Concrete foundations

KEYWORDS:

Special properties

Strongest foundation

Economical aspects

Expensive

Stability

Very good

Skills required

Skilled labour

Equipment required

Form work, cement mixer

Resistance to earthquake

Very good

Resistance to hurricane

Very good

Resistance to rain

Very good

Resistance to insects

Very good

Climatic suitability

All climates

Stage of experience

Commonly used worldwide

SHORT DESCRIPTION:

• Concrete foundations on hard, uniform ground can be made without steel reinforcement, if not in an earthquake or hurricane prone area.

• All non-uniform andproblem soils require reinforced concrete foundations, especially in areas of medium to high rainfall and natural hazard regions.

• Depending on the strengths required, concrete mixes can vary from 1: 3: 4 (cement: sand : gravel) to 1: 4: 7, the higher proportion of cement being required for reinforced concrete.

• Water contents of fresh mixes should make them just easily workable. Excessive water leaves pores in the concrete, making it weak and water absorbent. Foundation trenches should also be properly wetted to avoid excessive absorption of the water from the mix.

• The concrete should be wet-cured for 3 to 7 days before building the walls. A damp-proof course should be laid between foundation and wall.

Further information: Bibl. 20.03, 20.04, 20.05.


Cast Concrete Foundations (Bibl. 20.05)


Reinforced Foundations

Placing concrete footing without shuttering: the reinforcement is laid after the lowest course of lean concrete is hardened. The richer second layer holds the reinforcement.

Foundation strip poured into shuttering of wood or plywood. These should be oiled before pouring concrete, to facilitate removal after hardening.

The finished foundation, with the trench filled up with the previously excavated soil and well compacted.

Foundations on Expansive Clay (Bibl. 20.03)

• Certain clayey soils respond to moisture movements (in rainy and dry seasons, moisture extraction by trees, etc.) with excessive swelling and shrinkage, which can severely damage foundations and consequently entire buildings.

• Damage can be avoided by either installing foundations which penetrate through the zone of ground movement, or by constructing foundations and superstructures which are tolerant of ground movement.

• Pile-and-beam-foundation: Small diameter piles are installed below the zone of clay movement; RC ground beams, which span between pile heads are constructed on compressible material (eg expanded polystyrene), which absorbs ground movement without affecting the beams and superstructure.

• Pad-and-beam-foundation: Pads are installed on stable ground below the movement zone; RC columns support ground beams, which are constructed in the same way as in the pile-and-beam-foundation.


Pile-and-beam-foundation; Pad-and-beam-foundation

Split-bamboo piles

KEYWORDS:

Special properties

Used for subsoil stabilization

Economical aspects

Low cost

Stability

Good

Skills required

Special training

Equipment required

Drop hammer

Resistance to earthquake

Good

Resistance to hurricane

Good

Resistance to rain

Good, helps to drain water

Resistance to insects

Low

Climatic suitability

All tropical areas

Stage of experience

Experimental

SHORT DESCRIPTION:

• Split-bamboo piles have been developed to improve the bearing capacity of soft compressible soils and to reduce settlements for various types of construction works, such as buildings, roads, etc.

• The hollow bamboo culms are filled up with loosely wound coconut coir and jute thread wrapped in jute fabric; holes in the culm permit the water in the soil to tackle in, thus drying out the soil and improving its load-bearing capacity.

Further information: Dr. M.A. Aziz or Dr. S.D. Ramaswamy, Department of Civil Engineering, National University of Singapore, 10 Kent Ridge Cresent, Singapore 0511; Bibl. 20.01.

Split-Bamboo Pile

Split-bamboo piles filled up with loosely wound coconut coir strands of about 6 mm diameter each tied up with spirally wound jute thread along its length and wrapped with a layer of thickly knit jute burlap have been successfully used. Treated split-bamboo steps were holed at random points and tied up together at regular intervals with galvanized iron wire after putting the coconut coir wicks inside along its entire length (Fig. 1).


FIGURE 1; FIGURE 2

Stabilized Area

These specially made split-bamboo piles were used in stabilizing the soft compressible subsoil of an actual construction site (Fig. 2) which consisted of a top layer of about 2 m thick soft to medium stiff sandy clayey silt underlain by a layer of about 6 m thick very soft silty clay which was again underlain by a layer of medium dense silty clayey sand. The split-bamboo piles, each about 8 m long, 80 to 90 mm diameter, were driven by a drop hammer at 2 m spacing in a square grid. After installation of the piles the entire area was covered with about 2 m surcharge of sandy materials (Bibl. 20.01).

Wooden post foundation

KEYWORDS:

Special properties

Used for spot and pile foundations

Economical aspects

Low cost, if sufficient timber is available

Stability

Low to good

Skills required

Carpentry and construction skills

Equipment required

Carpentry and masonry equipment

Resistance to earthquake

Low to good

Resistance to hurricane

Low to good

Resistance to rain

Low to good

Resistance to insects

Low

Climatic suitability

All, except consistently wet climates

Stage of experience

Traditional methods

SHORT DESCRIPTION:

• Wooden post foundations can only be used for lightweight structures, that is buildings made of timber, bamboo and/or other vegetable material.

• The main drawback of using timber for foundations is the risk of weakening due to attack by insects (mainly termites and beetles), fungus and rodents. Hence, protective measures are necessary. (See sections on Timber and PROTECTIVE MEASURES.)

• Timber posts can be driven into the ground, if the climate is predominantly dry, the site is well drained and destructive biological agents (mainly termites) are not common in the area. Further information: Bibl. 14.18, 14.22, 20.04, 20.05.

Simple Wooden Post Foundations (Bibl. 20.05)


Only for dry areas without termites.


Wooden Posts on Concrete Footings (Bibl. 20.05)

Only for dry areas without termites.


Wooden Posts without Ground Contact (Bibl. 20.05)