FOUNDATION

FOUNDATION Lowermost part of a building which transmits

the load of building to the underlying earth.

Major functions of the foundation It distribute non-uniform load of the superstructure

evenly on the subsoil hence it minimize chances of

differential settlement.

It provides stability against scouring flood water.

It provides stability against sliding.

It provides a level surface for the construction of

the superstructure

TYPES OF FOUNDATION

WALL FOOTING/SPREAD

FOOTING

Footing provided under a

wall.

light load- simple footing

is provided.

Heavy load- stepped

footing is provided.

ISOLATED FOOTING/COLUMN FOOTING

It is used to support isolated columns

Size of footing is very large- stepped or sloped

foundation

Reinforced cement concrete footing is provided for

heavy loads.

Load transmitted through the foundation to soil should

be less than bearing capacity of soil.

COMBINED FOOTING

It is constructed for two or more column

Isolated footings of individual column overlaps or

when external column is situated near the boundary.

Footing: Rectangular or trapezoidal.

Rectangular footing

provided when load acting on two columns are almost equal.

Trapezoidal footing

Provided when load acting on the column is very high

When one of the column is very close to the boundary.

Rectangular footing

Trapezoidal footing

MAT /RAFT /FLAT FOUNDATION

It is a concrete slab which cover the entire area below the building.

Column loads are heavy.therfor reinforced concrete slabs are provided

Mat foundation are used When Soil is soft clay or made up land Highly compressible soil to reduce settlement. It can face large settlement without causing any

harm to the super structure.

Raft Foundation

Raft Foundation

Foundation for Steel columns- Grillage foundation

High rise Buildings are built with steel columns encased in concrete. Such columns carry heavy load and hence, they need special foundation to spread the load over a large area of soil. Grillage foundation is one such foundation. It consists of one or more tiers of I section steel beams as shown in figure. The top tier consists of fewer but large sized steel beams while the lower tier consists of large number but smaller sized steel beams. The column load is transmitted to the top tier through a base plate. The steel beams are not painted but they are encased in concrete with a minimum cover of 100mm beyond the edges

1 .PILE FOUNDATION

The top soil is not capable of taking the load even at 3m depth.Then we go for pile foundation.Loads taken to a lower level by means of long vertical member made up of timber, steel, concrete.

Deep Foundation

PILE FOUNDATION

A pile is a slender column made of wood,concrete or steel. A plie is either driven into the soil or formed in situ by cutting a core in the dround and then filling with concrete.A group of piles are provided up to the required depth and are capped with RCC slab.The structure is built over the pile cap.Piles transfer the load to the soil by friction or by direct bearing.In case of direct bearing,the piles are taken up to the hard strata

Classification of Piles according to method of load

transfer

Bearing pile

Friction piles

Bearing piles rest on hard strata and transfer the load by direct bearing. Such piles are preferred, if hard layer is available at reasonable depth.

Friction Piles transfer the load by friction between the soil and pile. This type of pile is preferred if hard strata is not available even at considerable depth. The frictional resistance is assessed before deciding the length of the pile. The surface of such piles is made rough to increase the skin friction so as to reduce the required length,

Based on material

Wooden or Timber pile

Concrete pile

Steel piles

Composite piles

Sand piles

Concrete piles

Precast concrete piles

Cast-in-situ piles

Pre-cast concrete piles Are reinforced with steel and

manufactured in factories

Square section , Circular, and

Octagonal sections with chamfered

corners

crossectional dimension of piles –

25cm to 60cm

Length of piles – 3 to 30m

At lower end, shoes are provided.

Shoes of 20cm depth and 15cm

width

Advantages

Piles can driven under water also.

High resistance to biological action of the soil.

Disadvantage

They need more time to manfacture

They are heavy to handle.

Cast in situ piles

Cast at the place where they have to function by

driving a casing into an excavated hole

Filling up the casing with concrete.

If the hole is filled with plain concrete only, it is

known as Pressure pile.

Cast in situ piles

The load carrying capacity of concrete piles may be

increased by inserting reinforcement caging in the bored

hole and by providing one or two under reams. This is

followed by concreting. Such piles are known as under-

reamed piles. These piles are provided at regular intervals

of 2-3m and then capping beam is provided over them.

Pressure pile & Under – reamed pile

Under –reamed pile

Timber Piles

• Seasoned wooden piles • Square or circular piles• Cross-sectional dimension 20 to 40cm• length 20 times the cross sectional dimension• Bottom is sharpened and provided with Iron Shoe• To avoid decay, the top of wooden piles should be below water

table since wooden piles should not be subjected to alternate wet and dry conditions .Hence, they are preferred for positions below water table .The portions above water table are built with concrete.

• Cheap and can be driven Easily• Load carrying capacity low• Likely to be damaged while being driven into the soil.

TIMBER PILES

Composite Piles

Composite piles may be timber and concrete or steel and concrete.

Steel Piles

Tube

I section or H section

Steel Piles

Steel Piles

Box - section

Cross section of steel piles

STEEL PILES :

A steel pile may be rolled steel I-section , or a box type fabricated section or a tube.

These piles are used as bearing piles .

If tube or box section is used , the soil inside the section is driven out by compressed air and concrete is filled .

They are commonly used for columns very close to the existing structures , as they disturb the soil least.

Sand Piles : These piles are formed by boring a hole of the required diameter and then filling it with sand .

The sand is rammed until it doesn’t escape or settle.

The top of the sand pile is fitted with concrete to prevent the movement of sand at the top.

Diameter of sand pile is 30 cm and the length is 12 times the diameter.

It can take loads up to 1000 kN/m2 or 10000 t/m2

They are economical .

They should not be used in earthquake prone regions.

Pile caps are provided over a group of piles as shown in figure.They are usually a concrete platform to provide a platform to build the structure over them. The pile cap distributes the load evenly to all pilesThe pile should project at least 10cm inside the capPile caps provided to single piles also protects the head of the pile,

PILE CAPS

PILE SHOES

Theory from test book

Pile Driving and Load test on piles

Well foundation

Well FoundationWell foundations are required in areas surrounded by water, Such foundations are usually required for foundations of bridge pier,

A cofferdam is a temporary structure built around a construction site to remove water and make the construction area reasonably dry.

Caisson is a watertight chamber in which underwater construction work can be done. After the work is completed, the caisson becomes a permanent part of the construction work.

Caissons

Open Caissons

STEINING

Box caisson

Box Caisson

Box Caissons

They are open at top and closed at the bottom.

They are made up of timber, RCC or steel.

They are built on land and then floated to the site and sunk

Before sinking the box caisson, the bearing surface is levelled by sand filling

The caisson is sunk by filling with sand or gravel.

The top of the caisson is then plugged.

Pneumatic Caissons