foundation -rahul

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FOUNDATION:-A Foundation is that part of structure which is in direct contact with the

ground to which the loads of the superstructure are transmitted to the sub soil.

The basic function of foundation is to transmit the dead loadas,super imposed loads and

wind loads from a building to the soil on which the building rests.

FUNCTIONS OF FOUNDATIONS:-

1.Reduction of load intensity

2.Even distribution of load

3.Provision of level surface

4.Lateral stability

5.Safety against undermining

6.Protection against soil movements


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TYPES OF FONDATIONS:- Shallow Foundation

Deep Foundation

SHALLOW FOUNDATION:-When depth of foundation is less than its width is called shallow

foundation.

Types of Shallow Foundation:-

1)Spread Footings:-spread footings are those which spread the super imposed load of wall

or column over a larger area.

a)single footing for a column:-In which the loaded area of the column has been spread

through spread.the base is made of concrete.


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b) Stepped footing for a column:- it is used for heavily loaded column which requires

greater spread.

c)slopped footing:- In this case the concrete base does not have uniform thickness

,but is made sloped.

d)Grillage Foundation:-It is a special type of isolated footing generally provided for

heavily loaded steel stanchions and used in those locations where bearing capacity of

soil is poor.The depth of such a foundation is limited to 1 to 1.5 m.


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2)Combined Footings:-A spread footing which supports two or more columns is termed as

combined footing.the combined footing for columns will be rectangular in shape if they

carry equal loads.If the columns carry unequal loads the footing is of trapezoidal shape.


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3) Strap Footings:- If the independent footings of two columns are connected by a

beam,it is called a strap footing. A strap footing may be used where the distance

between the columns is so great that a combined trapezoidal footing becomes quite

narrow,with high bending moments.in this case each column is provided with its

independent footings and a beam is used to connect the two footings.

The strap is used to transfer the column loads on to the soil with equal and uniorm soilpressure under both footings.


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4)Mat Founda tion:-A raft or mat is a combined footing that covers the entire area beneath

a structure and supports all the walls and columns.

Use:- 1) when the allowable soil pressure is low or the building loads are heavy.

2) they also used where the soil mass contains compressible lenses or the soil is

sufficienty erratic .

3) It is used to bridge over the erratic deposits and eliminates the differential settlements.

4) it is also used to reduce settlement above highly compressible soils by making the

weight of the structure equal to the weight of the soil excavated.


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A large, thick concrete slab that sustains the load imposed by a number of

columns and walls.

The method to reduce or distributed building loads in order to reducedifferential settlement between adjacent areas.

Mat Foundations are generally used with soil that has a low bearing capacity.

ADVANTAGES

1)Good in low soil bearing conditions.2)Can distributed the building pressure over a large area, so the soil can bear

the stress.

Reducing differential settlements as the concrete slab resists differential

movements between loading positions.

Have haunches that go below the slab portion to resists punching shear from

column or large concentration loads.


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2)DEEP FOUNDATION:-When depth of foundation is greater than its with is called deep

foundation.

TYPES OF DEEP FOUNDATION:-

1)Pile Foundation:-pilefoundation is that type of deep foundation in which the loads are

taken to a low level by means of vertical members .

USE:- 1)where no firm bearing strata exists at any reasonable depth and the loading is

uneven.

2)when a firm bearing strata exist but at a depth such as to make strip or spread

footing uneconomical.

3)when pumping of sub soil water would be too costly.


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Well Foundation:-Well foundations or cassions are box like structure-circular or rectangular

-which are sunk from the surface of either land or water to the desired depth.

USES:-

1)Bridges piers and abutments in rivers,lakes etc.

2)Wharves,quay walls,docks.

3)break waters and other structures for shore protections.

4)Large water front structures such as pump houses,subjected to heavy vertical and

horizontal loads.


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