FoundationsFoundations

DefinitionDefinition Foundation is the lowest part of a structure which Foundation is the lowest part of a structure which

provides a base for the super- structure proper.provides a base for the super- structure proper.

Purpose of FoundationPurpose of Foundation To distribute the weight of the structure To distribute the weight of the structure

over large area son as to avoid over-over large area son as to avoid over-loading of the soil beneath.loading of the soil beneath.

To load the sub-stratum evenly and thus To load the sub-stratum evenly and thus prevent unequal settlement.prevent unequal settlement.

To take the structure deep into the ground To take the structure deep into the ground and thus increase its stability ,preventing and thus increase its stability ,preventing overturning.overturning.

Types Of FoundationsTypes Of Foundations Foundations can be broadly Foundations can be broadly

classified into two typesclassified into two types (i). Deep Foundations(i). Deep Foundations (ii). Shallow Foundations(ii). Shallow Foundations Again Deep Foundations can be Again Deep Foundations can be

classified as Pile, Cofferdams classified as Pile, Cofferdams and Caisson Fall Foundations.and Caisson Fall Foundations.

Shallow FoundationsShallow Foundations When the foundation is placed immediately When the foundation is placed immediately

beneath the lowest part of the super structure, it beneath the lowest part of the super structure, it is termed as the Shallow Foundations.is termed as the Shallow Foundations.

The object of this type of foundation is to The object of this type of foundation is to distribute the structural loads over a wide distribute the structural loads over a wide horizontal area at shallow depth below the horizontal area at shallow depth below the ground level.ground level.

Various types of Shallow Foundations are as Various types of Shallow Foundations are as followsfollows

1.Spread Footings 2.Grillage 1.Spread Footings 2.Grillage FoundationsFoundations

3. Eccentrically Loaded footings 4. Combined 3. Eccentrically Loaded footings 4. Combined FootingsFootings

5. Mat or Raft Foundations.5. Mat or Raft Foundations.

Spread FootingsSpread Footings As the name suggests, in case of Spread As the name suggests, in case of Spread

Footings ,the base of the member Footings ,the base of the member transmitting load to the soil is made transmitting load to the soil is made wider so as to distribute the load over wider so as to distribute the load over wider area. wider area.

The various Footings described under The various Footings described under this category are:this category are:

(a). Wall Footings (a). Wall Footings (b). Reinforced Concrete footings (b). Reinforced Concrete footings (c ). Inverted Arch Footings(c ). Inverted Arch Footings (d). Column Footings (d). Column Footings

Wall FootingsWall Footings It consists of several courses of It consists of several courses of

bricks ,the lowest course being usually bricks ,the lowest course being usually twice the breadth of the wall abovetwice the breadth of the wall above

The depth of each course is usually 10 The depth of each course is usually 10 cm.cm.

A bed of lean concrete of uniform A bed of lean concrete of uniform thickness is first spread over the entire thickness is first spread over the entire length of the wall.length of the wall.

The concrete bed provides a plain The concrete bed provides a plain surface upon which the masonry work surface upon which the masonry work for wall footing can be started directlyfor wall footing can be started directly..

Reinforced Concrete Reinforced Concrete FootingsFootings

In places where the wall are subjected to In places where the wall are subjected to relatively heavy loading and the bearing relatively heavy loading and the bearing capacity of the soil on which the wall footing capacity of the soil on which the wall footing is to rest is low.is to rest is low.

In such cases it is desirable to provide In such cases it is desirable to provide reinforced concrete footing below the wall.reinforced concrete footing below the wall.

This appreciably reduces the volume of This appreciably reduces the volume of masonry work in footing and depth of bed masonry work in footing and depth of bed concrete and as such proves to be concrete and as such proves to be economical.economical.

A 7 to 8 cm. thick bed of lean concrete is A 7 to 8 cm. thick bed of lean concrete is provided below the reinforced concrete provided below the reinforced concrete footing to perform the function of concrete footing to perform the function of concrete bed block. bed block.

Inverted Arch FootingsInverted Arch Footings This type of foundation used to be This type of foundation used to be

provided for multistoried buildings in provided for multistoried buildings in olden times.olden times.

However with the advent of However with the advent of reinforced cement concrete reinforced cement concrete construction practice ,inverted ach construction practice ,inverted ach construction is rarely done these days.construction is rarely done these days.

The advantage of inverted arch The advantage of inverted arch construction is that in soft soils the construction is that in soft soils the depth of foundation is greatly reduceddepth of foundation is greatly reduced. .

Column Footings Column Footings (Independent) (Independent)

An Independent footing is one which is An Independent footing is one which is provided under the column or other similar provided under the column or other similar member for distributing the concentrated member for distributing the concentrated loads in the form of uniformly distributed loads in the form of uniformly distributed load on the soil below.load on the soil below.

The footings may be square, rectangular The footings may be square, rectangular or circular in plan.or circular in plan.

Depending upon the load to be carried and Depending upon the load to be carried and the bearing capacity of the soil, the bearing capacity of the soil, independent footing may be of brick independent footing may be of brick masonry, stonemasonry, R.C.C., steel masonry, stonemasonry, R.C.C., steel Grillage Etc. Grillage Etc.

(i). Footing for brick pillar: Square footing (i). Footing for brick pillar: Square footing is the simplest and most economical to be is the simplest and most economical to be provided under pillar ,columns.provided under pillar ,columns.

(ii). R.C.C Column Footings: On account of (ii). R.C.C Column Footings: On account of their low bending strength the footings their low bending strength the footings constructed with brick ,stone or plain constructed with brick ,stone or plain concrete require considerable depth to be concrete require considerable depth to be safe to carry loads. R.C.C column footings safe to carry loads. R.C.C column footings may be circular, rectangular, or square in may be circular, rectangular, or square in plan. plan.

(iii). Stone Pillar Footings: This type of (iii). Stone Pillar Footings: This type of footing is similar in construction to the footing is similar in construction to the footing for brick pillar. In this case, the footing for brick pillar. In this case, the regular offsets on all the four sides of pillar regular offsets on all the four sides of pillar are slightly bugger in width and depth. are slightly bugger in width and depth.

Grillage FoundationsGrillage Foundations When heavy structural loads from columns , When heavy structural loads from columns ,

piers or stanchions are required to be piers or stanchions are required to be transfer to a soil of low bearing transfer to a soil of low bearing capacity ,grillage foundation is often found capacity ,grillage foundation is often found to be lighter and economical.to be lighter and economical.

This avoids deep excavation and provides This avoids deep excavation and provides necessary area at the base to reduce the necessary area at the base to reduce the intensity of pressure within safe bearing intensity of pressure within safe bearing capacity of soil.capacity of soil.

Grillage Foundations can be broadly divided Grillage Foundations can be broadly divided in the following two categories.in the following two categories.

1.Steel Grillage1.Steel Grillage 2.Timber Grillage 2.Timber Grillage

Ecentrically Loaded Ecentrically Loaded FootingsFootings As far as practically , the foundation, should As far as practically , the foundation, should

be so shaped and proportions that the centre be so shaped and proportions that the centre of gravity of the imposed loads coincide with of gravity of the imposed loads coincide with the CG of the supporting area of base.the CG of the supporting area of base.

However, when walls or columns are to be However, when walls or columns are to be placed close to property lines, the required placed close to property lines, the required supporting areas of the base cannot be supporting areas of the base cannot be placed concentrically with the imposed placed concentrically with the imposed loads without overlapping the property lines.loads without overlapping the property lines.

Hence , different methods are adopted to Hence , different methods are adopted to ensure the stability of wall or column ensure the stability of wall or column without encroaching the area outside the without encroaching the area outside the property line of building.property line of building.

Combined FootingsCombined Footings A combined footing is so proportioned that A combined footing is so proportioned that

the centre of gravity of the supporting the centre of gravity of the supporting area is in line with the CG of the two area is in line with the CG of the two column loads.column loads.

A Combined Footing may be rectangular A Combined Footing may be rectangular or trapezoidal in shape. or trapezoidal in shape.

Rectangular shape is only possible where Rectangular shape is only possible where loading condition is such that either the loading condition is such that either the two columns are equally loaded or the two columns are equally loaded or the interior column carries greater load.interior column carries greater load.

On the other hand, in case of trapezoidal On the other hand, in case of trapezoidal footing , no such condition is applicable. footing , no such condition is applicable.

Raft FoundationRaft Foundation In made-up ground , soft clay or marshy In made-up ground , soft clay or marshy

site having low value of bearing site having low value of bearing capacity, heavy concentrated structural capacity, heavy concentrated structural loads are generally supported by loads are generally supported by providing raft foundation.providing raft foundation.

It provides an economical solution to It provides an economical solution to difficult site conditions.difficult site conditions.

Raft foundation consists of thick Raft foundation consists of thick reinforced concrete slab covering the reinforced concrete slab covering the entire area of the bottom of the entire area of the bottom of the structure like a floor.structure like a floor.

Deep FoundationsDeep Foundations In case, the strata of good bearing In case, the strata of good bearing

capacity is not available near the capacity is not available near the ground, the foundation of the structure ground, the foundation of the structure has to be taken deep with the purpose of has to be taken deep with the purpose of attaining a bearing stratum which is attaining a bearing stratum which is suitable in all respects.suitable in all respects.

The most common forms of construction The most common forms of construction pertaining to Deep foundation arepertaining to Deep foundation are

(a). Piles(a). Piles (b). Cofferdams(b). Cofferdams (c ). Caissons(c ). Caissons

Pile FoundationsPile Foundations Pile Foundation is generally used when simple Pile Foundation is generally used when simple

spread foundation at a suitable depth is not spread foundation at a suitable depth is not possible either because the stratum of required possible either because the stratum of required bearing capacity is at a greater depth.bearing capacity is at a greater depth.

Depending upon their function or use of Piles Depending upon their function or use of Piles may be classified into the following types.may be classified into the following types.

(i). Bearing Piles(i). Bearing Piles (ii). Friction Piles(ii). Friction Piles (iii).Sheet Piles(iii).Sheet Piles (iv).Anchor Piles(iv).Anchor Piles (v). Batter Piles(v). Batter Piles (vi). Fender Piles(vi). Fender Piles (vii). Compaction Piles.(vii). Compaction Piles.

Bearing Piles: Bearing Piles are those which Bearing Piles: Bearing Piles are those which are driven into the ground until a hard are driven into the ground until a hard stratum is reached. Such piles act as pillars stratum is reached. Such piles act as pillars supporting the super structure and supporting the super structure and transmitting the load down to the level at transmitting the load down to the level at which it can be safely borne by the ground.which it can be safely borne by the ground.

Friction Piles: When piles are required to be Friction Piles: When piles are required to be driven at a side where the soil is weak or driven at a side where the soil is weak or soft to considerable depth, the load carried soft to considerable depth, the load carried by a pile is borne by the friction developed by a pile is borne by the friction developed between the sides of the pile and the between the sides of the pile and the surrounding ground.surrounding ground.

Sheet Piles: Sheet Piles differ from bearing Sheet Piles: Sheet Piles differ from bearing or friction piles in that they are rarely used or friction piles in that they are rarely used to furnish vertical support but are used to to furnish vertical support but are used to function as retaining wall. function as retaining wall.

Anchor Piles: When Piles are used to provide Anchor Piles: When Piles are used to provide anchorage against horizontal pull from sheet anchorage against horizontal pull from sheet piling walls are pulling forces, they are piling walls are pulling forces, they are termed as Anchor Piles.termed as Anchor Piles.

Batter Piles: When Piles are driven at an Batter Piles: When Piles are driven at an inclination to resist large horizontal or inclination to resist large horizontal or inclined forces ,the piles are termed as Batter inclined forces ,the piles are termed as Batter Piles.Piles.

Fender Piles: When the Piles are used to Fender Piles: When the Piles are used to protect concrete deck or other water front protect concrete deck or other water front structures from the abrasion or impact that structures from the abrasion or impact that may be caused from the ships they are called may be caused from the ships they are called Fender Piles.Fender Piles.

Compaction Piles: When Piles are driven in Compaction Piles: When Piles are driven in grannular soil with the aim of increasing the grannular soil with the aim of increasing the bearing capacity of the soil. These are bearing capacity of the soil. These are Compaction Piles. Compaction Piles.

Depending upon the materials used Depending upon the materials used in their manufacture, piles can be in their manufacture, piles can be broadly classified as broadly classified as

1. Timber Piles1. Timber Piles 2. Concrete Piles2. Concrete Piles 3. Composite Piles3. Composite Piles 4.Steel Piles.4.Steel Piles.

CofferdamsCofferdams A Cofferdam May be defined as a temporary A Cofferdam May be defined as a temporary

structure constructed in a river or lake or any structure constructed in a river or lake or any other water bearing surface for excluding other water bearing surface for excluding water from a given site to enable the building water from a given site to enable the building operation to be performed on dry surface. operation to be performed on dry surface.

Considering the materials used in Considering the materials used in construction , cofferdams may be divided into construction , cofferdams may be divided into the following categoriesthe following categories

1. Earthen Cofferdam1. Earthen Cofferdam 2. Rockfill Cofferdam2. Rockfill Cofferdam 3.Single Walled Cofferdam3.Single Walled Cofferdam 4.Double Walled Cofferdam4.Double Walled Cofferdam 5. Crib Cofferdam5. Crib Cofferdam 6.Cellular Cofferdam6.Cellular Cofferdam

Earthen Cofferdam: It essentially consists of an Earthen Cofferdam: It essentially consists of an earthen embankment built around the area to be earthen embankment built around the area to be enclosed. It is constructed in places where the enclosed. It is constructed in places where the depth of water is not much, and the velocity of the depth of water is not much, and the velocity of the current is very low.current is very low.

Rock fill Cofferdams: If the depth of water to be Rock fill Cofferdams: If the depth of water to be retained by the embankment of cofferdam is of retained by the embankment of cofferdam is of order 1.8 to 3 m. Stone or rubble is used for the order 1.8 to 3 m. Stone or rubble is used for the embankment .embankment .

Single Walled Cofferdam: This type of Cofferdam is Single Walled Cofferdam: This type of Cofferdam is used in places where the area to be enclosed is very used in places where the area to be enclosed is very small and the depth of water is more.small and the depth of water is more.

Double Walled Cofferdam: For Cofferdams required Double Walled Cofferdam: For Cofferdams required to enclose larger areas in deep water, single walled to enclose larger areas in deep water, single walled type becomes un economical as larger sections type becomes un economical as larger sections trussed struts would be necessary to resist the trussed struts would be necessary to resist the water pressure.water pressure.

Crib Cofferdams: In deep waters where Crib Cofferdams: In deep waters where it is difficult to penetrate the guide piles it is difficult to penetrate the guide piles or sheet piles into the hard bed below or sheet piles into the hard bed below crib cofferdam is used.crib cofferdam is used.

Cellular Coffer dam: This type of Cellular Coffer dam: This type of cofferdam is mostly used for dewatering cofferdam is mostly used for dewatering large areas in places where the depth of large areas in places where the depth of water may be of the order of 18-21m.water may be of the order of 18-21m.

The two common shapes of cellular The two common shapes of cellular cofferdam arecofferdam are

1.1. Circular type cellular CofferdamCircular type cellular Cofferdam

2.2. Diaphragm type cellular CofferdamDiaphragm type cellular Cofferdam

CaissonsCaissons A Caisson may be defined as a water A Caisson may be defined as a water

light structure made up of wood, steel or light structure made up of wood, steel or reinforced concrete constructed in reinforced concrete constructed in connection with excavation for connection with excavation for foundation of bridges ,abuttments in foundation of bridges ,abuttments in rivers and lakes.rivers and lakes.

Types of CaissonsTypes of Caissons 1.Open Caisson1.Open Caisson 2.Box Caisson2.Box Caisson 3.Pneuamtic Caisson3.Pneuamtic Caisson

Open caissonOpen caisson

Box caissonBox caisson

Pneumatic caissonPneumatic caisson

Thank youThank you