3 Foundation Introduction : Objectives of a foundation : A structure essentially consists of two parts, namely the super structure which is above the plinth level and the substructure which is below the plinth level.Substructure is otherwise known as the foundation and this forms the base for any structure. Generally about 30% of the total construction cost is spent on the foundation.The soil on which the foundation rests is called the “foundation soil”.Objectives of a foundation :A foundation is provided for the following purposes:To distribute the total load coming on the structure on a larger area.To support the structures.To give enough stability to the structures against various disturbingforces, such as wind and rain.To prepare a level surface for concreting and masonry work.
4 Foundation… Types of foundation : Types of Pile foundation : The two main types of foundation are :Shallow foundation (spread foundation) andDeep foundationTypes of Shallow foundation :Isolated footing (single footing, Column footing)Combined footingTypes of Deep foundation :Pile foundationPier foundationTypes of Pile foundation :Friction pileLoad bearing pileNote : Under-reamed piles is atype of load bearing pile
5 Foundation… Shallow foundation (spread foundation): Depth of foundation is less than or equal to its width.Isolated footing (single footing, column footing):In framed structures where several columns are to be constructed, isolated footings can be adopted.The columns involved can be provided with masonry or concrete footing.If masonry footing is provided, steps are given and the foundation area is thus increased so that the stresses developed at the base is within the limit.In case of masonry footing, the projection of each step must be ½ brick thick and each step is made of 1 or 2 bricks put together.Concrete can be moulded to any shape and hence a concrete footing may be a sloping one to provide sufficient spread.
9 Foundation… Combined footing: This type of footing is adopted when the space between two columns is so small that the foundation for individual columns will overlap.Combined footings are proportioned in such a way that the centre of gravity of the loads coincides with the centre of gravity of the foundation. Hence these footings have either a trapezoidal or a rectangular shape.Footing :Footings are structural members used to support columns and walls and to transmit and distribute their loads to the soil in such a way that the load bearing capacity of the soil is not exceeded. Also excessive settlement, differential settlement or rotation are prevented and adequate safety against overturning or sliding is maintained.
10 Foundation… Pile : A slender, structural member consisting steel or concrete ortimber.It is installed in the ground to transfer the structural loads to soils at some significant depth below the base of the structure.
11 Foundation…Pile caps are thick slabs used to tie a group of piles together to support and transmit column loads to the piles.
12 Foundation… Deep foundation : Deep foundation consists of pile and pier foundations.This consists in carrying down through the soil a huge masonry cylinder which may be supported by the sides of soil or may be supported on solid rock (hard stratum).Pile foundation :Pile is an element of construction used as foundation. It may be driven in the ground vertically or with some inclination to transfer the load safely.
13 Foundation… Pile foundation… Loads are supported in two ways. If the load is supported by the effect of friction between the soil and the pile skin, it is called friction pile.Friction piles may be made of cast iron, cement concrete, timber, steel, wrought iron and composite materials.If the load is supported by resting the pile on a very hard stratum, it is called load bearing pile.Load bearing piles are steel sheet piles, concrete piles and timber piles.Piles may be cast-in-situ orprecast.They may be cased or uncased.
16 TYPES OF PILES Concrete Piles i) Cast-In-Situ Concrete Piles a) Cased cast-in-situ b) Uncased cast-in-situii) Precast Concrete PilesSteel Pilesi) H-Piles ii) Cylindrical piles iii) Tapered pilesTimber PilesComposite Piles
17 TYPES OF PILE CONSTRUCTION Displacement PilesIt cause the soil to be displaced radially as well as vertically as pile shaft is driven or jacked into the ground.b) Non Displacement Piles (Replacement piles)It cause the soil to be removed and the resulting hole filled with concrete or a pre cast concrete pile is dropped into the hole and grouted in.Displacement Pile Non Displacement pile
18 METHOD OF INSTALLATION Dropping Weight or Drop Hammers- commonly used method of insertion of displacement pilesDiesel Hammers-Most suitable to drive pile in non cohesive granular soilVibratory Hammers or vibratory method of pile driving-very effective in driving piles through non cohesive granular soilJacking Method Of Insertion4 November 2010
20 Pile Driving Rig - temporarily support the pile that being driven and to support the pile hammer.
21 Jacking Method Of Insertion Jacked Piles are most commonly used in underpinning structuresBy excavating underneath a structure short lengths of pile can be inserted and jacked into the ground using the underside of the existing structure as a reaction.