The design and selection of a particular type of foundation is a work of the RCC consultant The construction person must know the background so that the interaction with the designer is easy. Read this article so that you know the basics.

The hard strata at this location is not available till almost 7 Meters and hence PILING was considered as a better option as compared to OPEN foundations

You shall see the piling work actually taking place here.

What you are seeing in this picture is the TRIPOD used for the piling which is done by the HAMMERING METHOD.On the right side, you can see the WINCH which pulls the dead weight ( HAMMER ) upto the top of the TRIPOD through a steel wire.

The Hammer gets dropped from a height of 6 m and penetrates the ground.

For the upper most soil which is liable to collapse inside the bore , a casing pipe of about 2 M length is used. After this depth , there is a reasonably soft soil and hence soil does not collapse.

You can see the CASING PIPE in this photograph.

After doing the boring for about 7.25 M to 7.5 M , hard rock is available.

The hard rock is also cut through CHISELING [ mounted with the dead weight ].

So pile goes inside the hard rock for about 300 mm to 450 mm.

The specimens of soil and rock fragments collected from different depths are properly preserved and tagged with information like Pile no , depth ,time etc. [ This is used for exact analysis of the strata when needed ]

Now the Re-Bar cage is lowered inside the fresh boring .

You might be interested to know the details of the PILES.

PILE Dia : 500 mm.

REBARS :

Main bars :6 Nos x 20 Ribbed bars of Grade 500.

Rings :

Circular rings 6 Dia. MS @ 200 mm C/C on the inside of cage

Helical rings 6 Dia. MS @ pitch of 200 mm on the outside of cage

Set of helical rings ready for fixing on the cage.

Following picture shows the drum on which these helical rings are mould.

This picture shows the stand on which the PILE CAGE is prepared.

After lowering the REBAR cage , concreting is done for the pile.

It is done with a TREMIE so that concrete can be poured directly at the base of the PILE.

This is important so that segregation of concrete does not take place.

Remember : The practice is to cast all PILES which are bored in a day. This is important from :

Safety point of view.

To avoid the risk of soil getting collapsed overnight

As a construction person , you should also be able to calculate the material required for the construction . Today , we shall learn how to calculate the materials required for the Pile foundations.

Data :

Pile Shape : Circular

Pile Diameter : 600 mm

Pile Depth : 8.35 M.

Mix of concrete : M20

Reinforcement: 6 HYSD bars of 16mm diameter .

Stirrups : 8 mm diameter bars provided at a spacing of 200 mm C/C [ Center to Center ]

As a construction person , we know the following :

1.Unit weight of 16mm dia HYSD bars : 1.58 Kg/m

2.Unit weight of 8mm dia HYSD bars : 0.39 Kg/m

3.Cover for Pile reinforcement : 50 mm

4.Material consumption for Concrete M20 :

Cement : 7.87 Bags/ CuM

Sand : 0.41 CuM.

Aggregate : 0.83 CuM.

4.Formula for volume of the cylinder = (0.785).D^{2}.H where D : Pile diameter in M & H : Pile height in M.

Having thus prepared , we shall now go for the actual calculations as follows .

Part A : REINFORCEMENT :

A.01 : Longitudinal bars :

Cutting Length of bar : 8350 –( 50+50 ) = 8250 mm = 8.25 M.

Weight :

6 Nos X 8.25 m X 1.58 Kg/m = 78.21 Kg.

A.02 : Stirrups :

Stirrup diameter : 600 –( 50+50 ) = 500 mm.

Cutting length : ( 3.14) D +( 2x10d )

D : Stirrup Diameter =500 mm

d: Diameter of bar used for stirrup = 8 mm.

= (3.14 x 500 )+( 2x 10×8) = 1730 mm = 1.73 M.

No of stirrups : ( 8350 / 200 )+1 = 43 Nos

Weight : 43 Nos x 1.73M x 0.39 Kg/m = 29 Kg.

Summary of Reinforcement :

16mm dia HYSD bars : 78 Kg / Pile

8mm dia HYSD bars : 29 Kg / Pile

Part B : M20 Concrete :

Volume of pile :

(0.785).D^{2}.H

=0.785 x 0.6 x 0.6 x 8.35

=2.36 CuM /Pile

Cement required :

2.36 x 7.87 bags = 18.57 bags

Sand Required :

2.36x 0.41 CuM = 0.968 CuM.

Aggregate Required :

2.36x 0.83 CuM = 1.96 CuM.

Final Summary :

Material required per pile of 600 mm dia. having a length of 8.35 M.