Pile Design Theory

 Pile is designed as a short column except in the week the soil may be designed as a long column.

The lateral load-carrying capacity of a pile depends on a

1)   Structural strength

2)   Subgrade modulus.

When the pile projected above the ground level the top potion behave as a cantilever

The point of contraflexural, depending on the soil.it is generally taken 1 m below the ground surface level but not less than the three-time diameter of the pile.

For a long flexible pile, the determination of the depth of fixity and the equivalent length of the cantilever is obtained with the help of the graph given in the code.

Use:

Where the presence of water makes it difficult or impossible to provide normal foundation without the use of a caisson or cofferdam.

B Precast concrete pile

The precast pile is cast in the casting yard and subsequently transported to the site and then hoisted.

B1 Lifting and transporting of the pile from casting bed.

          The precast pile have to be lifted from the casting bed and then transported to the site with minimum damages (due to handling). Piles are normally subjected to bending moment and shear stress.

The piles are generally lifted from their bed either at

1)   One point

2)   Two points and

3)   Three points

During lifting the pile is suspended at mid-point and then lifted. The bending moment induced is given by

B.M. = (wl^ 2)/8

Where w = Intensity of uniformly distributed load due to self-weight of the                         pile

          L=Length of pile

Pile suspended at two points

The maximum bending moment to be small as possible (6/2) the location of the point shall be at a distance of 0.207L.

The bending moment induced

             B.M. = ((wL^2)/ 46.6) = 0.0215 wl^2

Where w = Intensity of uniformly distributed load due to self-weight of the pile

          L=Length of the pile.

Pile suspended at three points

 One point at the middle span and the other two at a distance of 0.145L From either end.

The bending moment induced

                 B.M. = ((wl^2) 95)

Where,  w = The intensity of uniformly distributed load due to self-weight of                     the pile

          L=Length of pile

Hosting of pile

In this process, one end of the pile is res on the ground and the end is suspended at a distance of 0.293L from the cantilever end.

The bending moment induced is ((wl^2)/ 23.3)

Detailing Requirements

1)   Grade of concrete:- the minimum grade of concrete is M20

2)   Nominal cover:-

a.     Cover is measure clear from main and longitudinal reinforcement including binding wire

b.    Nominal cover shall not be less than 40 mm

c.     In severe condition nominal cover should not less than 50 mm

3)   Reinforcement:-

a.     Longitudinal reinforcement:-

                                                             i.      The area of main longitudinal reinforcement with,

1.    Length less than 30 times the least width should be less than 1.25%

2.    Length 30 to 4 times the least width should not be less than 1.5%

3.    Length greater than 40 times the least width should be less than 2 %

b.    Lateral reinforcement:-

                                                             i.      The lateral reinforcement shall be in the form of hoops or links of diameter not less than 8 mm

                                                          ii.      The volume of lateral reinforcement shall not be less than the following

1.    At each end of the pile for a distance of about 3 times the least width. Not less than 0.6 % of the gross volume of piles.

2.    In the body of pile-not less than 0.2 % of the gross volume of the piles.

4)   The transition between the close spacing of lateral reinforcement near the ends and the maximum shall be gradually over the length of 3 times the least width of the pile.