The ultimate load carrying capacity of a pile is the maximum load that it can carry without failure or excessive settlement of the ground.

Bearing capacity of pile mainly depends on 3 factors as given below,

- The type of soil through which the pile is piled
- Pile Installation Method
- Pile Dimensions (Cross Section and Pile Length)

When calculating the pile load capacity for cast in situ concrete piles, using static analysis, we need to use the soil shear strength parameter and the dimension of the pile.

Table of Contents

**Load Bearing Capacity of Heap Using Static Analysis**

The pile transfers the load to the soil in two ways. First, through tip-in compression, which is called “*end bearing*” or “*point bearing*“; secondly, by shearing along the surface” is termed as*skin friction*,

**Load bearing capacity of cast in-situ piles in cohesive soils**

Final load carrying capacity (Q.)_{You}) The pile in the connective soil is given by the formula given below, where the first term denotes *end bearing resistance* (Why_{b}) and gives the second term *skin abrasion resistance* (Why_{s},

Where,

Why_{You} = final load capacity, kN

a_{P} = area of cross section of the top of the pile, m. In^{2}

n_{C} = bearing capacity factor, 9. can be taken as

α_{I} = the adhesion factor for the ith layer depending on the consistency of the soil. It depends on the non-irrigated shear capacity of the soil and can be obtained from the figure given below.

C_{I} = average cohesion for the ith layer, kN/m . In^{2}

a_{SI} = surface area of the pile shaft in the ith layer, m. In^{2}

A minimum factor of 2.5 is used to arrive at a safe pile load capacity (Q.)_{Safe}) from final load capacity (q.)_{You},

Why_{Safe} = Q_{You}/2.5

**Load bearing capacity of cast in-situ piles in non-cohesive soils**

The final load carrying capacity of the pile, “Q_{You}“There are two parts. One part is caused by friction, which is called *skin friction* or *shaft friction* or *side shear* denoted as “Q”_{s}“And the second reason is *end bearing* at the base or tip of the pile toe, “Q_{b},

The equation given below is used to calculate the final load carrying capacity of the pile.

Where,

a_{P} = area of cross section of pile base, m^{2}

D = diameter of pile shaft, m

= effective unit weight of soil at the tip of the pile, kN/m^{3}

n_{I}= bearing capacity factor

n_{Why} = bearing capacity factor

= angle of internal friction at the end of the pile

P_{D} = effective overburden pressure at the pile tip, kN/m. In^{2}

K_{I } = coefficient of earth pressure applied to the ith layer

P_{d} = kN/m . Effective overburden pressure for the inth layer^{2}

I_{I} = angle of friction of the wall between the pile and the soil for the ith layer

a_{SI} = surface area of the pile shaft in the ith layer, m. In^{2}

The first term is the expression for the final bearing capacity of the pile (**Why _{b}**) and the second term is the expression for the skin friction capacity of the heap (

**Why**,

_{s}A minimum factor of 2.5 is used to arrive at the safe stack capacity (q.)_{Safe}) from final load capacity (q.)_{You},

**Why _{Safe}**

**= Q**

_{You }/ 2.5**Important Notes to Remember**

- Bearing capacity factor N. value of
_{Why}Obtained from the picture below.

- Bearing capacity factor N. value of
_{I}The calculation is done using the equation given below.

- 30. For pile driven in loose to dense sand with varying between
^{0}to 40^{0}, K_{I}Values in the range 1 to 1.5 can be used. - , the angle of friction of the wall can be taken as the angle of friction of the soil around the stem of the pile.
- The maximum effective overburden at the pile base should correspond to the critical depth, which can be taken as 15 times the diameter of the pile shaft for 30 s.
^{0}and 40. increasing up to 20 times for^{0} - For piles passing through cohesive stratum and ending in granular stratum, a diameter of at least twice the diameter of the pile shaft must be provided in the granular stratum.

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