HOW TO CALCULATE PILE LOAD CAPACITY? (STATIC ANALYSIS)

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,

  1. The type of soil through which the pile is piled
  2. Pile Installation Method
  3. 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.

Pile Load Capacity - Static Analysis

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 asskin 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 (Whyb) and gives the second term skin abrasion resistance (Whys,

stacked in unison



Where,

WhyYou = final load capacity, kN

aP = area of ​​cross section of the top of the pile, m. In2


nC = bearing capacity factor, 9. can be taken as

αI = 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.

Transformation of alpha with harmonization
Transformation of alpha with harmonization

CI = average cohesion for the ith layer, kN/m . In2

aSI = surface area of ​​the pile shaft in the ith layer, m. In2

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


WhySafe = QYou/2.5

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

The final load carrying capacity of the pile, “QYou“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, “Qb,

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

Pile Load Capacity Formula-1

Where,

aP = area of ​​cross section of pile base, m2


D = diameter of pile shaft, m

= effective unit weight of soil at the tip of the pile, kN/m3

nI= bearing capacity factor


nWhy = bearing capacity factor

= angle of internal friction at the end of the pile

PD = effective overburden pressure at the pile tip, kN/m. In2


KI = coefficient of earth pressure applied to the ith layer

Pd = kN/m . Effective overburden pressure for the inth layer2

II = angle of friction of the wall between the pile and the soil for the ith layer

aSI = surface area of ​​the pile shaft in the ith layer, m. In2


The first term is the expression for the final bearing capacity of the pile (Whyb) and the second term is the expression for the skin friction capacity of the heap (Whys,

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

WhySafe = QYou / 2.5

Important Notes to Remember

  • Bearing capacity factor N. value ofWhy Obtained from the picture below.
bearing factor value
bearing factor value
  • Bearing capacity factor N. value ofI The calculation is done using the equation given below.

formula n gamma

  • 30. For pile driven in loose to dense sand with varying between0to 400 , KI 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.0and 40. increasing up to 20 times for0
  • 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.

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.