Awarded as the best online publication by CIDC

# Piles Engineering

Axial Load Capacity of Single Pile

To calculate Axial Load capacity of a single pile, we should first understand how the pile behaves and what are the resistances offered by it.

Basically we have a shaft resistance Qsu and a Toe resistance Qbu. The total pile capacity is calculated by summing up these two, i.e. Pile capacity Qu is the sum of the shaft resistance Qsu and toe resistances Qbu.

Foundation – Stability Analysis

The maximum load that can be sustained by shallow foundation elements due to the bearing capacity is a function of the cohesion and friction angle of bearing soils as well as the width B and shape of the foundation. The net bearing capacity per unit area, qu, of a long footing is expressed as: where
(alpha)f= 1.0 for strip footings and 1.3 for circular and square footings
cu= Un-drained shear strength of soil
(sigma) vo = effective vertical shear stress in soil at level of bottom of footing

(beta)f = 0.5 for strip footings, 0.4 for square footings, and 0.6 for circular footings
gamma =unit weight of soil

B=width of footing for square and rectangular footings and radius of footing for circular footings
Nc, Nq, N=bearing-capacity factors, functions of angle of internal friction (phi)

Groups of Piles

Group of piles means when we have more than 1 pile in a row. Many factors influence the pile group stability. The major factors are Geometry of the group, soil conditions and direction of loads.

The efficiency factor Eg is defined as the ratio of the ultimate group capacity to the sum of the ultimate capacity of each pile in the group. It is this factor which is mostly used to express the ultimate load considerations.

In case of piles being driven in cohesive soils, the ultimate load is alculated by using the followinf formula

Qbu=Abq=AbNccu