G-2 Piles in Cohesive Soils

The ultimate load capacity $(Q_{\mathrm{u}})$ of piles, in kN, in cohesive soils is given by the following formula:

The first term gives end bearing resistance and the second term gives the skin friction resistance.

where

$A_{\mathrm{p}} =$ cross-sectional area of pile tip, in $\mathrm{m}^2$

$N_{\mathrm{c}} =$ bearing capacity factor, may be taken as 9;

$c_{\mathrm{p}} =$ average cohesion at pile tip, in $\mathrm{kN / m^2}$;

$\sum_{i=1}^{n} =$ summation for layers 1 to $n$ in which pile is installed and which contribute to positive skin friction;

$\alpha_{i}=$ adhesion factor for the ith layer depending on the consistency of soil (see Note);

$c_{\mathrm{i}} =$ average cohesion for the ith layer, in $\mathrm{kN / m^2}$; and

$A_{\mathrm{si}} =$ surface area of pile shaft in the ith layer, in $\mathrm{m}^2$

NOTE — The value of adhesion factor, $\alpha_{i}$ depends on the undrained shear strength of the clay and may be obtained from Fig. 12.

11A BEARING CAPACITY FACTOR, $N_{\mathrm{q}}$ FOR DRIVEN PILES

11A BEARING CAPACITY FACTOR, $N_{q}$ FOR DRIVEN PILES

11B BEARING CAPACITY FACTOR, $N_{\mathrm{q}}$ FOR BORED PILES

11B BEARING CAPACITY FACTOR, $N_{q}$ FOR BORED PILES

FIG. 11 BEARING CAPACITY FACTOR, $N_{\mathrm{q}}$

FIG. 12 VARIATION OF $\alpha$ WITH $C_{\mathrm{u}}$