Question

A 0.5 x 0.5 m square concrete pile is to be driven in a homogenous clayey soil having undrained shear strength $C_u=50\text{kPa}$ and unit weight, $\gamma =18.0{\text{kN/m}}^3$. The design capacity of the pile is 500kN. The adhesion factor $\alpha$ is given as 0.75. The length of the pile required for the above design load with a factor of safety of 2.0 is

• A. $5.2\text{m}$
• B. $5.8\text{m}$
• C. $11.8\text{m}$
• D. $12.5\text{m}$

Answer 1

The correct option is C $11.8\text{m}$

$Given,Sizeofpile=0.5\text{m}\times 0.5\text{m}$

$Undrainedshearstrength,C_u=50\text{kPa}$

$Unitweight,\gamma =18{\text{kN/m}}^3$

$Adhesionfactor,\alpha =0.75$

$Factorofsafety=2$

$Designcapacityofpile=500\text{kN}$

$\therefore Ultimatecapacityofpile{Q}_u=500\times 2=1000\text{kN}$

$Q_u=C{N}_C{A}_P+\alpha C_{u}PL$

$1000=9\times 50\times 0.5\times 0.5+0.75\times 50\times 4\times 0.5L$

$L=11.83\text{m}$

$L=11.8\text{m}$