Question

A concrete pile of 500 mm in diameter is proposed to be driven in a layer of uniform clay. The pile tip is assumed to carry 30% of load. The length of pile required to carry a safe load of 250 kN with a factor of safety 3.
(Shear mobilization factor, $\alpha =0.4$)

• A. 6.56 m
• B. 7.98 m
• C. 3.13 m
• D. 11.15 m

Answer 1

The correct option is A 6.56 m

$\therefore Q_s=\frac{Q_u}{F}$

$\therefore Q_u=250\times 3=750kNd=500m$

$Q_b=30\%of{Q}_{u}d=0.5m$

$Q_b=0.3Q_u=C.N_c.\frac{\pi }{4}{d}^2{Q}_b=f_b.A_b$

$0.3\times 750=C\times 9\times \frac{\pi }{4}\times {0.5}^2$

$\therefore C=127.32kPa$

$\therefore Q_s=Q_u-Q_b=0.7Q_u$

$Q_s=f_s.A_s$

$Q_s=\alpha C^{\prime }.\pi dL$

$\therefore UniformClay{C}^{\prime }=C$

$0.7\times 750=0.4\times 127.32\times \pi \times 0.5\times L$

$\therefore L=6.56m$