Refer to Ex. 15.23. If the pile is embedded in medium dense sand, determine the net pullout capacity and the net allowable pullout load with F_{s}=3.
Given: L=30 ft , \phi=38^{\circ}, \bar{K}_{s}=1.5 \text {, and } \delta=25^{\circ}, \gamma \text { (average) }=110 lb / ft ^{3}.
The water table is at great depth. Refer to Section 15.25.
Downward skin resistance Q_{f}
Q_{f}=\bar{q}_{0}^{'} \bar{K}_{s} \tan \delta A_{s}
where \bar{q}_{o}^{\prime}=\frac{1}{2} \times 30 \times 110=1650 lb / ft ^{2}
A_{s}=3.14 \times 1.25 \times 30=117.75 ft ^{2}
Q_{f}(\text { down })=\frac{1650 \times 1.5 \tan 25^{\circ} \times 117.75}{1000}=136 kips
Based on the recommendations of Poulos and Davis (1980)
Q_{f}(\text { up })=\frac{2}{3} Q_{f}(\text { down })=\frac{2}{3} \times 136=91 \text { kips }
Q_{f a}(\text { up })=\frac{91}{3} \approx 30 \text { kips }