22.6 A large sign is to be supported on two steel poles, each of which will be supported by an 18 in diameter drilled shaft. The lateral wind load acting on the sign will be 3,000 lb and distributed evenly between the two piles. The centroid of this wind load will be \( 30 \mathrm{ft} \) above the ground surface. The soils are sandy clays with \( s_{u}=2,500 \mathrm{lb} / \mathrm{ft}^{2} \). Using a rigid analysis, compute the required depth of embedment and the maximum moment in each drilled shaft. Use a factor of safety of 3.0.