Using the normal soil setting formula, what is the setting depth for a soil depth of 20 feet?

• A. 3 ft
• B. 4 ft
• C. 5 ft
• D. 2 ft

Answer: (B)

In the normal soil setting approach, the setting depth is taken as one-fifth of the actual soil depth. This rule of thumb helps ensure enough embedment in typical soil conditions. For a soil depth of 20 feet, you divide by 5: 20 ÷ 5 = 4 feet. So the setting depth is 4 feet. The other options don’t fit the one-fifth rule (they would correspond to dividing by 6, 4, or 10), so they’re not the correct application of the standard formula.