A rectangular excavation is 12 feet deep, 20 feet long, and 8 feet wide in Type B soil. What is the minimum horizontal distance required for a simple slope from the top of the excavation to the bottom?
Correct Answer
C) 12 feet
For Type B soil, OSHA requires a 1:1 slope ratio (45 degrees). With a 12-foot deep excavation, the horizontal distance must be equal to the depth, which is 12 feet.
Why This Is the Correct Answer
OSHA excavation standards specify that Type B soil requires a 1:1 slope ratio, which equals a 45-degree angle. This means for every foot of vertical depth, you need one foot of horizontal distance. Since the excavation is 12 feet deep, the minimum horizontal distance from the top edge to the bottom must be 12 feet. The length and width dimensions (20 feet and 8 feet) are irrelevant to the slope calculation.
Why the Other Options Are Wrong
Option A: 6 feet
6 feet would only be correct for an excavation that is 6 feet deep in Type B soil, or it might apply to a different soil type with a steeper allowable slope. This distance is insufficient for a 12-foot deep excavation.
Option B: 9 feet
9 feet does not correspond to any standard OSHA slope requirement for Type B soil. This distance would leave the excavation walls too steep and unsafe according to OSHA standards.
Option D: 15 feet
15 feet exceeds the minimum requirement for Type B soil. While this would be safe, it's more than necessary and would result in unnecessary excavation and material removal costs.
Memory Technique
Type B = 'Be' equal - the horizontal distance equals the depth (1:1 ratio). Type A is steeper (3/4:1), Type C is flatter (1.5:1).
Reference Hint
OSHA 29 CFR 1926.652 - Requirements for protective systems, Table B-1 for soil classification and allowable slopes
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