A rectangular excavation is 12 feet deep, 8 feet wide, and 20 feet long in Type B soil. What is the minimum horizontal distance required from the toe of the excavation for a simple slope?
Correct Answer
D) 9 feet
For Type B soil, the maximum allowable slope is 1:1 (45 degrees). With a 12-foot depth, the horizontal distance from the toe must be at least 12 × 0.75 = 9 feet for a simple slope.
Why This Is the Correct Answer
For Type B soil excavations, OSHA requires a maximum allowable slope of 1:1 (45 degrees) for simple slopes. This means for every foot of depth, there must be at least 0.75 feet of horizontal distance from the toe of the excavation. With a 12-foot deep excavation, the minimum horizontal distance is calculated as 12 × 0.75 = 9 feet. This ensures proper slope stability and worker safety in Type B soil conditions.
Why the Other Options Are Wrong
Option A: 12 feet
12 feet would be the horizontal distance for a 1:1 slope ratio, but OSHA's requirement for Type B soil simple slopes is 3/4:1 (0.75:1), not 1:1. Using 12 feet would create an unnecessarily conservative slope that exceeds minimum safety requirements, wasting space and potentially increasing project costs without additional safety benefits.
Option B: 18 feet
18 feet represents a 1.5:1 slope ratio, which is extremely conservative and far exceeds OSHA requirements for Type B soil. This would be wasteful of space and resources while providing no additional safety benefit beyond what the required 9-foot distance provides for proper slope stability.
Option C: 15 feet
15 feet represents a 1.25:1 slope ratio (15÷12), which is more conservative than required for Type B soil. This would be appropriate for Type C soil conditions, but Type B soil has better stability characteristics and only requires a 0.75:1 slope ratio according to OSHA standards.
Memory Technique
Remember 'Type B = 3/4 to Be safe' - Type B soil requires 3/4 horizontal distance for every 1 foot of depth (0.75:1 ratio).
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