You are excavating a trench that is 8 feet deep in Type C soil. What is the minimum required slope ratio for the sides of this excavation?
Correct Answer
D) 1.5:1 (34 degrees)
For Type C soil (the least stable), OSHA requires a slope ratio of 1.5:1 (34 degrees from horizontal) to ensure worker safety in excavations.
Why This Is the Correct Answer
OSHA 29 CFR 1926.652 specifies that Type C soil, being the least stable soil classification, requires the most conservative slope ratio of 1.5:1 (34 degrees from horizontal). This means for every 1.5 feet of horizontal distance, the excavation can drop 1 foot vertically. Type C soils include granular soils, submerged soil, and soil from which water is freely seeping, all of which have poor cohesive properties and require maximum sloping for safety.
Why the Other Options Are Wrong
Option A: 3/4:1 (53 degrees)
The 3/4:1 ratio (53 degrees) is the required slope for Type A soil, which is the most stable soil type. Type C soil requires a much more gradual slope due to its instability.
Option B: 1/2:1 (63 degrees)
The 1/2:1 ratio (63 degrees) is too steep and dangerous for any soil type under OSHA standards. This steep angle would not provide adequate protection against cave-ins in Type C soil.
Memory Technique
Remember 'ABC = 3/4, 1, 1.5' - Type A soil uses 3/4:1, Type B uses 1:1, Type C uses 1.5:1. Think 'C is Crappy soil, needs the most Conservative slope of 1.5:1'
Reference Hint
OSHA 29 CFR 1926.652 - Requirements for protective systems, Table B-1 in Appendix B shows the maximum allowable slopes for different soil types
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