A construction crew is excavating a trench that is 8 feet deep and 4 feet wide in Type B soil. What is the minimum allowable slope ratio for the sides of this excavation?
Correct Answer
C) 1:1 (45 degrees)
For Type B soil, OSHA requires a minimum slope of 1:1 (45 degrees) for excavations. This means for every foot of depth, the excavation must be sloped back one foot horizontally.
Why This Is the Correct Answer
OSHA 29 CFR 1926.652 specifically requires a minimum slope ratio of 1:1 (45 degrees) for Type B soil excavations. This means that for every foot of vertical depth, the excavation must slope back horizontally one foot from the edge. Type B soil has moderate cohesive strength and requires this specific slope ratio to prevent cave-ins and ensure worker safety. The 8-foot depth and 4-foot width mentioned in the question don't change this fundamental requirement.
Why the Other Options Are Wrong
Option A: 1/2:1 (63 degrees)
A slope ratio of 1/2:1 (63 degrees) is too steep for Type B soil and would create an unsafe condition. This steep angle doesn't provide adequate protection against soil collapse.
Option B: 3/4:1 (53 degrees)
A slope ratio of 3/4:1 (53 degrees) is still too steep for Type B soil according to OSHA standards. While less steep than option A, it still doesn't meet the minimum safety requirements.
Option D: 1 1/2:1 (34 degrees)
While a slope ratio of 1 1/2:1 (34 degrees) would be safer than the minimum requirement, it's not the minimum allowable slope. The question asks for the minimum allowable slope, making this option incorrect despite being acceptable.
Memory Technique
Type B = 1:1 = 45 degrees. Remember 'B for Basic 45' - Type B soil needs the basic 45-degree angle slope for safety.
Reference Hint
OSHA 29 CFR 1926.652 - Requirements for protective systems, Table B-1 for soil classification and sloping requirements
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