A trench is being excavated to a depth of 8 feet in Type B soil. What is the maximum allowable slope ratio for the sides of this excavation?
Correct Answer
A) 1:1 (45 degrees)
For Type B soil, OSHA requires a maximum slope of 1:1 (45 degrees) for excavations. Type B soil includes angular gravel, silt, sandy loam, and previously disturbed soils.
Why This Is the Correct Answer
OSHA 29 CFR 1926.652 specifically requires a maximum slope ratio of 1:1 (45 degrees) for Type B soil excavations. This means for every 1 foot of depth, the excavation must slope back 1 foot horizontally from the vertical face. Type B soil has moderate cohesive strength and includes materials like angular gravel, silt, sandy loam, and previously disturbed soils. The 1:1 slope provides adequate stability to prevent cave-ins in this soil classification.
Why the Other Options Are Wrong
Option B: 1.5:1 (34 degrees)
The 1.5:1 slope ratio is actually steeper than required and would not provide adequate safety margin for Type B soil. While a flatter slope would be safer, OSHA specifically mandates 1:1 as the maximum allowable slope, meaning you cannot go steeper than this ratio.
Option C: 0.75:1 (53 degrees)
The 0.75:1 slope ratio (53 degrees) is much too steep for Type B soil and would create dangerous conditions. This steep angle would likely result in soil failure and cave-ins, violating OSHA safety requirements for excavation work.
Option D: 2:1 (27 degrees)
While a 2:1 slope ratio would be safer than required, it is not the maximum allowable slope. The question asks for the maximum allowable slope, which means the steepest slope permitted by OSHA regulations, not the safest possible slope.
Memory Technique
Remember 'Type B = 1:1' - the letter B looks like the number 1 stacked, helping you recall that Type B soil requires 1:1 slope ratio.
Reference Hint
OSHA 29 CFR 1926.652 - Requirements for protective systems, Table B-1 for soil classification and slope requirements
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