A construction site has an excavation that is 8 feet deep with Type B soil. What is the maximum allowable slope ratio for the sides of this excavation?
Correct Answer
A) 1:1 (horizontal to vertical)
For Type B soil, OSHA requires a maximum slope of 1:1 (45 degrees) or 1 horizontal to 1 vertical. This provides adequate stability for most cohesive soils with unconfined compressive strength greater than 0.5 tsf.
Why This Is the Correct Answer
According to OSHA 29 CFR 1926.652, Type B soil requires a maximum allowable slope of 1:1 (45 degrees) for excavations. Type B soil includes cohesive soil with unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf. The 1:1 slope ratio means for every 1 foot of depth, the excavation must slope back 1 foot horizontally from the edge, providing adequate stability and worker safety.
Why the Other Options Are Wrong
Option B: 3/4:1 (horizontal to vertical)
A 3/4:1 slope ratio (0.75:1) is steeper than the maximum allowable 1:1 slope for Type B soil. This steeper angle would create an unsafe condition as it doesn't provide sufficient slope-back distance to prevent cave-ins. OSHA specifically requires at least 1:1 for Type B soil to ensure excavation stability and worker protection.
Option C: 1.5:1 (horizontal to vertical)
A 1.5:1 slope ratio is flatter than required and represents the minimum slope for Type C soil, not Type B. While this would be safe, it's unnecessarily conservative for Type B soil conditions. OSHA allows the steeper 1:1 slope for Type B soil due to its better cohesive properties compared to Type C soil.
Option D: 2:1 (horizontal to vertical)
A 2:1 slope ratio is much flatter than required for Type B soil and would be unnecessarily conservative, wasting space and increasing excavation costs. This slope ratio might be used for very unstable Type C soils or special conditions, but exceeds OSHA requirements for standard Type B soil excavations.
Memory Technique
Remember 'B for Basic 1:1' - Type B soil gets the basic 45-degree angle (1:1 slope). Think of it as 'B = Balanced' where horizontal equals vertical distance.
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