A construction site has a trench that is 8 feet deep in Type B soil. What is the maximum allowable slope ratio for the sides of this excavation?
Correct Answer
D) 1:1 (45 degrees)
For Type B soil, OSHA requires a maximum slope of 1:1 (45 degrees) for excavations. Type B soil has moderate cohesion and 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. Type B soil is defined as cohesive soil with an unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf, which includes angular gravel, silt, sandy loam, and previously disturbed soils. The 1:1 slope ratio means for every 1 foot of depth, the excavation must slope back 1 foot horizontally from the edge. This slope provides adequate stability to prevent cave-ins while allowing safe access for workers.
Why the Other Options Are Wrong
Option A: 1.5:1 (34 degrees)
0.75:1 (53 degrees) is steeper than what OSHA allows for Type B soil and would create an unsafe condition. This slope ratio would not provide adequate protection against cave-ins in Type B soil conditions.
Option C: 2:1 (26.5 degrees)
1.5:1 (34 degrees) is the maximum allowable slope for Type A soil, which has higher cohesion and stability than Type B soil. Type A soil can support steeper slopes due to its greater structural integrity.
Memory Technique
Remember 'B for Basic 1:1' - Type B soil gets the basic 45-degree angle (1:1 ratio). Type A is 'Advanced' so it can handle steeper slopes (1.5:1), while Type C is 'Careful' requiring more protection.
Reference Hint
OSHA Construction Standards 29 CFR 1926 Subpart P - Excavations, specifically section 1926.652 Requirements for protective systems
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