A trench is being excavated 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) or 1 horizontal to 1 vertical.
Why This Is the Correct Answer
OSHA Appendix B to 29 CFR 1926 Subpart P specifies slope ratios by soil type. For Type B soil, the maximum allowable slope is 1:1 (horizontal:vertical), which equals 45 degrees. This means for every 1 foot of vertical depth, the slope must extend at least 1 foot horizontally.
Why the Other Options Are Wrong
Option A: 1-1/2:1 (34 degrees)
A 1.5:1 slope (34 degrees) is the requirement for Type C soil — the least stable classification. Type C requires a gentler, more spread-out slope. Applying a Type C slope to a Type B question would be using the wrong soil classification.
Option B: 3/4:1 (53 degrees)
A 3/4:1 slope (53 degrees) is steeper than what OSHA allows for Type B soil. This steeper ratio is not an OSHA-recognized standard slope for any standard soil type.
Option C: 1/2:1 (63 degrees)
A 1/2:1 slope (63 degrees) is the maximum allowed for Type A soil — the most stable classification. Applying a Type A slope to Type B soil would create an unsafe condition because Type B is less stable than Type A.
Memory Technique
Alphabetical order = increasing gentleness: Type A (most stable) = 3/4:1 steep, Type B (middle) = 1:1 square, Type C (least stable) = 1.5:1 gentle. Think ABC = increasingly cautious slopes. Type B = '1 to 1' = perfectly square = easy to remember as the middle ground.
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