Calculate the required slope for a 15-foot deep excavation in Type A soil. What is the horizontal distance from the toe of the slope to the top edge?
Correct Answer
A) 11.25 feet
Type A soil allows 3/4:1 slope ratio. For 15 feet deep: 15 × 0.75 = 11.25 feet horizontal distance required.
Why This Is the Correct Answer
OSHA 29 CFR 1926.652, Appendix B designates Type A soil as the most stable (massive rock, hardpan, cemented soils with no fissures, cracks, or signs of prior disturbance). It allows the steepest permissible slope: 3/4:1 (0.75 horizontal to 1 vertical). For 15 feet deep: 15 × 0.75 = 11.25 feet horizontal distance required.
Why the Other Options Are Wrong
Option B: 18.75 feet
18.75 feet would result from a 1.25:1 ratio, which is not an OSHA-defined slope ratio for any soil type. This is a plausible-looking distractor but does not correspond to any standard.
Option C: 15 feet
15 feet results from a 1:1 ratio, which is required for Type B soil. Applying the Type B ratio to Type A soil is unnecessarily conservative and not the correct OSHA minimum for Type A.
Option D: 22.5 feet
22.5 feet results from a 1.5:1 ratio, which is the Type C soil requirement. Applying this to Type A would require far more space than necessary and indicates a confusion of soil classifications.
Memory Technique
Type A soil is the most stable—think 'A for Awesome stability.' Awesome soils don't need much horizontal setback: 0.75 × depth. Type A = 0.75, Type B = 1.0, Type C = 1.5. Each step from A to C adds 0.25 more horizontal factor per foot of depth.
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