For excavation work in Type A soil, a contractor wants to use a simple slope. If the excavation is 10 feet deep, what is the minimum distance from the toe of the slope to the edge of the excavation?
Correct Answer
B) 7.5 feet
Type A soil allows 0.75:1 slope ratio. For 10 feet deep: 10 × 0.75 = 7.5 feet horizontal distance required.
Why This Is the Correct Answer
Cal/OSHA and OSHA 29 CFR 1926 Subpart P classify Type A soil (the most stable) with a maximum allowable slope of 3/4:1 (horizontal:vertical), expressed as a 0.75:1 ratio. For a 10-foot-deep excavation the required horizontal setback is 10 ft × 0.75 = 7.5 feet. This slope ratio reflects Type A soil's cohesive strength and resistance to movement.
Why the Other Options Are Wrong
Option A: 20 feet
20 feet would correspond to a 2:1 slope ratio (10 ft × 2 = 20 ft), which is the requirement for Type C soil — the least stable classification. Using that distance for Type A soil would be overly conservative and incorrect for this calculation.
Option C: 15 feet
15 feet would equal a 1.5:1 ratio, which is the standard for Type B soil. Type B soil is less cohesive than Type A, requiring a shallower, wider slope. Applying Type B requirements to Type A soil overstates the hazard.
Option D: 10 feet
10 feet would be a 1:1 slope (45 degrees). While this might seem intuitive, a 1:1 slope is actually the OSHA requirement for Type B soil in some configurations, not Type A. Type A allows a steeper 0.75:1 cut, meaning you need less horizontal distance.
Memory Technique
Use the ABC mnemonic for soil slope ratios: - Type A = 0.75:1 (three-quarters horizontal per 1 foot of depth) — 'A' for Awesome stability - Type B = 1:1 (one foot horizontal per 1 foot of depth) - Type C = 1.5:1 (one-and-a-half feet horizontal per 1 foot of depth) — 'C' for Crumbly For 10-foot depth: A=7.5 ft, B=10 ft, C=15 ft.
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