An excavation in Type B soil is 10 feet deep. Using the simple slope method, what is the minimum horizontal distance required from the toe of the slope to achieve a safe 1:1 slope ratio?
Correct Answer
D) 10 feet
For Type B soil with a 1:1 slope ratio and 10 feet depth, the horizontal distance equals the vertical distance. Therefore, 10 feet horizontal distance is required from the toe of the slope.
Why This Is the Correct Answer
For Type B soil, OSHA's simple slope method requires a 1:1 slope ratio — meaning 1 foot of horizontal distance for every 1 foot of vertical depth. With a 10-foot deep excavation: Horizontal distance = 1 × Vertical depth = 1 × 10 = 10 feet. This 10-foot setback from the toe (bottom edge) of the slope to the top creates the required angle. Each side of the trench needs this 10-foot horizontal setback, making the total trench opening width = trench bottom width + 20 feet.
Why the Other Options Are Wrong
Option A: 7.5 feet
7.5 feet would correspond to a 0.75:1 ratio, which is steeper than allowed for Type B soil (closer to a Type A slope ratio). This provides insufficient protection against cave-in in moderately stable soil.
Option B: 15 feet
15 feet would correspond to a 1.5:1 ratio, which is the requirement for Type C soil — the least stable classification. While this would be even safer than required, the question asks for the minimum distance for Type B soil at a 1:1 ratio.
Option C: 5 feet
5 feet would correspond to a 0.5:1 ratio (steeper than 1:1), which applies to Type A soil — the most stable category. Applying a Type A slope to Type B soil creates an unsafe, over-steep condition.
Memory Technique
For a 1:1 slope, horizontal always equals vertical — it's symmetrical. So for any 1:1 slope question: horizontal distance = depth. No conversion needed. For Type B at 10 ft deep: 1 × 10 = 10 ft. Simple ratio math.
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