A trench is 8 feet deep, 4 feet wide, and 100 feet long in Type C soil. How much horizontal space is required on each side if using sloping instead of shoring?
Correct Answer
C) 12 feet
Type C soil requires a 1.5:1 slope ratio. For an 8-foot deep trench, the horizontal distance = 8 feet × 1.5 = 12 feet on each side from the bottom of the trench.
Why This Is the Correct Answer
Type C soil is the least stable soil classification and requires the most conservative slope ratio of 1.5:1 (horizontal:vertical) for excavation safety. With an 8-foot deep trench, you multiply the depth by the slope ratio: 8 × 1.5 = 12 feet of horizontal space required on each side. This ensures the soil slope is stable enough to prevent cave-ins and protect workers in the excavation.
Why the Other Options Are Wrong
Option B: 6 feet
16 feet would represent a 2:1 slope ratio (8 × 2 = 16), which is more conservative than required and would be unnecessarily wasteful of space and resources.
Option D: 8 feet
8 feet represents a 1:1 slope ratio, which is used for Type B soil, not Type C soil which requires the more conservative 1.5:1 ratio.
Memory Technique
Remember 'ABC = 0.75, 1, 1.5' - Type A soil = 0.75:1, Type B = 1:1, Type C = 1.5:1. Type C is the 'Crappiest' soil, so it needs the most slope (1.5).
Reference Hint
OSHA Construction Standards 29 CFR 1926.652 - Requirements for protective systems, or Florida Building Code Chapter 18 - Soils and Foundations
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