A construction site has an excavation that is 8 feet deep in Type C soil. What is the maximum allowable slope ratio for the sides of this excavation?
Correct Answer
B) 1.5:1 (34 degrees)
For Type C soil (the least stable), OSHA requires a maximum slope of 1.5:1 or 34 degrees from horizontal. This provides adequate protection against cave-ins in unstable soil conditions.
Why This Is the Correct Answer
Type C soil is the least stable soil classification under OSHA standards, consisting of cohesive soil with an unconfined compressive strength of 0.5 tons per square foot or less. For excavations in Type C soil, OSHA 29 CFR 1926.652 specifically requires a maximum allowable slope of 1.5:1 (1.5 horizontal to 1 vertical) or 34 degrees from horizontal. This slope ratio provides adequate protection against cave-ins by creating a stable angle that accounts for the poor cohesive properties of Type C soil.
Why the Other Options Are Wrong
Option A: 1:1 (45 degrees)
A 1:1 slope (45 degrees) is too steep for Type C soil and would create an unsafe condition prone to cave-ins, as it doesn't account for the unstable nature of Type C soil
Option C: 0.75:1 (53 degrees)
A 0.75:1 slope (53 degrees) is much too steep for any soil type and would be extremely dangerous, creating an almost vertical cut that would likely result in immediate cave-in
Option D: 2:1 (26.5 degrees)
While a 2:1 slope would be safer than required, it's not the maximum allowable slope specified by OSHA regulations and would result in unnecessary excavation and increased costs
Memory Technique
Use 'ABC-123': Type A soil = 0.75:1, Type B soil = 1:1, Type C soil = 1.5:1 - each gets progressively more gradual as soil stability decreases
Reference Hint
OSHA 29 CFR 1926.652 - Requirements for protective systems, Table B-1 for maximum allowable slopes
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