A trench is being excavated in Type C soil. What is the maximum allowable slope ratio for the sides of the trench?
Correct Answer
A) 1.5:1 (34°)
For Type C soil (the least stable), OSHA requires a maximum slope of 1.5:1 (1.5 horizontal to 1 vertical), which equals a 34-degree angle from horizontal.
Why This Is the Correct Answer
Type C is the least stable soil classification under OSHA. It includes granular soils (gravel, sand, loamy sand), submerged soil, soil from which water is freely seeping, or soil in a sloped layered system. Because of its instability, OSHA requires the most gradual slope: 1.5H:1V (1.5 feet horizontal for every 1 foot vertical), which equals approximately 34 degrees from horizontal. This wide, gentle slope reduces the load on trench walls and minimizes cave-in risk.
Why the Other Options Are Wrong
Option B: 1/2:1 (63°)
A 1/2:1 slope (63 degrees) is the standard for Type A soil — the most stable classification (hard clay, cemented soils). Applying a Type A slope to Type C soil would create dangerously steep walls with high cave-in risk.
Option C: 3/4:1 (53°)
A 3/4:1 slope (53 degrees) applies to Type B soil — moderately stable soil (angular gravel, silt, previously disturbed soil). It is less steep than Type A but still too steep for unstable Type C conditions.
Option D: 1:1 (45°)
A 1:1 slope (45 degrees) also applies to Type B soil in some configurations. It is too steep for Type C soil and would not provide adequate protection against cave-in in granular or unstable ground.
Memory Technique
Use the alphabet and steepness: A soil is best → steepest allowed slope (1/2:1). C soil is worst → flattest required slope (1.5:1). As the letter gets worse (A → B → C), the slope gets flatter. Or: 'C for Caution — 1.5 to 1, lay it flat or it won't last.'
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