OSHA 10-Hour Construction ReviewExcavationsMedium
A construction crew is excavating a trench for a new pipeline. The trench is 6 feet deep, 3 feet wide, and the soil has been classified as Type C. What is the maximum allowable slope ratio for this trench if no protective system is used?
- A0.5:1 (63 degrees)
- B2:1 (26.5 degrees)
- C1:1 (45 degrees)
- D1.5:1 (34 degrees)
Show answer & explanationAnswer & explanation
Correct answer: D. 1.5:1 (34 degrees)
For Type C soil, OSHA mandates a maximum allowable slope of 1.5:1 (horizontal to vertical), which corresponds to an angle of 34 degrees from the horizontal. This is a critical safety measure to prevent trench collapse.
Why the other options are wrong
- A. This slope is too steep and extremely unsafe for Type C soil, significantly increasing the risk of collapse.
- B. This slope is too gradual and not required for Type C soil, exceeding the minimum safety requirements and potentially increasing excavation costs unnecessarily.
- C. This slope ratio is typically allowed for Type B soil, not Type C.
Type C Soil Sloping
Type C soil is the least stable soil type and requires the gentlest slope when open excavation is used, with a maximum allowable slope of 1.5:1 (34 degrees).
- Least stable soil type.
- Maximum allowable slope is 1.5:1.
- Angle of 34 degrees from the horizontal.
- Requires significant protective measures.
Memory trick: Slopes Classify Safety Carefully