CSLB C-27 Landscaping ContractorSite Preparation and DrainageHard
A landscape contractor is tasked with excavating a trench for a new drainage pipe. The trench is 3 feet deep, 1.5 feet wide, and 50 feet long. The soil is classified as Type C-60, which is a cohesive soil. According to Cal/OSHA regulations, what is the maximum allowable slope for the sides of this trench if no shoring or shielding is used?
- A1.5:1 (34 degrees)
- B2:1 (26.5 degrees)
- C1:1 (45 degrees)
- D0.75:1 (53 degrees)
Show answer & explanationAnswer & explanation
Correct answer: A. 1.5:1 (34 degrees)
Cal/OSHA regulations (and federal OSHA) classify Type C soil as having a maximum allowable slope of 1.5:1 (horizontal to vertical), which corresponds to 34 degrees from the horizontal. This is a critical safety standard for preventing trench collapses.
Why the other options are wrong
- B. 2:1 (26.5 degrees) would be overly conservative for Type C soil and is not the specified maximum, potentially requiring more excavation than necessary.
- C. 1:1 is the maximum allowable slope for Type B soil, which is more stable than Type C.
- D. 0.75:1 (53 degrees) is the maximum allowable slope for stable rock, which is significantly more stable than Type C soil.
Cal/OSHA Max Trench Slope (Type C)
For Type C soil, Cal/OSHA mandates a maximum allowable trench side slope of 1.5:1 (horizontal to vertical) or 34 degrees from the horizontal, when no shoring or shielding is used.
- Type C soil is cohesive, but less stable than Type A or B.
- 1.5:1 slope means for every 1.5 feet horizontally, the trench can go 1 foot vertically.
- This is a critical safety regulation to prevent cave-ins.
- Slopes must be measured from the horizontal plane.
Memory trick: Type C: Can't go steeper than one and a half to one!