CSLB C-27 Landscaping ContractorSite Preparation and DrainageHard
A landscape contractor is excavating a trench for a new underground utility line. The trench is 5 feet deep, 3 feet wide, and the soil is classified as Type B. According to Cal/OSHA regulations, what is the maximum allowable slope for the sides of this trench if shoring or shielding is not used?
- A1:1 (45 degrees)
- B0.75:1 (53 degrees)
- C2:1 (26.5 degrees)
- D1.5:1 (34 degrees)
Show answer & explanationAnswer & explanation
Correct answer: D. 1.5:1 (34 degrees)
Cal/OSHA regulations (8 CCR 1541.1 Appendix B) specify maximum allowable slopes for excavations greater than 5 feet in depth, but for trenches up to 20 feet deep, the maximum allowable slope for Type B soil is 1.5:1 (horizontal to vertical), which corresponds to approximately 34 degrees from the horizontal. This ratio means for every 1 foot of depth, the trench side must extend 1.5 feet horizontally.
Why the other options are wrong
- A. 1:1 (45 degrees) is the maximum allowable slope for Type A soil, not Type B.
- B. 0.75:1 (53 degrees) is too steep and would be unsafe for Type B soil, exceeding the maximum allowable slope.
- C. 2:1 (26.5 degrees) is the maximum allowable slope for Type C soil, which is less stable than Type B.
Cal/OSHA Trench Slope (Type B Soil)
For trenches in Type B soil up to 20 feet deep, Cal/OSHA's maximum allowable slope for trench sides is 1.5:1 (horizontal:vertical), or 34 degrees.
- Type B soil is cohesive with an unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf.
- Slope ratio is horizontal run to vertical rise.
- Applies when shoring or shielding is not used.
Memory trick: Different soil types need different 'leans' to be safe.