CSLB C-27 Landscaping ContractorSite Preparation and DrainageHard
A landscape contractor is excavating a trench for a new underground utility line. The trench is 3 feet deep in Type B soil, which is cohesive with a high unconfined compressive strength. According to Cal/OSHA regulations, what is the maximum allowable slope for the sides of this trench if no shoring or shielding is used?
- A0.5:1 (63 degrees)
- B1.5:1 (34 degrees)
- C1:1 (45 degrees)
- D0.75:1 (53 degrees)
Show answer & explanationAnswer & explanation
Correct answer: B. 1.5:1 (34 degrees)
Cal/OSHA (and federal OSHA) regulations specify maximum allowable slopes for trench excavations based on soil type. For Type B soil, the maximum allowable slope is 1.5:1 (horizontal to vertical), which corresponds to an angle of 34 degrees from the horizontal.
Why the other options are wrong
- A. 0.5:1 (63 degrees) is significantly steeper than allowed for Type B soil and is not a standard maximum slope for any soil type without protection.
- C. 1:1 (45 degrees) is the maximum slope for Type A soil, which is more stable than Type B.
- D. 0.75:1 (53 degrees) is steeper than allowed for Type B soil and is the maximum for Type A soil when conditions allow.
Cal/OSHA Trench Slope (Type B Soil)
According to Cal/OSHA, the maximum allowable slope for an open excavation in Type B soil is 1.5:1 (horizontal to vertical), or 34 degrees from the horizontal, when no shoring or shielding is used.
- Type B soil is cohesive with moderate compressive strength.
- Sloping prevents trench wall collapse.
- A 'competent person' must determine soil type.
- Different soil types have different maximum slopes (e.g., Type A = 0.75:1 or 1:1, Type C = 2:1).
Memory trick: Type B, one and a half to one, or the job is undone.