CSLB C-36 Plumbing ContractorPlanning and EstimatingHard
A plumbing contractor is developing a safety plan for a trenching operation to install a new sewer line. The trench will be 6 feet deep in Type C soil. According to OSHA regulations, what is the MINIMUM acceptable slope for the sides of the trench if shoring or shielding is not used?
- A1.5:1 (34 degrees)
- B1:1 (45 degrees)
- C2:1 (26.5 degrees)
- D0.75:1 (53 degrees)
Show answer & explanationAnswer & explanation
Correct answer: A. 1.5:1 (34 degrees)
OSHA regulations (29 CFR 1926.652) for trenching and excavation require specific maximum allowable slopes for different soil types when shoring or shielding is not used. For Type C soil, the maximum allowable slope is 1.5 horizontal to 1 vertical (1.5:1), which corresponds to an angle of 34 degrees from the horizontal. This is the minimum acceptable slope to prevent collapse.
Why the other options are wrong
- B. 1:1 is for Type B soil. It is not sufficient for Type C soil.
- C. 2:1 is for very stable conditions or Type A soil, which is overly conservative for Type C and not the minimum.
- D. 0.75:1 (53 degrees) is steeper than 1:1 and would be unsafe for Type C soil.
OSHA Trench Sloping (Type C Soil)
OSHA mandates a maximum allowable slope of 1.5 horizontal to 1 vertical (34 degrees) for Type C soil in trenches 5 feet or deeper, if shoring or shielding is not used.
- Type C soil is cohesive soil with an unconfined compressive strength of 0.5 tsf or less, or granular soils.
- Sloping is one method of protecting workers from trench collapse.
- Alternative methods include shoring, shielding, or benching.
Memory trick: C for 'Crumbling' soil needs a 'Cushy' slope: 1.5 horizontal for every 1 vertical.