NASCLA Accredited Commercial General ContractorSite WorkMedium
A utility contractor is trenching for a new water main in a residential area. The trench is 5 feet deep and the soil is classified as Type B. According to OSHA standards, what is the maximum allowed slope ratio for the sides of the trench if no shoring or shielding is used?
- A1:0.75 (53 degrees)
- B1:2 (26.5 degrees)
- C1:1.5 (34 degrees)
- D1:1 (45 degrees)
Show answer & explanationAnswer & explanation
Correct answer: C. 1:1.5 (34 degrees)
OSHA regulations (29 CFR 1926.652) specify maximum allowable slopes for excavations based on soil type. For Type B soil, the maximum allowable slope is 1:1.5 (horizontal to vertical), which corresponds to an angle of 34 degrees from the horizontal.
Why the other options are wrong
- A. 1:0.75 is for Type A soil (53 degrees) or stable rock, making it too steep for Type B soil.
- B. 1:2 is for Type C soil, which is less stable than Type B, meaning 1:1.5 is less steep and thus safer for Type B.
- D. 1:1 is for Type A soil, which is more stable than Type B.
OSHA Excavation Sloping (Type B Soil)
OSHA's maximum allowable slope for excavations in Type B soil, which is cohesive soil with an unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf, or granular non-cohesive soil (e.g., silts, sandy loams).
- Maximum slope: 1:1.5 (horizontal to vertical).
- Equivalent to 34 degrees from the horizontal.
- Applies to trenches 20 feet deep or less.
Memory trick: A is Aggressive (1:1), B is Better (1:1.5), C is Cautious (1:2).