OSHA 10-Hour Construction ReviewFocus Four HazardsHard
An excavation project requires workers to enter a trench that is 6 feet deep. The soil type has been classified as Type B. According to OSHA, what is the maximum allowable slope ratio for the sides of this trench if shoring is not used?
- A1:1.5 (34 degrees)
- B0.75:1 (53 degrees)
- C1:1 (45 degrees)
- D1:2 (26.5 degrees)
Show answer & explanationAnswer & explanation
Correct answer: C. 1:1 (45 degrees)
According to OSHA 1926 Subpart P, Appendix B, Table B-1, for excavations less than 20 feet deep in Type B soil, the maximum allowable slope is 1:1 (45 degrees). This means for every 1 foot of vertical rise, there can be 1 foot of horizontal run. This angle provides adequate protection against cave-ins for this soil type.
Why the other options are wrong
- A. This slope (1.5:1, 34 degrees) is the maximum allowable slope for Type C soil, not Type B.
- B. This slope (0.75:1, 53 degrees) is for stable rock, not Type B soil.
- D. This slope is for Type C60 soil, a more unstable variant, and is even more conservative than Type C.
Excavation Sloping (Type B Soil)
For excavations in Type B soil, sloping is a protective system where the sides of the excavation are cut back to a stable angle of repose to prevent cave-ins.
- Type B soil is cohesive or granular, but less stable than Type A.
- Maximum allowable slope for Type B soil is 1:1 (45 degrees).
- Applies to excavations less than 20 feet deep.
Memory trick: A-Type 3/4, B-Type 1 to 1, C-Type 1 and a half, then you're done!