NASCLA Accredited Commercial General ContractorSite WorkHard
A construction crew is performing an excavation for a new building basement. The soil is classified as Type C, and the excavation will be 10 feet deep. According to OSHA regulations, what is the maximum allowable slope ratio for the sides of the excavation, assuming no shoring or shielding is used?
- A1.5:1 (34 degrees)
- B2:1 (26.6 degrees)
- C1:1 (45 degrees)
- D0.75:1 (53 degrees)
Show answer & explanationAnswer & explanation
Correct answer: A. 1.5:1 (34 degrees)
OSHA regulations (29 CFR 1926, Subpart P, Appendix B) specify the maximum allowable slopes for excavations based on soil type. For Type C soil, the maximum allowable slope is 1.5H:1V (1.5 horizontal to 1 vertical), which corresponds to approximately 34 degrees. This means for every 1 foot of vertical depth, the horizontal distance must extend 1.5 feet.
Why the other options are wrong
- B. 2:1 (26.6 degrees) is a much flatter slope than required, exceeding the minimum safety standard but not the 'maximum allowable' specific to Type C.
- C. 1:1 (45 degrees) is for Type B soil, not Type C.
- D. 0.75:1 (53 degrees) is steeper than allowed for Type C soil; this is for Type A soil.
OSHA Excavation Sloping (Type C Soil)
OSHA 29 CFR 1926.652(b)(1)(iii) mandates a maximum allowable slope of 1.5H:1V (1.5 horizontal to 1 vertical) for excavations in Type C soils that are 20 feet or less in depth, when no shoring or shielding is used.
- Type C soil: least stable.
- Maximum slope: 1.5H:1V (approx. 34 degrees).
- Applies to excavations 20 feet or less.
- Requires competent person classification.
Memory trick: A is steep, B is medium, C is flat, for safety, that's that.