OSHA 10-Hour Construction ReviewFocus Four HazardsMedium
A construction crew is performing excavation work for a new building foundation. The excavation is 8 feet deep and 4 feet wide. The soil type has been classified as Type B, granular soil with some cohesion. What is the maximum allowable slope ratio for the sides of this excavation?
- 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)
For Type B soil, OSHA requires a maximum allowable slope of 1.5:1 (horizontal to vertical), which equates to an angle of 34 degrees from the horizontal. This ratio ensures the stability of the excavation walls and prevents cave-ins.
Why the other options are wrong
- B. This slope ratio (1:1 or 45 degrees) is typically allowed for Type A soil, which is more stable than Type B.
- C. This slope ratio (2:1 or 26.5 degrees) is typically required for Type C soil, which is the least stable soil type and needs a gentler slope.
- D. This slope ratio (0.75:1 or 53 degrees) is steeper than allowed for Type B soil and is only permissible for stable rock or Type A soil in specific conditions.
Excavation Sloping (Type B Soil)
OSHA's requirement for the maximum angle of repose for excavation walls in Type B soil to prevent cave-ins.
- Type B soil is granular with some cohesion.
- Maximum allowable slope is 1.5:1 (horizontal to vertical).
- This slope corresponds to an angle of 34 degrees from the horizontal.
Memory trick: B for 'B'etter be 1.5:1, or you'll be buried!