OSHA 10-Hour Construction ReviewExcavationsMedium
A competent person is evaluating an excavation site where the soil is moist, cohesive, and exhibits an unconfined compressive strength of 0.9 tons per square foot (tsf). Based on OSHA's soil classification, how should this soil be categorized?
- AType A
- BType B
- CType C
- DStable Rock
Show answer & explanationAnswer & explanation
Correct answer: B. Type B
OSHA classifies cohesive soils with an unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf as Type B soil. Given the soil's strength of 0.9 tsf, it falls squarely within the Type B criteria.
Why the other options are wrong
- A. Type A soil has an unconfined compressive strength of 1.5 tsf or greater.
- C. Type C soil has an unconfined compressive strength of 0.5 tsf or less, or consists of granular soils.
- D. Stable Rock is natural solid mineral matter, not a cohesive soil with a measured compressive strength in this range.
Type B Soil Classification
Type B soil is a cohesive soil type with intermediate stability, characterized by an unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf.
- Unconfined compressive strength: >0.5 tsf to <1.5 tsf.
- Includes granular cohesionless soils if they are moist and have some cohesion.
- Requires moderate sloping or other protective systems.
Memory trick: A-B-C: A is Strongest, C is Weakest, B is Between.