OSHA 10-Hour Construction ReviewExcavationsMedium
A competent person is evaluating an excavation site. They observe a trench 7 feet deep where the soil is cohesive and has an unconfined compressive strength of 1.6 tons per square foot (tsf). How should this soil be classified according to OSHA standards?
- AType B
- BType A
- CType C
- DStable Rock
Show answer & explanationAnswer & explanation
Correct answer: B. Type A
OSHA classifies cohesive soils with an unconfined compressive strength of 1.5 tsf or greater as Type A. Since the soil in the scenario has a strength of 1.6 tsf, it falls into the Type A category.
Why the other options are wrong
- A. Type B soil has a strength between 0.5 tsf and less than 1.5 tsf, so 1.6 tsf is too high for Type B.
- C. Type C soil has a strength of 0.5 tsf or less, making 1.6 tsf much too high for this classification.
- D. Stable rock is solid mineral matter, not soil with a compressive strength measurement.
Type A Soil Classification
Type A soil is a cohesive soil with an unconfined compressive strength of 1.5 tons per square foot (tsf) or greater. It is the most stable type of soil (excluding stable rock) for excavation purposes.
- Cohesive soil type.
- Unconfined compressive strength ≥ 1.5 tsf.
- Most stable soil (besides stable rock).
- Can be sloped at 0.75:1 (53 degrees).
Memory trick: Strength Grades A, B, C Soil