CSLB General Building (B)Site Work, Foundations and ConcreteMedium
During a trench excavation, a soils engineer classifies the soil as Type A under OSHA/Cal-OSHA excavation standards. Which characteristic best describes Type A soil?
- ACohesive soil with an unconfined compressive strength of 1.5 tons per square foot or greater
- BPreviously disturbed soil that does not meet the criteria for stable soil
- CSoil that is subject to vibration from heavy traffic or equipment
- DGranular soil with no cohesion, such as loose sand
Show answer & explanationAnswer & explanation
Correct answer: A. Cohesive soil with an unconfined compressive strength of 1.5 tons per square foot or greater
Type A soil is the most stable classification and is defined as cohesive soil with an unconfined compressive strength of 1.5 tsf (144 kPa) or greater, such as clay, silty clay, or hardpan, provided it is not fissured or subject to vibration.
Why the other options are wrong
- B. Previously disturbed soil is excluded from Type A regardless of strength.
- C. Soil subject to vibration cannot be classified as Type A even if otherwise cohesive.
- D. Granular, cohesionless soil like sand is typically Type C, the least stable.
OSHA Soil Classification
A system (Type A, B, C) used to classify soil stability for excavation safety, based on cohesion, unconfined compressive strength, and site conditions.
- Type A: cohesive soil, UCS ≥ 1.5 tsf, most stable
- Type B: cohesive soil, UCS 0.5-1.5 tsf, or unstable fissured soil
- Type C: granular soil or UCS < 0.5 tsf, least stable, requires most protection
Memory trick: A is for 'awesome strength,' C is for 'crumbly and weak.'