What are the soil classification categories in excavation? (OSHA)

Some of the compliance methods permitted under the Excavation standards require a competent person to classify soil and rock deposits as:

• Stable rock
• Type A soil
• Type B soil
• Type C soil

Stable Rock

Natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed.

Type A

Cohesive soils with an unconfined compressive strength of 1.5 tons per square foot (tsf) (144 kPa) or greater. Examples include: clay, silty clay, sandy clay, and clay loam. Certain conditions preclude soil from being classified as Type A. For example, no soil is Type A if:

1. The soil is fissured; or
2. The soil is subject to vibration from heavy traffic, pile driving,
   or similar effects; or
3. The soil has been previously disturbed; or
4. The soil is part of a sloped, layered system where the layers dip
   into the excavation on a slope of four horizontal to one vertical (4H:1V)
   or greater; or
5. The material is subject to other factors that would require it to be
   classified as a less stable material.

Type B

Includes cohesive soil with an unconfined compressive strength greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa) and granular cohesionless soils (such as angular gravel, similar to crushed rock, silt, silt loam, sandy loam, and, in some cases, silty clay loam and sandy clay loam). “Type B” means:

1. Cohesive soil with an unconfined compressive strength greater than
   0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa); or
2. Granular cohesionless soils including: angular gravel (similar to
   crushed rock), silt, silt loam, sandy loam and, in some cases, silty clay
   loam and sandy clay loam.
3. Previously disturbed soils except those which would otherwise be
   classed as Type C soil.
4. Soil that meets the unconfined compressive strength or cementation
   requirements for Type A, but is fissured or subject to vibration; or
5. Dry rock that is not stable; or
6. Material that is part of a sloped, layered system where the layers
   dip into the excavation on a slope less steep than four horizontal to one
   vertical (4H:1V), but only if the material would otherwise be classified
   as Type B.

Type C

Cohesive soil with an unconfined compressive strength of 0.5 tsf (48 kPa) or less, granular soils (including gravel, sand, and loamy sand), submerged soil or soil from which water is freely seeping, submerged rock that is not stable, or material in a sloped, layered system where the layers dip into the excavation or with a slope of four horizontal to one vertical (4H:1V) or steeper. “Type C” means:

1. Cohesive soil with an unconfined compressive strength of 0.5 tsf (48
   kPa) or less; or
2. Granular soils including gravel, sand, and loamy sand; or
3. Submerged soil or soil from which water is freely seeping; or
4. Submerged rock that is not stable, or
5. Material in a sloped, layered system where the layers dip into the
   excavation or a slope of four horizontal to one vertical (4H:1V) or
   steeper.

---

At Ron Meyer & Associate Excavating, Inc, we’ve been providing underground and commercial construction to private and commercial businesses for 39 years. As the general contractor or subcontractor, our experienced foremen, equipment operators, pipe layers, truck drivers and well-maintained equipment fleet make us an undeniable choice for your excavating services. Let’s talk about your project!

Sources:

• https://www.osha.gov/Publications/osha2226.pdf
• https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10931