OSHA classifies soil into 4 types as outlined below, 29 CFR 1926 Subpart P Appendix A

Stable rock
means natural solid mineral matter that can be excavated with vertical sides and
remain intact while exposed.

Type A means cohesive soils with an unconfined, compressive strength of 1.5 ton per square foot (tsf)
(144 kPa) or greater. Examples of cohesive soils are: clay, silty clay, sandy clay, clay loam and, in some
cases, silty clay loam and sandy clay loam. Cemented soils such as caliche and hardpan are also
considered Type A. However, no soil is Type A if:
a) The soil is fissured; or
b) The soil is subject to vibration from heavy traffic, pile driving, or similar effects; or
c) The soil has been previously disturbed; or
d) 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
e) The material is subject to other factors that would require it to be classified as a less stable material

Type B means:
a) Cohesive soil with an unconfined compressive strength greater than 0.5 tsf (48 kPa) but less than 1.5
tsf (144 kPa); or
b) 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.
c) Previously disturbed soils except those which would otherwise be classed as Type C soil.
d) Soil that meets the unconfined compressive strength or cementation requirements for Type A, but is
fissured or subject to vibration; or
e) Dry rock that is not stable; or
f) 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. 4)

Type C means:
a) Cohesive soil with an unconfined compressive strength of 0.5 tsf (48 kPa) or less; or
b) Granular soils including gravel, sand, and loamy sand; or
c) Submerged soil or soil from which water is freely seeping; or
d) Submerged rock that is not stable, or
e) 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.

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