The OSHA standards define soil classifications within the simplified soil classification systems, which consist of four categories:
a-             Stable Rock
b-            Type A Soil
c-             Type B Soil
d-            Type C Soil

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Stability is greatest in stable rock and decreases through type A and B to type C, which is the least stable.

Stable Rock: is defined as natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed. (Example: granite or sandstone).

Type A Soil: are cohesive soils with unconfined compressive strength of 1.5 tons per square foot or greater. (Example: clay, silty clay, sandy clay, clay loam)

Type B Soil: are cohesive soils with an unconfined compressive strength greater than 0.5 tons per square foot but less than 1.5 (tsf)
(Example: angular gravel, silt, silt loam)

Type C Soil: are cohesive soils with an unconfined compressive strength of 0.5 tsf or less.(Example: gravel, sand and loamy sand, submerged soil, soil from which water is freely seeping.


Many kinds of equipment and methods are used to determine the type of soil prevailing in an area, as described below:

Pocket Penetrometer: Penetrometers are direct - reading, spring - operated instruments used to determine the unconfined compressive strength of saturated cohesive soils. Once pushed into the soil, an indicator sleeve displays the reading.

Visual Test: If the excavated soil is in clumps, it is cohesive. If it breaks up easily, not staying in clumps, it is granular.

Thumb Penetration Test: The thumb penetration procedure involves an attempt to press the thumb firmly into the soil in question. If the thumb makes an indentation in the soil only with great difficulty, the soil is probably type A. If the thumb penetrates no further than the length of the thumb nail, it is probably Type B soil, and if the thumb penetrates the full length of the thumb it is type C.

Dry Strength Test: Try to crumble the sample in your hands with your fingers. If itcrumbles into grains, it is granular. Clay will not crumble into grains, only into smaller chunks.

Wet Manual Test: Wet your fingers and work the soil between them. Clay is a slick paste when wet, meaning it is cohesive. If the clump falls a part in grains, it is granular.

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