Humboldt H-4200F Soil Penetrometer - Manual (Page 3)

OSHA Soil Categories
OSHA categorizes soil and rock deposits into four types, A through D, as
follows:
Stable Rock: is natural solid mineral matter that can be excavated with
vertical sides and remain intact while exposed. It is usually identified by a
rock name such as granite or sandstone. Determining whether a deposit is of
this type may be difficult unless it is known whether cracks exist and whether
or not the cracks run into or away from the excavation.
Type A Soils: are cohesive soils with an unconfined compressive strength
of 1.5 tons per square foot (tsf) (144 kPa) or greater. Examples of Type A
cohesive soils are often: clay, silty clay, sandy clay, clay loam and, in some
cases, silty clay loam and sandy clay loam. (No soil is Type A if it is fissured,
is subject to vibration of any type, has previously been disturbed, is part of a
sloped, layered system where the layers dip into the excavation on a slope of
4 horizontal to 1 vertical (4H:1V) or greater, or has seeping water.
Type B Soils: are cohesive soils with an unconfined compressive strength
greater than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa). Examples of
other Type B soils are: angular gravel; silt; silt loam; previously disturbed
soils unless otherwise classified as Type C; soils that meet the unconfined
compressive strength or cementation requirements of Type A soils but are
fissured or subject to vibration; dry unstable rock; and layered systems
sloping into the trench at a slope less than 4H:1V (only if the material would
be classified as a Type B soil).
Type C Soils: are cohesive soils with an unconfined compressive strength
of 0.5 tsf (48 kPa) or less. Other Type C soils include granular soils such as
gravel, sand and loamy sand, submerged soil, soil from which water is
freely seeping, and submerged rock that is not stable. Also included in this
classification is material in a sloped, layered system where the layers dip into
the excavation or have a slope of four horizontal to one vertical (4H:1V) or
greater.
Layered Geological Strata: Where soils are configured in layers, i.e., where
a layered geologic structure exists, the soil must be classified on the basis of
the soil classification of the weakest soil layer. Each layer may be classified
individually if a more stable layer lies below a less stable layer, i.e., where a
Type C soil rests on top of stable rock.