Pocket Penetrometers

Penetrometer, Pocket

Humboldt's pocket penetrometers for soil is used by field personnel to check visual classification of soils. The pocket penetrometer, or hand penetrometer can be used to make quick estimates of unconfined compressive strength of cohesive soils, especially in field applications.

The pocket penetrometer can quickly verify whether excavation side walls require shoring, based on OSHA cohesive soils classifications. The penetrometer indicates consistency, shear strength, and approximate unconfined shear strength. It has a direct-reading scale—in tons/sq ft, or kg/sq cm, which corresponds to equivalent unconfined compressive strength. The range of this penetrometer is: 0 to 4.5 tons. It features high-quality construction and includes a belt-loop style carrying case and operating instructions. While the pocket penetrometer is a great tool for fast evaluations of soil in the field, it should not be used to replace laboratory testing or field analysis, or be used to produce foundation design data.

In use, the pocket penetrometer's penetration piston is pushed into the soil surface to a calibration groove machined into the piston at 0.25" (6.4mm) from the end. The resistance of a calibrated internal spring registers the penetration force on an engraved scale.

When used on-site for use in OSHA soil classification applications the following soil categories would apply.

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.