Documentation:Soiltest Pocket Penetrometer

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Soiltest Pocket Penetrometer

The Pocket Penetrometer is a hand operated device that uses a calibration spring with a 1/4" diameter piston, designed as a lightweight instrument for use by field personnel to check visual classification of soils. It can be used to verify whether excavation side walls require shoring, based on OSHA cohesive soils classifications. It indicates consistency, shear strength, and approximate unconfined shear strength. Direct-reading scale—in tons/sq ft, or kg/sq cm—corresponds to equivalent unconfined compressive strength. The readings obtained from the Penetrometer do not replace laboratory test results due to the fact that a small area of penetration test could give misleading results. The instrument should not be used for obtaining foundation design data.

Taking measurements

  1. It is best to take your measurements on intact cores, in the field, or undisturbed samples. Take care to remove any softened materials and avoid large stones or roots.
  2. Push the red ring on the barrel of the penetrometer against the handle (knurled portion) of the penetrometer.
  3. Hold the penetrometer upright (at a 90 degree angle to the soil). Grip the handle and push the tip of the penetrometer into the soil so the groove marked on the tip is even with the level of the soil.
  4. Read the scale to determine the unconfined compression strength directly from the scale in tons per square foot (TSF) or kilograms per square centimeter (kg/cm2 ).
  5. The reading should be taken from the lower side of the red ring, i.e. the side closest to the knurled handle to the nearest .1 .
  6. Clean off the penetrometer between readings.
  7. The scale is calibrated in tons per square foot or kilograms per square centimeter unconfined compressive strength.
  8. Take at least three measurements near each other to obtain an average.
  9. Ensure that only one user is completing the measurements, as user, angle of insertion, and instrument condition all affect the results.