Manual Tests For OSHA Regulations
Pocket Penetrometer
These devices are direct-reading, spring operated instruments used to determine the unconfined compressive strength of cohesive soils. Once pushed into the soil, an indicator sleeve displays the reading. The instrument is calibrated in either tons per square foot (tsf) or kilograms per square centimeter. Note: These instruments have an error rate of +-30%.
Torvane (or shearvane)
These devices measure a soils cohesion. They consist of vanes that are pressed into a level section of undisturbed soil, and the torsional knob is slowly turned until soil failure occurs. These measurements need to be multiplied by 2 to give unconfined compressive strength. Careful attention needs to be payed to reading the dial measurement.
Thumb Penetration Test
This 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 effort, the soil is probably Type A. If the thumb penetrates no further than the length of the thumb nail, it is probably Type B, and if the thumb penetrates the full length of the thumb, it is probably Type C. This is a very subjective test and has a large degree of inaccuracy.
Dry Strength Test
Dry soil that crumbles freely or with moderate pressure into individual grains is granular. Dry soil that falls into clumps that subsequently break into smaller clumps (and the smaller clumps can be broken only with difficulty) is probably clay in combination with gravel, sand, or silt. If the soil breaks into clumps that do not break into smaller clumps (and the soil can be broken only with difficulty), the soil is considered unfissured unless there is visual indication of fissuring.
A drying test is used to differentiate between cohesive material with fissures,
unfissured cohesive material, and granular material. The procedure for the drying
test involves drying a sample of soil that is approximately one inch thick (2.54 cm) and
six inches (15.24 cm) in diameter until it is thoroughly dry.
I. If the sample develops cracks as it dries, significant fissures are indicated.
II. Samples that dry without cracking are to be broken by hand. If
considerable force is necessary to break a sample, the soil has significant cohesive
material content. The soil can be classified as an unfissured cohesive material and
the unconfined compressive strength should be determined.
III. If a sample breaks easily by hand, it is either a fissured cohesive material or
a granular material. To distinguish between the two, pulverize the dried clumps of
the sample by hand or by stepping on them. If the clumps do not pulverize easily,
the material is cohesive with fissures. If they pulverize easily into very small
fragments, the material is granular.
Plasticity (or ribbon test)
This test is generally run on soil that passes the #40 sieve. The saturated fine soil and fine sands are rolled together between the palms of the hands until a cylinder approximately 3/4 inch thick by approximately 6 inches long is formed. The cylinder is then placed across the palm of the hand and squeezed between the thumb and index finger until it is approximately 1/8 inch thick. The squeezed portion is allowed to hand over the side of the hand. If it forms ribbons 6 inches in length or longer it is said to be clay. The longer the ribbon the more clay, the shorter the ribbon the more silt (or sand) content.
For questions or comments regarding these pages contact Dr. Alan Scott / scotta@uwstout.edu / this page was last updated April 03, 2000