These tests are conducted to determine quantitative as well as qualitative properties of soil and to provide more information in order to classify soil properly.

1. Plasticity: Mold a moist or wet sample of soil into a ball and attempt to roll it into threads as thin as 1/8" in diameter. Cohesive material can be successfully rolled into threads without crumbling. For example, if a 1/8" thread at least 2" in length of can be held on one end without tearing, the soil is cohesive.

2. Dry Strength: If the soil is dry and crumbles on its own or with moderate pressure into individual grains or fine powder, it is granular (any combination of gravel, sand, and silt). If the soil is dry and falls into clumps that break up into small clumps but the smaller clumps can only be broken up with the difficulty, it may be clay in combination with gravel, sand, or silt. If the dry soil breaks into clumps that can be broken only with difficulty and there is no visual indication that the soil is fissured, the soil may be considered unfissured.

3. Thumb Penetration: The thumb penetration test can be used to estimate the unconfined compressive strength of cohesive soils.

Type A: Soil can be readily indented with the thumb only with very great effort.

Type B: Soil can be readily indented with the thumb with some effort.

Type C: Soil can be easily penetrated several inches into the soil with no effort and can be easily molded with light finger pressure. This test is to be conducted on an undisturbed soil sample, such as a clump of soil, as soon as practicable after excavation to keep to a minimum the effects of exposure to drying influences.

Reclassification is needed if the excavation is later exposed to wetting (rain, snow, or flooding) and documented accordingly.

Rev. January 2021

Page 1 of 2

The following manual tests may be taken to verify the employer's results.

4. Estimates of unconfined compressive strengths of soils can also be obtained by use of a pocket penetrometer or by using a hand-operated shearvane.

5. Drying Test: The basic purpose of the drying test is 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 approximately 1" thick and 6" in diameter until it is thoroughly dry.

a. If the sample develops cracks as it dries, significant fissures are indicated.

b. Samples that dry and do not crack are to be broken by hand. If considerable force is necessary to break the sample, the soil has significant cohesive material content. The soil can be classified as unfissured cohesive material, and the unconfined compressive strength is to be determined.

c. 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 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.

Rev. January 2021

Page 2 of 2