Visual and Manual Soil Tests: How a Competent Person Classifies Soil

Classifying soil is not guesswork. Appendix A lists acceptable visual and manual tests, and the competent person must use at least one of each. Used together, they answer three questions: Is the soil cohesive or granular? How strong is it? Is it fissured, layered, wet or disturbed?

Visual analysis

A visual analysis looks at the excavation, the soil next to it, the spoil and the surrounding area. Appendix A lists what to look for:

• Particle size. Fine-grained soil is cohesive material. Soil made mostly of coarse sand or gravel is granular.
• How the spoil behaves. Soil that stays in clumps when excavated is cohesive. Soil that breaks up easily and does not stay in clumps is granular.
• Cracks. Look for crack-line openings and spalling on the sides of the excavation and in the surface next to it. They can mean fissured material.
• Layers. Note layered systems and whether layers dip toward the excavation.
• Previously disturbed soil. Look for utility lines, old backfill and other underground structures.
• Water. Look for standing water, water seeping from the sides, and the level of the water table.
• Vibration. Identify sources of vibration that may affect the stability of the face, such as traffic, compactors and pile driving.

Manual tests

Manual tests are done on a sample taken from the excavation. Appendix A requires samples to be tested as soon as practical so they do not dry out and give a misleading result. Take the sample from the soil that matters, such as a large clump of spoil fresh from the wall, not a crust that has been sitting in the sun.

Plasticity (thread) test

Mold a moist or wet sample into a ball and try to roll it into threads as thin as ⅛ inch in diameter. Cohesive material can be rolled into threads without crumbling. Appendix A's benchmark: if at least a 2-inch length of ⅛-inch thread can be held on one end without tearing, the soil is cohesive.

Dry strength test

If the soil is dry:

• It crumbles on its own or with moderate pressure into individual grains or fine powder: granular (some combination of gravel, sand or silt).
• It falls into clumps that break into smaller clumps, and the smaller clumps can only be broken with difficulty: it may be clay in combination with gravel, sand or silt.
• It breaks into clumps that do not break into smaller clumps and can only be broken with difficulty, with no visual sign of fissures: it may be considered unfissured.

Thumb penetration test

This test estimates unconfined compressive strength. Press your thumb firmly into a fresh, undisturbed clump of soil:

Results in between suggest Type B. The test is quick but rough, so many competent persons back it up with a penetrometer.

Pocket penetrometer and shear vane

A pocket penetrometer is a spring-loaded plunger pushed into a soil sample to a marked line. The scale reads in tons per square foot of unconfined compressive strength, which maps directly to the Type A, B and C limits. A shear vane (torvane) measures shear strength, and the reading is doubled to estimate UCS. Both tools are only as good as the sample, so take several readings and use the lowest.

Drying test

The drying test separates fissured cohesive material, unfissured cohesive material and granular material. Dry a sample about 1 inch thick and 6 inches across until thoroughly dry:

1. If the sample develops cracks as it dries, significant fissures are indicated.
2. If it dries without cracking, break it by hand. If considerable force is needed, the soil has significant cohesive content and can be classified as unfissured cohesive material, and its UCS should be determined.
3. If it breaks easily by hand, it is either fissured cohesive material or granular material. Pulverize the dried clumps by hand or by stepping on them: if they do not pulverize easily, the material is cohesive with fissures; if they pulverize easily into very small fragments, it is granular.

Putting the tests together

Document what you tested, where, and the result. If the weather turns, the walls start to dry and crack, or water appears, test again and reclassify.

Key takeaways

• Use at least one visual and one manual test, every time.
• Visual: particle size, clumping, cracks, layers, water, disturbance, vibration.
• Manual: plasticity thread (2 inches of ⅛-inch thread), dry strength, thumb penetration, penetrometer or shear vane, and the drying test.
• Test fresh samples from the soil that matters, take the lowest reading, and reclassify when conditions change.

Last reviewed: October 25, 2026 · Free general education based on OSHA 29 CFR 1926 Subpart P. It does not replace the site-specific training and competent person your employer must provide, and it does not issue a certificate. Nothing you enter on this page is saved or sent.