Visual examination should establish the color, grain size, grain shapes (of the coarse-grained portion), some idea of the gradation, and some properties of the undisturbed soil.

Color is often helpful in distinguishing between soil types, and with experience, one may find it useful in identifying the particular soil type. Color may also indicate the presence of certain chemicals. Color often varies with moisture content of a soil. For this reason, the moisture content at the time of color identification should be included. Some of the more familiar color properties are listed below.

. Generally, colors become darker as the moisture content increases and lighter as the soil dries.

. Some fine-grained soils (OL, OH) with dark drab shades of brown or gray, including almost black, contain organic colloidal matter.

. In contrast, clean, bright looking shades of gray, olive green, brown, red, yellow, and white are associated with inorganic soils.

. Gray-blue or gray- and yellow-mottled colors frequently result from poor drainage.

. Red, yellow, and yellowish brown result from the presence of iron oxides.

. White to pink may indicate considerable silica, calcium carbonate, or aluminum compounds.

The maximum particle size of each sample considered should always be estimated if not measured.

This establishes the upper limit of the gradation curve. Gravels range down to the size of peas. Sands start just below this size and decrease until the individual grains can barely be seen by the naked eye. The eye can normally see individual grains about 0.05mm in size or about the size of the No. 200 screen. Thus silt and clay particles (which are smaller than this dimension) are not detected as individual grains.

While the sample for grain sizes is being examined, the shapes of the visible particles can be determined. Sharp edges and flat surfaces indicate an angular shape; smooth, curved surfaces are associated with a rounded shape. Particles may not be completely angular or completely rounded. These particles are called subangular or subaounded, depending on which shape predominates.

Laboratory analysis must be performed when accurate grain size distribution is to be determined. However, you can approximate the distribution by visual examination using the following steps:

1. Separate the larger grain particles from the rest of the soil sample by picking them out one at a time.

2. Examine the remainder of the soil and estimate the proportion of visible individual particles (larger than the No. 200 sieve) and the fines.

4. Examine the coarse-grained soil for gradation of particle sizes from the largest to the smallest. A good distribution of all sizes without too much or too little of any one size means the soil is well-graded (W). Overabundance or lack of any size means the material is poorly graded (P).

6. If the fine-grained portion (Step 5 above) exceeds 12 percent, the soil is either silty (M) or clayey (C) and requires further testing to identify.

8. Fine-grained soils (M, C, or O) from Step 3 above require other tests to distinguish them further. Grain size distribution of fine portions is normally not performed in field identification. However, should it become necessary, you can approximate the grain size of the fines by shaking them in a jar of water and allowing the material to settle. The materials settle in layers of different sizes from which the proportion can be estimated. It should be kept in mind that gravel and sand settle into a much denser mass than either clay or silt.

 If you use the characteristics determined up to this point, it is possible to evaluate the soil as it appeared in place (undisturbed). Gravels or sands can be described qualitatively as loose, medium, or dense. Clays maybe hard, stiff, or soft. The ease or difficulty with which the sample was removed from the ground is a good indicator. Soils that have been cultivated or farmed can be further evaluated as loose and compressible. Highly organic soils can be spongy and elastic. In addition, moisture content of the soil influences the in-place characteristics. This condition should be recognized and reported with the undisturbed soil properties.