Particle Characterization
Soil & Sediment Applications
Soil and sediments scientists have long understood the importance of particle size distribution to their field. Various approaches have been developed to classify samples into formats useful for categorizing samples and predicting behavior. Some soil scientists classify soil particles into sand, silt and clay, and the relative quantities are used to define the texture of a sample. Sizes of soil separates according to the U.S. Department of Agriculture classification system are as follows:
| Very coarse sand | 2.0-1.0 mm |
| Coarse sand | 1.0-0.5 mm |
| Medium sand | 0.5-0.25 mm |
| Fine sand | 0.25-0.10 mm |
| Very fine sand | 0.10-0.05 mm |
| Silt | 0.05-0.002 mm |
| Clay | <0.002 mm |
Analysis and classification of the sample can be used to create a texture triangle as shown below:
Soil fractions give specific characteristics to the soil. Clay improves the nutrient holding capacity, increases water retention, soil stability, but is sometimes difficult to till. Soils high in sand characteristically have good drainage, aeration, and are relatively easy to till. Soils high in silt will be intermediate.
Another approach to classifying soil and sediment samples uses the Phi scale – see below:
Particle size information of sediments can also be used in conjunction with current velocity data to predict whether the sample is more likely to deposit in the river bed or be transported downstream. The Hjulstrom diagram shown below is used for this kind of prediction.
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