must be compared to published gradation criteria. Criteria for grading soils The following criteria are in accordance with the Unified Soil Classification System: For a gravel to be classified as well graded, the following criteria must be met: Cu > 4 & 1 < Cc < 3 If both of these criteria are not met, the gravel is classified as poorly graded or GP. If both of these criteria are met, the gravel is classified as well graded or GW. For a sand to be classified as well graded, the following criteria must be met: Cu ≥ 6 & 1 < Cc < 3 If both of these criteria are not met, the sand is classified as poorly graded or SP. If both of these criteria are met, the sand is classified as well graded or SW. Importance Soil gradation is very important to geotechnical engineering. It is an indicator of other engineering properties such as compressibility, shear strength, and hydraulic conductivity. In a design, the gradation of the in situ or on site soil often controls the design and ground water drainage of the site. A poorly graded soil will have better drainage than a well graded soil because there are more void spaces in a poorly graded soil. When a fill material is being selected for a project such as a highway embankment or earthen dam, the soil gradation is considered. A well graded soil is able to be compacted more than a poorly graded soil. These types of projects may also have gradation requirements that must be met before the soil to be used is accepted. When options for ground remediation techniques are being selected, the soil gradation is a controlling factor. References Sedimentology Granulometric analyses