CE 210Dr SaMeH1 Soil Mechanics & Foundation 1 (CE 210) [9] Associate Professor of Environmental Eng. Civil Engineering Department Engineering College Majma’ah University faculty.mu.edu.sa/smohamed/SaMeH Feb Dr. Sameh S. Ahmed

Soil gradation is a classification of a coarse- grained soil that ranks the soil based on the different particle sizes contained in the soil. Soil gradation is an important aspect of soil mechanics (why?) because it is an indicator of other engineering properties such as compressibility, shear strength, and hydraulic conductivity. CE 210Dr SaMeH2 Soil Gradation

CE 210Dr SaMeH3

CE 210Dr SaMeH4 Soil Coarse grained Well graded Gravel WSand W Poorly graded Uniformly Gap- graded Fine- grained AtterbergLL, PL, SL

A well graded soil is a soil that contains particles of a wide range of sizes and has a good representation of all sizes from the No. 4 to No. 200 sieves. A well graded gravel is classified as GW while a well graded sand is classified as SW CE 210Dr SaMeH5 Well Graded Soil

A poorly graded soil is a soil that does not have a good representation of all sizes of particles from the No. 4 to No. 200 sieve. Poorly graded soils are either uniformly graded or gap-graded A poorly graded gravel is classified as GP A poorly graded sand is classified as SP CE 210Dr SaMeH6 Poorly Graded Soil

A uniformly graded soil is a soil that has most of its particles at about the same size. An example of a uniformly graded soil is one in which only sand of the No. 20 size is present CE 210Dr SaMeH7 Uniformly Graded Soil

A gap-graded soil is a soil that has an excess or deficiency of certain particle sizes or a soil that has at least one particle size missing. An example of a gap-graded soil is one in which sand of the No. 10 and No. 40 sizes are missing, and all the other sizes are present. CE 210Dr SaMeH8 Gap-graded Soil

The coefficient of uniformity, C u is a crude shape parameter and is calculated using the following equation: where D 60 is the grain diameter at 60% passing, and D 10 is the grain diameter at 10% passing. CE 210Dr SaMeH9 Coefficient of Uniformity C u

The coefficient of curvature, C c is a shape parameter and is calculated using the following equation: where D 60 is the grain diameter at 60% passing, D 30 is the grain diameter at 30% passing, and D 10 is the grain diameter at 10% passing. CE 210Dr SaMeH10 Coefficient of Curvature C c

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: C u > 4 & 1 < C c < 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. CE 210Dr SaMeH11 Criteria for Grading

For a sand to be classified as well graded, the following criteria must be met: C u ≥ 6 & 1 < C c < 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 CE 210Dr SaMeH12 Criteria for Grading..cont.

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. CE 210Dr SaMeH13 Conclusion

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. CE 210Dr SaMeH14 Conclusion