# Cohesion Intercept of Soils + Typical Values

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## Introduction on Cohesion Intercept of Soils + Typical Values :

The cohesion intercept is a term used in describing the shear strength soils. Its definition is mainly derived from the Mohr-Coulomb failure criterion and it is used to describe the non-frictional part of the shear resistance which is independent of the normal stress. In the stress plane of Shear stress-effective normal stress, the soil cohesion is the intercept on the shear axis of the Mohr-Coulomb shear resistance line.

## Concepts and Formulas of Cohesion Intercept of Soils + Typical Values:

### Difference between Cohesive and Granular soil

"Granular soil" means gravel, sand, or silt (coarse-grained soil) with little or no clay content. Granular soil has no cohesive strength. Some moist granular soils exhibit apparent cohesion. Granular soil cannot be molded when moist and crumbles easily when dry.

"Cohesive soil" means clay (fine-grained soil), or soil with a high clay content, which has cohesive strength. Cohesive soil does not crumble, can be excavated with vertical sideslopes, and is plastic when moist. Cohesive soil is hard to break up when dry, and exhibits significant cohesion when submerged. Cohesive soils include clayey silt, sandy clay, silty clay, clay and organic clay.

### Typical values of soil cohesion "C" for different soils

Some typical values of soil cohesion are given below for different soil types. The soil cohesion depends strongly on the consistence, packing, and saturation condition. The values given below correspond to normally consolidated condition unless otherwise stated. These values should be used only as a guideline for geotechnical problems; however, specific condition of each engineering problem often needs to be considered for an appropriate choice of geotechnical parameters.

 Description USCS Cohesion [kPa] Reference min max Specific value Well graded gravel, sandy gravel, with little or no fines GW - - 0 [1],[2],[3], Poorly graded gravel, sandy gravel, with little or no fines GP - - 0 [1],[2], [3], Silty gravels, silty sandy gravels GM - - 0 [1], Clayey gravels, clayey sandy gravels GC - - 20 [1], Well graded sands, gravelly sands, with little or no fines SW - - 0 [1],[2], [3], Poorly graded sands, gravelly sands, with little or no fines SP - - 0 [1],[2], [3], Silty sands SM - - 22 [1], Silty sands - Saturated compacted SM - - 50 [3], Silty sands - Compacted SM - - 20 [3], Clayey sands SC - - 5 [1], Clayey sands - Compacted SC - - 74 [3], Clayey sands -Saturated compacted SC - - 11 [3], Loamy sand, sandy clay Loam - compacted SM, SC 50 75 [2], Loamy sand, sandy clay Loam - saturated SM, SC 10 20 [2], Sand silt clay with slightly plastic fines - compacted SM, SC - - 50 [3], Sand silt clay with slightly plastic fines - saturated compacted SM, SC - - 14 [3], Inorganic silts, silty or clayey fine sands, with slight plasticity ML - - 7 [1], Inorganic silts and clayey silts - compacted ML - - 67 [3], Inorganic silts and clayey silts - saturated compacted ML - - 9 [3], Inorganic clays, silty clays, sandy clays of low plasticity CL - - 4 [1], Inorganic clays, silty clays, sandy clays of low plasticity - compacted CL - - 86 [3], Inorganic clays, silty clays, sandy clays of low plasticity - saturated compacted CL - - 13 [3], Mixture if inorganic silt and clay - compacted ML-CL - - 65 [3], Mixture if inorganic silt and clay - saturated compacted ML-CL - - 22 [3], Organic silts and organic silty clays of low plasticity OL - - 5 [1], Inorganic silts of high plasticity  - compactd MH - - 10 [1], Inorganic silts of high plasticity - saturated compacted MH - - 72 [3], Inorganic silts of high plasticity MH - - 20 [3], Inorganic clays of high plasticity CH - - 25 [1], Inorganic clays of high plasticity - compacted CH - - 103 [3], Inorganic clays of high plasticity - satrated compacted CH - - 11 [3], Organic clays of high plasticity OH - - 10 [1], Loam - Compacted ML, OL, MH, OH 60 90 [2], Loam - Saturated ML, OL, MH, OH 10 20 [2], Silt Loam - Compacted ML, OL, MH, OH 60 90 [2], Silt Loam - Saturated ML, OL, MH, OH 10 20 [2], Clay Loam, Silty Clay Loam - Compaced ML, OL, CL, MH, OH, CH 60 105 [2], Clay Loam, Silty Clay Loam - Saturated ML, OL, CL, MH, OH, CH 10 20 [2], Silty clay, clay - compacted OL, CL, OH, CH 90 105 [2], Silty clay, clay - saturated OL, CL, OH, CH 10 20 [2], Peat and other highly organic soils Pt - -

REFERENCES

1. Swiss Standard SN 670 010b, Characteristic Coefficients of soils, Association of Swiss Road and Traffic Engineers
2. Minnesota Department of Transportation, Pavement Design, 2007
3. NAVFAC Design Manual 7.2 - Foundations and Earth Structures, SN 0525-LP-300-7071, REVALIDATED BY CHANGE 1 SEPTEMBER 1986

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