Cohesion Intercept of Soils + Typical Values
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Introduction
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
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
- Swiss Standard SN 670 010b, Characteristic Coefficients of soils, Association of Swiss Road and Traffic Engineers
- Minnesota Department of Transportation, Pavement Design, 2007
- NAVFAC Design Manual 7.2 - Foundations and Earth Structures, SN 0525-LP-300-7071, REVALIDATED BY CHANGE 1 SEPTEMBER 1986
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