The soil permeability is a measure indicating the capacity of the soil or rock to allow fluids to pass through it. It is often represented by the permeability coefficient (k) through the Darcy’s equation:
V=ki
Where v is the apparent fluid velocity through the medium i is the hydraulic gradient , and K is the coefficient of permeability (hydraulic conductivity) often expressed in m/s
K depends on the relative permeability of the medium for fluid constituent (often water) and the dynamic viscosity of the fluid as follows.
K= (Gamma_w)*K/ (eta)
where Where Gamma_w is the unit weight of water Eta is the dynamic viscosity of water K is an absolute coefficient depending on the characteristics of the medium (m2)
The permeability coefficient can be determined in the laboratory using falling head permeability test, and constant head permeability test. On the field, the permeability can be estimated using Lugeon test.
Typical values of soil permeability
Some typical values of permeability coefficient are given below for different soil types. It refers to normally consolidated condition unless otherwise mentioned. These values should be used only as guidline for geotechnical problems; however, specific conition of each engineering problem often needs to be considered for an appropriate choice of geotechnical parameters.
| Description | USCS | min (m/s) | max (m/s) | Specific value (m/s) | Reference |
| Well graded gravel, sandy gravel, with little or no fines | GW | 5.00E-04 | 5.00E-02 | [1], | |
| Poorly graded gravel, sandy gravel, with little or no fines | GP | 5.00E-04 | 5.00E-02 | [1], | |
| Silty gravels, silty sandy gravels | GM | 5.00E-08 | 5.00E-06 | [1], | |
| Alluvial sand and gravel | (GM) | 4.00E-04 | 4.00E-03 | [2&3 in 4] | |
| Clayey gravels, clayey sandy gravels | GC | 5.00E-09 | 5.00E-06 | [1], | |
| Well graded sands, gravelly sands, with little or no fines | SW | 1.00E-08 | 1.00E-06 | [1], | |
| Very fine sand, very well sorted | (SW) | 8.40E-05 | [5] , | ||
| Medium sand, very well sorted | (SW) | 2.23E-03 | [5] , | ||
| Coarse sand, very well sorted | (SW) | 3.69E-01 | [5] , | ||
| Poorly graded sands, gravelly sands, with little or no fines | SP | 2.55E-05 | 5.35E-04 | [1], [2&3 in 4] | |
| Clean sands (good aquifers) | (SP-SW) | 1.00E-05 | 1.00E-02 | [5], | |
| Uniform sand and gravel | (SP-GP) | 4.00E-03 | 4.00E-01 | [2&3 in 4] | |
| Well graded sand and gravel without fines | (GW-SW) | 4.00E-05 | 4.00E-03 | [2&3 in 4] | |
| Silty sands | SM | 1.00E-08 | 5.00E-06 | [1], | |
| Clayey sands | SC | 5.50E-09 | 5.50E-06 | [1], [5] | |
| Inorganic silts, silty or clayey fine sands, with slight plasticity | ML | 5.00E-09 | 1.00E-06 | [1], | |
| Inorganic clays, silty clays, sandy clays of low plasticity | CL | 5.00E-10 | 5.00E-08 | [1], | |
| Organic silts and organic silty clays of low plasticity | OL | 5.00E-09 | 1.00E-07 | [1], | |
| Inorganic silts of high plasticity | MH | 1.00E-10 | 5.00E-08 | [1], | |
| Inorganic clays of high plasticity | CH | 1.00E-10 | 1.00E-07 | [1], | |
| Compacted silt | (ML-MH) | 7.00E-10 | 7.00E-08 | [2&3 in 4] | |
| Compacted clay | (CL-CH) | - | 1.00E-09 | [2&3 in 4] | |
| Organic clays of high plasticity | OH | 5.00E-10 | 1.00E-07 | [1], | |
| Peat and other highly organic soils | Pt | - | - |
Empirical relations for dtermine the soil permeability coefficient
For Sands, the coefficient of permeability can be estimated from the Hazen's equation:
is the effevtive size in mm.
REFERENCES
- Swiss Standard SN 670 010b, Characteristic Coefficients of soils, Association of Swiss Road and Traffic Engineers
- Carter, M. and Bentley, S. (1991). Correlations of soil properties. Penetech Press Publishers, London.
- Leonards G. A. Ed. 1962, Foundation ENgineering. McGraw Hill Book Company
- Dysli M. and Steiner W., 2011, Correlations in soil mechanics, PPUR
- West, T.R., 1995. Geology applied to engineering. Prentice Hall, 560 pp.
Citation :
Geotechdata.info, Soil void ratio, http://geotechdata.info/parameter/permeability.html (as of October 7, 2013).