Soil unit weight, as referred to as Specific weight, is the weight per unit volume of soil. It may refer to
- Wet unit weight: Unit weight of the soil when the pore are fully or partially filled with water.
- Dry unit weight: Unit weight of the soil the pores are filled only with air without any water.
Gamma_d = Gamma / (1 + w)
where
Gamma_d : dry unit weight
Gamma : unit weight
w: soil water content
Typical values of soil porosity for different soils
The soil unit weight, of course, depends on the packing, compaction, and humidity condition of the soil. Some typical values of dry unit weight are given below for different soils. The values correspond to normally consolidated condition unless otherwise stated. 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.
| USCS | Description | Average value (kN/m3) | References |
| GW | Well graded gravel, sandy gravel, with little or no fines | 21 ± 1 | [1]; |
| GP | Poorly graded gravel, sandy gravel, with little or no fines | 20.5 ± 1 | [1]; |
| GM | Silty gravels, silty sandy gravels | 21.5 ± 1 | [1]; |
| GC | Clayey gravels, clayey sandy gravels | 19.5 ± 1.5 | [1]; |
| SW | Well graded sands, gravelly sands, with little or no fines | 20.5 ± 2 | [1]; |
| SP | Poorly graded sands, gravelly sands, with little or no fines | 19.5 ± 2 | [1]; |
| SM | Silty sands | 20.5 ± 2.5 | [1]; |
| SC | Clayey sands | 18.5 ± 1.5 | [1]; |
| ML | Inorganic silts, silty or clayey fine sands, with slight plasticity | [1]; | |
| CL | Inorganic clays, silty clays, sandy clays of low plasticity | [1]; | |
| OL | Organic silts and organic silty clays of low plasticity | [1]; | |
| MH | Inorganic silts of high plasticity | [1]; | |
| CH | Inorganic clays of high plasticity | [1]; | |
| OH | Organic clays of high plasticity | [1]; | |
| Pt | Peat and other highly organic soils | [1]; |
REFERENCES
- Swiss Standard SN 670 010b, Characteristic Coefficients of soils, Association of Swiss Road and Traffic Engineers
Citation :
Geotechdata.info, Dry unit weight, http://geotechdata.info/parameter/soil-dry-unit-weight.html (as of August 29, 2013).