Friction Angle of Soft Clay: Unit Weight, Cohesion, Permeability
The friction angle of soft clay typically runs from 18 to 25 degrees, with a bulk unit weight of 15 to 18 kN/m3 and effective cohesion of 5 to 20 kPa. Permeability is on the order of 1e-9 to 1e-11 m/s. The table collects the screening values and the note explains what moves them.
| Property | Typical range |
|---|---|
| Friction angle | 18 to 25 degrees |
| Bulk unit weight | 15 to 18 kN/m3 |
| Effective cohesion | 5 to 20 kPa |
| Permeability | 1e-9 to 1e-11 m/s |
What moves the numbers
The settlement machine: low strength now, less later under load, and consolidation measured in years. Effective cohesion is modest; undrained strength governs short term. These are screening ranges for preliminary work and study: design values come from site specific testing, and the tools below show how each property is used once you have it.
Use these values
- Free Online Slope Stability Risk Calculator to turn these ranges into a probability of failure.
- Lateral Earth Pressure Calculator for the pressures this friction angle implies.
- Hazen Permeability Calculator for estimating permeability from grain size.
- The Property Library for every soil, rock, and mineral on this site.
Related Calculators and Reference
- Terzaghi Bearing Capacity Calculator for Shallow Foundations, to turn this friction angle into an allowable bearing pressure.
- Retaining Wall Pressure Calculator (Rankine and Coulomb), because the same friction angle sets both the active and the passive side.
- Void Ratio, Porosity and Unit Weight Converter, to move between the density terms this table quotes.
- Slope Stability Factor of Safety Calculator, for when this material forms a slope rather than a foundation.
- Friction Angle of Silt, for the neighbouring soil type when a borehole log is ambiguous.
- ASTM D2487, the standard practice behind the classification these values are grouped by.