Friction Angle of Silty Sand: Unit Weight, Cohesion, Permeability
The friction angle of silty sand typically runs from 27 to 35 degrees, with a bulk unit weight of 17 to 20 kN/m3 and effective cohesion of 0 to 5 kPa. Permeability is on the order of 1e-5 to 1e-7 m/s. The table collects the screening values and the note explains what moves them.
| Property | Typical range |
|---|---|
| Friction angle | 27 to 35 degrees |
| Bulk unit weight | 17 to 20 kN/m3 |
| Effective cohesion | 0 to 5 kPa |
| Permeability | 1e-5 to 1e-7 m/s |
What moves the numbers
A few percent of silt quietly kills drainage and complicates compaction; the friction stays decent, the permeability does not. 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, when the next question is what the ground will carry.
- Retaining Wall Pressure Calculator (Rankine and Coulomb), for the earth pressures this angle produces behind a wall.
- Void Ratio, Porosity and Unit Weight Converter, when your source quotes one density term and you need another.
- Slope Stability Factor of Safety Calculator, if the same soil is holding up a cut or an embankment.
- Friction Angle of Loose Sand, for the next entry along when you are bracketing a description.
- ASTM D2487, the standard practice behind the classification these values are grouped by.