Silt is a granular sediment having a particle size between 0.002 to 0.05mm. The size of silt particles is between that of sand and clay. Water, ice, and wind are all capable of carrying and depositing it. Silt can be discovered in soil, just like clay, sand, and gravel. Silt can also be sediment that has been suspended in water. The spherical shape of silt allows it to hold a lot of water. It is well known that silty soil is more fertile than other soils and that a wide variety of creatures thrive there.
The following particle size distribution indicates the position of the silt in the soil.
| Particle size class | Size/(mm) |
| Boulders | >200 |
| Vary coarse gravel | 200-60 |
| Coarse gravel | 60-20 |
| Medium gravel | 20-6 |
| Fine gravel | 6-2 |
| Coarse sand | 2.0-0.6 |
| Medium sand | 0.6-0.2 |
| Fine sand | 0.2-0.06 |
| Silt | 0.06-0.002 |
| Clay | <0.002 |
Silt is produced when water and ice erode, or wear away, rock. Small rock fragments are carried by moving water and scrape against the sides and bottoms of stream banks, chipping away additional rock. As they collide and grind, the particles get smaller and smaller until they are silt-sized. Silt can be produced by glaciers eroding rock fragments as well. Finally, wind can carry rock fragments across a canyon or over a landscape, causing the fragments to clash with one another or the canyon wall. Silt is produced by all three processes.
Silt Soil Characteristics
Some of the important characteristics are as follows.
- Rock and mineral particles larger than clay but smaller than sand make silt. Various sand grains
- Along with other types of sediment including clay, sand, and gravel, silt is a type of sediment that is present in the soil.
- Silty soil, not rocky or gritty, is slippery when wet.
- If the soil contains more than 80% silt, it can be called silt.
- The three main modes of transportation are glacial grinding, aeolian attrition, and river comminution.
- Clay and silt both cause turbidity in water. Since it is so tiny, silt may be easily transported in both water and air and can travel great distances in the form of dust.
- Loess is a term used to describe thick deposits of silty material that are the product of aeolian processes.
- Clay and silt are chemically different, and unlike clay, silt grains are roughly the same size in all dimensions.
- Silt can appear as deposits at the bottom, silt suspended in water in rivers and streams, or as soil, frequently mixed with sand and clay.
Test to Identify the Silt
The following test can be used for silt testing.
- Dry Strength Test
- Dilatancy or Shaking Test
- Roughness / Plasticity Test
- Dispersion Test
Engineering Properties of Silt Soil
It is very important to be aware of the engineering properties of soil geotechnical engineers. Some of the important properties of these soils are as follows.
- Permeability
- Compressibility
- Elasticity
- Cohesion
- Angle of Internal Friction
