Silt and Clay Properties
This is about Silt and Clay Properties. Silt and Clay are two smallest parts of soil group in size. Although they are small in size, they have great effect in constructions or road works. Let us say that we have 10 percent of the particles in sand and gravel that are smaller than No 200 sieve size, the soil will be quite impervious. This is especially if the coarse grains (Gravel and Sand) are well graded.
Silt and Clay Properties are unique. They are, actually dangerous for constructions. Soils which contains large quantities of silt and clay are considered as the most troublesome by most engineers. Those type of soils have conditions which are really unstable. The soils can become really hard, just like rock. At the other times, it can be really soft, just like a kind of jelly. Those conditions are led by the change in water content of the soils.
The unstable of Silt and Clay Properties make the age of a construction or road work shortened. If we do not design the structure in stiff design, the structure will easily broken. If you put or build a foundation on a hard and dry clay, it may be suitable even though the load is heavy. But this only happens when the soil is dry. When the clay is wet, the foundation will suffer from deformation. This will affect the above structure, which is dangerous.
We have to understand that when silt and clay are in deposit by natural conditions, Silt and Clay Properties are unique. When they are disturbed by some activities (excavations, pile driving etc), the condition or properties will change greatly.
Silt and Clay Properties are actually different. Some people may make some mistake to determine whether the soil is silt or clay. In dry condition, silt and clay are indistiquishable. They are really almost same. But we can distinguish them very easily by pouring some water on them.
Silts are not stable, just like clay. We can tell that they have character of fluid which can flow. Actually Silts are impervious. It difficult to compact. The volume of silt can change during the change of its shape. This is affected by water. When it is dry, we can feel the grittiness of fine sand by touching it. Clays are not stable too. Different from silts, clays volume do not change upon the shape change.
Going to the field, we can do some Field Tests to determine the Silt and Clay Properties. We posted the Field Tests before. Practically, we can do these tests to see the difference between silt and clay properties.