Silt In the Unified Soil Classification System (USCS) and the AASHTO Soil Classification system, the sand–silt distinction is made at the 0.075 mm particle size (i.e., material passing the #200 sieve). Silts and clays are distinguished mechanically by their plasticity. Silt is easily transported in water or other liquid and is fine enough to be carried long distances by air in the form of dust. Thick deposits of silty material resulting from deposition by aeolian processes are often called loess. Silt and clay contribute to turbidity in water. Silt is transported by streams or by water currents in the ocean. When
Internal erosion a larger cavity. The process continues until the formation of a sinkhole. It is possible for a cavity to not collapse; this will lead to backward erosion occurring. Soil contact erosion can occur between any granular layer and a finer soil such as in silt-gravel, and often results in a loss of stability, increases in pore pressure and clogging of the permeable layer. Experimental results show that close to the geometrical limit, the point at which the fine particles can "just pass" between the coarse particles(the filter criterion), erosion initiation and failure are much more likely. It is possible to