Fine-grained soils are soils finer than a ___________.

Fine-grained soils are defined as those that pass through the No. 200 sieve. This means that any soil that has particle sizes smaller than the openings of a No. 200 sieve is classified as fine-grained. The No. 200 sieve has an opening size of 0.075 mm (or 75 microns), which allows for the categorization of particles that are cohesive, such as silts and clays.

In contrast, materials larger than this sieve would fall into the category of coarse-grained soils (such as sands and gravels). Understanding this classification is vital for engineers and constructors, as the behavior of fine-grained soils differs significantly from that of coarse-grained soils, particularly in terms of compaction, drainage, and load-bearing capabilities. Hence, identifying soils based on sieve size is a fundamental concept in geotechnical engineering and construction.