Final answer:
The moisture content at which soil begins to flow is called the Liquid Limit. It marks the transition between the plastic and liquid states of soil and is determined through standard laboratory tests. The Liquid Limit is a key parameter in soil classification and geotechnical engineering.
Step-by-step explanation:
The moisture content at which soil begins to flow is called the Liquid Limit. This is one of the Atterberg limits used in soil classification and geotechnical engineering to describe the water content of a soil at the boundary between the liquid and plastic states. Below the liquid limit, soil behaves in a plastic manner, and above this limit, the soil starts to behave as a liquid. This limit can be determined from laboratory tests where the soil slurry is manipulated in a standard manner, and the water content is measured when the soil begins to flow.
The other limits, such as the Plastic Limit and the Shrinkage Limit, define different states of soil consistency. The Plastic Limit is the moisture content at which soil starts to exhibit plastic properties and can be rolled into threads without crumbling. The Shrinkage Limit represents the moisture content at which further loss of moisture does not result in a volume decrease of the soil. The Plasticity Index is a calculated value representing the range of water content over which soil remains plastic; it is the numerical difference between the Liquid Limit and the Plastic Limit.