How does cohesive soil respond to manual strength tests?

Cohesive soil is characterized by its ability to stick together due to the closely-packed nature of its particles and the presence of clay minerals. When conducting manual strength tests, one of the key indicators of cohesive soil is its plasticity, which allows it to be molded and shaped. A defining trait of cohesive soil is its capacity to be rolled into threads without disintegrating, indicating good plasticity and cohesion. This property is crucial for determining its usability in various construction applications, as cohesive soil is often used for making earth structures due to its strength and ability to retain shape under pressure.

In contrast, other options do not accurately describe the behavior of cohesive soil under strength tests. For example, while cohesive soil can become soggy when saturated, this trait is not a measure of its strength, nor does it apply specifically during manual testing. The notion that cohesive soil crumbles easily does not hold true; instead, it tends to hold together unless significantly disturbed or compromised by excess water. Lastly, while cohesive soil can be hard when dry, it is not characterized as always hard because its consistency can vary widely based on moisture content. The correct response highlights a fundamental understanding of the properties of cohesive soil in the context of manual strength assessments in construction.