The number of shocks needed to close the groove of each sample is used to determine what property of the soil?

The correct answer is liquid limit, as the number of shocks necessary to close the groove of a soil sample is directly related to its moisture content and indicates its transition from a plastic to a liquid state. This test is known as the “liquid limit test,” where the soil sample is placed in a device called a Casagrande cup. The shock or blows applied to the cup are counted until the soil flows together, closing the groove made in the sample. This flow point signifies the liquid limit, a critical property that describes the moisture content at which soil transitions from a plastic condition to a liquid one. Understanding the liquid limit is vital in classifying soils and determining their engineering behavior, which is essential for design and construction purposes.