The consistency and behavior of soils vary throughout. Therefore, qualities such as moisture content, hardness and reliability are important to test within specimens in order to assure stability in the structures they support. To assess these characteristics, Atterberg limit tests are done often to measure water content within on-site soil.One way to measure the critical water content of fine-grained soil is through its liquid limit. Liquid limit is defined as the water content at which the behavior of clayey soil changes from plastic to liquid. Using ASTM Standard D4318, the liquid limit test of soil determines this transition over a range of water contents. More specifically, it gives valuable information regarding the state of consistency of soil on-site.

A liquid limit test of soil can be determined using two methods:

The Casagrande cup method, which is widely used in the United States, defines liquid limit as the moisture content required to close a metal cup filled with soil paste a distance of 0.5 inches using a liquid limit machine. This method is normally run at several moisture contents to determine which requires 25 blows to close the groove.
The cone penetration test for liquid limit is more prevalent in Europe and measures the moisture content at which a cone will penetrate a soil sample a distance of 20 mm in approximately 5 seconds. This less is less dependent on the operator when determining a soil’s liquid limit.
In each testing type, many data points are collected and used to plot a flow curve which ultimately establishes a liquid limit. To ensure an accurate curve, high-quality equipment must be used in these tests. These liquid limit machines and accessories should follow ASTM standards and produce error-free results time and time again.