The Liquid Limit of a soil is an index corresponding to the moisture content at which the soil passes from a plastic to a liquid state. This property is very useful to correlate mechanical properties of soil, such as compressibility and lower shear strength. Liquid limit is used in conjunction with the Plastic Limit to determine the Plasticity Index (PI) of a soil.

Liquid Limit Device and PI are used to determine clayeyness of a soil. Material with a high Liquid Limit and PI will be unsuitable for many construction applications. On the other hand, material with a relatively low Liquid Limit and PI is generally desirable in highway construction.

Specification of Liquid Limit Device

• The liquid limit device consists of a brass cup held on an adjustable bracket.
• The cup can be adjusted for a height of 1 cm and can be lifted and dropped on a rubber base of standard hardness by cam action.
• Complete device consists of one casagrande grooving tool, one ASTM grooving tool and a height gauge block.

Determination of Liquid Limit

For determination purpose, liquid limit is that moisture content at which a part of soil, cut by a groove of standard dimensions, will flow together for a distance of 1.25 cm under an impact of 25 blows in a standard liquid limit apparatus. The soil at the water content has some strength which is about 17 gms/sq cm. At this water content, soil just passes from liquid state to plastic state.

Application

Liquid limit devices are mainly used to determine plasticity index of a soil. Some of the areas where they are used are :

• Construction (Roadways, Buildings, etc.)
• Agriculture
• Fertilizers
• Mining
• Irrigation
• Geophysical/Seismology
• Soil Analysis
• Research & Development
• Railways