Atterberg Limits of Soil Prepared by: Marcia C. Belcher Construction Engineering Technology University of Akron

Atterberg Albert Atterberg was a Swedish chemist and agricultural scientist. Conducted studies to identify the specific minerals that give a clayey soil its plastic nature Stated that depending on the water content, soil may appear in four states: Solid (no water) semi-solid (brittle, some water) plastic (moldable) liquid (fluid) In each state the consistency and behavior of a soil is different and thus so are its engineering properties. The boundary between each state can be defined based on a change in the soil's behavior. The

Atterberg Limits wll Solid Brittle Plastic Liquid Wpl (Non-Plastic ) Plasticity Index Solid Brittle Plastic Liquid Water Content w%=0 Wpl wll Plastic Limit Liquid Limit

Plastic limit The plastic limit (PL) is the water content (w%) where soil starts to exhibit plastic behavior.

Liquid limit The liquid limit (LL) is the water content where a soil changes from liquid to plastic behavior Determined using a Casagrande cup (lab) or cone penetrometer (field) Casagrande subsequently standardized the apparatus and the procedures to make the measurement more repeatable. Soil is placed into the metal cup portion of the device and a groove is made down its center with a standardized tool. The cup is repeatedly dropped 10mm onto a hard rubber base until the groove is closed for 13 mm (½ inch). The moisture content at which it takes 25 drops of the cup to cause the groove to close is defined as the liquid limit. Another method for measuring the liquid limit is the Cone Penetrometer test. It is based on the measurement of penetration into the soil of a standardized cone of specific mass

Shrinkage limit The shrinkage limit (SL) is the water content where further loss of moisture will not result in any more volume reduction The shrinkage limit is much less commonly used than the liquid limit and the plastic limit.

Use of Plasticity Index The PI is the difference between the liquid limit and the plastic limit (PI = LL-PL). The plasticity index is the size of the range of water contents where the soil exhibits plastic properties. Meaning: High PI tend to be clay Low PI tend to be silt PI of 0 tend to have little or no silt or clay.

Use of Liquid & Plastic Limits Used internationally for soil identification and soil classification (AASHTO)