Determining the Atterberg limits according to DIN EN ISO 17892-12
Status: 10.12.2024
The tests according to Atterberg yields the water contents of the soil at liqid limit wL, at plastic limit wP, and at shrinkage limit wS. From these values and the natural water content w, various index values are derived:
- Plasticity index IP = wL-wP. If the plasticity index is small, the soil is very sensitive to water, i.e. it quickly changes from a stiff to a soft or mushy consistency.
- Consistecy index IC = (wL-w)/(wL-wP). The consistency (deformability) of cohesive soils depends largely on the water content. As the water content decreases, the consistency of the soil becomes liquid, mushy, soft, stiff, semi-solid.
- Liquidity index IL = 1-IC
- Activity index according to Skempton IA is the ratio of the plasticity index to the mass fraction of particles < 0.002 mm at sieve passage < 0.4 mm.
The water contents at the transitions from liquid to plastic (yield limit), stiff to semi-solid (plasticity limit) and semi-solid to solid (shrinkage limit) were defined experimentally by Atterberg.
Figure: Casagrande cup
Determination of liquid limit
The yield point is determined using the Casagrande yield limit device. It can also be determined using the falling cone device, see Figure above.
Determination of plastic limit
The plastic limit is reached when the soil begins to crumble into rolls of 3 mm thickness when rolled out on filter paper.
Determination of shrinkage limit
A soil sample has the water content at the shrinkage limit if it no longer changes its volume when it dries out further.