7Soil PlasticityPlasticity is a property that enables a soil to undergo deformation without breaking.Clays for instance are moulded into earthen pots when its plastic state.This property is characteristic on fined grained soils only, in the presence of water.When water is replaced by some other liquid , say kerosene, the clay will behave as a granular mass.
8Plasticity is due to clay minerals in the soils and is exhibited only over a specific range of moisture content.Excessive water turns the soil into a suspension (liquid state).With gradual decrease in the water content, the soil passes into a plastic state, then into a semi-solid (or semi-plastic) state and finally into a solid state.
9Plastic state Semi-solid state VOLUME MOISTURE CONTENT SOLID STATE WATERCONTENTDECREASINGLiquid limitPlastic limitShrinkage limitSolidSOLID STATEMOISTURE CONTENTSOLIDSTATESEMIPLASTICLIQUIDVOLUMEPlastic stateSemi-solid state
10The water content at which these changes of state occur called limits or indices. Albert Atterberg, Swedish Soil Scientist ( )…..series of tests for evaluating soil plasticity. He defined these limits as follows: the liquid limit (LL) is the water content at which a soil passes from liquid to plastic state; the plastic limit (PL) is the water content at which a soil passes from plastic to semi-solid state; and the shrinkage limit (SL) is the water content at which a soil passes from semi solid state.
11Further classification within fine-grained soils (i. e Further classification within fine-grained soils (i.e. soil that passes #200 sieve) is done based on soil plasticity.Arthur Casagrande adopted these tests for geotechnical engineering purposes
12Atterberg LimitsConsistency of fine-grained soil varies in proportion to the water contentShrinkage limitPlastic limitLiquid limitsolidsemi-solidplasticliquidPlasticityIndex(cheese)(pea soup)(pea nut butter)(hard candy)
13Liquid Limit (LL or wL) Empirical Definition The moisture content at which a 2 mm-wide groove in a soil pat will close for a distance of 0.5 in when dropped 25 times in a standard brass cup falling 1 cm each time at a rate of 2 drops/sec in a standard liquid limit device
14Engineering Characterization of Soils Soil Properties that Control its Engineering BehaviorParticle Sizecoarse-grainedfine-grainedParticle/Grain Size DistributionParticle ShapeSoil Plasticity
15Clay Morphology Scanning Electron Microscope (SEM) Shows that clay particles consist of stacks of plate-like layers
16Soil Consistency Limits Albert Atterberg ( ) Swedish Soil Scientist….. Developed series of tests for evaluating consistency limits of soil (1911)Arthur Casagrande ( )……Adopted these tests for geotechnical engineering purposes
17Arthur Casagrande ( )Joined Karl Terzaghi at MIT in 1926 as his graduate studentResearch project funded by Bureau of Public RoadsAfter completion of Ph.D at MIT Casagrande initiated Geotechnical Engineering Program at HarvardSoil Plasticity and Soil Classification (1932)