Plastic limit (PL)Plasticlimitis moisture contentat which threads of 3 mm dia-metercanjustberolled.3mm16August31,2025TUDelft
August 31, 2025 16 Plastic limit (PL) Plastic limit is moisture content at which threads of 3 mm diameter can just be rolled. 3 mm
Plasticity index PIPI = LL-PL17TUDelftDelft University of Technology
Vermelding onderdeel organisatie August 31, 2025 17 Plasticity index PI PI = LL - PL
Meaning of Atterberg's limitsSoilswithahighLL and highPI can take up andlooselarge quantities of moisture.· Losing moisture meansincreasein strength butalso loss in volume (shrinkage),SoilswithhighPIexhibitlargeamountofshrinkage and swell and cantherefore causelarge damage to structures,buildings androadsHighLLandhighPIareindicatorsofaproblemsoil.18August31,2025TUDelft
August 31, 2025 18 Meaning of Atterberg’s limits • Soils with a high LL and high PI can take up and loose large quantities of moisture. • Losing moisture means increase in strength but also loss in volume (shrinkage). • Soils with high PI exhibit large amount of shrinkage and swell and can therefore cause large damage to structures, buildings and roads. • High LL and high PI are indicators of a problem soil
Soil classification systemsBy now we have seen that the gradation,amount of fines and characteristics of the finesdetermine how suitable a soilis for roadconstruction.Systemshavebeendevelopedtoclassifythissuitability.Oneof these systems is theAASHTOclassification system.A-1verysuitable,A-7notsuitable.19August31,2025ATUDelft
August 31, 2025 19 Soil classification systems • By now we have seen that the gradation, amount of fines and characteristics of the fines determine how suitable a soil is for road construction. • Systems have been developed to classify this suitability. • One of these systems is the AASHTO classification system. • A-1 very suitable, A-7 not suitable
AASHTOsoilclassificationsystempx=percentagepasingsievenumberxIf p200 < 35% then soil is coarse grained (A-1,A-2or A-3): If p200 < 15%ANDp40 < 30%ANDp10 < 50%AND PI < 6 then soil is A-1-aIf p200<20%ANDp40<50%ANDPI<6thensoil is A-1-bIfp200<10%ANDp40≥50%ANDsoilisnotplasticthensoilisA-3If soil is coarse grained but not an A-1 or A-3, thenit is an A-2 soil20August31,2025TTUDelft
August 31, 2025 20 AASHTO soil classification system px = percentage pasing sieve number x • If p200 < 35% then soil is coarse grained (A-1, A-2 or A-3) • If p200 < 15% AND p40 < 30% AND p10 < 50% AND PI < 6 then soil is A-1-a • If p200 < 20% AND p40 < 50% AND PI < 6 then soil is A-1-b • If p200 < 10% AND p40 50% AND soil is not plastic then soil is A-3 • If soil is coarse grained but not an A-1 or A-3, then it is an A-2 soil