Abstract:
Major parts of the Eastern and Northern Provinces of Sri Lanka are covered wi
cohesionless soil. These locally available cohesionless soils have been utilized for construction of su
base in road constructions. Recently cracks, settlement and outward movement have been observed' -
the certain pavements constructed in the north and east. It is suspected that the poor plastic properti
of locally available soil would have caused this failure. Objective of this paper is to identify tne
influence of Plasticity Index on sub-base material properties and review the applicability of th
current specifications for selection of low plasticity soil as Sub-base materiaL Based on the collecte
information, a comprehensive laboratory tests program was formulated to investigate tinterrelationships
between the soil properties such as grading, maximum dry density, CBR valu
Plasticity Index, and Liquid Limit by mixing different type of clays with pure coarse sand (Ri
Sand). Relationships between CBR Vs Plasticity Index and MDD Vs Plasticity Index have b
established for a fine grade sub-base materiaL It was found that CBR is low at both low and hi
plasticity soil. ICTAD specification specified upper limit for Plasticity Index has been verified in}
experimental study. Experimental results emphasised the need of establishing a lower limit fort'
Plasticity Index in selection of sub-base materiaL
