EFFICACY OF OVERLYING COARSE AGGREGATE AND GEOSYNTHETIC SEPARATOR ON CBR VALUE FOR SOFT SUBGRADE OF VARYING PLASTICITY- A LAB STUDY

Soft subgrade soil poses challenge for construction of pavements. These soft subgrade soils have a tendency to absorb high moisture content and exhibit high compressibility. Under loads. Because of which the life of pavement constructed over these is highly suffered. Among notable properties plasticity index is a reliable property as listed in literature for identifying these soft soil and nature of compressibility. Soil stabilization is one of the techniques listed in literature for improving these soft soils. Often the stabilization suffers due to high cost particularly improving deep deposits of soft soil and time consuming.. Providing stiff layer with gravelly soil can solve the problem to majority extent. These gravelly layer of soils bear the load and distribute through arch action, to, minimize the stresses to soft soil..However the efficiency of these gravely layer depends on their relative thickness and prevention from mixing with soft subsoil. This paper discusses the efficacy of overlying aggregate to improve CBR values of soft subgrade in the presence of separator geotextile. The thickness of aggregate is varied and expressed by Hr (a fraction to soil thickness given as Ha/Hs.). Laboratory CBR tests are conducted on four subgrade types with varying in plasticity & fines content overlying with gravelly aggregate with Hr varied from 0, to 0.5 in increments of 0.1.It is observed that PI, Hr and fines content effect CBR. The influence is more pronounced with Plasticity and percent fines. Also the increase (%) is marginal for samples with high Hr. The problem of mixin