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

Abstract

Soft subgrade soil poses challenge for construction of pavements. These soft subgrade soils have a ten dency to absorb high moisture content and exhibit high compressibility. Under loa ds. Because of which the life of pavement construct ed over these is highly suffered. Among notable properties plasticity index is a reli able 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 dee p deposits of soft soil and time consuming. . Provi ding stiff layer with gravelly soil can solve the problem to majority extent. These gra velly layer of soils bear the load and distribute tarch 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 val ues of soft subgrade in the presence of separator geotextile. The thickness of aggregate is varied and expressed by H r (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 H r varied from 0, to 0.5 in increments of 0.1.It is observed that PI, H r and fines content effect CBR. The influence is more pronounced with Plasticity and percent fines. Also the increase (%) is marginal for samples with high H r. The problem of mixing of aggregate with soft soil tested without separato r is more with H r.