Effect of nonplastic-silt and sand content on plasticity and CBR of clay soil

Abstract

Recently it has been observed that many national highways and other important roads are seriously damaged after one/two years of construction. Therefore it is necessary to investigate the causes of damage of roads. In most places soils are silty clay or clayey silt. During rainy season and flooding, these soils become saturated and soft. Suitability of subgrade material should be investigated using Liquid limit, Plastic Limit and soaked CBR values. The study aims to investigate the suitability of sandclay and silt-clay mixtures as subgrade material for highways and roadways construction. From the study it was found that with the increase of sand content in sand-clay mixture and silt content in silt-clay mixture, maximum dry density increased but optimum moisture content decreased. Soaked CBR values increased with the increase of the percentage of sand while they reduced gradually with the reduction of sand in the Clay-Sand mixture. When a comparison is drawn between Soaked CBR of Clay- Sand mixture and that of Clay-Silt mixture, it has been found that soaked CBR values in the Clay-Sand mixture are much higher. It can thus be concluded that Clay-Sand mixture is a good subgrade material while Clay-Silt mixture is a poor subgrade material for the purpose of road construction.