STUDY OF IMPROVEMENT OF SUBGRADES BY GEOSYNTHETICS AND SOIL STABILISERS

Abstract

An experimental investigation on the improvement of a subgrade soil by the use of soil stabilisers and geosynthetics is presented in this study. A weak subgrade soil was chosen for the investigation and it was treated with varying amounts (1% to 8%) of a soil stabiliser. The experimental investigation on treated soil samples included compaction test, tests for plasticity, CBR test, UCS test, triaxial test, permeability test, free swell index test and SEM analysis. The test results showed improvement in the CBR value, UCS value and shear strength characteristics of the soil by treatment with soil stabiliser. The plasticity characteristics of the soil were also modified by adding the stabiliser. In using geosynthetics for the study, soaked CBR tests were conducted on soil samples reinforced with biaxial geogrid and geotextile, for two different depths of placement. The test results did not show any favourable improvement in the strength of the soil thus restricting the function of the geosynthetics as a separator layer only. Hence conclusion was drawn like, for the soil of the given type, the soil stabilisation technique proved to be more efficient. As high strength improvement was obtained by the use of the soil stabiliser the possibility of using it in flexible pavement design was studied by proposing two flexible pavement designs using stabilised soil as subgrade and sub-base material respectively. A cost analysis of the proposed flexible pavement designs were also undertaken, which proved the soil stabilisation to be an economical solution in this case.