Cost Comparison Between Soil Replacement And Lime Stabilization To Improve Engineering Properties Of Expansive Subgrade Soils

Abstract

Expansive soils are characterized by volume change due to variation in moisture content. The cyclic wetting and drying process cause vertical movements in expansive soils and these movements lead to failure of pavements. These soils have very low load bearing capacity when wet. These problematic expansive soils, therefore, when encountered as sub-grade should be avoided or treated properly. The sub grade material for road construction in most part of Addis Ababa city is highly dominated with such type of expansive soils. Methods to be applied to improve the engineering property of such soil will be either to stabilize the existing soil or to replace the soil with non expansive soil to the depth affected by seasonal moisture changes. The main objective of this thesis work was an attempt to investigate the cost effectiveness of lime stabilization of the expansive sub grade soil predominantly available in the city of Addis Ababa where a massive construction work is undertaken. The cost of optimum amount of lime used in stabilizing the expansive soil to achieve the minimum sub grade requirement has been compared with the cost of improving the expansive sub grade soil with select material. To achieve the present research objective, expansive soil samples and replacing material were collected from the Road Project and hydrated lime was used as stabilizing agent. The laboratory tests conducted include grain size analysis, Atterberg limits, proctor test, specific gravity, CBR and CBR swell. The laboratory test result indicated that the existing expansive soil needs improvement to serve as subgrade soil for road construction. Following the test result, cost analysis was carried out to make comparison between these two options. Total cost of replacing the existing expansive soil with locally available suitable material was found to be 1,987,745.83 Birr/km and total cost of stabilizing the existing expansive soil with lime was found to be 1,643,251.09 Birr/km with a saving cost of 17.3%. From the study, the result of stabilizing the existing expansive soil as compared to replacing with non-expansive soil has become economical.