Cost-Benefit Analysis of Replacing versus Stabilizing Expansive Soils in Road Construction (Case study for Gambella-Alwero-Rice-Project)

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Addis Ababauniversity


Expansive soils are soils that have a property of large volumetric changes, both shrinkage and swell, due to variations in their moisture content. Their bearing capacity is poor. For road to be constructed on such soils, the subgrade should be designed to minimize subsequent changes in moisture content and consequent volume changes thereby improving bearing capacity of the soil. The subgrade material for road construction within the project of Gambella-Alwero-Rice- Project, located in Gambella National Regional State - Abobo Wereda, is highly dominated with such type of expansive soils. Methods applied to improve the engineering property of such soil were either to stabilize the existing soil or to replace the soil with nonexpansive impermeable soil to the depth affected by seasonal moisture changes. The decision on which method should be used was made based on cost-benefit analysis of stabilizing versus replacing for the existing expansive soil. To come up with the cost-benefit result, initially expansive soil samples from different road section were taken. Quality test for the collected soil samples have been made in the laboratory. The laboratory test result has indicated as the existing expansive soil needs improvement to serve as subgrade for the road within the project. Following the test result, selection of relevant replacing material and stabilizing agent was done. Replacing material within 2km radius was found satisfying all tests and lime was selected as stabilizing agent. With those selected materials and stabilizing agent, cost-benefit analysis was carried out. Total Cost of Replacing the existing expansive soil with locally available suitable material was found to be 2,862,247.71 (Birr/Km) and total cost of stabilizing the existing expansive soil with Lime from Derba Cement Factory was found to be 1,974,821.28 (Birr/Km) amounting to a saving cost of 32%. From the study, the result of stabilizing the existing expansive soil as compared to replacing with non-expansive soil from the nearby forest has become economical



Soils in Road Construction