Assessing The Impact of Fly Ash and Geogrid on Improving the Engineering Properties of Expansive Subgrade soil

Abstract

Expansive soil is known as a cause of different types of failures in lightweight structures such as road, light weight buildings, pipeline and the like. The solution of such problems should have to consider environmental safe, cost, readily availability, and long term performance. This study therefore, aims to improve the index and engineering property of selected expansive subgrade soil collected from Koye feche area by using fly ash and geogrid material. To achieve this, soil samples were collected from study area and various laboratory tests such as Atterberg limit, free swell index, specific gravity, proctor compaction, unconfined compressive strength (UCS) and California bearing ratio (CBR) tests before and after treating with fly ash ratio (0%, 5%, 10%, 15%, 17.5% and 20%) by dry weight were carried out. And also, to investigate the impact of geogrid with and without fly ash concentration, stabilization of the same subgrade material using two layers of geogrid reinforcement before and after treating with 17.5% fly ash concentration were performed. The test result indicated that the use of fly ash and geogrid reinforcement can significantly improve the bearing capacity of the selected expansive subgrade soils. At 17.5% fly ash and the first layer of geogrid application the CBR was increased by 10. 33% (sufficiently satisfying the requirement set by the ERA design standard) compared to the un-stabilized subgrade soil which is 2.7%. The results also showed a 5.44% increase in soaked CBR when using 20% fly ash alone, while a 6.17% improvement in CBR was achieved by applying only geogrid reinforcement to the expansive soil. Moreover, considerable improvement in CBR value was observed while using combined fly ash and geogrid material. This highlights the importance of geogrid and fly ash as a viable method for soil stabilization with high expansiveness tendency of the given soil.