Physical Improvement Of Weak Expansive Subgrade Soil Using (Geosynthetics) Geogrid Material

Abstract

The quality and life of pavement is greatly affected by the index and engineering properties of subgrade materials. But in Ethiopia most of the pavements are constructed over weak and problematic sub grades like expansive soil. When there is moisture in expansive soils, volume of soil gets increased therefore swelling pressure of soil is greater than the downward pressure of lightweight structures like road. Conversely; when the soil gets dry the structures face become uneven settlement. Such cyclic movements of soil mass cause different structures like road, light weight buildings, and pipeline to have excessive differential settlement, deformation and cracks. Hence, this study aims the use of geogrid material to improve the strength of poor expansive subgrade soil which plays an important role in load bearing and supporting different traffic load. To do the above objective, first different relevant literatures were reviewed intensively then disturbed soil sample was taken from Bole Arabsa area at specified depth of 2m then index property tests like liquid limit, plastic limit, plasticity index, sieve analysis, free swell, specific gravity and density - moisture tests were carried out, based on which the soil was classified as highly plastic expansive (A - 7 ?��? 5(20)) soil. Since main objective of this study is physical improvement of weak expansive subgrade soil, four day soaked and unsoaked CBR tests were conducted with before and after inclusion of geogrid material at first (25%), second (50%) and third (75%) layers on a given CBR mold m