Arba Minch University Institute of Technology School of Graduate Studies Road and Transport Engineering Stream

Abstract

Dispersive soils are structurally unstable soil and the soil aggregates-small clods – collapse when the soil gets wet because the individual clay particles disperse in to solution. The use of dispersive soils in roadway embankments and structures can lead to serious engineering problems and has undesirable characteristics such as non-cohesive, low strength (CBR), and tendency to swell. In order to improve the previous mentioned characteristics from the dispersive soil, a technique of mechanical soil stabilization should be made for this type of soil to enhance some of its properties. In this study, the experimental works have been made to study the suitability of natural gravel from Gidole town near Maremya bet quarry site to improve properties of dispersive soil. The important parameters to be determine the geo-technical properties such as Specific gravity, Liquid limit, Plastic limit, Plasticity index, dry density and California Bearing (CBR) ratio values. The laboratory work involved sieve analysis along with consistence test to classify the soil sample. The preliminary investigation of the soil shows that it belongs to A-7-5 class of soil in AASHTO and MH in USCS soil classification system. Soils under this class are generally of poor for subgrade road construction. Atterberg limits, compaction and CBR tests were used to evaluate properties of stabilized soil. The soil would be stabilized with natural gravel in stepped concentration of 5%, 10%, 15%, 20%, 25%, 30% and 35% by dry weight of the soil. Analyses of the results are showed the addition of natural gravel improve the geotechnical properties of the dispersive soil. The addition of natural gravel reduces plasticity index, swelling and OMC with an increase in MDD and CBR with all increased natural gravel contents. The addition of 30% and 35% of natural gravel established an increased CBR value by 1,096% and 1,223% respectively, indicating both the subgrade class falling under S4 and S5. From this study it was found out that natural gravel stabilized with soil do meet the minimum requirement of ERA pavement manual specification for use as a sub-grade material in road construction. For this study to increase the strength of subgrade dispersive soil type one is mechanical stabilization method and double hydrometer test are used to identify dispersivity of soil.