STABILIZATION OF EXPANSIVE SOIL FOR SUBGRADE USING CEMENT: A CASE OF GURAGE ZONE, ABESHIGE WOREDA

Abstract

Soil stabilization is one of the ground improvement methods of treating expansive soils. The expansive soil is a serious threat as it possesses seasonal variations on moisture content.Most parts of Ethiopia are covered by expansive soils. This type of soil leads to severe damage to pavements and foundations of structures. A lot of infrastructures like pavements and buildings were damaged due to this problem.Hence, the soil on which the structuresare to be built must be capable of withstanding the load imposed on it. In order to minimize this problem, it needs to be stabilized. Therefore, this research aims to evaluate the effect of an addition of cement to improve the expansive soils for subgrade use and to determine the optimum percentages of cement for stabilizing expansive soils in the study area. To achieve the objective of this research experimental method was applied after collecting representative soil samples. Three soil samples were collected from three different Keble’s found in Abeshige Woreda, Gurage Zone, Ethiopia and index and engineering properties of soils wereconducted on original soils followingAmerican Association of Highway and Transportation Office (AASHTO) procedure.To improve the weak subgrade soil obtained from study area natural soil was mixed with different percentages of cement by weight starting from 4 up to 16% of cement and itseffects on Atterberg limits, free swell index, Modified proctor test, California Bearing Ratio, and swell were studied.Based on laboratory test results from natural soils before treatment the soils obtained from study area were considered as expansive clay soils. The result indicatedthat the proportion of fines passing no 200 sieve 95.45,92.33, and 92.2%, liquid limit 99.6, 89.80, and 95.90%, and plasticity index 59, 59.80, and 61.4%, the free swell index of 110, 90.9, and 90%, the California Bearing Ratio and percent swell with 0.6, 0.8, 0.90% and 13.70, 12, and 10.80% for Abuko, Bedo, and Fintjeju Keble soil samples respectively. Soil samples are classified into A-7-5 as per the American Association of Highway and Transportation Office (AASHTO)and high plasticity clay soil (CH) as perUnified Soil Classification System (USCS) classification system. An addition of cement on natural soil decreases the liquid limit, increases plastic limit and decreases plasticity indexes (PI) by 71.02, 89.80, and 88.11% for (Abuko, Bedo, and Fintjeju Keble) respectively. The maximum dry density (MDD) shows a slight increase and the optimum moisture content (OMC) shows a decrease in the treatment of weak subgrade soil with addition of cement. California Bearing Ratio values increased from 0.6 to 45.20%, 0.8 to 57.9%, and from 0.9 to 54.5% for Abuko, Bedo, and Fintjeju Keble’s soil samples, respectively.It has been confirmed that 12% cement is an effective chemical stabilizer to improve both the index and strength properties of the soil of the study area.Despite the fact that this thesis work is limited in terms of time and budget, it is hoped that the finding will serve as a good starting point of the future