Improvement of Weak Subgrade Soil Using Naturally Occurring Lime (Limestone) (Case Study in Sheka Zone)

Abstract

The successful construction of highways requires the construction of a structure that is capable of carrying the imposed traffic loads. One of the most important layers of the road is the actual foundation, or subgrade. Where the subgrade is founded in an inherently weak soil, this material is typically then removed and replaced with a stronger granular material. This “remove and replace” technique can be both costly and time consuming. Soil stabilization has become a major issue in construction engineering and the researches regarding the effectiveness of using industrial wastes are rapidly increasing. The common soil stabilization techniques are becoming costly day by day due to the rise of cost of the stabilizing agents like, cement, lime, etc. The cost of stabilization may be minimized by replacing a good proportion of stabilizing agent using naturally occurred admixtures. The general objective of this study was improving weak subgrade soil using natural lime in case of Sheka Zone. Subgrade soil sample had been taken from road location at Masha in Sheka Zone and natural lime from local area at Degele Kebele in Sheka Zone. The relevant laboratory tests have been; Proctor test, Grain size analysis test, Specific gravity, Atterberg test, CBR of the soil, optimum lime content, Chemical content and engineering properties of the lime. Soil sample taken for the study is clay with high plasticity (CH) and group A-7-5 which truly requires to be strengthened. The soil was stabilized with different percentages of lime. Observations were made for the changes in the properties of the soil such as Maximum dry density (MDD), Optimum moisture content (OMC), Plasticity Index (PI) and California bearing ratio (CBR). The results obtained shown that the increase in lime content increases the OMC but decreases the MDD and the PI. Also, the CBR value of soil considerably improved with the lime content. From the observation of maximum improvement in strength, 7% lime content was concluded as optimum amount for practical purposes. Observing the tremendous improvement of CBR value of soil, the present soil stabilization technique may considerably be recommended for construction of pavement.