Combined Effects Of Lime And Marble Dust On The Properties Of Expansive Subgrade Soil In Jimma Town

Abstract

The expansive soil is one of the most problematic grounds which cause extensive damage in civil engineering structure; mainly on the building, shallow foundation or other lightly loaded structure including roads, airport pavement, pipelines. This type of soil occurs in many parts of the world, Ethiopia is one of those countries. Some land areas in Jimma town is covered with expansive soil. The problematic nature of such lands can be improved by employing chemical stabilization techniques such as lime, cement and enzyme stabilization. However, as these methods are expensive to develop, countries such as Ethiopia, locally available low-cost materials such as marble dust can be used as a full or partial replacement of those elements to improve the engineering properties of expansive soils. Since, marble dust up to 30% alone has not shown significant improvement on properties highly expansive grounds of Jimma town especially on bearing capacity, it may not suitable and meet the minimum requirements of ERA pavement manual specification for use as a sub-grade material in road construction. Relative to this, this research work is aimed to investigate combined effect lime and marble dust on expansive clay soils of Jimma town. The study is carried out on highly expansive soils of the study area. To achieve the objectives of the research, first field investigation work involved during dry season to identify the area of expansive soils and based on the properties that described under field investigations, five places (samples) with different location was determined. Free swell test was carried out for each sample, two samples with high free swell value had been selected, and then various laboratory tests were carried out on both two samples to classify the soil. The result from laboratory tests showed that both soil sample belonged to A-7-6 class according to AASHTO and CH (fat clay) according to ASTM soil classification system and rated as poor (unsuitable) subgrade materials. The soil was stabilized with a combination of lime and marble dust, (1-3%) Fixed percentage of lime blended with a different portion of marble dust (5-30%) by weight of soil. The laboratory tests carried out to evaluate the stabilized soil sample were; Atterberg limits, free swell, compaction and CBR tests. The result indicated that the addition of marble dust with small percentage dosage of lime showed significant improvement on the geotechnical properties of both selected expansive soil samples. It reduces plasticity index, swelling, and OMC with an increase in MDD and CBR values with all combinations. The maximum improvement achieved at a combination 3% lime and 30% marble dust for both soil samples. Comparison of the results obtained with some specifications showed that the improvements obtained from this stabilization, and it was satisfied ERA Standard Specification for subgrade materials hence, Combination of lime and marble dust is an effective soil stabilization agent based on the results observed and described in this thesis. It is recommended that it can be considered for use in the stab ilization of soil for sub-grade materials