Application of Marble Dust to Improve the Engineering Properties of Expansive Soils to be used as Road Bedding Material

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Addis Ababa University


Expansive soils are characterized by volume change due to variation in moisture content. The cyclic wetting and drying process causes vertical and horizontal movement in expansive soils leading to failure of civil engineering structures found on such soils. The problematic nature of such soils can be improved by employing chemical stabilization techniques such as lime, cement and enzyme stabilization. However, as these techniques are expensive to developing countries such as Ethiopia, locally available low cost materials can be applied as alternative to improve the engineering properties of expansive soils. In the present research work, the performance of marble dust to improve the problematic nature of expansive soils is investigated. The study is carried out on a highly expansive soil section of selected road project. The natural subgrade soil obtained from the highly expansive section of the road is characterized for its engineering and strength properties and it is found to be highly expansive soil with low bearing capacity, high swell and characterized as A-7-5 according to the AASHTO classification and rated as poor (unsuitable) subgrade material. The expansive subgrade soil is blended with increasing percentage by weight (5% to 30%) and the improvements in engineering properties are studied and it is noted that it improves with increasing percentage of marble dust and with increased periods of curing though it is not significant as compared to specification requirements of several standards. With the higher percentage of marble dust (30%), the swelling potential of the natural soil changed from ‘High’ to ‘Medium’, LL reduced from 88% to 63%, PI reduced from 52% to 34%, CBR increased from 0.9% to 2.25% and the CBR swell reduced from 8.6% to 5.3%. Un-soaked CBR test is conducted on the natural subgrade soil and the 30% marble dust blended sample and it has been noted that the subgrade class improves for both indicating significant reduction in project cost as result of reduction in pavement thickness. Thus, marble dust can be recommended as an alternative stabilizing agent for expansive soils by itself or being blended with small percentage (1-3%) of effective stabilizing agents such as lime so that significant project cost reduction and minimal environmental degradation can be assured.



Geotechnical Engineering