Fat or elastic: an inquiry into classification of black clay soils of Addis Ababa around Tulu Dimtu area

Abstract

Addis Ababa Black clays are one of two dominant clay found in the city and known for its expansive nature. Using the unified soil classification system, such soil, traditionally, is classified by the group name fat clay and group symbol of CH. But some investigations on local soil have resulted in classifying the soil as elastic silt, MH. In this research laboratory investigation is conducted to determine if in fact Addis Ababa black clays may end up being classed as elastic silts and if so, what may be the parameters that play a role in such a classification. For the study three samples were collected from Tulu-Dimtu, where previous investigations have resulted in the discrepancy. Simple classification tests were conducted on the samples. In addition, the effect of sample preparation, utilization of tap water, experience level of operator and variations among laboratories investigated. It was found that Addis Ababa black clay soils mayend up being classified as elastic silts but in general remain within the boundary region of the A-line on both sides. The experience level of the operator was found to have the most profound effect on index tests and classification.