Engineering Geological Investigation of Jimma Town for Engineering Practice

Abstract

Jimma is one of the major and densely populated towns in Ethiopia. It is located 348.5 km southwest of Addis Ababa. As in many towns of Ethiopia, very little is known about the soil and rock engineering properties and subsurface conditions of the town. Therefore, the present research work aimed to evaluate the geological and engineering geological condition of the town. Detailed field survey, in-situ strength test, sampling, geological mapping, and laboratory testing of samples were conducted. A total of 12 disturbed soil samples were collected from 12 test pits, which were dug manually up to 3 m depth. Geological and engineering geological maps were prepared at a scale of 1:25,000. Laboratory results revealed that the natural moisture content, liquid limit, plastic limit, plasticity index, specific gravity, and free swell of the soils range from 41.97–62.45%, 66–101%, 31–62%, 19–59%, 2.36–2.75, and 33–130% respectively. The area is dominantly covered by high plastic silt and clay soil type. Basalt, ignimbrite and tuff are the lithological rock units identified in the study area, which are classified into three major engineering geological subunits: very high Strength, high strength, and very low strength (soft) rock units. Flooding and the high swelling potential of the soils are the main geological hazards that require due consideration in the study area.