Engineering Geological Investigation of Adama Town: Implication to Engineering Practice

Abstract

Adama was founded hundred years ago and is one of the major and densely populated towns in Ethiopia. It is located 100 km south–east of Addis Ababa and the hub of a vast region of immense economic potentials accessible by means of rail way and expressway. Due to the mentioned reasons, the urbanization is rapid. However as in many towns of Ethiopia, very little is known about the soil and rock engineering properties. Moreover, the town is located in the southern extreme of the active volcano-tectonic segment of the northern Main Ethiopian Rift (MER). The present research work is, therefore, aimed at assessing and evaluating the geological and engineering geological condition of the rocks and soils of the town. Detailed field investigation, in-situ rock strength test and laboratory tests were carried out. A total of 30 soil samples were taken from 16 test pits, which were dug manually to 3 m depth. The natural moisture content of the soil of the study area ranges from 6.34 - 25.2%, liquid limit 26.06 - 54%, plastic limit 7.5 - 40.83%, plasticity index 2.22 - 26.83%, free swell 0 - 40%, specific gravity 2.12 - 2.67, and pH 4.48 - 6.7. Low to medium plastic silty sand and sand are the dominant soil type in the study area. The rocks of the study area were classified into Low Strength, Medium Strength and High Strength rock mass units based on the strength (Unconfined Compressive Strength) of intact rock and discontinuity characteristics. Gully erosion, land slide, seismic activity and flooding are the main geo-hazard that need attention in the study area