Geology

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Browsing Geology by Author "Ayenew, Tenalem (Prof.)"

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    Engineering Geological Mapping and Land Slide Assessment of Dessie Town
    (Addis Ababa University, 2001-06) Terefe, Kefyalew; Ayenew, Tenalem (Prof.)
    In order to understand the geotechnical properties of soils and rocks and the slope stability in Dessie, field traverses, digging of test pits, drilling of bore hole, vertical electrical sounding test, standard penetration test, point load test, Schmidt hammer test and various type of laboratory tests have been carried out. The purpose of this work is to ensure those geological factors affecting planning, design, construction of engineering structures related to soils and rocks and to assesses the landslides to give a mitigation and control methods related to slope gradient classification map, Geomorphological map, Engineering geological map, landslide hazard classification map, land use and land cover map have been performed. Dessie is situated in a graben formed by successive parallel faults that run in the north south direction. The geomorphology of Desire is governed by, the geology, the regional tectonic activity, erosion and depositional process. The study area is covered with alternate layers of basalt and quaternary deposits of colluvial, alluviall and residual soils. Alternate layers of stratoid and degreaded basalt separated by thin palleosoil are typical layers along the escarpments of Tosse and Azewa Gedel. The centeral part of the town is characterised by scattered hills of vesicular basalt. The thickness of colluvial and alluvial deposits vary according to the palemorphology of the garben. Three borehole were drilled during the field work in selected areas and show that the thickness of these colluvial - alluvial soils reaches about 40m. Landslides, especially induced by gully erosion and rockfalls down the slope is nowadays a common phenomena in Desire Town. About 20 landslides including rock fall prone areas have been recognised. Most of them are resulted from the lack of proper surface drainage system on the thick colluvial - alluvial sediment and rockfalls toppleing from the steep cliffs. The landslides are aggravated by natural and man made activities, such as rainfall, change in the slope gradient, human intervention, gullies and streambed erosion.