Engineering geological Characterization of Aleta Wondo town, Southern Ethiopia: implication to engineering practice

Abstract

Site characterization is a prerequisite for the successful and economic design of engineering structures and earthworks. It is also necessary to obtain sufficient information on the type, characteristics, and distributions of rock and soil underlying at a site of proposed structures for feasibility and economic studies for the proposed project. This study was conducted to obtain geotechnical information of ground at Aleta Wondo Town. Aleta Wondo Town found in Sidama regional state. The main research goal is to characterize the engineering geological and geotechnical properties of soils and rocks and develop a detailed multi-purpose engineering geological map. To reach this goal laboratory and field tasks were performed. Engineering geological and geotechnical characterization of soils and rocks are based on their index and engineering properties and their classification is according to the standard proposed by the Unified Soil Classification System (USCS), British standard system, and unconfined compressive strength. Based on the USC system the soil type of study area fall into CL (inorganic clays of low to medium plasticity) and MH (inorganic silts, elastic silts).according to BSS the study area soil is classified as compressible silt, medium plastic inorganic clay. According to the Rock Mass Rating, unconfined compressive strength and degree of weathering, study area rock classified as, good basalt with slightly weathered and very high strength, good ignimbrite with slightly weathered and high strength, and poor ignimbrite with highly weathered very low strength. To address the Engineering geological and geotechnical characterization of soils, representative samples are collected and analyzed their index properties (Natural Moisture Content, specific gravity, Atterberg limits ) and engineering properties (compaction, shear strength, and free swell behavior) in the labs and interpreted based on standard soil characterization techniques. From those tests, the Moisture content of the soils varies from 23.27 to 48. The Grain size analysis result of the study area show percent of sand 47%, silt 37.5-73.9%, and clay 50%. Laboratory consistency limit test result of the soil in the study area shows LL of 38.93- 71% %, Pl of 15.8-49.5%, and The plasticity index of soil 10- 23.13. The activity of soil of the study area ranges from medium to inactive. The potential expansion behavior or swelling nature of the soils is found to be low to medium. The specific gravity of study area soil range from2.47-2.61. The optimum moisture content and maximum dry density results of the study area range32.8-28 and 1.6-1.21kg/m3 respectively. The shear strength results indicate that the cohesion of the soils varies from 38.4 to 54kpa, whereas the angle of shearing resistance varies from 18˚ to 22.99˚. The main geotechnical problems that affect the design and development of civil structures in the town were identified as the existence of shallow Ground Water table and cohesive soils of high plasticity character