INVESTIGATING ANDGEOTECHNICAL MAPPING OF SOILS IN BIRBIRTOWN, SOUTHERN ETHIOPIA

Abstract

The ultimate foundational component supporting the construction is soil. The index and engineering qualities of the underlying soil will determine how well the structure operates. The goal of this study is to use various sorts of laboratory tests to look into the index and engineering features of soils found in Birbir town and to create a soil map using ArcGIS. This study is helpful in supplying the knowledge or data needed for designing Birbir town's civil engineering structures. Fifteen test pits were selected based on variation of the soil of the town and the current distribution of the residences to the municipality of Birbir town. The soil samples were collected from pits by direct manual excavation. From collected soil samples laboratory tests were conducted. From laboratory tests both index and engineering properties were carried out and all laboratory tests were conducted by ASTM standards. Laboratory tests carried out on disturbed samples revealed that the natural moisture content ranges from 10.88 to 32.91%, specific gravity of the soil’s ranges from 2.65 to 2.83. Results of Atterberg limits tests shows that of soils of Birbir town have liquid limits ranging from 16.41 to 78.93%, plastic limit ranges from 9.73 to 37.36% and plastic index from 7.03 to 51.48%. These values indicate that the plasticity of the soils of the study area ranges from low to high plastic. The grain size distribution indicates that most of the soil samples have clay material more than 30%. Therefore, clay type of soil is dominantly located in the study area. The free swell test result indicates that soils of the study area are expansive and non-expansive which means degree of swell of the soils is swelling and non-swelling. The degrees of activity of all of the study area soils are normal and Inactive with valuesof Activity less than 1.25.Soils of the study area are classified according to USCS and AASHTO. According to USCS soils are mainlyclassified in tohigh plastic clay soil (CH) and silty soils have high plasticity (MH). The research area's soils are classified by AASHTO as A-7-5, which denotes clay soil of poor quality as a sub grade material. The findings of the compaction test revealed that the study area's maximum dry density (MDD) ranges from 1.34 to 1.86 gm/cm3, and its ideal moisture content (OMC) ranges from 14.81 to 40.. the silty sand soil has angle of internal friction ranges from 30.10 to 32.600 and cohesion ranges from 8 to 10 kpa. The consolidation test results showed that the compression index ranges from 0.044659- 0.127020 and recompression index ranges from 0.0030088 to 0.0920423.Finally, the CBR test shows the CBR value ranges from 2.20 to 21.64 %