Geotechnical And Geophysical Investigations On Soils Found In Dole Town, Ethiopia.

Abstract

Knowing the engineering properties of soil is very important before designing any structure. The study area for this research is located at Dole Town, south-east of Addis Ababa, as part of the West Arsi Zone. Even though the area is a highly attractive tourism area of the country, due to a lack of soil investigation, there is no confidence to construct huge buildings and infrastructures in the area, and this highly affects the development of the town. The objective of this study is to investigate the Geotechnical and Geophysical properties of the soil found in Dole Town. Representative disturbed and undisturbed samples from five test pits were collected from different parts of the town. Laboratory tests were carried out, including specific gravity, natural moisture content, Atterberg limits, undrained shear strength, consolidation, gradation analysis, permeability, and electrical resistivity tests. The apparatus and procedures used for analysis for all tests were done in accordance with American Society for Testing Materials (ASTM) Standards. Based on the results of this study, less than 50% of the particles pass through a 0.075 mm sieve. The soils are categorized as coarse-grained soils. The specific gravity of the soil ranges from 2.39 to 2.59, while the Atterberge limit tests were done using the cone penetrometer method, and the results are; liquid limits range from 18.29% to 37.82%, plastic limits vary from 14.81% to 34.79%, and the plasticity index was below 7%, which indicates the soil varies from "well-graded gravel with sand" to "silty sand soil," and as per the AASHTO classification system, these soils are classified as "gravel and silty sand soil". The compaction test result shows the maximum dry density (MDD) ranges from 0.89 g/cm3 to 1.55 g/cm3, and the optimum moisture content (OMC) ranges from 8.50% to 43.0%, which shows the soil is mediumly compressive and intermediately strength. One-dimensional consolidation test results show the soils' compression index ranges from 0.122 to 0.421 and their swelling index ranges from 0.0363 to 0.0742. The coefficient of permeability ranging from 0.02 x 10-4 to 1.16 x 10-4 cm/sec which indicates the soil investigated is a permeable soil. Shear strength characteristics of the soil were determined by using a direct shear test. The cohesion (Cu) of the Dole town ranges from 5.7 KN/m2 to 45.8 kN/m2 , and the internal frictional angle (Øo ) of the study area was from 26.4o to 43.8o , indicating the soil is a cohesive-friction soil. The result of electrical resistivity ranges from 3.22 to 368.56 Ώm, which shows the soil is weathered and fractured ignimbrite, a mixture of gravel, pumice sand, and silt. The results imply the soil is light weight porous materials.