CHARACTERIZING AND MAPPING OF SUBGRADE SOILS ON FUTURE EXPANSION ROADS BETWEEN KULFO AND HARE RIVERS

Abstract

Subgrade soil characterizing plays a vital role for examining the suitability of the subgrade soils for proposed project work. This paper presents the field and laboratory test results of subgrade soils that were performed to characterize and mapping the subgrade soils of Arba Minch town on future lateral expansion roads between Kulfo and Hare River. In order to characterize subgrade soil field and laboratory tests were accompanied on selected 16 soil samples which are taken from the road section at not more than 1km interval. The test results showed that the field dry density ranges from 1.77g/cc to 1.89g/cc, NMC ranges from 8.33% to 16.8%, LL ranges from 35.3% to 60.5%, PI ranges from 8.08% to 28.2%, OMC ranges from 10.6% to 18.7%, MDD ranges from 1.8g/cc to 1.95g/cc, GI ranges from 4 to 24, CBR ranges from 3.89% to 7.95% and CBR swell ranges from 0.95% to 2.92%. Based on the laboratory test result the study area was characterized as silty clay soil with soil class of A-4, A-5 and A-7-5 according to AASHTO soil classification scheme. From which soil classes A-4 and A-5 are categorized as subgrade strength class of S3 and A-7-5 are categorized as subgrade strength class of S2 according to ERA pavement design manual, and the load bearing capacity of the problematic subgrade soils (subgrade strength class S2) are improved by blending with locally available low swelling soil. The data (field and laboratory test results of the study area) were input into a Geographical Information System (GIS) frame work to provide interactive maps that show the spatial distribution of the variables and identify their characteristics. This maps are then used to easily identify the values of field and laboratory results at various locations of study area. Key words;