INVESTIGATION AND MAPPING OF SUB-GRADE SOILS ON ROAD SECTION BETWEEN CHENCHA AND EZO TOWNS

Abstract

In the flexible pavements, Subgrade soil is the undermost layer for pavement structure constructed on it and used to resist traffic load. This paper presents the field and laboratory test results of subgrade soils that were performed to an investigation and mapping the subgrade soils of road section between Chencha to Ezo towns. Geographically, the altitude of the Ezo metropolis stages 2845 meter above sea latitude 6 21' 09"N and longitude 3735' 45"E. The altitude of Chencha city is 2686 meters above sea latitude of 614 '41 "N and longitude 3734' 45" E. It is now a low-quality gravel road constructed with the aid of utilizing Unversal Rural Road Access Programs (URRAP). The study area mainly falls within the Dega climatic zone, as the altitude of the alignment mainly lies 2300 – 3300 m a.s.l. The study area is the mean annual temperature of 10ºC -15ºC, mean annual rainfall of 159.78mm and the prevailing wind direction is from southeast to northwest of Chencha to Ezo towns. In order to investigate subgrade soil, field and laboratory tests were accompanied on selected 18 soil samples which are taken from the road section at not more than 1km interval. The test results showed that the field dry density range from 1.375g/cc to 1.721g/cc, NMC range from 27.23% to 62.74%, LL ranges from 35.3% to 60.5%, PI ranges from 5% to 29%, OMC ranges from 10.6% to 16.0%, MDD ranges from 1.70g/cc to 1.99g/cc, GI ranges from 0 to 14, CBR ranges from 5.13 to 12.65% and CBR swell ranges from 0.50% to 2.92%. Based on the laboratory test results the study area was silt and clay soil with soil class of A-2-4, A-2-6, A-4, A-5 and A-7-5, A-7-6 according to AASHTO soil classification scheme. From soil classes A-2-4, A-2-7, A-4 and A-5 are categorized as subgrade strength class of S4, A-7-5, A-7-5are categorized as subgrade strength class of S3 according to ERA pavement design manual. The data (site and laboratory test results of the study area) were input into a Geographical Information System (GIS) frame to provide interactive maps that display the spatial distribution of the variables and discover their characteristics. These maps are then used to easily identify the values of field and laboratory results at various location of study area.