Index And Engineering Properties Of Subgrade Soils: A Study In Areka Town, Wolaita Zone, Southern Ethiopia

Civil engineering structures are designed from the knowledge of soil properties at the given site. This research work is for the Investigation of index and engineering properties of Areka town subgrade soils. To investigate these ten test pits were selected by dividing the total area of the town in to ten parts based on the expansion potential of the town and the current distribution of the gravel road according to the municipality of Areka town. The soil samples per pit up to 3m depth, were collected from open pits by direct manual excavation. During field testing, field density and natural moisture content tests were done.[15] The laboratory tests that were carried out includes natural moisture content, particle size distribution, specific gravity, Atterberg limits (LL and PL), compaction (OMC and MDD), CBR and CBR swelling potential tests were conducted. From the results that were obtained for grain size analysis, Atterberg limits and from soil classification systems (USCS and AASHTO). According to the results of this research, Natural Moisture content ranged between 8.0-12.0%, field dry density ranged between 1.66 – 1.87( g/cc) , gravel fraction between 9.18-16.19 %, sand fraction between 22.30-54.26 %, silt fraction between 15.82-47.69 %, Clay fraction between 9.0-35.5%, Specific Gravity ranges between 2.58-2.78, Plasticity Index between 8.21- 14.61%,, GI ranges from 4 to 11 and for the soil classification under A-4, A-6, A-7-5 and A-7-6 according to AASHTO M145 and inorganic silts of medium compressibility according to unified soil classification system and the OMC ranges from 10.14% to 21.37 %, MDD ranges from 1.77 g/cc to 1.98g/cc, CBR swell ranges from 1.42- 1.92% and CBR value ranges from 6.31-8.76 (%) as the test result indicate that CBR swelling potential values were below 2%, therefore they were good to use as a subgrade soil for pavement construction [6]. The CBR values for the soil samples were above 5% so they were good to use as a subgrade soil for pavement construction [11]. From all soil samples the subgrade strength class based on CBR value TP1, TP6, TP9, TP10 were S3; and the remaining were S4 [7].; thus, the subgrade soil has good bearing capacity for the pavement construction based on [4].