Stabilization Of Expansive Soil By Using A-1-B Soil In Subgrade Materials A Study In Boditi Town, Wolaita Zone, Southern Ethiopia

In road subgrade construction, all the naturally available material cannot be utilized as sub grade material as there exists some problematic soils such as expansive soils. The problematic nature of such soils can be improved by application of stabilizing agents. [11].A sub grade soil should fulfill the minimum requirement and soils with less bearing capacity and high swelling characteristics should be treated in order to use as a sub grade material [6]. Mechanical stabilization of problematic soils with local materialsis one of the cheapest methods of improving the soils in order to use as a subgrade material [9]. Thus, in this study stabilization of Expansive soil by taking the four samples test pits, because this soil is unsuitable to use as subgrade material. To achieve these objectives four soils sample pits were selected from different representative parts of the existing sub grade. To understand the basic characteristics of this soil and stabilization there were different field and laboratory tests such as field dry density, natural moisture content, particle size distribution, specific gravity, Atterberg limits (Liquid Limit and Plastic Limit), compaction (Optimum Moisture Content and Maximum Dry Density), CBR and CBR swelling potential tests were concerned. The test results showed that the Natural Moisture Content ranges from 15.40% to 20.50%, the field dry density ranges from 1.53 g/cc to 1.61 g/cc, percentage finer ranges from 87.23 % to 91.23 %, Specific Gravity ranges from 2.57 to 2.65, Liquid Limit ranges from 62.81% to 71.87%, Plasticity Index ranges from 37.97 % to 44.75%, Group Index ranges from 27 to 30, Optimum Moisture Content ranges from 20.38 % to 22.60 %, Maximum Dry Density ranges from 1.65 g/cc to 1. 68g/cc, CBR ranges from 2.20% to 2.75% and CBR swell ranges from 3.51 % to 3.94%. Based on these results the study area was soil classification under A-7-6and inorganic clays with high plasticity. according to AASHTO M145 and USCS soil classification system respectively.As the result indicates that the soil samples characterized as Expansive clay soil, and those were unsuitable to use as a subgrade material for pavement construction based on [10] manual specification; thus, stabilize by mechanical method of stabilization by local materials (A-1-b soil), with different percentages ratio (15%,20% and 25% of A-1-b soil) by weight, were used to get appropriate mixing ratio, finally it was found that 25% mixing of A-1-b soil were efficient to use those as a subgrade material.