GEOTECHNICAL CHARACTERIZATION AND LIME STABILIZATION OF COLLAPSIBLE SUBGRADE SOILS: - (THE CASE OF SHASHAMANE-AJE ROAD, SOUTH EAST ETHIOPIA

Abstract

The construction of the various flexible pavement layers is very much dependent on the geotechnical characteristics of the subgrade soils. Collapsible soils show relatively high apparent strength in their dry state, but have low density, porous structure. One of the most important problems concerning collapsible soils is instability and considerable settlement due to minor changes in the water content which can cause remarkable damages to overlying structures. These problematic collapsible soils, therefore, when encountered as sub-grade should be avoided or treated properly. This thesis work aims to characterize and lime stabilization of collapsible subgrade soils of Shashamane-Aje road because this road was failed and has continuous maintenance on most parts of the section. To characterize sub grade soil of study area, Laboratory tests such as dry density, natural moisture content, particle size distribution, specific gravity, Atterberg limits (LL and PL), compaction (OMC and MDD), Direct shear test, Unit Weight, Consolidation, CBR, and CBR swelling tests were conducted in this thesis work. The test results showed that the NMC ranges from 9.46% to 32%, the field dry density ranges from 1.21 g/cm3 to 1.81 g/cm3, LL ranges from 0% to 44%, PL ranges from 0 to 38, PI ranges from 0% to 19%, Specific gravity ranges from 2.49 to 2.72, GI ranges from 0 to 6, OMC ranges from 17.00% to 30%, MDD ranges from 1.33 g/cm3 to 1.84 g/cm3, CBR ranges from 5.00% to 25% and CBR swell ranges from 0.02% to 0.55%. Based on laboratoryresults the study area soil was characterized as A-1, A-2, A-3, A-4, and A-5 according to the AASHTO M145 soil classification system. From test result, all test at failed section of road shows collapse nature of soil but PTR3 is the worst sample to use as a subgrade material for pavement construction due to the existence of highest collapsibility potential (5.81%). After adding lime at different percentages by weight (0%, 3%, 5%, and 8%) tests such as grain size analysis, Atterberg limit, specific gravity, Modified Procter test, Consolidation, and California Bearing Ratio test was conducted and decreased collapsible potential from 5.81% to 0.61% at 8% lime. So 8% lime is optimum to make soil stable by reducing collapsible Potential below 1% and the test result also shows that lime provides better index properties. Additionally providing an appropriate drainage system to avoid wetting of collapsible soil, and dynamic compaction is a proper mitigation measure of the unsuitablesubgrade soil of the study area