EVALUATION OF GEOTECHNICAL PROPERTIES AND MATHEMATICAL MODELING FOR SWELLING PRESSURE FROM INDEX CHARACTERISTICS OF EXPANSIVE SOILS FOUND IN GEDEB

Abstract

Expansive soils are clayey soil that swells or shrinks, which increases in volume when in contact with water, but decreases in volume when the water is removed. Therefore, these soils are problematic soils when the fluctuation of moisture occurs. In these problematic soils rapid development of urbanization, rapid increases of population force them to construct different infrastructures over the expansive soils even without proper geotechnical evaluations. The study area is identified to experience existence of expansive soils and also rapidly expanding town due to the new master plan on the other hand. This study was undertaken to evaluate the geotechnical properties of expansive soils and multiple linear regressions adopting SPSS26 software was used to develop a mathematical model between swelling pressure and index characteristics of expansive soils found in Gedeb town after evaluating existing index characteristics. A total of eighteen expansive soil samples were collected from nine test pits at 1.5 and 3m depth from different locations of the study area which were manually excavated by systematic random sampling techniques. Bulk samples for in-situ dry density and moisture content determination were collected by the core cutter method. The geotechnical properties used in this study include; in-situ moisture content, in situ dry density, Atterberg limit test, grain size, specific gravity, free swell, standard proctor test, unconfined compression test, and one-dimensional consolidation test are conducted on those soil samples following ASTM standards. The experimental test results of the study area indicate that LL, PL, PI & LI ranges 84.20 to 108.80, 28.37 to 34.85, 53.71 to 75.98, and 0.020 to 0.174(%) respectively. ranged from 2.66 to 2.78. The in-situ dry density and moisture content ranged from (1.11 to 1.37) g/cc and (34.35 to 39.85) % whereas OMC ranges from (21.19 to 34.46) % and MDD from (1.15 to 1.52) g/cc. The clay content of soils of the study area ranged from (45.99 to 58.94) % with activity from 1.168 to 1.323. According to the relationship between consistency of clays and unconfined compression strength the all samples value ranges (100 to 200) which indicates it as stiff. Free swell ranged from (102 to 180) % whereas 470) . ranged (4.53 to14.59) % with Ps from (145 to Based on these results study area soils were justified as highly to very highly expansive. The newly developed models are, developed by taking one or more five independent variables ( , , PI & LI) in different combinations. Among the developed model, equation better than the other is proposed.