Soil Water Characteristic Curve Predictive Model from Index Properties for Red Clay Soils, case in Jimma, Ethiopia

Abstract

The Soils in tropical and arid regions which found above the groundwater table is known as unsaturated soils. Ethiopia is also considered to be in this region. Jimma is found in Ethiopia with high precipitation and evaporation through the year this causes the dominancy of unsaturated soil broadly in the city. Because most of our infrastructures built on unsaturated soils, the response of unsaturated soils is the most important consideration for many geotechnical projects. The testing of unsaturated soils required significantly more money and time. In addition, laboratory equipment for determining unsaturated soil properties has established to be technically challenging and difficult to use. For the characterization of unsaturated soil property functions, indirect estimation procedures were developed. Combined with saturated soil properties, the SWCC helped a means of moving unsaturated soil mechanics into real engineering practice. Therefore the aim of this research was to predictive SWCC by developing an empirical relationship between simple tests and those requiring complicated test equipment and procedures. SWCC data point was measured by contact filter paper method, and the measured data point optimized using MATLAB® R2019a to obtain the model fitting parameters. The linear regression was conducted with the help of JMP® Pro14 statistical software to correlate the optimized model fitting parameters with index properties. Based on index properties, a general equation for the soil-water characteristic curve was developed. The accuracy of the developed model was checked through different error measurement mechanisms .In this study, red clay soils were obtained from eight field sites. Laboratory experiments including index testing and SWCC testing carried out on the soil samples. The water content measurements were in the range of 35.44 percent to 43.09 percent. From the gradation test result the content of gravel soil ranges from 0 to 0.3%, sandy soils ranges from 1.21 to 4.03%, silt soil range from 28.25 to 33.85% and clay soil range from 61.9 to 70.38%. The specific gravity of the selected soil samples were ranges 2.69-2.76. Plasticity index of the soil was ranges 35.14 to 45.41. The X-ray diffraction results show that the kaolinite was the dominant clay mineral for all test pits. Based on the index properties result the developed af was 5.558+1.032wPI,nf equal to 0.471+0.397(1/mf),mf equal to 0.184+0.000351wPI2 ,and residual suction vale equal to-2830.57+2.84wPI2 . Furthermore the proposed model was validated with other works and it reveals that the result was in acceptable range