Abstract:
Unsaturated soils are a common feature in many regions worldwide and play a crucial
role in various geotechnical engineering applications. However, the complex and timeconsuming nature of determining unsaturated soil properties limit the practical
application of unsaturated soil mechanics. As a result, various simpler and indirect
methodologies have emerged to quantify unsaturated soil properties. These indirect
procedures, primarily utilize the soil water characteristic curve and saturated soil
properties. Thus, analysis of unsaturated soils behavior requires the knowledge of soil
water characteristics curve, which is the relation between soil matric suction and water
content. The soil water characteristics curve serves as a valuable tool for measuring
unsaturated soil properties, but conducting laboratory tests to establish it involves
significant time and cost. The laboratory equipment for measuring soil water
characteristic curve is also not commonly available. Therefore, a predictive
mathematical model based on basic index soil properties is needed. In this study, a
simplified model that can predict the Fredlund & Xing (1994) model fitting parameters
which used to establish the soil water characteristic curve from basic index soil
properties for red clay soils found in Bahir Dar was proposed. This study is done on the
basis of experimental findings. Various laboratory tests were performed on fifteen soil
samples obtained from Bahir Dar city. The soil water characteristic curve data points
determined from filter paper method were curve fitted with Fredlund & Xing (1994)
model and the corresponding fitting parameters were generated. After obtaining the
curve fitting parameters, regression analyses were performed with JMP® Pro14
statistical software to predict the relationships between the Fredlund & Xing (1994)
curve fitting parameters and basic index soil properties. A new prediction model of
fitting parameters was proposed for estimating soil water characteristic curve. The
proposed model was verified by applying them to primary and secondary soils data,
which were not included in developing the model. This study brings out that an
improvement over the existing models. The results of validation studies suggest that
the proposed model can provide relatively better prediction of the soil water
characteristic curve of the soils in study area.
Keywords: Filter paper, Matric suction, Prediction model, Soil water characteristics
curve, Unsaturated soil