Abstract:
The infrastructure is constructed in unsaturated soils. However, the principle of saturated soil
mechanics is adopted in the geotechnical design of structures. To follow a sustainable approach
and reduce costs, it is necessary to apply the principles of unsaturated soil mechanics in the design
of civil structures. Furthermore, to predict unsaturated soil properties by direct measurement of
soil water characteristic curve using the pressure plate test is time - consuming, and measureme nt
of soil parameters for the constitutive unsaturated soil model requires extensive laboratory testing.
Moreover, a rapid increase in the use of the soil - water characteristics curve to determine the
unsaturated soil property functi ons is desired. However, the complex interrelationship between
soil water content and soil suction requires indirect determination of the unsaturated soil property
functions. There are many aspects to be considered when using SWCC for predicting mechanica l
or hydraulic behaviors of the soil. Hence, to simplify the problem this study aims to develop a
prediction model for simplifying Freduland and Xing (1994) model fitting parameters and SWCC
shape parameters based on correlation with simple basic soil properties. Hence, predictive models
to evaluate unsaturated soil properties are very important in practice. It can be measured easily
from basic soil properties and is highly desirable because of its low cost and simple testing
procedure. Fourteen red clay soi ls were collected from di fferent field sites of Debre Markos in this
study. The soil samples were subjected to laboratory testing that includes compaction testing, basic
soil property testing , and pressure plate test to determine the discrete soil - water characterist ics
curve data points. The pressure plate test was used to measure the matric suction for differe nt
moisture contents. Regressi on models were conducted to examine the relationship between
Fredlund & Xing (1994) model fitting parameters, the SWCC shape parameters, and basic soil
properties. SWCC for fourteen red clay soil s (i.e compacted initial conditions) was measured by
pressure plate test, and regression was performed with the help of the SAS JMP® Pro- 14 statistica l
software package. A statisti cal simple regression model of Freduland and Xing (1994) model
fitting parameters was developed. To validate the rationality of the prediction model a cross-validation technique was used. The models found excellent correlation with the basic soil property
test results of the soil. Hence, the developed model can be used to predict the drying SWCC of
Debre Markos red clay soil considering the compacted initial condition.
Keywords: SWCC, model parameters, unsaturated soil, pressure plate, matric suction, predictive
model, model fitting parameter, SAS JMP Pro- 14