Investigation and Modification of Hyperbolic Model as a Constitutive Model for Unsaturated Soils

The present study has mainly focused on the modification of the hyperbolic model formulation so that the shortcomings of the said model can be corrected and more conformity with the experimental results can also be provided. This model, also known as Duncan-Chang model, is a two parameter model for obtaining the stress-strain curve of the triaxial test. The hyperbolic model which is indicative of the ideal characteristics of the soil is particularly advantageous in that it does not require the presence of extensive test programs and can easily be implemented through computer programs. As the results show, although numerous studies have already been carried out to address the model shortcomings, this model fails to predict the plastic behavior of the subsaturated soils. Among the shortcomings of the said model are the insufficiency of the hyperbolic model relations for the analysis of the stage related to the soil instability, uselessness of the relations in case of soil volume variation, experimental nature of the used coefficients in the relation. Hyperbolic relations are useful in solving different problems of engineering and geotechnics since numerical values of hyperbolic model parameters can be extracted from the experimental results and all the relations that are used for the drained soils can also be applied to non-drained and unstable soils. Furthermore, numerous values of parameters have been tested and utilized for different kinds of soil over the past thirty years. Therefore, a rich source is available for comparison and interpretation of the obtained results from different projects.