Author ORCID Identifier

Date Available


Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation




Civil Engineering

First Advisor

Dr. L. Sebastian Bryson


Constitutive models that can provide useful insight into the deformational mechanism induced by hydrologic variations are vital for design and analysis of structures where unsaturated regime predominates. An accurate description of unsaturated soils’ behavior not only requires a vigorous constitutive model, but essentially is achievable using real-time mechanical (e.g. small-strain shear modulus) and hydrologic data sets. The main objective of this research was to develop a robust constitutive scheme that is compatible to quick fluctuations in hydrologic conditions.

The first step towards accomplishing this aim involved proposing a novel methodology to estimate the small-strain shear modules with respect to the variations in net normal stress and matric suction. Fundamental of the proposed scheme was established on the inverse relationship between the small-strain shear modulus and soil-water characteristic curve (SWCC). The model proved to be highly reliable in estimating real-time values of the small-strain shear modulus along several loading and hydrologic scenarios.

Furthermore, a dependable and robust constitutive scheme, identified as SFG model was selected and further modified to simulate hydraulic characteristics and elastoplastic deformations of the unsaturated soils as direct responses to isotropic/triaxial loads and hydrological variations. The modifications involved reformation of hysteresis and elastic shear strain components of the original model. The modified-SFG model was fitted against several case studies representing various hydrologic conditions. The model successfully reproduced hydro-mechanical characteristics of the studied soils. More significantly, the modified-SFG model offers possibility of a real-time simulating of hydro-mechanical behavior of unsaturated soils with respect to rainfall and evapotranspiration events.

Likewise, in this dissertation, long-term hydrologic variations within the soil’s body was simulated under transient infiltration framework. Correlation between various parts of hydrologic data was used to estimate different components of hydrological dataset. The transient infiltration model was subsequently coupled with the modified-SFG scheme and hydro-mechanical behaviors of an unsaturated hillslope was incrementally simulated with respect to hydrologic variations. The outcome of this study provides geotechnical engineers with a capability of estimating the deformational behavior of unsaturated soils, particularly stability of hillslopes, under various real-time rainfall and evapotranspiration conditions, and thus aids effectual risk assessments and construction managements.

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