2025 Theses Doctoral

Unified Generalized Plasticity Model for Geotechnical Applications

Zheng, Yuning

The accurate modeling of soil behavior under static and dynamic loading remains a fundamental challenge in geotechnical engineering. Traditional plasticity-based constitutive models often oversimplify cyclic loading and complex stress paths, motivating the need for more adaptable frameworks.

This dissertation addresses constitutive modeling challenges through the calibration, validation, application and development of a unified generalized plasticity model capable of simulating a wide range of soil behaviors, including liquefaction, partially saturated cohesive soil mixture responses, and true three-dimensional stress states.

In terms of materials and methods, the research integrates laboratory-based calibration with numerical simulations. First, ten centrifuge tests involving saturated soil deposit of Toyoura and Nevada sands were used to validate two-dimensional unified generalized plasticity model for effective stress under dynamic loading. Next, the model is extended to analyze fine grained soils, where newly calibrated parameters for unsaturated silty clay mixture backfills enabled the simulation of two full-scale shaking table tests on geosynthetic-reinforced soil retaining walls. Finally, the model is extended and advanced into full three dimensions, validated against a series of element-level experiments, such as true triaxial and torsional shear tests. Throughout these stages, both models demonstrated reliability and flexibility in replicating various soil states and behaviors.

The conclusions confirmed the robustness and versatility of both the original and extended unified generalized plasticity model. Numerical predictions of liquefaction, seismic retaining wall performance, and multiaxial soil responses show strong agreement with experimental data. Notably, the three-dimensional extension accurately captures principal stress rotations and anisotropic effects. Collectively, these findings underscore the model’s potential as a powerful tool for both academic investigation and engineering design, providing a consistent unified framework that bridges the gap between standard 2D analyses and more complex real-world 3D soil behaviors.