Behavior and modeling of fiber-reinforced clay under triaxial compression by combining the superposition method with the energy-based homogenization technique

Modeling approaches to fully capture the behavior of fiber-reinforced clay remain lacking, although the beneficial role of discrete short fibers in reinforcing soils is an established concept. This lack results from tremendous difficulties in characterizing the complex interaction mechanism between fiber and soils. Based on a thorough analysis of the interaction mechanism in terms of stress and deformation pattern, this paper developed a modeling approach to predict the before-failure and failure behaviors of fiber-reinforced clay subjected to triaxial compression. The approach was built on the innovative combination of the superposition method with the energy-based homogenization technique by using two reasonable assumptions about the interaction mechanism: (1) the active fibers work in their elastic domains throughout the entire loading process; and (2) the active fibers' partial slippage along the interactive course controls the composite's before-failure behavior, whereas the failure of the composite is governed by fiber pullout. The before-failure behavior was modeled by establishing an elastoplastic stiffness matrix derived from superimposing the incremental stress contributions of the fiber phase and the clay phase described by the modified Cam-clay (MCC) model that is capable of reflecting the nonlinearity. A macroscopic failure criterion that can be used as an alert for the attainment of the failure state was developed based on the equilibrium of the rates of work dissipated on the interactive course and in the clay matrix. Good agreement of the predicted behavior with the observed response in drained triaxial compression tests verified the approach's ability in accurately reproducing the stress-strain and volumetric behavior of fiber-reinforced clay despite some discrepancies between the predicted and experimental results. The discrepancies direct the further refinement of the proposed modeling approach, which is expected to serve as an effective tool that can be used for deformation and stability analysis of fiber-reinforced geotechnical structures.