Description of solid-rich suspensions in the model of internal structure

Abstract

Solid-rich suspensions play a crucial role in many areas of civil engineering, including fresh concrete, controlled low-strength materials, fluidized backfill materials, and bentonite support suspensions used in geotechnical applications. Due to the interaction between granular particles and the surrounding fluid phase, these materials exhibit complex rheological behavior that cannot be fully described by classical generalized Newtonian fluid models. In particular, structural changes within the granular network during deformation often lead to deviations between experimentally observed flow behavior and numerical predictions. This contribution presents a conceptual framework for describing such materials using an internal structure model. The approach introduces two phenomenological parameters: the angle of internal structure, representing the preferred orientation of contact networks and momentum transfer within the material, and a cohesive potential, describing the intrinsic ability of the granular-fluid system to maintain structural integrity. These parameters are interpreted as state variables that evolve with deformation and energy dissipation in the system. The model concept is motivated by observations from granular mechanics, rheological experiments, and structural analyses of particle networks. Experimental findings from oscillatory and rotational rheometry on solid-rich suspensions demonstrate how structural rearrangements influence energy dissipation and resistance to shear. The proposed framework aims to incorporate these structural effects into the description of momentum diffusion in the Navier–Stokes equation, thereby improving the representation of highly concentrated suspensions in analytical and numerical models. The presented concept provides a phenomenological bridge between classical continuum rheology and the evolving granular microstructure of solid-rich suspensions. Future work will focus on deriving explicit formulations for the modified momentum diffusion term and implementing the model in numerical simulations.