We present a constitutive model for the mechanical behavior of granular flow for both solid-like and fluid-like regimes. The stress rate tensor is decomposed into rate-independent and rate-dependent parts. The hypoplastic model is used for the rate-independent part, while the mu(I)$\mu (I)$-type rheological model is employed for the rate-dependent part. The Stokes number is introduced to capture the influence of interstitial fluid viscosity within the rate-dependent part of the model. The model performance is demonstrated through numerical simulations of element tests, encompassing both granular materials and granular-fluid mixtures.

We propose a constitutive model for both the solid-like and fluid-like behavior of granular materials by decomposing the stress tensor into quasi-static and collisional components. A hypoplastic model is adopted for the solid-like behavior in the quasi-static regime, while the viscous and dilatant behavior in the fluid-like regime is represented by a modified mu(I)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu (I)$$\end{document} rheology model. This model effectively captures the transition between solid-like and fluid-like flows. Performance and validation of the proposed model are demonstrated through numerical simulations of element tests.