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.