Dense granular suspensions that consist of concentrated mixtures of non-Brownian particles suspended in a liquid are ubiquitous in many natural phenomenon (e.g. landslides, debris flows, and sediment transport) and industrial processes (e.g. concrete and pastes). Their rheology is not fully understood and establishing a unified theoretical framework across the different flowing regimes is still challenging. The present work describes precise rheological measurements of granular suspensions in the dense regime utilizing a unique custom-built rheometer able to perform pressure- and volume-imposed rheometry. It addresses the transition from a Newtonian rheology in the Stokes limit to a Bagnoldian rheology when inertia is increased and examines whether the inertial and viscous regimes can be unified as a function of a single dimensionless number based on stress additivity. This work has been done in collaboration with M. Ichihara, O. Pouliquen and F. Tapia.