  A numerical model is used to simulate rheometer experiments at constant
normal stress on dense suspensions of spheres. The complete model includes
sphere-sphere contacts using a soft contact approach, short range hydrodynamic
interactions defined by frame-invariant expressions of forces and torques in
the lubrication approximation, and drag forces resulting from the
poromechanical coupling computed with the DEM-PFV technique. Series of
simulations in which some of the coupling terms are neglected highlight the
role of the poromechanical coupling in the transient regimes. They also reveal
that the shear component of the lubrication forces, though frequently neglected
in the literature, has a dominant effect in the volume changes. On the other
hand, the effects of lubrication torques are much less significant.
  The bulk shear stress is decomposed into contact stress and hydrodynamic
stress terms whose dependency on a dimensionless shear rate - the so called
viscous number $I_v$ - are examined. Both contributions are increasing
functions of $I_v$, contacts contribution dominates at low viscous number
($I_v<$0.15) whereas lubrication contributions are dominant for $I_v>$ 0.15,
consistently with a phenomenological law infered by other authors. Statistics
of microstructural variables highlight a complex interplay between solid
contacts and hydrodynamic interactions. In contrast with a popular idea, the
results suggest that lubrication may not necessarily reduce the contribution of
contact forces to the bulk shear stress. The proposed model is general and
applies directly to sheared immersed granular media in which pore pressure
feedback plays a key role (triggering of avalanches, liquefaction).
