  Investigating the dynamical evolution of dust grains in proto-planetary disks
is a key issue to understand how planets should form. We identify under which
conditions dust settling can be constrained by high angular resolution
observations at mm wavelengths, and which observational strategies are suited
for such studies. Exploring a large range of models, we generate synthetic
images of disks with different degrees of dust settling, and simulate high
angular resolution (~ 0.05-0.3") ALMA observations of these synthetic disks.
The resulting data sets are then analyzed blindly with homogeneous disk models
(where dust and gas are totally mixed) and the derived disk parameters are used
as tracers of the settling factor. Our dust disks are partially resolved by
ALMA and present some specific behaviors on radial and mainly vertical
directions, which can be used to quantify the level of settling. We find out
that an angular resolution better than or equal to ~ 0.1" (using 2.3 km
baselines at 0.8mm) allows us to constrain the dust scale height and flaring
index with sufficient precision to unambiguously distinguish between settled
and non-settled disks, provided the inclination is close enough to edge-on (i
>= 75{\deg}). Ignoring dust settling and assuming hydrostatic equilibrium when
analyzing such disks affects the derived dust temperature and the radial
dependency of the dust emissivity index. The surface density distribution can
also be severely biased at the highest inclinations. However, the derived dust
properties remain largely unaffected if the disk scale height is fitted
separately. ALMA has the potential to test some of the dust settling
mechanisms, but for real disks, deviations from ideal geometry (warps, spiral
waves) may provide an ultimate limit on the dust settling detection.
