  We explore several classes of quadrupolar ordering in a system of
antiferromagnetically coupled quantum spin-1 dimers, which are stacked in the
triangular lattice geometry forming a bilayer. Low-energy properties of this
model is described by an $\mathcal{S}=1$ hard-core bosonic degrees of freedom
defined on each dimer-bond, where the singlet and triplet states of the
dimerized spins are interpreted as the vacuum and the occupancy of boson,
respectively. The number of bosons per dimer and the magnetic and density
fluctuations of bosons are controlled by the inter-dimer Heisenberg
interactions. In a solid phase where each dimer hosts one boson and the
inter-dimer interaction is weak, a conventional spin nematic phase is realized
by the pair-fluctuation of bosons. Larger inter-dimer interaction favors Bose
Einstein condensates (BEC) carrying quadrupolar moments. Among them, we find
one exotic phase where the quadrupoles develop a spatially modulated structure
on the top of a uniform BEC, interpreted in the original dimerized spin-1 model
as coexistent $p$-type nematic and 120$^\circ$-magnetic correlations. This may
explain an intriguing nonmagnetic phase found in Ba$_{3}$ZnRu$_{2}$O$_{9}$.
