  The aim of this paper is to calculate the expansion law and chemical
enrichment of a supershell powered by the energetic feedback of a typical
Galactic OB association at various galactocentric radii. We study then the
orbits of the fragments created when the supershell breaks out and we compare
their kinetic and chemical properties with the available observations of high -
and intermediate - velocity clouds. We use the Kompaneets (1960) approximation
for the evolution of the superbubble driven by sequential supernova explosions
and we compute the abundances of oxygen and iron residing in the thin cold
supershell. We assume that supershells are fragmented by means of
Rayleigh-Taylor instabilities and we follow the orbit of the clouds either
ballistically or by means of a hybrid model considering viscous interaction
between the clouds and the extra-planar gas.Given the self-similarity of the
Kompaneets solutions, clouds are always formed ~ 448 pc above the plane. If the
initial metallicity is solar, the pollution from dying stars of the OB
association has a negligible effect on the chemical composition of the clouds.
The maximum height reached by the clouds above the plane seldom exceeds 2 kpc
and when averaging over different throwing angles, the landing coordinate
differs from the throwing coordinate ~ 1 kpc at most. The range of heights and
[O/Fe] ratios spun by our clouds suggest us that the high velocity clouds
cannot have a Galactic origin, whereas intermediate velocity clouds have
kinematic properties similar to our modeled clouds but overabundance observed
for the [O/Fe] ratios which can be reproduced only with initial metallicities
which are too low compared for those of the Galaxy disk.
