  It is shown that in a supercritical pomeron model the contribution of the
tirple-pomeron diagrams violates the unitarity bound for cross-section even
with account of the multiple pomeron exchanges between the initial hadrons.
Asymptotic behaviour of the single diffractive dissoci\-ation cross-section is
calculated in the approximation where every pomeron in the $3P$-diagram is
eikonalized as well as an elastic interaction of initial hadrons is taken into
account. In this approximation $\sigma^{SD}/\sigma_{tot}\rightarrow 0$ at
$s\rightarrow \infty.$
