  The $abcd$-Boussinesq system is a model of two equations that can describe
the propagation of small-amplitude long waves in both directions in the water
of finite depth. Considering the Hamiltonian regimes, where the parameters $b$
and $d$ in the system satisfy $b=d>0$, small solutions in the energy space are
globally defined. Then, a variational approach is applied to establish the
existence and nonlinear stability of the set of solitary-wave solutions for the
generalized $abcb$-Boussinesq system. The main point of the analysis is to show
that the traveling-wave solutions of the generalized $abcb$-Boussinesq system
converge to nontrivial solitary-wave solutions of the generalized Korteweg-de
Vries equation. Moreover, if $p$ is the exponent of the nonlinear terms for the
generalized $abcb$-Boussinesq system, then the nonlinear stability of the set
of solitary-waves is obtained for any $p$ with $ 0 < p < p_0$ where $p_0 $ is
strictly larger than $4$, while it has been known that the critical exponent
for the stability of solitary waves of the generalized KdV equations is equal
to $ 4$.
