  A number of recent experiments have highlighted a remarkable transformation
of a large cuprate Fermi surface into small pockets in the underdoped region
signalling a breakdown of a conventional Fermi liquid theory in the PG phase. A
few phenomenological models have been recently put forward to account for this
transformation. However, none of those models have been derived microscopically
nor are totally compatible with experimental data. In the present work we show
that the observed Fermi-surface reconstruction can be accounted for directly
within a standard microscopic $t-J$ model of correlated electrons, provided
strong electron correlations are properly taken into account.
