  The compressive yield stress of particle gels shows a highly nonlinear
dependence on the packing fraction. We have studied continuous compression
processes, and discussed the packing fraction dependence with the particle
scale rearrangements. The 2D simulation of uniaxial compression was applied to
fractal networks, and the required compressive stresses were evaluated for a
wide range of packing fractions that approached close packing. The compression
acts to reduce the size of the characteristic structural entities (i.e. the
correlation length of the structure). We observed three stages of compression:
(I) elastic-dominant regime; (II) single-mode plastic regime, where the network
strengths are determined by the typical length scale and the rolling mode; and
(III) multi-mode plastic regime, where sliding mode and connection breaks are
important. We also investigated the way of losing the fractal correlation under
compression. It turns out that both fractal dimension $D_{\mathrm{f}}$ and
correlation length $\xi$ start to change from the early stage of compression,
which is different from the usual assumption in theoretical models.
