  The stability of sand castles is determined by the structure of wet
granulates. Experimental data about the size distribution of fluid pockets are
ambiguous about their origin. We discovered that contact angle hysteresis plays
a fundamental role in the equilibrium distribution of bridge volumes, and not
geometrical disorder as commonly conjectured, which has substantial
consequences on the mechanical properties of wet granular beds, including a
history dependent rheology and lowered strength. Our findings are obtained
using a novel model where the Laplace pressures, bridge volumes and contact
angles are dynamical variables associated to the contact points. While
accounting for contact line pinning, we track the temporal evolution of each
bridge. We observe a cross-over to a power-law decay of the variance of
capillary pressures at late times and a saturation of the variance of bridge
volumes to a finite value connected to contact line pinning. Large scale
simulations of liquid transport in the bridge network reveal that the
equilibration dynamics at early times is well described by a mean field model.
The spread of final bridge volumes can be directly related to the magnitude of
contact angle hysteresis.
