  An ensemble approach for force distributions in static granular packings is
developed. This framework is based on the separation of packing and force
scales, together with an a-priori flat measure in the force phase space under
the constraints that the contact forces are repulsive and balance on every
particle. We show how the formalism yields realistic results, both for
disordered and regular ``snooker ball'' configurations, and obtain a
shear-induced unjamming transition of the type proposed recently for athermal
media.
