Energy Scale in lj units

I am using lj units to simulate sheared granular flows involving cohesive particles. According to 'LIGGGHTS Documentation', in lj units mass , sigma and epsilon of particle are set to one. In case of chemical bonds, epsilon is depth of the potential well. In case of granular matter what exactly is epsilon ? How do you define this quantity for granular matter ? Can somebody please help me ?? I am stuck here for a long time....