Coastal boundaries where fast flowing ice shelves shear past stagnant, grounded ice are typically riven with surface crevasses, seawater-filled basal crevasses, and tidal strand cracks. Here we formulate a boundary condition describing stress transmission through these fractured boundaries in terms of the Coulomb law. As a result of this formulation, agreement between finite element simulations of the Ross Ice Shelf flow and field observations is improved over agreement obtained with formulations which do not account for ice failure. Our results additionally suggest that shear stress transmitted through ice shelf boundaries is lower than previously thought.