Abstract Stability analyses of reinforced soil structures are traditionally based on limit equilibrium calculations. Results from such analyses are sometimes ambiguous because of different assumptions made in addition to the limit state. It is shown in this paper that these ambiguities can be removed if the kinematic approach of limit analysis is used, in which a rigorous bound to the required strength of reinforcement is sought. The required strength of reinforcement is the strength needed to maintain stability of the structure. Since limit analysis leads to a rigorous bound on the reinforcement strength, limit loads, or a safety factor, the geometry of the failure mechanisms considered can be optimized, so that the best bound is obtained (a solution closest to the exact solution). A dual formulation of kinematic limit analysis is possible in terms of limit force equilibrium, but the former is preferable since the kinematics of collapse mechanisms appeals to engineering intuition more than the distribution of forces does.