The optimal placement of geogrid reinforcement in clay liners subject to differential settlement was investigated both numerically and with centrifuge modelling. Two unreinforced liners, a liner reinforced at the top-quarter depth, a liner reinforced at the bottom-quarter depth and a double reinforced liner were modelled in the centrifuge. Differential settlement was induced on the model liners by lowering a trapdoor overlain with sand. By considering: 1) the magnitude of differential settlement required to induce micro-cracks in the liners, 2) the strain fields across the liners during differential settlement and 3) the distribution of these strain fields, it was found that dividing the available reinforcement equally between the top-quarter and bottom-quarter of the liner, i.e. double reinforcement, represents the optimal reinforcement strategy.