The relations between boundary yielding and the state of lateral stress in unreinforced and reinforced sand backfills has been investigated at laboratory model scale. The results have shown that lateral expansion of the backfill is necessary to attain the minimum force acting on a retaining structure. The study has also shown that such expansion of a reinforced backfill can reduce the lateral stresses to significantly below that corresponding to the 'active' earth pressure condition for an unreinforced fill. Descriptions are also given of methods of achieving controlled yielding of lateral boundaries to attain the minimum stresses acting on a wall and thus avoid problems of unserviceability of the wall or facing units. Although the results were obtained from laboratory models, such information is of considerable significance in relation to the economic design and construction of full-scale retaining structures.

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