Deformation and failure modes of drystone retaining walls

In this paper, the factors controlling the deformation of drystone retaining walls are investigated by means of discrete element analyses. It is shown that toppling failure of unweathered drystone retaining walls is likely to occur in a brittle manner, with wall crest deflections not exceeding 1% of the backtill height until the factor of safety (based on soil strength) falls below 1.05. A compressible sub-base and weathering of the blocks will both tend to reduce the backfill height at failure to below that indicated by a limit equilibrium analysis. Bulging failure is more likely to be associated with a deterioration in block joint stiffness due to weathering than a compressible sub-base, although the latter will decrease the reduction in joint stiffness needed to cause bulging failure. Bulging is much less brittle than toppling, and the proximity to failure of bulging walls could in some circumstances be assessed on the basis of the size of the bulge.