Serviceability limit state design in geogrid reinforced walls and slopes

The design of geogrid reinforced walls and slopes, although a well-established science, still contains many unknowns, particularly around long-term serviceability. Serviceability, for walls and slopes, is associated with excessive deformation or damage affecting appearance, maintenance or service life. In most designs, the serviceability limit state is not considered critical. Currently, most serviceability checks do not attempt to determine or prescribe deformation limits on the built wall or slope, but rather impose limits on the theoretical mobilised strains of geogrid reinforcement, considering the unfactored imposed loads. In many cases, these prescribed post-construction allowable strain limits are based on long-term, or accelerated creep testing, undertaken when the geogrid is not interacting with soil. In some situations, designs are grossly overconservative. This paper reviews the current state of practice, summarising some of the serviceability design issues around geogrid reinforced walls and slopes, with a particular focus on long-term post-construction deformations. The paper goes on to highlight areas of non-conformity in serviceability design, between the major national codes in Europe, assessing their strengths and weaknesses. Additionally, the paper highlights potential areas of on-going and further work that may offer a better understanding of the serviceability limit state of geogrid reinforced soil walls and slopes.