Geosynthetic-reinforced soils above voids: Observation of soil and geosynthetic deformation mechanisms

Understanding how a geosynthetic-reinforced soil deforms in response to the formation of an underlying void is crucial to provide appropriate designs of these systems. Centrifuge models employing a trapdoor to simulate the void formation below a geosynthetic-reinforced sand were conducted to investigate the behaviour in a controlled environment at realistic stress levels. The plane-strain models allowed visual observations of the deformation mechanisms using Particle Image Velocimetry (PIV). These observations were used to validate assumptions about the geosynthetic behaviour made in current design recommendations, and address limitations related to the fill behaviour. Soil expansion was observed to be confined to a parabolic zone above the void related to the soil dilatancy, rather than with a single, unique coefficient of expansion. The zone of subsidence was characterised by an initial vertical prism with a funnel to the surface, with the surface settlement profile better described by a Gaussian distribution rather than the parabolic profile used historically. Detailed interpretation of the centrifuge tests has given new insight into the soil and geosynthetic behaviour relevant to how these systems deform in practice. This paves the way for more efficient design recommendations and consequently will facilitate better predictions of geosynthetic-reinforced soil behaviour above voids.