Confined-reinforced earth with various geogrid lengths in reducing differential settlement

Reducing differential settlement between bridges and their embankments caused by an earthquake is necessary to maintain traffic, especially emergency vehicles accessing affected areas. The confined-reinforced earth (CRE) method has been proposed to strengthen the subgrade layer at the bottom of a road pavement and to ultimately reduce road surface unevenness. The method uses granular soil, geogrid layers and confining tie rods. This study presents model experiments designed to investigate the effects of embedded geogrid lengths on CRE behavior under differential settlement and cyclic (vehicle) loads. The CRE was constructed on a fixed plate to simulate a bridge abutment, and on a movable plate to simulate the settlement of an embankment. The results showed that the surface settlement distribution and the maximum surface slope of the CRE decreased with an increase in embedded geogrid length until the geogrids are sufficiently long. Beyond this length value, the deformation only changed slightly. The tensile strain in the geogrids also increased with increased embedded geogrid length under settlement, and the maximum tensile strain increased linearly with increasing settlement. The increment of tensile strain due to the cyclic load was larger for lower geogrid layers than for upper geogrid layers.