An experimental study to determine the location of the critical height in piled embankments

Geosynthetic reinforced piled embankments (GRPE's) have become an increasingly popular means of constructing on unsuitable foundation soils. However the design of GRPE's is extremely complex and relies on determining the magnitude of arching in the embankment fill and the tension in a geosynthetic reinforcement layer at the base of the embankment. Several design methods are available for estimating the magnitude of arching and the tension in the geosynthetic reinforcement. Naughton (2007) showed that the magnitude of arching and therefore the tension in the geosynthetic reinforcement can be estimated based on the concept of critical height. The critical height is a function of the frictional characteristics of the embankment fill and pile-pile cap spacing at the base of the embankment. An instrumented laboratory 1:3 scaled model of typical piled embankment geometries was used to investigate the influence of the embankment fill material properties on the location of the plane of equal settlement and therefore the influence of the critical height in the design of GRPE's. Three sand types with different strength and gradation characteristics were examined. The model was used to quantify the unrestrained arching in the model embankment. The influence of the angle of internal friction on the location of the critical height was investigated and the critical height was found to increase as the angle of internal friction increased. It was observed that when the peak angle of friction was used in the method suggested by Naughton (2007) that good agreement was found with the experimental data.