Scaled model tests on influence factors of full geosynthetic-reinforced pile-supported embankments

A geosynthetic-reinforced pile-supported (GRPS) embankment that consists of embankment fill, geosynthetic, piles, and foundation soils is a complex soil–structure system. Its key load transfer mechanisms include soil arching and tensioned membrane effects and subsoil resistance. Type of embankment fill (cohesive or cohesionless) and type of pile (end-bearing or floating) are expected to affect these load transfer mechanisms; however, their influence has not been well investigated. Six scaled model tests were conducted in this study to investigate the influence of the embankment fill properties, the clear spacing of pile caps, and the pile type on soil arching and tensioned membrane effects. This study used cohesive and cohesionless embankment fills and end-bearing and floating piles. The test results show that the cohesive embankment fill strengthened the soil-arching effect, increased the pile efficacy, and reduced the settlements of the subsoil between pile caps and the embankment crest under the same load as compared with the cohesionless embankment fill. The soil arching-effect was inversely proportional to the clear spacing of pile caps. Soil arching initiated at a low ratio of the embankment height to the clear spacing of pile caps (i.e. 0.5 to 0.7) and became stable at a higher ratio (i.e. 1.1 to 1.5). The embankment height when the soil arching becomes stable is also referred to as the critical height, at which full soil arching is formed. The measured vertical earth pressures at the edges of the pile caps were higher than those in the middle of the pile caps in all six model tests. When the end-bearing or floating piles were used, the loads on the piles (i.e. the pile efficacy) increased during the construction of the embankment. However, when the floating piles started to penetrate into the underlying soil under a higher load; the pile efficacy decreased with the embankment and the surcharge load. Floating piles resulted in less soil arching and larger settlement.