An investigation of geosynthetic reinforced piled embankments with particular reference to embankment extremities

Abstract

The design of reinforced piled embankments is a complex soil-structure interaction problem involving embankment fill, geosynthetic reinforcement, a pile group and the soft underlying soil. In designing a reinforced piled embankment both vertical and horizontal equilibrium must be achieved. Lateral outward forces exist at the outer extremities of reinforced piled embankments and in order to achieve structural stability, this destabilizing force must be restrained to maintain equilibrium within the embankment and to limit excessive deformations. In this study, plane strain physical models of a reinforced piled embankment were investigated in a geotechnical centrifuge at up to 60 times Earth’s gravity (g). The centrifuge model facilitated the capturing of photographic images in-flight to allow the deformational response of the piled embankment to be assessed. Numerical analyses, using Plaxis 2D, replicated the centrifuge model testing to allow further assessment of the deformational response, the stress along the geosynthetic and stress in the embankment fill above the reinforcement. Direct comparison of the data from the physical and numerical models largely validated Plaxis 2D for use in the analysis of reinforced piled embankment. The analysis indicates that significant horizontal and vertical deformations occur in the reinforcement under the side slopes of reinforced piled embankments. Significant bending moments and pile head deflections were observed in the outer row of piles. Bending moments and deflections were present in all piles within the pile group. The analysis indicates that the pile group should extend for a greater distance towards the toe of the embankment than that currently recommended in BS 8006 (2010). The analysis indicated that an increase in the pile bending moment correlated to an increase of the horizontal and vertical deformation of the reinforcement and a decrease in the pile group efficacy. Significant axial tensions were recorded in the reinforcement and were seen to increase from near the crest of the embankment approximately linearly until dropping shapely to zero at the toe of the embankment.