Piled embankments, influence of installation and type of loading Bezuijen, A. & Eekelen, S.J.M. van Deltares/Delft University of Technology, Delft, The Netherlands Duijnen, P. van Movares, Utrecht, The Netherlands Keywords: Piled embankments, soil support, installation procedure ABSTRACT: A calculation method for piled embankments is developed that takes into account the influence of the slack in the geotextile reinforcement (GR) after installation and the influence of a stiffer soil response during a dynamic loading. It was found that some slack in the GR before applying the fill results in less ten- sile force in the GR, but more settlement during construction. In case of significant soil support (50% of the load), 1 cm slack in a GR installed on piles spaced at 1.5 m distance led to a calculated load reduction of 16%. The extra tensile force in the geosynthetic reinforcement is significantly less for a dynamic, short duration load than for the same load when applied as a static load. 1 INTRODUCION Various calculation methods exist for the design of the geosynthetic reinforcement (GR) in an embank- ments on piles (for example BS8006, 1995 and EB- GEO, 2009). These take into account the weight of the fill and the traffic load. Some (for example EBGEO) also take into account the resistance of the soft soil between the piles against deformation. This resistance may reduce the tensile force in the GR significantly. All calculation methods however, only take into account the traffic load as a static one and only static parameters for the reaction of the soft subsoil. Heitz (2006) showed the degradation of the subsoil due to long-term dynamic loading in a large compression test. Furthermore, with piled embankment experi- ments he found that dynamic loading may disrupt the soil arch in the embankment, leading to a larger loading on the GR. This last phenomenon is also found in field measurements (Eekelen et al, 2010). An ‘advantage’ of dynamic loading is, however, that it is present only for short periods. In a real situ- ation, for example in a piled embankment below a railway, there will be a static loading, (the fill on top of the piles and the GR) and a short time dynamic loading when a train passes. For saturated subsoil the effective stiffness will be much larger in a dy- namic situation than in a static one because consoli- dation is hardly possible in a dynamic situation. This paper describes the influence of the higher dynamic stiffness of the subsoil on the loading on the GR. It uses elements from the existing calcula- tions methods to calculate the static loading situation and uses that situation as a starting point for the dy- namic loading. No real dynamic calculation is per- formed but the dynamic load is added as a static load, assuming a stiffer soil response (load part C). The method shows, apart from the influence of the static and dynamic soil stiffness, also the influence of the installation of the GR. Some slack in the GR during installation leads to more settlement of the embankment during the construction phase, but after this settlement, a stiffer reaction occurs. 2 FORCES IN A PILED EMBANKMENT In a piled embankment the weight of the embank- ment is distributed into three parts (Eekelen et al, 2010), see Figure 1. A A A A C C C C C C B B B B B B A A A A C C C C C C C C B B B B B B B B Figure 1. Sketch of a piled embankment with the distribution of the weight of the embankment in the load parts A, B and C, see text. • Load part A is transferred directly to the pile caps through arching, 9 th International Conference on Geosynthetics, Brazil, 2010 1921