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publicatie: Design Guideline Basal Reinforced Piled Embankments

Chapter 1 Introduction

Chapter 1 Introduction

1.1 General

Worldwide, more and more basal reinforced piled embankments are being constructed for transport infrastructure. A basal reinforced piled embankment (Fig.1.1, Fig.1.2) consists of a reinforced embankment on a pile foundation. The reinforcement consists of one or more horizontal layers of geosynthetic reinforcement (GR) installed at the base of the embankment. In use, these structures exhibit little or no residual settlement.

The force transfer in the reinforced embankment is determined by arching. This is the phenomenon where loads are transferred preferentially to the stiffer elements in the ground, in this case the piles.

Fig.1.1 A basal reinforced piled embankment.

The pile caps are preferably positioned with their tops above the groundwater level.

All possible pile systems may be used for piled embankments, providing that the difference in stiffness between the piles and the surrounding soil is sufficiently great; see Table 4.2, boundary condition 8. Important points in the structural design are the calculation of the piles’ bearing capacity, for which the regulations in force for the design of piles are used, and the dimensioning calculation for the geosynthetic reinforcement itself.

a. b.
c. d.
e. f.

Fig.1.2 Basal reinforced piled embankments under construction. (a) Krimpenerwaard N210 (Ballast Nedam, Huesker, Fugro, Movares), (b) A-15 MAVA project, source: Royal TenCate, contractor: A-Lanes (c) Piled embankment for an abutment necessary for the widening of the A2 near Beesd, the Netherlands (Voorbij Funderingstechniek, Heijmans, CRUX Engineering, Huesker and Deltares), (d) Houten railway (Movares, de Bataafse Alliantie, (ProRail, Mobilis, CFE en KWS Infra), Huesker, Voorbij Funderingstechniek, CRUX Engineering and Deltares), (e) Krimpenerwaard N210 (Ballast Nedam, Huesker, Fugro, Movares), (f) Hamburg (Naue).
Figure published before in van Eekelen (2015), [23].
Piles for the A15 piled embankment, the Netherlands

The design process for a basal reinforced piled embankment proceeds as indicated in Table 1.1. The steps 1 to 3 may be seen as the preliminary design. In these steps, the pile arrangement including pile type and GR strength are determined. Step 4 may be seen as the final design, in which additional calculations are done to determine for example bending moments in the piles, with the help of numerical calculations.

The following are considered in this publication:

  • requirements for the reinforced embankment;
  • requirements for the piles and pile caps and recommendations for pile and pile cap design;
  • design of the reinforced embankment, including calculation examples;
  • evaluation of pile moments with numerical calculations (finite element method, FEM);
  • transition zones;
  • construction and maintenance of the piled embankment.

Table 1.1 Stages of piled embankment design.

Step Designation Parts
1 Overall dimensions
  1. The geometry (thickness, width) of the embankment taking into account requirements from the surrounding area, freeboard and punching.
  2. The fill material of the embankment is chosen; the various standards impose environmental and structural requirements on the fill.
2 Calculation of the bearing capacity of the piles
  1. Both geotechnical and structural; determination of the centre-to-centre spacing of the piles. See the considerations in Chapter 3. The piles are often the largest cost item of the structure.

    At the transition to a non-piled road section, the pile spacing is sometimes increased gradually and/or the pile toe depth is reduced.
3 Design of the reinforced embankment
  1. Design calculation for the geosynthetic reinforcement (GR).
    • vertical load, based on the arching theory; this calculation is done using analytical formulae, see Chapter 4.3.2;
    • horizontal load, due to vehicle braking, centrifugal forces; see Chapters 2.4 and 6.2.;
    • horizontal load, due to lateral thrust in the slope; this calculation is done using analytical equations, see Chapter 4.3.3.
4 Checking the settlement and stability
  1. Expected settlement of the pile foundation, both geotechnical and structural.
  2. Possible bending moment in the piles, using FEM calculations, see Chapter 6.
  3. Total GR strain and in-service GR strain (due to traffic load and creep), or the expected settlement due to the GR strain.
  4. Check of the overall stability.
  5. Check of the subsoil support (if applicable).

    The settlement of the reinforced embankment and piles occurs fairly quickly after the application of load, depending on the rate at which the subsoil permits any deformation in the reinforcement. The overall settlement of a basal reinforced piled embankment is negligible, if it is designed and constructed correctly.

1.2 Eurocode

This 2016 publication update has been brought into conformity with the requirements of the European Eurocode. Table 1.2 gives an overview of the Eurocodes applied.

Table 1.2 Overview of Eurocodes*

Eurocode NEN-EN Title
NEN-EN 1990+A1+A1/ C2:2011 [3] National annex to NEN-EN 1990+A1+A1/C2: Eurocode: Basis of structural design
NEN-EN 1991-1-4+A1+C2:2011 [4] National annex to NEN-EN 1991-1-4: Eurocode 1: Loads on structures
NEN-EN 1992-1-1+C2:2011/NB:2011 [5] National annex to NEN-EN 1992-1-1+C2 Eurocode 2: Design of concrete structures - Part 1-1: General rules and rules for buildings
NEN 9997-1+C1:2012 [8] Geotechnical design of structures - Part 1: General rules
NEN-EN-ISO 22477-1:2006 [9] Geotechnical investigation and testing - Testing of geotechnical structures - Part 1: Pile load tests by static axial compression

* as valid and in force on date of this 2016 edition of this publication

The European standards mainly concern the structural design of buildings. The requirements specified in them do not always apply to other civil engineering structures, such as embankments, bridges and viaducts.