EPS 2011 Lillestrøm, Norway, June 2011 LIGHTWEIGHT EMBANKMENTS WITH EPS BLOCKS ABOVE PRESS SEWERS OF A2 EINDHOVEN BY-PASS MOTORWAY

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1 EPS 2011 Lillestrøm, Norway, June 2011 LIGHTWEIGHT EMBANKMENTS WITH EPS BLOCKS ABOVE PRESS SEWERS OF A2 EINDHOVEN BY-PASS MOTORWAY Milan Duškov InfraDelft BV, The Netherlands Eric Nijhuis Nijhuiskunststoffen BV, The Netherlands Summary Eindhoven by-pass motorway has been recently thoroughly reconstructed, including redesign of the junctions and road widening of the most sections. In the scope of road widening on two locations (at chainage 10.2 and 11.3 km) new lanes of the motorway A2 were realized above the existing pressure sewer pipes. The complicating factor here was relatively high altitudes of both the motorway and the exit roads. If a conventional embankment with sand had been applied it would have damaged the pressure sewer pipes. The implemented embankments with built-in ultra lightweight EPS blocks guaranteed sufficiently reduced vertical loads on the present sewer pipes. This paper describes the design optimization by means of the Plaxis finite element models of the lightweight embankment under consideration. INTRODUCTION Recently the extensive works on the Eindhoven by-pass motorway are completed. The sections of the A2/A67/A58 belonging to the bypass motorway were thoroughly reconstructed including redesign of the junctions and road widening of numerous sections. Also the junction De Hogt (connected the motorways A2 and A67) was completely rebuilt with new flyovers and additional lanes for all direction. Just north of the junction De Hogt the A2 motorway (at chainage 10.2 km) crosses the pressure sewer pipe Veldhoven (Figure 1). The new lanes on both sides of the A2 lie above the existing sewer pipe. The complicating factor here was the relatively high altitude of both the motorway and the exits/access roads. The maximum height of the proposed embankment or earth cover above the top the sewer pipe is 6.5 m. On the other hand, the local subsoil has good bearing capacity. No significant settlement is expected. However, a sufficiently high conventional embankment with sand would cause unacceptable vertical stresses on the pressure sewer pipes. Therefore the road widening on both sides of the motorway at chainage 10.2 km of the A2 are realized using a lightweight EPS-blocks. The preliminary design of lightweight embankment positioned above the pressure sewer pipe had to be proven as an economically justifiable solution. In the scope of the design optimization all relevant aspects were fully taken into account. The required dimensions of the EPS fill embankments were optimized regarding the allowable stress values for the sewer pipes both with and without a steel core. Therefore the cross and longitudinal sections of the alignment with the sewer pipe were modelled and analysed with the method of finite elements (program Plaxis-2D). 1

2 Figure1 The junction De Hogt of the Eindhoven bypass motorway with the pressure sewer Veldhoven at chainage 10.2 km of the motorway A2 SITUATION DESCRIPTION AND PRELIMINARY DESIGN The pressure sewer Veldhoven under the A2 motorway consists of a concrete pipe with a steel core. This tube is capable of bearing both ground pressure and the dead weight of the A2 pavement layers. (After all, the current A2 is located above the pipe section for a long time). However, the pipe under the new traffic lanes consists of a concrete sewer pipe without a steel core. Such a sewer pipe is not necessarily able to carry a conventional embankment with sand, The inner diameter of the pressure sewer pipe is 1500 mm with its upper side at 16.5 m above (Dutch) mean sea level (=AMSL). The cross section with respect to the sewer pipe route (= longitudinal profile of the A2 motorway align) with preliminary designed lightweight EPS fill is illustrated in Figure 2. The road surface is at m AMSL. Preliminary designed light weight embankment contained a 6.0 m thick EPS fill (between and m AMSL). The EPS top and bottom layer was, respectively, 12.0 and 20.0 m wide. Figure 2 Cross section with respect to the pressure sewer (= longitudinal profile of the A2 motorway) with preliminary designed 6.0 m thick lightweight embankment fill of EPS 2

3 Figure 3 illustrates the longitudinal profile (with respect to the sewer pipe route) of the eastern parallel road align. The drawing belonged to the preliminary design with undefined shape of the EPS layers in the direction of the existing traffic lanes. The lengths of the EPS layers ought to be specified according the acceptable stress values for the sewer pipe. Obviously, the pipe with a steel core can bear more and the position of the steel core boundary had significant influence on the final design. In the case of the eastern parallel road also the load caused by (the foundation of) the 3 m high noise barrier (GP04 in Figure 3) had to be taken into account. steel core boundary Figure 3 Longitudinal profile compared with respect to the pressure sewer route (= cross section of the A2 parallel roadway), including the noise barriers GP04, with preliminary (partially) designed eastern lightweight embankment with 6.0 m thick EPS fill and the road surface at to m AMSL above the pressure sewer pipe DESIGN OPTIMIZATION When dimensioning the embankment composed of EPS-blocks the maximum allowed vertical soil load as a consequence of the additional traffic lanes acted as the criterion. Two-dimensional models based on finite element program Plaxis were used to calculate the stress values along the upper side of the sewer pipe. In this way we were able to assess the effects of applying various quantities/forms of the EPS geofoam fill. The aim was to determine the actual effects of smaller widths of the EPS layers for a possible reduction of the total (preliminary prescribed) volumes. Cross section relative to sewer pipe route In the preliminary design the EPS layer was 22.0 m wide (see Figure 2) at the bottom of the embankment in the transverse direction relative to the pipe. How the upper part of the finite element models look for the selected cross-sections (relative to the pipe route) is illustrated in 3

4 Figure 4. The preliminary design was compared with (among others) an EPS geofoam fill with uniformly wide EPS layers. In all the models all surface layers were implemented as separate EPS layers as well as the subsoil layers. This also applies to the pressure sewer with an internal diameter of 1.5 m. Figure 4 - Plaxis-models of the cross sections relative to the pressure sewer route with both the preliminary and laterly reduced lightweight EPS embankment fill, and the road surface at 24.5 m AMSL above the pressure sewer pipe Plaxis calculations (Figure 5) confirmed that the preliminary design (according Figures 2 and 4 - left part) was not well thought-out. The calculated stress values on the EPS-blocks on both sides of the lowest EPS layer would definitely lead to significant permanent deformations. The sand column has locally a thickness of more than 6 m. Having in mind a representative density of sand of approximately 18 kn/m³ it would mean a total vertical stresses higher than 100 kn/m². Under such high vertical stress values even in the case of heavy EPS-types an unacceptable compression of the blocks would occur. Figure 5 - Calculated vertical deformations in the Plaxis model of the cross section related to the pressure sewer pipe route (=longitudinal profile of the A2 motorway) with the preliminary design of a lightweight embankment with a 6.0 m thick EPS geofoam fill, and the road surface at 24.5 m AMSL 4

5 Longitudinal section relative to sewer pipe route In the longitudinal direction relative to the sewer pipe route the lightweight EPS fill under the eastern parallel lanes was modelled as shown in Figure 6. The noise barriers GH02 and GP04 were also included. Actually 6.0 m high noise concrete screen GH02 was adopted as weightless because of the pile foundation. The dead weight of the 3-meter-high concrete noise barrier GP04 was implemented, and as such influenced the results of the Plaxis calculations. Figure 6 - Plaxis finite element model of the longitudinal profile with respect to the pressure sewer route (= cross section of the A2 ) of the existing and eastern new traffic lanes with the noise barriers Figure 7 - Calculated vertical displacements in the longitudinal profile relative to the sewer pipe route with a lightweight embankment under the new lanes east to the main traffic lanes of the A2 motorway Figure 7 shows the calculated vertical deformations in the longitudinal profile (with respect to the sewer pipe route) with a lightweight embankment under the new lanes east to the main traffic 5

6 lanes of the A2 motorway. Unfortunately, these results are not directly comparable with the results in the cross sections. Due to the limitations of a 2-D model, the influence of sand layers on the sides of the EPS layers on the model behaviour is excluded. In that sense there is a relatively more favourable situation than in the models for the cross sections. In any case, the figure confirms the necessity of an extra concrete slab to limit impact of the dead weight of the noise barrier GP04 on the EPS geofoam fill. Thanks to both the foundation plate and the recommended concrete slab above the EPS top layer sufficient load distribution is guaranteed. FINAL COMMENT The applied lightweight embankments with EPS-blocks enabled adequate reduction of the vertical stresses on the pressure sewer pipe after completing the new traffic lanes. In the scope of performed design optimization we paid attention to the following two aspects: 1) the possibility of designing EPS-packages with/without slope gradient in the cross-section, 2) the realization of adequate pavement structures in the longitudinal section both with and without a concrete slab above the EPS top layer, depending on the resulting load on the sewer pipe. The analysis with Plaxis provided extremely cost-effective tailor-made solutions. Figure 8 illustrates how the EPS blocks were exactly built-in under the eastern parallel lane at chainage 10.2 km of the A2 motorway. no concrete concrete slab steel core boundary Figure 8 Longitudinal profile of realized lightweight embankment below the eastern parallel lane with the installation plan for an improved and optimized 6.0 m thick EPS geofoam fill above the pressure sewer pile at chainage 10.2 km of the A2 motorway REFERENTIES 1. Duškov, M., Yap, H.S., Kreling, M. en Berkel van, P. Lichtgewicht ophogingen met EPS-blokken boven persriolen van A2 Randweg Eindhoven (in Dutch), CROW Wegbouwkundige Werkdagen, Delft - June