Piled Embankments Decide & Design

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Piled embankments in the Netherlands;how to decide, how to design?

Eekelen, Suzanne J.M. van1)

and Venmans, Arjan A.M.2)

1) Deltares, Technical University Delft, chair person Dutch CUR Task group ‘Design Guideline

Piled Embankments’2) Deltares and Technical University Delft

P.O. Box 177, 2600 MH Delft, The Netherlands, [email protected]

KEYWORDS Piled embankments, decision support systems, road construction methods,

soft soils, design guideline, history

ABSTRACT In the thirties of the last century, public opinion and minimizing traffichindrance were carefully considered when making choices for road constructionmethods in the Netherlands. Later, technical and financial considerations became more

leading and the public opinion less. Now, decision processes are changing further andcriteria as whole life costs and traffic hindrance are becoming more important again. Inaddition, new construction methods, such as piled embankments, including their designguidelines have become available.

The last years have brought decision support systems to quantify the impacts of choices,making the selection process more transparent. A case study for the widening of the

highway A2, and in addition several successful examples show that a contractor isstimulated to offer innovative solutions such as piled embankments when the principlesets requirements for construction time, protection of vulnerable objects or a period ofmaintenance for the contractor.

When design guidelines for these innovative solutions become available, like therecently introduced Dutch Piled embankment Design Guideline, the application of thesetechniques is further stimulated and the public demands are more easily fulfilled.

1 THE HISTORY OF ROAD CONSTRUCTION IN THE NETHERLANDS

During the last eight centuries, the Dutch have built nearly half of their

country themselves: the polders. Usually, the weak and compressible soil in

these polders gives major problems while constructing roads or railroads.

The subsoil typically consists of 6 to 18 meters of very soft and

compressible organic clay and peat deposits, and below that a firm stratum

of sand. The ground water is table just below ground surface. During many

centuries, the Dutch in these areas therefore mainly chose to travel by boat.


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However, cars and trains were developed and the need for road and

railroads grew. So, the Dutch were faced with the problem of raising sand

embankments on ground that should be considered unsuitable. A project

that finally succeeded was the construction of the railroad between Gouda

and Schoonhoven, see figure 1.

FIG. 1 Railroad Gouda-Schoonhoven; construction 1855-1914, in service 1914-

1942

It took 59 years, from 1855 to 1914, to construct the around 16 km

long railway. Five times the scheduled amount of sand was needed to finish

it, which made 65 m3 sand per meter railroad. Finally, the trains have only

been in service during 28 years until 1942, when the occupier removed the

rail steel and melted it down for war purposes.

FIG. 2 Need for wider and more reliable roads in the thirties of the last century,

source: www3.picturepush.com/photo/a/2223576/1024/Friese-B-nummers-trucks/12515.jpg


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Since the thirties of the last century, the need for more reliable and

wider roads increased with the development of more reliable diesel engines.

Keverling Buisman and his co-workers at the Dutch Institute for Soil

Mechanics developed several construction methods to build roads in the soft

Dutch polders (Heemstra, 2008). They for instance developed the road on alightweight embankment (dried peat), the road on piles (concrete slabs on

timber piles) and embankments reinforced with fascines. In order to prevent

rotting of the fascines, these mattresses needed to remain completely below

ground water table during their service life.

FIG. 3 Fascine mattress in construction

In 1937, Keverling Buisman considered both applying a fascine

mattress and a road on piles for the regional road N210 through the

Krimpenerwaard polder. He finally recommended constructing a piled road

to prevent high maintenance costs, and to “prevent complaints and

unfavourable comments” because of traffic hindrance. He thought that the

piled road would meet more “appreciation”. In other words, the publicopinion was important if not a leading aspect for Keverling Buisman.

Between 1950 and 1980 the Dutch highway network grew from

approximately 500 km to 3000 km. Construction of embankments on soft

soil became common practice, and a standard practice developed. There was

a gradual development in soil improvement from excavating and filling

cunettes, via installation of sand drains to installation of prefabricated

drains. Construction took years. Contracts were awarded on the basis of the

lowest price for a design prepared by the principal. Decisions were


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motivated by technical considerations, not by the opinion of the general

public as in the days of Keverling Buisman.

Times changed. New materials became available. For example, the

development of geosynthetic reinforcement material made it possible to

combine fascine mattresses and piled roads with concrete slabs into piledreinforced embankments. Newly developed guidelines give more security

and safety for these new construction types.

Times changed for the decision processes as well. More people and

more stakeholders have become involved. Road users cry out for solutions

for the growing traffic jams. Criteria such as whole life costs and traffic

hindrance are becoming more important again. Decision support systems

have been developed to quantify and keep track of the impacts of design

choices. Keverling Buisman would have welcomed this development!

This paper describes the current state-of-the-art in the Netherlands with

respect to selection of construction methods for embankments on soft soil,

with emphasis on the considerations related to piled embankments. In the

last decade, around 23 piled embankments have actually been constructed in

the Netherlands. Why were these actually built? In the beginning of 2010,

the Dutch Guideline for the design of piled embankments was introduced.

The clear design rules in this guideline give clarity, which makes decision

processes easier.

2 PILED EMBANKMENTS IN THE NETHERLANDS

In 1999, the construction of the first Dutch piled embankment started. Since

then, the Dutch have constructed around 22 piled embankments for roads. In

2008 the first railroad was build on a piled embankment (Van Duijnen en

Van Eekelen, 2010). The total area of these 23 piled embankments is around

300.000 m2.

From the 23 piled embankments, eight have been constructed for local

authorities (towns), six for the Dutch ministry of Public Works, five for

regional authorities (provinces) and the others for the Dutch Railways and a

knowledge institute. One of the most remarkable piled embankments is the

new N210 in the Krimpenerwaard polder, which is a 14 km long regional

road (Haring et al., 2008). The next chapter describes the main reasons for

the choice for this, and several other piled embankments.


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3 MAKING A CHOICE FOR A ROAD CONSTRUCTION METHOD

3.1 Requirements and demands

The choice for a method for road construction on soft and compressible soil

has serious implications for both construction phase and operation of the

road. Road users want the road to be available as soon as possible and do

not accept delays due to maintenance works.

In addition, when building in densely populated areas, owners of

nearby underground infrastructure or facilities do not want the construction

works to damage their property. However, the principal often has a limited

budget that is fixed in an early stage of the project.

These demands often are contradictory, as indicated in Table 1. Thetable compares the impacts of three categories of construction methods

commonly used in the Netherlands. Prefabricated vertical drains are the

default option, combined with some extra meters of sand loading as

temporary surcharge. The temporary surcharge will reduce creep

settlements during the service life of the road. The Beaudrain and IFCO

methods use a combination of underpressure in the drains and forced

dewatering to apply a temporary surcharge to the soft soil, adding to theeffect of the sand surcharge. The principle of both piled embankments and

Expanded Polystyrene (EPS) embankments is to prevent the compaction of

the soft soil, thus eliminating settlements. Although EPS is also a good

construction method, this will not be considered further in this paper.

TABLE 1 QUALITATIVE COMPARISON OF THREE CATEGORIES OF CONSTRUCTION METHODS FOR ROADCONSTRUCTION ON SOFT SOIL

Impact ofconstruction

method

Traditional: pre-fabricated vertical

drains with tempor-ary surcharge

Beaudrain or IFCOmethod withtemporarysurcharge

Piled embankment /EPS embankment

Construction time long medium short

Maintenance frequent frequent - medium none

Construction costs low medium high

Damage to nearbystructures

additional measuresrequired

can be avoided bycareful execution

unlikely

No single method fulfils all requirements. Piled embankments meet the

demands of road users and local stakeholders best, but the construction is


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generally more expensive for the principal. In the example of the N210,

strict requirements were set for creep settlements and the availability of the

existing very vulnerable road during construction. With these requirements,

and with inclusion of 20 years of maintenance in the contract, the piled

embankment came out as the most reliable solution with lowest overall cost.Another example is the piled embankment of the railroad in Houten. Here,

very limited construction time was available, and with a vulnerable

foundation next to the railroad, an innovative solution was necessary. The

piled embankment again came out as the most reliable solution with lowest

overall costs.

However, the definition of ‘lowest overall cost’ is not straightforward.

This is illustrated in the next paragraph for the widening of Dutch national

highway A2.

3.2 Case study: widening highway A2

Highway A2 is one of the main North-South arteries of the Netherlands,

stretching 200 km from Amsterdam to Maastricht. The section between

Amsterdam and Utrecht persistently topped the chart of most congestedhighways, causing an estimated loss of production of 50 million Euros

annually. It was decided to widen the existing 2x2 lane highway to 2x4

lanes, by building a new road embankment adjacent to the existing one.

Construction started in 2006, and will be completed in 2010.

The subsoil consists of 5 to 7 m of very weak and compressible peat

and organic clay deposits, with occasional buried sand channels of former

rivers. Embankments up to 8 m above ground level are required at

intersections with other infrastructure, some located at the weakest spots.

Construction settlements using conventional methods may be as large as 3

m; with a temporary surcharge of 4 m the total fill thickness reaches 15 m.

The time available for embankment filling and preloading is two years. In

this time, congestion is worse then ever because of the reduced width of the

lanes due to the construction works.

The project took off with the traditional construction method,

prefabricated vertical drains and temporary surcharge, selected for most

locations. For the high embankments, the Beaudrain and IFCO methods


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were employed. However, application of piled embankments could have

reduced both construction time and congestion during construction

significantly. What would have been the additional costs? And why were

the piled embankments not preferred over the traditional methods, given the

huge benefits for the road users?The usual approach to answer these questions is to make a design for

all construction options as basis for a cost estimate. This is often avoided

because this is time-consuming. However, the last years have brought

decision support systems to quantify the impacts of choices, making the

selection process more transparent. Computational power has increased

such that all calculations only take a few hours.

Most calculations for this case study were done with MRoad, a

decision support system dedicated to the selection of construction methods

for highways on soft soil (Venmans et al., 2005). Given the standard end

user requirements, construction time, subsoil and geometry data, the

program automatically performs settlement analysis for 8 common

construction methods. MRoad predicts maintenance actions for every

construction method, and the whole life costs for construction and

maintenance. The economic loss due to congestion during construction and

maintenance is not automatically calculated, but can be entered manually.

The case study concerns the widening in a 7 km subsection of the

project between the river Holendrecht and the town of Vinkeveen. The

subsection was characterized by 14 different combinations of subsoil

stratigraphy and road geometry. For every combination, the three

construction options presented in Table 1 have been compared. The center-

to-center distance of the prefabricated vertical drains is 1 m; the thickness of

the temporary surcharge is 2 m. The case study assumes the application of

timber piles for the piled embankment. The high ground water table in the

area is ideal for timber piles, and timber piles may be more cost effective

than concrete piles.

Three sets of calculations have been compared, assuming a required

construction time of successively 2 years, 1 year and half a year. For every

set, a combination of the three construction methods was chosen, assuming

zero maintenance in the first 10 years after opening of the road. Figure 4shows the results of the calculations.


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FIG. 4 Construction methods selected for different construction times

When the principal requires a construction time of 2 years, most parts

of the project can be realized using the traditional construction method (red)

and Beaudrain or IFCO methods (yellow). Large quantities of sand are

required to compensate settlements and for the temporary surcharge, and

substantial quantities of temporary surcharge need to be removed again.

Piled embankments (green) are necessary only in places where the new

embankment crosses the existing road and no settlements are allowed.

If the principal would allow only 1 year for construction, the traditional

and Beaudrain / IFCO methods cannot fulfil the zero maintenance

requirement. Piled embankments are the only solution for transitions to

bridges with pile foundations and in areas with strong subsoil heterogeneity.

If only half a year is available for construction, piled embankments are

the only option. The logistics of sand transport alone prohibit other

construction methods.


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The cost comparison learns that the acceleration of construction by one

and a half year would have required 8 million Euros. Asking each road user

for a fee of 0.25 Euro for one year would have raised this amount. The

Dutch economy looses 50 million Euros every year due to congestion on

highway A2 between Amsterdam and Utrecht. The subsection in the casestudy covers one third of this, but it is clear that the profit for the Dutch

economy outweighs the additional construction costs for piled

embankments. In addition, to be effective as a criterion for selecting

construction methods, the ‘overall costs’ should clearly include the profit

for society.

At the same time this – academic – case study was performed, the road

administration asked the contractor to reduce the construction time by one

year. The new design involved significant lengths of piled embankments,

probably resembling the 1 year option in Figure 4. It was for contractual,

not technical reasons that piled embankments were no part of the solution

finally adopted. The matter even led to questions in the Dutch parliament.

When asked why piled embankments were withheld, the Minister of

Transport regarded piled embankments ‘too risky’. At the time, highways

on piled embankments were performing satisfactory at six locations in the

Netherlands.

In reality, the additional costs for acceleration of construction by one

year were 33 million Euros. The difference with the case study is largely

due to the costs of changing an existing contract. But how should the

principal have stimulated short construction times from the onset of the

project?

3.3 Stimulating short construction times

Faster construction of the road embankment does not necessarily lead to

faster completion of the entire project. The availability of grounds,

relocating underground infrastructure, legal procedures and coordination

with other construction works may seriously jeopardize the theoretically

feasible gain. The present Design & Construct contracts do not give the

contractor much room to operate, since the principal has arranged most of

these matters before contracting. Accelerated completion of projects will

require either more focus on acceleration for the principal, or more freedom


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for the contractor in dealing with other stakeholders. The last is a shared

concern of contractor and principal, and it is only logical that also revenues

and the losses are shared.

Various projects in the Netherlands show what can be reached with the

changing attitude of the authorities. In the case of N210, the strictrequirements for availability and integrity of the existing road, and the

responsibility for the maintenance for the first 20 years, forced contractors

to offer innovative solutions. Lightweight EPS foam allowed the nearby 2

km long N475 to be reconstructed within a month, a bonus/penalty system

stimulating fast construction. The lightweight solution was hardly more

expensive than the traditional construction. A piled embankment turned out

to be more expensive because the logistics were less suitable for that

location. In both cases, the principal gave priority to the interests of the road

user. And in both cases, the additional costs of innovative construction

methods turned out to be limited.

4 MAKING A DESIGN FOR A EMBANKMENT

At the time that the Dutch Minister of Transport regarded piled

embankments ‘too risky’, several design methods for piled embankmentsexisted. These models tended to give completely different designs, up to a

factor 10 difference in design strength of the geosynthetic reinforcement.

For the Dutch it was not clear yet what method should be followed.

Since then, the Dutch Task Group ‘Design Guideline for Piled

Embankments’, has introduced the Dutch Design Guideline (Van Eekelen et

al., 2010a). Why should this Guideline ensure the Minister that it gives

reliable piled embankments?

The Task group evaluated the existing methods mathematically (Van

Eekelen and Bezxuijen, 2008a) and predictions were compared to finite

element calculations (Van Eekelen and Jansen, 2008b and appendix of

CUR, 2010) and several field tests. For this purpose, monitoring programs

were carried out in the Houten railway (Van Duijnen en Van Eekelen, 2010)

and in a pilot piled embankment ‘the Kyoto Road’, (Van Eekelen et al,

2010b)) and the results of the monitoring carried out by the contractor of the

N210 were also involved (Haring et al., 2008).


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The agreement between finite element calculations and the German

EBGEO was very good, the agreement between EBGEO and the field

monitoring results was better than with one of the other design methods.

Therefore, it was concluded that the arching model given in the EBGEO,

was the best available model.Thus, major parts of the EBGEO had been adopted in the Dutch

Guideline. However, constraints are adapted for Dutch circumstances as

described in Van Eekelen et al. (2010a). One of them is the reduction of the

minimum embankment height, which makes the guideline more suitable for

the flat Dutch country. In addition, the guideline has been extended with

several chapters, such as the traffic load that has to be taken into account

and two approaches for the pile design.

5 CONCLUSIONS AND FUTURE DEVELOPMENTS

While making a decision for a road construction method in the Netherlands,

the authorities increasingly often consider more aspects than construction

costs only. This leads to application of innovative techniques more

frequently. For example, when construction time and reduction of traffic

hindrance are paramount, more often innovative constructions, like a piledembankments, come out as the best option. In specific cases a piled

embankment is anyway one of the best feasible solutions, for instance if a

nearby sensitive construction has to be protected, or the available

construction time is limited.

A Dutch guideline has been introduced in the beginning of 2010,

which makes it more feasible to apply a piled embankment in the

Netherlands. Experiences with the guideline are now being acquired in

several piled embankments projects. Meanwhile, measurements continue in

the piled embankments of the N210, Houten and (only since a few months)

Woerden and laboratory experiments are being carried out in the laboratory

of Deltares. In the coming period, these measurements in field and

laboratory will be further evaluated and possibly, the Dutch Guideline can

be further improved in a few years.

R EFERENCES

CUR, 2010 Design Guideline for Piled Embankments, CUR report


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Duijnen, Piet, van, Eekelen, Suzanne, J.M. van, 2010, Monitoring of a

Railway Piled Embankment, paper nr 186 in the proc. of 9ICG,

Eekelen, S.J.M. van, Bezuijen, A. 2008a, Design of piled embankments,

considering the basic starting points of the British Design Guideline,

paper number 315 in the proceedings of EuroGeo4, September2008, Edinburgh UK

Eekelen, Suzanne van, Jansen, Hein, 2008b, verslag van een case studie, op

weg naar een Nederlandse ontwerprichtlijn voor paalmatrassen,

Geotechniek July 2008, pp. 66-71

Eekelen, S.J.M., van, Jansen, H.L., Duijnen, P.G., van, De Kant, M, Dalen,

J.H., van, Brugman, M.H.A., Stoel, A.E.C., van der., Peters,

M.G.J.M (2010a). The Dutch Design Guideline for Piled

Embankments, paper nr 120 in the proc. of 9ICG, Brazil, 2010.

Eekelen, Suzanne van, Bezuijen, Adam and Alexiew, Dimiter (2010b), The

Kyoto Road, monitoring a piled embankment, comparing 31/2 years

of measurements with design calculations, paper nr 461 in the proc.

of 9ICG, Brazil, 2010

EBGEO: Bewehrte Erdkörper auf punkt- und linienformigen Traggliedern,

Empfehlung für den Entwurf und die Berechnung von Erdkörper

mit Bewehrungen als Geokunststoffen, Ausgabe 02/2009, Kapitel

6.9. Deutsche Gesellschaft für Geotechnik e.V. Arbeitskreis 5.2

Eurocode NEN-EN 1990 – Grondslagen van het constructief ontwerp

Haring, W., Profittlich, M. & Hangen, H., 2008, Reconstruction of the

national road N210 Bergambacht to Krimpen a.d. IJssel, nl: design

approach, construction experiences and measurement results, 4th

European Geosynthetics Conf., September 2008, Edinburgh, UK .

Heemstra, Jan, 2008, Wat wij nu nog van Keverling Buisman kunnen leren:

De betekenis van klassieke matrassen in de wegenbouw voor de

paalmatras van vandaag. GeoKunst juli 2008, nr. 2, pp 54-57.

Keverling Buisman, A.S., 1937, letter to the Dutch Province of South-

Holland, February 8th, 1937, available at Deltares

Venmans, A.A.M., Förster, U., Hooimeijer, R.H. 2005. Integral design of

motorways on soft soil on the basis of whole life costs. Proc. of the

16th Int. Conf. on Soil Mechanics and Geotechnical Engineering.Osaka, Japan, Vol. 4:2867-2870. Rotterdam: Millpress.

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