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WL | delft hydraulics

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i p t i o n Design of bed- and bank protection for the bridge of

the High Speed Train (HSL)

assignment

The High Speed Train (in Dutch abbreviated into HSL), connecting Amsterdam with Paris and London, has to cross several rivers. One of them is the Hollandsch Diep river estuary. This river stretch of 1000 m wide will be crossed by a bridge with 10 piers standing in the river bed. Due tothe high flow velocities at peak discharges and the increased turbulence in the flow, induced bythe bridge piers, severe scour can be expected. Therefore, the river bed around the piers has to be protected against erosion. A new design for the bed protection was needed for different reasons.Firstly, the present bed protection of the old Moerdijk railroad bridge, built in 1872 and standingclosely to the new bridge location, is not sufficient, as every couple of years new rock had toadded. Secondly, the protection scheme of the old Moerdijk bridge is highly irregular. It variesfrom complete protection in between several piers to only local protection around some other individual piers. Thirdly, the new bridge pier design including foundation differs too much fromthe old bridge pier design.

The Engineering Consortium Hollandsch Diep, a cooperation of two Engineering Consultants,commissioned WL | Delft Hydraulics to investigate: the design reasons of the bed protection of the old Moerdijk railroad bridge; the current design hydraulic loads: flow velocities and wave loads; the conceptual design (dimensions and extension) of the new bed- and bank protection; implementation aspects.

client

Engineering Consortium Hollandsch Diep (IHD).(a cooperation of IV-Infra group and the Engineering Consultants of the city of Rotterdam).

period

2001

The location of bridge in the Northern Delta Bassin in the Netherlands

(left); a section of the bridge with a bridge pier and the river bed (middle);and a 2-D plot of the calculated wave heigths

2917

eywords:our

ydraulic structuresed protection

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project description, 2002

WL | Delft Hydraulics

WL | Delft Hydraulics

Rotterdamseweg 185

p.o. box 1772600 MH DelftThe Netherlandstelephonetelefax e-mailinternet

+31 15 285 85 85+31 15 285 85 82info@wldelft.nl

www.wldelft.nl

Decisive advice: from multidisciplinary policy

studies to design and technical assistance on

all water related issues.

the Hollandsch Diep estuary

The Hollandsch Diep is a tidal estuary and located in the lower Rhine part of the Netherlands. The river width nowadays is1000 m. Peak discharge is about 12.000 m3/sand the tidal volume is approximately 65million m3. The flow velocity is approx. 0.5m/s on average, but can increase up to morethan 1.5 m/s at peak discharges.

a historical overview

The old railroad bridge at Moerdijk was built

in 1872. In that time the Hollandsch Diepestuary was 2500 m wide, and branches and shoals covered the river bed. The constructionof the Moerdijk bridge resulted in a 1000 mnarrower Hollandsch Diep. The bridge at thattime consisted of 14 piers, two abutments and 15 spans of 100 m each. In 1872 two major branches ran through the Hollandsch Diep atthe bridge location: At the north-side the branch called the Gat van Kielen, at thesouth-side the actual branch of the HollandschDiep with in between a shoal. During bridgeconstruction these branches eroded and theengineers decided to fix both branches with

revetment in order to protect them againstfurther erosion. At the other piers rip-rap wasapplied only around the piers. When in 1932,600 m downstream of the rail road bridge, theMoerdijk bridge for traffic was constructed,the Hollandsch Diep was narrowed again for more then 400 m. This resulted in the fillingup of the Gat van Kielen at the north side of the Hollandsch Diep and the loss of 5 spans.This exists until the present day.

the design conditions

Numerical wave- and flow calculations werecarried out with the Delft Systems SWAN and SOBEK and resulted in the dominant hydraulic

design conditions for the bank- and bed protection. It showed that flow velocities upto 1.5 m/s just above the river bed and bed protection can occur. Furthermore, wind generated waves in the order of 1.5 m have to be taken into account. However, the generated orbital velocities are low due to deep water conditions and hence more or less negligiblecompared to the dominant flow conditions justabove the river bed.

conceptual design of the bed- and bank protection

The analysis of historical data and the actualdesign rules, using the present topography and flow conditions, resulted in an advice for thedimensions and extension of the bank- and bed protection, including the implementationaspects in practice. It turned out that, incontrast with the applied bed protection at theold Moerdijk bridge, bed protection isnecessary only around the piers and not in between. The involvement of WL | Delft Hydraulics has led to acost-efficient design and optimisation of implementation conditions.

Historical sketch of the cross-section of the Hollandsch Diep in 1872(left = south, right = north)

Cross-section and top-view of a pier and the bed protection