Flood Protection System – Oriental Sheet Piling

About The Project


The flood of the century in Poland along the Vistula and Odra river in 1997, and the following flood in 2001 clearly showed that the state of Polish flood protection systems required urgent modernization to fit present needs. An extensive analysis of the situation pointed out the weakest links. Further recent flood protection references rehabilitated with steel sheet piles are briefly described at the end: Lipki-Oława, Sartowice and Płonie Channel.

Flood Protection Systems Using Steel Sheet Piles


Steel sheet piling is a technology that can be utilized to achieve the objectives of modernization and improvements of dykes and flood walls. This case study focuses on the modernization and reconstruction of the Wroclaw Floodway System, currently the largest European flood protection project under construction, and the Radunia Channel in Gdansk.


Steel sheet piles have been utilized for more than 100 years, proving that it is a reliable and cost-effective solution. Typical application fields are harbour construction and temporary cofferdams.

However, steel sheet piles have also been widely used in river control structures and flood defence. They have traditionally been used for the reinforcing and protection of river banks, lock and sluice construction, and flood protection.

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Ease of use, speed of execution, long service life and the ability to be driven in the water make sheet piles the obvious choice for permanent and temporary structures.

The design of the shape of the profiles provides the maximum strength and durability at the lowest possible weight, and takes into account driveability. Depending on type of structure, applicable surcharge loads, soil and water conditions, standard hot rolled Z-type or U-type sections, as well as combined walls executed with box piles or the HZ/AZ system can be installed.

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Dyke Structures & Flood Protection Systems

 

Sheet pile walls can be used in a variety of ways for flood-defence systems or for bank protection. For new embankments they can ensure watertightness, support, and stabilization. They are also used to strengthen existing embankments. When space is an issue, e.g. in ports or urban areas, sheet pile walls can form freestanding or anchored floodwalls.

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In flood protection embankments, sheet pile walls can serve as a cutoff. The required watertightness of sheet pile cutoffs is often obtained through natural deposition of soil in the interlocks. If necessary, seepage through a sheet pile cutoff can be reduced by introducing highly effective sealing systems into the interlocks. A sheet pile cutoff not only reduces leakage, but also improves the overall stability of an embankment: sheet piles intersecting slip circles stabilize both the inner shoulder and the crest; the outer shoulder is stabilized by the lowering of the seepage line.

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Stabilization of an existing dyke
with steel sheet piles
 
With a sheet pile wall, seepage can be controlled: making the interlocks watertight reduces leakage, while natural flow can be recreated by making weep holes (see EAU 2012,R.51[1]). In the latter case the embankment is protected from drying out. A sheet pile wall cannot be burrowed through by animals or penetrated by tree roots. This eliminates the risk of backward erosion outside the wall due to prefere tial flow pathways (piping).
Extension of the flood protection system
height
Extension of the flood protection system height
with a brick wall cladding

An embankment with sheet piles can be made watertight, but it can also be modified to hold back a larger design flood without increasing the footprint of the embankment. This is a simple matter of designing the sheet pile wall to project the requisite height above the crest.

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Because of their bending strength, cantilevered sheet pile walls have no difficulty transferring high-water pressures into the body of the embankment below. And just as when they stop at the crest, cantilevered sheet pile walls also stabilize the inner shoulder, together with the crest, and lower the seepage line in the outer shoulder.

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Widening of the river cross-section and flood
retaining wall
In addition to purely static stabilization, a sheet pile wall can also - indirectly - produce beneficial effects on the overall stability of an embankment:

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• Lowering the seepage line enhances the stability of the outer shoulder which can consequently be steeper or optimized in other ways.
• Lengthening the seepage line enhances safety with respect to the risk of hydraulic failure.
• In the event of a leak through the impervious layer, a central sheet pile wall prevents the migration of fines, thereby preventing backward erosion in the landward shoulder. In addition, the wall significantly reduces the risk of piping caused by burrowing animals.
In certain river configurations, steel sheet piles can also be used to widen the cross-section of the river and act at the same time as a flood retaining wall.

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Floodway System In Wroclaw


The Wroclaw Floodway System in Poland is one of the largest European flood protection projects currently under work. Steel sheet piles from ArcelorMittal manufactured in Luxembourg and Poland are playing a crucial role in the rehabilitation of the flood protection. Wroclaw is quite an exceptional European city in many aspects. The fourth largest city in Poland has grown along River Odra which has its source in the mountains of Czech Republic. The challenge for a town planner is to cope with 12 islands and its 117 bridges. The residents of the city have a long history of fighting against floods caused by river. The construction of flood embankments dates back to the middle of the 19th century, which were upgraded with each major flood.

The existing Wroclaw Floodway System was built around 1923. It provided a high level of protection for decades until the night of the 11th of July 1997. The largest flood wave ever recorded flooded the whole city except the historic Old Town which was saved through thousands of volunteers that erected temporary barriers with sand bags. This flood left huge damages which were estimated to several billions US$.

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A consortium of highly experienced international design engineering firms has been awarded a contract to rehabil tate the existing system of river channels and flood defences, taking into account the devastating flood as well as constraints from navigation. The river Odra is still an important navigation route. To be noted that around 4 millions of cubic meters of material will be moved during this project. Additionally, one critical issue are the bridge foundations and its structure that have to be protected during the whole project.

The civil works started in 2012 and will last until 2015. ArcelorMittal has supplied more than 14000 tonnes of steel sheet piles to four different Polish general contractors. The project is funded by the Polish Government, the World Bank and the European Union Cohesion Fund.

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Borelogs

Reconstruction of the Project


The reconstruction of Weir Wroclaw no.1 is one of the major projects of the retrofit of the flood protection system in Wroclaw. The weir is located in the middle of the town, on the Odra River. It was built between 1921 and 1924, and later rehabilitated from stone & piling to a concrete structure for the purpose of increasing the level of the dam by 0.96m. It has 3 spans: left with 6.5m and 3 valves, middle with 22.4m co stant - without valves, right with 11.0m and 4 valves. The River Odra has a catchment area of over 20,000km2 at Wroclaw and has been an important route of transport tion for a long time.

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Although frequency of shipping has decreased recently, the river remains heavily regulated for navigation purposes with five gated weirs, ship locks, and two navigation canals along the flood channel.
Steel sheet piling was selected for the execution of all the works below ground water level and in the river. The investment consists in reconstructing part of the weir: the demolition of the existing weir’s middle span and construction of a new flap weir with spans of 2 x 20m directly below the existing one. To enable a safe working environment during the construction period, a cofferdam built with steel sheet piles was installed downstream, around the existing bottom concrete reinforcement, and connected to the wall surrounding the right abutment.

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Wroclaw. Weir no.1


Owner The Regional Water Management Board (RZGW) in Wroclaw
Engineer Halcrow Group Ltd | Scott Wilson | BRL Ingenierie
General Contractor Hydrobudowa Gdańsk S.A.
Sheet Piles GU 16N S 390 GP 10.0 – 15.0m
 

The sheet pile wall parallel to the axis of the weir is also used as a permanent formwork for the concrete structure. After completion of the works the downstream sheet pile wall will be cut off at river bed elevation, at the basin entrance point, and will serve as an anti-erosion protection. Model analysis showed the need of improving the conditions of hydraulic inflow into the weir, which will be achieved with the reconstruction of the retaining structures.

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The scope of the projects encompasses also the construction of two fish passes to maintain morphological continuity of the river. A sheet piling cofferdam for this structure has been connected to the weir cofferdam. Its route is parallel to left hand waterfront edge. The sheet pile wall was anchored with drilled anchors every 1.0m. After completion the sheets will be cut off at the top of fish pass walls.

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The GU 16N sections, in S 390 GP, between 10 and 15m long, were driven down into an impervious layer (clay or silt) in order to minimize the flow of water into the pits. The sheet piles were driven with a vibratory hammer PVE 2319 VM mounted on a crane.

As a result of these civil engineering works the hydraulic capacity of the Odra river at this location will increase by almost 80%. Works on job site started in 2012 and will be finished by the end of 2014.