STRATEGIC FLOOD PROTECTION INFRASTRUCTURE: ALTERNATIVE TECHNOLOGIES
Flood embankments and retention reservoirs and other strategic elements of flood protection infrastructure, due to their function, require reliable design and implementation. The rising prices of construction materials and costs of transport have drawn the attention of investors to solutions alternative to steel and concrete for the construction of such infrastructure. This resulted in their increased interest in the technology of vinyl sheet piles and its competitive advantages over traditional solutions.
Contrary to structures designed to constantly dam water, the flood embankments and retention reservoirs are intended to retain water on a periodical basis. The flow of such water is very often extremely dynamic and carries a number of threats. Such strategic elements of flood protection infrastructure require exceptional care in the design and construction process to protect people, animals and buildings against the catastrophic consequences of floods.
In the face of rising prices of construction materials and the costs of their transport on a global scale, designers, contractors and, above all, investors are increasingly looking for alternative technologies to construct flood protection levees and cut-off walls in the ground.
Vinyl sheet piles, introduced in the USA in the 1980s, are one of such alternative solutions to choose from. The Pietrucha Group has been manufacturing vinyl sheet piles since 2006 and the company’s R&D team has been carrying out a number of projects intended to further develop the product. One of the research directions followed by the engineers has been the reduction of the filtration coefficient. The work resulted in a vinyl sheet pile with an integrated gasket made of soft PVC. The solution significantly increases the scope of projects where vinyl sheet piles can be used to build anti-filtration barriers in the ground.
The most conspicuous advantage of vinyl sheet piles with gaskets over other available technologies, e.g. steel sheet piles or CDMM/TrenchMix barriers, lies in achieving complete tightness of the vinyl sheet pile construction immediately upon installation. There is no need to wait for the soil to clog in the locks or for the cement-soil mixture to harden. The filtration coefficient through the vinyl profile locks was achieved not by reducing the loose space inside the locks or their dimensions, which could involve the risk of damaging the locks during installation of the sheet pile in the ground, but thanks to the PVC gasket that fills in the loose space under pressure and immediately tightens the construction preventing the filtration of water or other unwelcome substances through the lock. The gasket is a fully integrated with the profile, it is not glued or welded into the lock in any way, but is thermally bonded in the post-coextrusion process.
The advantages of vinyl sheet piles technology
The technology of vinyl sheet piles has a number of competitive advantages with lower costs of material and transport being the most conspicuous ones. Usually, the prices of popular vinyl sheet pile profiles used to build tight-walls are about 30-50% lower than their steel counterparts applied in similar projects.
PVC, i.e. the material used to manufacture vinyl sheet piles, is about five times lighter than steel. As a result, more square meters of vinyl sheet piles may be loaded using a single transport unit. That is why, the transport of profiles from the factory to the construction site allows for measurable savings. In addition, the impact on the environment is also lower since less fuel is used and less exhaust fumes are emitted to the air.
Vinyl sheet piles are resistant to chemical and biological factors, do not corrode in contact with water, including salty water, so they do not require additional protective layer.
They are also made of recycled material, which makes them more sustainable. According to the comparative Life Cycle Analysis, carried out by the Lodz University of Technology, the impact of steel sheet piles on the environment is several times higher than vinyl sheet piles, when it comes to their influence on health, ecosystems, natural resources and carbon footprint.
Installation of vinyl sheet piles is similar to the installation of steel sheet piles with the same equipment used i.e. excavators, cranes or piling machines equipped with vibratory hammers. When installing PVC sheet piles, a special steel guide in the shape of the installed profile is used. This element is made and supplied by the manufacturer together with the vinyl sheet piles. Acting as a blade, the steel guide removes obstacles in the path of the driven sheet pile, such as stones and roots. Thanks to this technology, it is possible to successfully and quickly install profiles up to 13 meters long. In difficult ground conditions, in the case of profiles longer than 8 meters or when profiles need to be driven to the depth exceeding 8 meters, the guide is made of reinforced steel, ensuring rigidity and adequate strength even in difficult ground conditions.
Overview of projects using vinyl sheet piles
For over 15 years, vinyl sheet piles from Poland have been used in thousands of flood protection projects carried out in over 40 countries around the globe. Some of them deserve special attention due to their specificity and complexity.
The Gardna Polder
One of such comprehensive projects was "Embankment construction around the Gardna Polder". The project implemented in 2012-2013 was the largest investment of this type in Europe, where a total of 72,400 m2 of vinyl sheet piles with the GW-270/5.5 profile were used.
The Wrocław Water Junction
The GW-610 profile with variable wall thicknesses was also used in another large project, "The Wrocław Water Junction", implemented by the regional environmental agency in Wrocław in South-Western Poland. Vinyl sheet piles were used to reinforce and tighten the flood protection levees. The structure made of sheet piles was additionally crowned with a reinforced concrete cap, exactly the same as used in the case of steel sheet piles. A total of over 25,000 m2 of vinyl sheet piles were used in the Wrocław project.
Flood infrastructure in the Częstochowa region
Another huge project using vinyl sheet piles is a multi-stage project of modernization, reconstruction and strengthening of flood protection infrastructure of the Warta River in the Częstochowa region, Central Poland. The works were carried out in several stages with the total length of the levees to be reinforced in this project amounting to nearly 19 km. The lengths of the profiles (4.0 m and 5.5 m) have been selected in such a way as to reinforce the embankment but, at the same time, allow the flow of groundwater from the area beyond the levees towards their natural estuary, i.e. the Warta River. It was assumed that groundwater would flow under the structure. In the event of heavy rains, this solution ensures quick drying of arable land and residential areas located east of the river.
Tailings reservoir in Kazakchstan
The most demanding project implemented by the Pietrucha Group was the construction of a cut-off around the tailings reservoir at the zinc and lead opencast mine in Kazakhstan. Extremely unfavorable ground conditions and extreme temperature amplitudes did not impede the construction works, which lasted over 12 months. As many as 69,000 m2 of vinyl sheet piles with a soft PVC gasket were installed in this project, and the length of the cut-off wall is almost 9 km. The lengths of the GW-610/7.2 and GW-610/9.0 profiles ranged from 6m to 11m.
The protection of the reservoir consisted in the construction of an anti-filtration barrier made of vinyl sheet piles which were embedded one meter into the impermeable layer around the entire reservoir. This was to ensure that the groundwater will not be contaminated with extremely dangerous substances retained in the tailings reservoir.
After the trial section was completed, the client wanted to make sure that the sheet piles formed a 100% watertight barrier. A number of tests were conducted on the vinyl sheet pile locks, which consisted of digging up the sheet piles installed in the ground on both sides to a depth of 4 m, and then pouring water coloured with ink into the trench on one side.
Fig. 3. Confirmation of the tightness of vinyl sheet pile locks with a gasket without the effect of soil clogging