Vinyl sheet piles used to reinforce and upgrade flood embankments which were heavily impacted with time and past floods.

This article provides insight into a project carried where vinyl sheet piles were used to successfully and, what is most important, very quickly reinforce and upgrade the existing flood embankments in an area which has been extremely susceptible to floods.

Flood embankments, due to their function, are very complex structures and their construction in Poland is subject to the provisions of the Ordinance of the Ministry of Environment*, which requires that such hydrotechnical structures be stable in all operating conditions, and in particular in the load conditions assumed in the construction design. These assumptions apply to the entire structure, as well as to its individual elements: body, escarpments, reinforcements, sealing, protective layers and drainage system.

Due to its subsurface and groundwater conditions, the region of Cz?stochowa is susceptible to floods. In 2010 and during the so-called Millennium Flood in 1997, all three rivers flowing through the city: Warta, Kucelinka and Stradomka flooded. As a result, over 36 kilometres of roads in Cz?stochowa were damaged. Losses were estimated at PLN 13 million. In the Cz?stochowa municipality, more than 2,000 residential buildings and 1,520 farm buildings were flooded. Water caused damage to 17 roads and 2 bridges. It was then that the attention was drawn to the need for reconstruction and modernisation of the over century-old flood protection structures in the region.

The challenge

In the area of Cz?stochowa, the Warta river divides into two streams, the left stream – the main river with its tributary, the Stradomka, and the right stream – the Kucelinka channel with a length of 6.87 km. Most of the flood walls in the area were built in the 1920s and 1930s from local material.

The century-old flood protection infrastructure in this area failed to fulfill its vital role, due to physical degradation resulting from repeated cycles of soaking, drying and freezing of the body of the flood embankments.

Additionally, flood embankments are subject to biological degradation as a result of decomposition of root systems and related organic decay processes. Such ecosystems are also impacted as a result of colonization by animals using walls as their habitat.

According to Polish classification, the flood embankments on both sides of the Warta were historically given Class IV importance. However taking into consideration their strategic function, they should have been classified in Class II and III, which was confirmed with the new guidelines entering into force in 2019. It became obvious that there is an urgent neet to modernize the flood protection infrastructure in the region.

This complex investment was divided into several stages, as the total length of embankments subject to reinforcement was nearly 19 kilometers.

In this publication, we focus on a section with a length of 1.7 kilometer wher our vinyl sheet piles helped expedite the construction works with minimum impact to the surrounding environment.

Subsurface and groundwater conditions

The analysis of the geological conditions confirmed that the walls were made of varying kinds of sand and covered with a layer of topsoil covered with grass. The substrate under the walls included layers of fine or medium sand. The results of the dynamic probing revealed that both the embankment and the substrate had low or medium density.

The groundwater level measured from the crown of the wall reached 3.2-4.2 m. A sample geological cross-section along the left wall of the Warta is shown in the figure below.

The solution

To ensure an efficient level of flood protection, the reinforcement of the walls included, inter alia, grubbing up trees and bushes, removing the topsoil layer, compacting the existing embankments, supplementing and compacting the earth masses to achieve the desired height of the embankment. In order to ensure the tightness of the embankment the EcoLock vinyl sheet piles GW-460/5.5 were used to form a tight-wall covered with the sysem vinyl cap. The project also assumed the construction of an emergency road with a width of 2 m at the crown of the wall. A project cross section through the crown of the wall is shown in the figure below.

The length of vinyl sheet piles was selected on the basis of the ground conditions analysis. The wall made of 4.0 m or 5.5 m long profiles ensured the tightness of the embankment but at the same time it did not prevent the flow of groundwater from adjacent area towards its natural outlet, the Warta river.

Based on the geological data, it was assumed that the groundwater will flow under the structure made of #vinylsheetpiles. In the event of heavy rainfall, such solution would ensure safety of agricultural land and residential area located east of the river.

Immediate water-tightness with the values added

It is worth highlighting that the very process of hammering of the vinyl sheet piles helped enhance the stability of the flood walls due to the additional compaction of soil in sections surrounding the sheet pile.

By performing as a retaining structure, the vinyl sheet piles also protected the area against local landslides (scouring) of the waterside slope of the wall.

What is more, vinyl sheet piles helped achieve the same level of water-tightness along the whole section, irrespective of the type of soil used in the body of the embankment and in the subsoil under the body of the wall.

The pace of the installation of vinyl sheet piles was carried out according to the guidelines of the project and it was quite impressive - 3,700 sheet piles were installed and the daily progress ranged between 30 and 40 m.

Conclusions:

The Cz?stochowa project proved that the EcoLock vinyl sheet piles serve as efficient alternative to common methods for modernising flood walls. Structures made of the vinyl sheet piles are resistant to corrosion, and their fast installation can expedite the investment, which is of special importance in cases where flood-risk is involved.

Thanks to their low weight and competitive price, the sheet piles, generate investment savings. The cost of 1 m2 of the PVC sheet pile used in this project together with its installation is several times lower than the cost of a steel sheet pile that could be used as an alternative solution in this project.

The total savings resulting from the technology of vinyl sheet piles used compared to steel sheet piling amounted to approximately PLN 3 million. Water engineering is still facing new challenges, and Pietrucha delivers solutions tailored to the needs of new realities resulting from the rapidly changing climatic conditions worldwide.

*Ordinance of the Minister of the Environment of April 20, 2007 on the technical conditions to be met by hydrotechnical structures and their location (Journal of Laws No. 86, item 579).