The first bored pile wall used to seal an earth dam in Finland is being constructed at the Melo hydropower plant. The dam, located on the Kokemäenjoki river in Nokia, will be repaired using nearly 200 bored piles. The project involves the deepest bored pile wall structure in Finland, as well as the largest dam ever repaired using this method.
The construction of the bored pile wall at the Melo hydropower plant started in the spring of 2022. The work is estimated to be completed by the end of the year. The repair project has already attracted interest both in Finland and abroad.
“I believe that the example of PVO-Vesivoima in the use of this new dam repair method will encourage other similar projects elsewhere. The significant thing is that the bored pile wall is a Finnish innovation, and the related competence in Finland is top-class”, says Matti Åman, asset management specialist at PVO-Vesivoima Oy.
Melo has already had visitors interested in the construction method from Central Europe, for example. The repair of the Melo hydropower plant is unique in that a bored pile wall has never before been used for repairing an earth dam in Finland. Bored pile walls are used as a permanent structure to support canal edges and bund walls, for example.
“Constructing a bored pile wall in an earth dam is exceptional. An earth dam that is subject to water pressure is a very sensitive structure, and the machines used for piling are heavy”, Åman says.
4,500 square metres of new, tight wall
A total of 193 piles will be bored in the Melo earth dam. The longest piles are nearly 70 metres long. The whole dam will be renovated. This means an area of approximately 4,500 square metres. The bottom part of the bored pile wall will be embedded into rock.
According to Åman, bored piles were chosen after years of repair efforts, as the grouting method used earlier did not yield the desired result. Sections of the earth dam where changes had been detected were earlier reinforced by grouting with concrete grout or bentonitic clay. Other repair options were not possible at Melo because they would have required the reservoir to be emptied for the repairs. The power plant will be in normal production during the work, and the repairs will not have any impact on the water level in Lake Pyhäjärvi upstream of Melo.
“As a one-time cost, the bored pile solution is more expensive, but we could not sufficiently ensure the proper condition of the dam through grouting. However, we can be sure that after this repair, the dam will be in excellent condition”, Åman says.
Finnish top-level expertise
Matti Åman appreciates the efforts of the partners taking part in the project. The contractor is KFS Finland Oy and the bored piles are delivered by SSAB. The project’s construction management and supervision consultant is Welado Oy.
“The project has progressed very well. Since this is a unique earth dam repair job, we did not have any earlier experience during the design stage on whether we could reach the rock with bored piles. However, KSF Finland is very competent and skilled for the job.”
“The success of this unique project at the Melo dam has been advanced by the excellent cooperation with PVO-Vesivoima. Our strong competences and innovative geotechnical solutions played a key role in this pioneering project, which only a few experts in special foundation construction can implement”, says Tommi Hakanen, CEO of KFS Finland.
Additional information: Matti Åman, specialist, asset management, PVO-Vesivoima Oy, matti.aman@pvo.fi, tel. +358 50 3038 621
The Melo hydropower plant
- The Melo hydropower plant was commissioned in 1971. The power plant became the property of PVO-Vesivoima in 1994. The power plant is located on the Kokemäenjoki river in Nokia, Finland.
- The capacity of the power plant is 67.9 megawatts. The plant’s head of fall is 20 metres.
- The earth dam section at Melo is about 20 metres, below which there is a 40-metre deep cast-in-place pile wall as a sealing. The total length of the dam is 123 metres. The dam has a surface area of 4,500 square metres.
- The longest piles bored into rock during the repair are 67 metres long. A total of 193 piles will be bored in the wall. The repair of the earth dam is implemented in close cooperation with the authorities supervising dams.
- A similar bored pile wall can be found at the Tripla shopping centre in Helsinki, for example.
- Bored pile walls are used in permanent structures that require a high capacity for vertical and horizontal loads.
PVO-Vesivoima Oy produces electricity with its hydropower plants on the Iijoki, Kemijoki and Kokemäenjoki rivers. The average total annual energy production output of the company is 1.7 TWh. The company is part of the Pohjolan Voima Group. www.pohjolanvoima.fi/en