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Blominmäki Wasterwater Treatment Plant – rock construction

A new underground cave system is being excavated in Blominmäki, Vantaa, for wastewater treatment basins and the related technology.

Project management, Site supervision and Safety coordination

After its completion in 2020, the new plant will replace the current Suomenoja wastewater treatment plant, at which point the wastewater of around 400,000 residents in Espoo, Kauniainen, Kirkkonummi, Siuntio and Western Vantaa will be treated there. By 2040, an estimated 150,000 cubic meters of wastewater per day is estimated to flow through the new treatment plant.

In the project, Sito Rakennuttajat Oy acts as the client’s developer consultant. At the excavation stage, the company will handle the duties of the developer consultant’s project manager and project engineer, site supervision, and safety coordination. If necessary, skilled rock construction personnel from Sito will also be involved in the project to carry out expert tasks. Sito Rakennuttajat has strong experience in different underground construction sites and has put together a capable workgroup for this demanding project to fulfill the client’s requirements and ensure that work progresses smoothly between the different stakeholders.

The demanding and multifaceted nature of the project necessitates a daily site supervision presence on the work site. Each week, the onsite situation is reported to the client. The safety coordinator makes weekly rounds of the work site and writes reports into the project bank. The developer consultant acts as the chair and takes minutes in site meetings. The situation on the work site will be reported to the client’s project management team monthly, and the developer consultant’s project manager will participate in the meetings of the project management team. Sito Rakennuttajat are also commissioned to undertake development of future sewer tunnel excavation contracts and the preparation of the competitive tendering for the contracts in cooperation with HSY. Competitive tendering will be arranged for the sewer tunnels in several separate contracts from 2017–2018, and they will be implemented in full by the time the new Blominmäki plant is brought into use.

The excavation of the Blominmäki wastewater treatment plant involves around 870,000 cubic meters of underground excavation, around 100,000 cubic meters of earth excavation and quarrying, several shafts and four large fermentation chambers. The project also includes a large amount of reinforcement and compacting work. The project is estimated to involve 1,800,000 drilling meters of grouting holes, with 1,650,000 kilograms of cement used in the grouting. Around 90,000 reinforcement bolts will be installed in the facility. The project also involves demanding reinforced concrete structures. The excavation project of the wastewater treatment plant began in September 2015, and it is scheduled to be completed by 15 January 2018.

Special features of the project include:
• particularly large amount of rock excavation, and the resulting logistics requirements for handling the blasted rock
• particularly large and high rock cavities
• the large amount of immediate reinforcement interrupting the excavation of the rock cavities
• excavation in rock that is of a poor quality in some places
• several shafts
• arranging ventilation and drying in a large cave system
• limitations on the amount of water removed from the work site due to the capacity of the sewer network:
max 5 l/s of water from Mikkelä into the sewer, and max 20 l/s from Blominmäki into the sewer
• the need to protect the soil above the rock cavity

Helsinki Region Environmental Services Authority HSY municipal federation, contact person Jukka Yli-Kuivila

Main design and architectural design / general design stage:
FCG Design and Engineering and Ramboll Finland Oy project conglomerate, contact person Juha Viitanen

Geotechnical and rock engineering design:
Pöyry Finland Oy, contact person Jari Haapala

Main contractor:
Lemminkäinen Infra Oy, contact person Pentti Nieminen