Underground wastewater treatment plant in Mikkeli, Finland

Mikkeli Water Utility developed new wastewater treatment plant, which is one of the most efficient and modern in Europe.

The contract covered excavation of the underground wastewater treatment plant in Metsä-Sairila, Mikkeli, grouting, rock support works, as well as the construction of a drive ramp and concrete structures in the cavity.

Mikkeli Water Utility was responsible for planning the wastewater treatment process and the procurement of equipment. We brought our special expertise in underground construction and excavation to the project. The client’s reasons for awarding the contract to us included our proven track record of equally complex excavation contracts, such as the Viikinmäki wastewater treatment plant in Helsinki and the Blominmäki wastewater treatment plant in Espoo, both in Finland.

The project involved excavation of a total of around 160,000 solid cubic metres of rock to make space for the new wastewater treatment plant. In addition to a staff of approximately 40, the construction site employed two jumbo drills, three excavators and wheeled machines, a grouting vehicle and a shotcreting robot.

The project made excellent progress, and was ahead of schedule. The rock engineering started in September 2016. By May 2017, the project progressed to the blasting of tunnel top headings, shaft excavation, and reinforcement. The horizontal excavation started in May, and the construction of concrete structures in August. The excavation and reinforcement was completed in autumn 2017, and the concrete structures in spring 2018.

The new treatment plant was due for completion in 2020, and serves a population of 69,000.

rock construction

water supply construction


Project name
Mikkeli underground wastewater treatment plant
Mikkeli Water Utility
Project status
Business segment
Tunnel excavation approx. 160,000 solid cubic metres, open excavation approx. 8,500 solid cubic metres Three shafts, approx. 2,400 solid cubic metres Rock chamber probing and grouting, approx. 30,000 metres drilled Cement used for grouting, approx. 210,100 kg The rock will be reinforced with around 14,000 bolts and 6,000 m3 of shotcrete. The rock engineering will use a total of approx. 2,700 m3 of concrete structures.