Underwater blasting at Finnfors power station

The old and historic power station in Finnfors outside Skellefteå has been completely renovated to produce electricity again. The power station was established in 1934 and has been idle for nine years. 

A major task in the renovation was to reinforce the building's foundations and repair a water gate. This work was done in a dry dock with steel sheet piling around it that was fixed with concrete. 

Sensitive blasting 
In early April, the groundwork was completed, after which the dock was filled with water, the steel sheet piles were cut down and the concrete was removed to allow the water flow to return to normal.

– We were given the task of blasting away the concrete, which had to be done carefully so that no sensitive parts at the power station's foundation and near the dam gate would be damaged, says Sune Grundström, at Norrbottens Bergteknik.

Co-operative projects
The renovation was a co-operation between several actors. Contractor was responsible for the construction contract, Land & Dykservice Nord was responsible for the diving and Norrbottens Bergteknik for the blasting.
- The divers cut away the sheet piling and drilled for the charges according to our instructions. They also assisted with the loading according to our instructions," says Sune.

Although not many cubic metres of concrete were blasted away, the project still took time. The work was done under water, the castings were made in different layers with a rubber sheet in one of the layers. In addition, the loose material had to be unloaded by crane. 

– The blasting took place about five metres below the surface and was carried out from a barge. We adapted the blasting to the conditions and whenever there is water, a larger charge is needed because it is always heavier to blast under water due to the pressure, explains Sune.

First time with divers
It is not often that underwater blasting is done in this way.
- This is probably the first time we have worked with divers that I know of. Usually we build a platform with fill material that we stand on, where we then drill a pipe into the rock and charge from above in the dry. But everything has gone well in Finnfors and each blast is visible as a controlled wave ripple on the surface.