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31.08.2020 16:49

Reinforcement of personnel shaft in ONKALO completed

The reinforcement of the personnel shaft in ONKALO® was completed in April. Leakage water channels and structures for the personnel lift will be installed next in the personnel shaft.

- The design process for the reinforcement work started in 2018. The method was tested in early 2019, because a fully identical structure had never been implemented before. At the same time it could be verified that the method meets both the requirements of authorities and technical criteria. The actual work started in May 2019, the Manager of Posiva's Shafts project, Mr. Jarno Säippä explains.

No major surprises were encountered in the course of the work, although it was known that there were some broken rock zones along the way. The main contractor for the work was YIT Suomi Oy.

- Bolt holes only needed to be sealed at two points due to seeping water, Mr. Säippä says.

The personnel shaft is one of the four vertical shafts in ONKALO. When the shaft is ready, vertical personnel traffic to ONKALO will take place using it. The raise boring of the personnel shaft started in 2007. The boring process was carried out in phases and completed in 2014. Other connections between the final disposal facility and the ground above include the access tunnel for vehicles, the canister shaft and two ventilation shafts.

- The reinforcement project is part of the preparations made for the installation of the lift. The purpose of reinforcement  is to prevent loose rock material from being detached from the rock and to ensure the safe operation of the personnel lift in the shaft.

The reinforcement was implemented with 1.5-metre long bolts. One reinforcement bolt was placed per every 1.4 x 1.4 -metre area, with a total of 3500 bolts installed in the shaft. The bolts and their washers also serve to anchor steel plates to the rock. The steel plates were installed in an overlapping pattern and fastened together with plate anchors. All in all, some 6600 anchors were needed.

- The lining of the shaft consists of plates made from strong and corrosion resistant duplex steel. Each plate is 2 metres thick, weighs 70 kilograms and has an area of 1.5 x 3 metres. Every reinforcement layer comprises 11 plates, Mr. Säippä says.

Installation proceeded top-down. A work platform was built in the shaft to facilitate working and lowered along the shaft as the work progressed.

- The platform could accommodate three persons at the same time. Installation work in the shaft calls for mental strength as well as technical skills. Due to the demanding conditions, special attention was naturally paid to occupational safety, Mr. Säippä stresses.
 
The personnel shaft will next be provided with leakage water channels which collect any leakage water moving behind the reinforcement structure. The installation of structures and technical systems related to the personnel lift will start in August. The lift itself will be installed in the autumn of 2021. The personnel lift delivered by KONE has a double deck lift car and a load capacity of 2 x 20 persons (or 2 x 1500 kilograms), a lifting speed of 8 metres per second and a lift travel height of 450 metres.

- The landing at a depth 437 metres will probably be the most frequently used with the lift in the personnel shaft as a lot of technical spaces are located there. The bottommost landing for the lift is at 455-metre depth where the access tunnel also terminates, Mr. Säippä concludes.

The reinforcement project of the canister shaft is also implemented this year. It follows the same principle as the reinforcement of the personnel shaft. 

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