By rosebell
In order to providing a zinc production smelter’s underground waste storage system, Metrostav Norge has broken through on the first level of a rock hall.
Digging two mountain caves, the company is creating the extension of a waste system for zinc and zinc alloy producer Boliden Odda, whereas waste from the zinc smelter in western Norway is piped in water in a closed circuit.
With a volume of 400,000m3, these two halls are 250m long, 30m wide and up to 75m high and are being excavated in five levels, the first three levels bored by drill and blast and the last two levels by quarrying.
Additionally, the extending process of the network of access tunnels by 540m as well as excavating a new 120m-long mercury storage hall which has a volume of 22,700m3, is up to Metrostav Norge.The total excavation volume is 881,000m3.
Considering that the process of transporting the rock mass is done through the tunnel system and dumped into the sea via barges, this process is carefully monitored and managed logistically, as there are strict regulations on where on the seabed the material can be spread.
August 13 was the date of starting tunnel excavation and the project has faced several challenges. One of the most challenging aspects was the entrance to the first tunnel hall, where there are steep gradients of up to 21.5%.
Moreover, Metrostav Norge has had to negotiate the close proximity to Boliden’s existing facilities, which remain operational, while the first blasting of one hall was only 3m from Boliden’s active installations. On October 31, work on the tunnel halls was halted for 17 hours when prolonged rainfall caused landslides and flooding on roads, blocking both access routes to the entrances.
