Reportage in Bergsäkert 2023#2
Cement rings strengthens ventilation shaft in the Renström mine
A new method using reinforced cement rings was employed when a new ventilation shaft was raisebored in the Renström mine last summer. Rock pressure is high at the site location and rock conditions are challenging.
The new shaft is 22 metres deep and begins at the mine’s 1480 metre level.
Lowering and stacking rings
The work begun by blast-hole drilling from below in the lower tunnel using a Simba production drill. Once the borehole was completed, the shaft was blasted out to a diameter of four metres. It was then filled with gravel, forming a bed for the 3.2-metre wide by 1.2-metre high cement rings. The gravel was then gradually loaded from below as each cement ring was lowered into place. Finally, the shaft opening was fitted with an iron guard ring with associated grating.
– Shaft reinforcement with cement rings is a new method; we wanted to try it as it felt right given the complicated rock conditions. Working together with Boliden, we discussed how to make the solution as good and safe as possible, says Mats Ragnarsson, Bergteamet´s Site Manager at the Renström mine.
Safe, long-term solution
Boliden Project Manager Jan Forsman agrees:
– Since we already knew the rock conditions at the shaft were difficult, we needed a safe, lasting reinforcement method. Because of the risk of rock fallout, a shaft platform with miners on to carry out reinforcement manually in the shaft was not considered safe enough, and so Bergteamet’s solution of lowering cement rings was ideal, he says.
The method was worked out in detail.
– First, Bergteamet provided a method description; this was followed by discussions in ongoing meetings, reviews and debriefings between site management, our rock engineers and Bergteamet where everyone got to have their say. We worked together and optimise the method to everyone’s satisfaction,” says Jan.
Smooth and well reinforced
The work was completed at the end of August.
– I think the result was very successful. The shaft looks good. It’s smooth, well reinforced and maintains its shape. Without a doubt, this is a really practical solution for short shafts, says Jan Forsman.
Reportage in Bergsäkert 2023#2