Stabilisation measures
- Date
- 03/02/2012
Comprehensive stabilisation measures are being carried out in the Asse II mine on account of the rock-mechanical conditions and as a precaution against an enhanced inflow of saline solutions, which it would no longer be possible to control in case of emergency. With these measures the BfS wants to achieve that
- the deformations of the mine openings reduce and
- thus the probability of an increase in inflowing solutions reduces.
The residual stability of the Asse mine can currently be prognosticated on a scientifically reliable basis until the year 2020.
Stabilisation measures are to reduce the risk that it will no longer be possible to decommission the Asse mine in an orderly manner. Among the stabilisation measures are the so-called filling of roof clefts as well as additional measures involving the backfilling of no longer needed cavities (blind shafts, galleries etc.) in the mine with concrete.
Backfilling of roof clefts
The cavities in the former mining chambers of the southern flank were already filled with loose rock salt material earlier on. Meanwhile this stowing material has set, so that new cavities have formed at the roofs of the chambers. These so-called roof clefts are now gradually filled with Sorel concrete. This is to reduce the deformation rate of the mine openings. The objective is to reduce the risk of an enhanced inflow of water.
In December 2009, one started filling the roof clefts of mining chamber 6 on the 532-m level. Prior to this, the accompanying drift situated above the mining chamber on the 511-m level had been widened in order to place a mobile building material facility. The salt material processed above ground (rock salt and the binder magnesium oxide) is mixed with the mixing liquid (magnesium chloride solution) in the building material facility and pumped into the mining chambers via pipelines.
Altogether, one intends to fill the roof clefts of about 90 mining chambers with Sorel concrete. This is a very laborious process, as numerous preliminary and accompanying works need to be carried out, such as the sealing of accesses to chambers, boreholes for backfilling purposes and control drillings. The salt for the Sorel concrete comes from the Grasleben salt mine near Helmstedt. The salt and other building materials, such as magnesium oxide, are delivered by rail and road.
Backfilling of the area below the 800-m level
In the past, part of the cavities below 850 m was already backfilled with salt grit and magnesium chloride. Sorel concrete is now to be pumped into the cavities that are still open. Part of the uncontaminated influent saline solutions is used to mix this type of concrete.
