Focus of activities

How stable is the mine structure?

The following project was initiated to guarantee the long term security of a number of redundant potassium salt workers in the South/Harz, Saale and Unstrut area. The project became necessary because of the following potential dangers, but most importantly to protect the surface areas above these workings:

• The process of sinking at a high yearly rate, and the negative impact this has on buildings, traffic routes and sewer systems in the region
• Mining-induced seismic activity in certain areas
• Latent danger of rock fall due to a large build-up of carnallitit.

Complex geomechanical surveillance of pits

Photographic documentation captures changes over a period of time in different areas of the mine. (macroscopic mine mechanics)

Intensive usage in a hard salt gallery

With the Hydraulic Fracturing method, systematic stress tests are carried out to determine the durability and load capacity of props.

On-site carrying out of stress measuring by means of hydraulic fracturing

Together with conventional measuring of deformation on the surface and underground (convergence)as well as recordings of sink, a reliable picture of the on-site stresses and resulting deformation is achieved. In addition, a general seismic surveillance is carried out with surface and underground sensors to orientate, investigate and geotechnically analyse seismic activity.

Principles of seismic observation		Cross section of Seismogram

Various substances and methods are used in filling the mine cavity. Waste from the mining process is also used to fill and stabilize conditions in the salt crystal mine.

Rock salt mine filling below the city area of Sondershausen

Since the beginning of the 90s more and more waste has been brought to the mine in the Central German potassium mine in the form of liquid filling. The development of a suitable filling material which will meet the continuous mechanical and thermal requirements, and at the same time won't cause any long-term chemical damage, is being carried out in the department of waste and filling technology at K-UTEC. Space-filling in the form of fluids is self-levelling and within a relatively short period of time achieves high gel strenghts and will expand into unfilled chambers and hydraulically stabilize the formation.

Dynamic pressure tests in a carnallitit chamber - 80% filled with non-mining waste		DIN 4094 ram probe in a filled cavity

Observation of the surface sinking process offers proof of the success of the above filling operation. In general, it can be seen that with the start of mining the rate of sinking gradually increases and only stops completely after the site has been successfully filled.

Development over time of sink to maximal levels on the surface of a fill removal site.