Proven support of underground stopes

The Borth underground salt mine, located nearby the city of Rheinberg in North Rhine-Westphalia, is amongst the largest underground mines in Central Europe. Operated by K+S Minerals and Agriculture GmbH, the annual production volume is in the range of 2 million tons of halite. For a long time and with success, DSI Inject Systems are used for consolidation and strengthening of underground excavations, and Mineral Bolt bolting resin is used for bonding of bolts type DSI Hollow Bar System R32-280.

All mined rock salt is transported to the central hoisting shaft with belt conveyor systems. To be able to ensure a safe and efficient operation of the main as well as auxiliary belt conveyors, the operating management planned and conducted – In cooperation with DSI Underground – precautionary support measures in geotechnically stressed areas of stopes No. 101, 103, and 105.

The innovative support concept developed for the Borth mine consists of a combination of the DSI Hollow Bar System type R32-280 and Mineral Bolt silicate bolting resin. For this project, hollow bars have been installed with a customized retaining element into pre-drilled boreholes. The load-bearing capacity of the retaining element was defined to be 70% of the yield load of the R32-280 hollow bar tendon. Mineral Bolt is a fast curing two-component bolting resin on silicate basis and processed with mixing ratio of 1:1. Key features of Mineral Bolt are an optimized workability, a defined reaction time, rapid curing, and excellent bonding properties. Mineral Bolt has been extensively tested and officially approved for bolting applications in combination with the DSI Hollow Bar System.

Fully grouted bolts with a length of 3,7 to 5,7 meters are installed in two working steps. At first, the DSI Hollow Bar System is installed and the bolt head consisting of domed plate and nut is fixed and tensed up. Bonding of the hollow bars with Mineral Bolt resin is accomplished in a separate working step using a custom-specific high-pressure injection pump unit provided by DSI Underground.

In total, 2.100 m² roof area in stopes No. 101, 103 and 105 have been rehabilitated with the combined support system R32-280 and Mineral Bolt. DSI Underground did provide all support systems, high-pressure injection pump units, and injection accessories. Bolt installation and testing has been accomplished with the support of DSI Underground application engineers. All work activities have been accomplished in advance of the predefined deadline and to the owner's complete satisfaction.