Closure of the Teutschenthal backfill mine

- challenge for a geomechanical safety concept -Till Popp, Wolfgang Minkley

Institute for Geomechanics (IfG)

Karsten Maenz, Erik FillingerGTS Teutschenthal

7th US/German Workshop on Salt Repository Research, Design and Operation

Washington, DCSeptember 7-9, 2016

ABSTRACT

Underground disposal of hazardous waste (UTD) offers the possibility of permanent and safe disposal, particularly for so-called conventional wastes (with a high proportion of toxic water-soluble materials and heavy metals). In Germany the 'TA Abfall' (Technical Instructions on Waste) only allows the construction and operation of underground disposals in salt formations. The unique host rock properties of salt rocks enable a fast and total inclusion / encapsulation of the waste and its hazardous constituents without any further barriers needed (in the best case). Furthermore, the utilization of non-mining wastes in salt mines is common for backfilling of unstable underground openings (UTV). The experiences gained from both mining applications in the past may act as industrial analogues giving useful practical information on aspects such as the design of tunnel backfills, plugs and seals for construction of radioactive waste repositories.

As prerequisite, both for UTD and UTV, a site-specific safety assessment of the random conditions (e.g. geological barrier, hydrology) has to be performed to verify that the waste will be separated from the biosphere permanently and reliably. If the used salt rock formation shows any deficits (e.g. homogeneity, thickness) properties of the host rock might become offset by means of a so-called multi-barrier system, consisting e.g. of geotechnical shaft and drift seals.

As an example with special challenges regarding the geological and mining random conditions the special situation of former potash salt mine Teutschenthal will be presented. Due to the risk of rock bursts backfilling measures with hazardous waste are being performed by the company GTS (Grube Teutschenthal Sicherungs GmbH & Co. KG) in the mined carnallite areas since 1992. Because most of the originally more than 15 mio. m3 underground openings are successfully backfilled the remaining stabilization period is around 10 y. Currently the planning run for the decommissioning of the mine consisting of a sophisticated safety concept. This paper provides a comprehensive overview of the current status and geotechnical closure concepts.