Schacht Asse II - Instability of The Pit

Instability of The Pit

No columns and struts are used in a salt mine. The extra stress in the remaining salt structure (the pit building) by constructing the chamber is handled in the capping mass. Plasticity effects are taken into account as they naturally occur in salt domes. Significant mechanical stress is built up between the surrounding diapirs and the artificial construction. The capping mass in Asse II moves 15 cm a year which undermines the strength of the construction.

Because of the high number of tunnel constructions and the decades of use, the deformation in Asse II has reached the state that the pressurised salt is losing its stability: "The supporting construction is softening by creep deformation, plasticity effects and local fractures from the ground pressure." The Institut für Gebirgsmechanik (IfG) in Leipzig which has been monitoring Asse II since 1996 predicted in 2007 that, from the beginning of 2014, an increase in the loss of the load carrying capacity will result in an increased displacement of the capping mass. The shifts may lead to an uncontrollable increase in water inflow and make the continued operation as a dry pit impossible.

In 1979 a report on the stability of the pit building was released by a working group under the leadership of HH Juergens which describes the now imminent scenario of uncontrolled inflow from the capping mass in the southern flank resulting in the subsequent loss of the load carrying capacity. The manager of Asse II in 1979 and his advisers categorised this report as "unscientific" and declared that there were no stability problems.