Erfassung und Auswertung gebirgsmechanischer Daten aus dem Salzbergwerk Berchtesgaden

Translated title of the contribution: Evaluation of rock mechanical data from the Berchtesgaden salt mine

Elisabeth Grossfurtner

Research output: ThesisMaster's Thesis

Abstract

The underground salt mine of Berchtesgaden is increasingly developing into depth. Currently, the implementation of an appropriate long-term mining system for the deeper deposit areas is under discussion. In order to maximise the extraction ratio while at the same time ensuring long-term stability, a three-dimensional geomechanical FLAC-3D model calculation of the mine workings was prepared in 2003 by the engineering office Müller & Hereth. The company's application for the enlargement of the excavation cavities at the Bavarian mining authorities is based on that calculation. In the course of the approval procedure, the authorities prescribed geomechanical in situ measuring installations to monitor the excavation cavities in the mine. The measurement data gained by these installations will be used to validate the existing rock mechanical FLAC-3D model calculation and serve as a basis for mine planning in the deeper mining areas. The present diploma thesis deals with the systematic collection and evaluation of information associated with rock mechanics in the salt mine of Berchtesgaden (e. g. historical reports of cave-ins in old caverns, results of long-term levelling observations as well as extensometer and stress monitoring measurements), with the aim of evaluating the input parameters used by Müller & Hereth for the geomechanical FLAC-3D model calculation. From historical records of visible deformations noted by miners underground (like spalling, opening and closing of fractures) no conclusions about the in situ stress situation can be drawn. Cave-ins in old workings mostly occurred when the cavern approached the layer of leached haselgebirge or inclusions of sandstone and anhydrite (Kellerbauer, 1996). The evaluation of long-term levelling data in an old mining cavern on an upper level, where no mining activities have taken place for decades, shows a maximum subsidence of the roof by 80 mm within 25 years. Due to the low overburden height and the historical cavern geometry, however, there is no direct comparability with modern caverns in salt mining regarding the rock mechanical behaviour. Rod extensometers and borehole cells to determine rock stresses were installed in 1997 in the drift above cavern no. 13 at the current extraction level in order to document the behaviour of the surrounding rock mass during the leaching process and the extension of the cavern roof area from 3.500m2 to 4.200m2. The extensometer heads also served as levelling points. Based on the evaluation of the extensometer data, the derivation of a creep rate of the haselgebirge is not possible because the measurement results do not distinguish between the creeping of saltrock and stress-induced deformations (convergence). There is also no data available from laboratory experiments. Due to the lack of information about the in situ stress situation and the creep rate, an assessment of the input parameters used by Müller & Hereth for the geomechanical model calculation is not possible. Nevertheless, as the measurements from cavern no. 13 show, the extension of the cavern roof area from 3,500m2 to 4,200m2 has no negative effects on the cavern stability. There is no formation of a fracture zone and only very slight movements (in the range of a few mm/year) around the cavern.
Translated title of the contributionEvaluation of rock mechanical data from the Berchtesgaden salt mine
Original languageGerman
QualificationDipl.-Ing.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Wagner, Horst, Supervisor (internal)
Award date25 Oct 2019
Publication statusPublished - 2019

Bibliographical note

embargoed until 07-09-2024

Keywords

  • Alpine salt mining
  • rock mechanics
  • creep behaviour of salt rock
  • bore hole cells
  • extensometer measurements
  • cavern stability

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