Back Analysis Of Rock Mass Behavior Of The Quintner Limestone At The Gonzen Mine Near Sargans, Switzerland

Iron ore has been mined from Gonzen mine, in Sargans, Switzerland, since Roman times. The mine has been inactive since it closed in 1966. Observations of different failure types have been used to calibrate the likely stress field using continuum models. Observed failures included, pillar instability averaging 0.7 m deep, intersection spalling, roof collapse, and stope collapse. The latter two being localized observations. A K-o (horizontal/vertical stress) ratio between 0.8-0.9 was found to adequately capture the observed depths of failure for the pillar and intersection models. The localized roof and stope collapse models required the inclusion of bedding weakness planes to induce and localize yielding which could correctly capture the region of failure, however, the dimensions could not be correctly captured. The 2-dimensional models calibrated to the pillar instability and intersection spalling can be used as a starting point for more complex 3-dimensional models, which can represent the complex stress field, influenced locally by the mine openings and faulting. This work is part of a large study of the behavior of limestone, with a particular focus on the long term influences on excavation stability.