Integrating microseismic and 3D stress monitoring with numerical modeling to improve ground hazard assessment

Abstract : INERIS and BOLIDEN are developing at Garpenberg mine (Sweden) new methodologies to monitor and to assess both quasi-static stress changes and ruptures in a seismic-prone area subject to deep mass-mining production. To achieve monitoring, a local mine seismic network has been deployed in the beginning of 2015 in the Lappberget area between 1100 and 1250 meter depth, in addition to 3D stress monitoring cells. Such network has been designed to fit with the sublevel stoping method and with the paste fill production/distribution system used by Boliden. Geophysical and geotechnical data are acquired continuously and near-to real time transferred to INERIS data centre through e.cenaris e.infrastructure for automated data processing and database management, along with mining datasets. In addition to continuous monitoring, a fine-grid 3D numerical model of the mine has been defined, in which the complex 3D shapes of the orebody and a major weakness unit are taken into account. It is submitted to successive step-by-step (exploited + backfilled stopes) simulations to assess the stress variations following a correct stress path, the plastic state, the safety factor, the strain and displacement fields, both elastic and plastic (shear and volumetric strain) energies in the mine in response to its development as stresses are monitored for quantitative comparison. Until November 2015, up to 20.000 m3 of ore were extracted within the monitored area, highlighting numerous stress shifts ranging from 0.1 MPa to 15 MPa with the stress cells. Methodology and data presented here are the preliminary results of the first year of monitoring. The study focuses on 3 main stress shifts recorded by the stress cells at level 1157, which are associated with the recorded seismicity, and then compared to the numerical model. Indeed significant immediate and differed stress shifts associated with induced microseismic events are recorded over a several-week period following the first blasts. In addition, modeling reveals that the presence of weak horizon (talc) influences the dynamic response of the mine by inducing creep and plasticity phenomena, which would explain the results obtained by geotechnical measurements and microseismicity.
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Alice Tonnellier, Christian Bouffier, Vincent Renaud, Pascal Bigarre, S. Mozaffari, et al.. Integrating microseismic and 3D stress monitoring with numerical modeling to improve ground hazard assessment. 8. International Symposium on Ground Support in Mining and Underground Construction, Sep 2016, Lulea, Sweden. ⟨ineris-01863848⟩

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