Monitoring the long term stability and sinkhole of shallow underground cavities using micro-seismic technique - gypsum mine (France)

Abstract : The collapse of underground cavities (natural and manmade) can produce subsidence events on surface. The evolution of the roof instability may develop during several years before reaching the surface. To anticipate damages of buildings and infrastructures, expensive techniques are available (backfilling, pillars and roof support). In some context, monitoring may constitute a promising alternative. Micro-seismic monitoring is probably one of the most monitoring techniques adapted to the underground context. It enables to record the acoustic activity produced by disorder development within the unstable cavities. This technique was tested in an underground gypsum mine (Jura, France). This mine has been closed after more than 50 years of undermining and appears sensitive to important probability of pillars failure and sinkholes (Figure 1). In order to understand the mechanical behaviors involved, and to record the eventual seismic precursors of collapse, two micro-seismic networks were installed within two unstable zones, one mainly concerned by roof failure, the other one characterized by risk of major superimposed pillar collapse. 6 years of micro-seismic data, corresponding to 650 events, were recorded, analyzed and located. Our study shows only few significant events recorded at the deeper zone with multi-levels structure. On the opposite, the sinkhole zone is characterized by a fast evolution with high seismic activity (cracks in the overburden and frequent block falls). Sinkholes development seems to occur preferentially through major crisis (up to 95 events per 24 hours), few days after the rainiest periods. The micro-seismic method appeared to be very efficient to follow the underground sinkhole activity and to anticipate the consequences at the surface. It so may be an interesting alternative to treatment during a transitional phase during which the probability of underground failure is high.
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  • HAL Id : ineris-00970564, version 1
  • INERIS : EN-2009-416

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Cyrille Balland, Marwan Al Heib, Christophe Didier. Monitoring the long term stability and sinkhole of shallow underground cavities using micro-seismic technique - gypsum mine (France). AGU Fall Meeting 2009, Dec 2009, San Francisco, United States. ⟨ineris-00970564⟩

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