ABSTRACT:

The underground limestone mining industry has one of the highest fatality rates compared to all other types of mining in the United States (MSHA, 2016). Ground control issues heavily contribute to these fatalities. According to the National Institute for Occupational Safety and Health (NIOSH, 2011), structurally controlled instability is a predominant failure mechanism in underground limestone mines. Existing analysis methods, such as the limit equilibrium method, do not represent the real structure and behavior of a rock mass in-situ. The Discrete Element Method (DEM) when coupled with representative Discrete Fracture Networks (DFN) has been proven to provide accurate models of the actual response of a rock mass undergoing excavation. However, considering the statistical nature of DFN's, multiple simulations need to be run in order to obtain statistically significant results of the model. The following paper introduces a stochastic approach for analyzing rock block falls in underground excavations. This approach utilizes DEM (Itasca's 3DEC) and DFN's representing virtually mapped discontinuities obtained from terrestrial laser scans. The numerical models were carried out considering rigid blocks. Failed blocks were defined as those blocks that had displaced more than 2 cm and presented velocities indicating that the block was still in movement. This approach allows engineers to define the probability of block failure based on the geometry and weight of failed blocks formed by the intersection of discontinuities in the section of interest, as well as to define kinematics of the blocks. Such information can provide mining operators control measures to evaluate, map and mitigate risks associated with rock falls in underground mines, ultimately improving safety in the underground limestone industry.

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