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  Reliability analysis of block fall in unsupported hard rock tunnels

  Underground structures such as tunnels require control and maintenance in order to ensure the appropriate use. A methodology for assessing the risk of block fall in unsupported tunnels was proposed using the reliability analysis, First Order Second Moment (FOSM), with the Unwedge software. This paper deals with a particular tunnel of the rail Vitoria-Minas Vale Company, Espirito Santo State, Brazil. Two types of assessment were performed, firstly with the mean values for the discontinuities properties and secondly considering the natural uncertainties of the discontinuities properties to estimate the probability of failure. The calculated factor of safety was considered acceptable (FS ranging from 1,4 to 2,0) whereas the reliability analysis revealed a high probability of failure (p~0,12) due to the high standard deviation of the orientation and the high dependency of the probability of the failure to the JRC parameter in the Barton-Bands criteria.

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