Abstract
Natural rock's geomechanical properties are inherently variable so geotechnical engineers are unavoidably faced with decision making under a degree of uncertainty. However, a traditional single property value numerical modelling design does not address this uncertainty other than by applying safety factors to the answer or using worst assumptions for parameters. With complex problems, these approaches are often impractical. To address the uncertainty involved in a roadway design, the authors have combined the popular Monte Carlo uncertainty analysis technique with a powerful non-linear numerical modelling method by means of a controlling Visual Basic program. The numerical model used is a 20 148 element representation of a stress-loaded, bolt-supported, coal mine roadway in a state of plastic yield. The combination of the time-consuming looping of the Monte Carlo technique with the already time-intensive non-linear numerical model is challenging and raises a number of issues the authors explore to assist others with this type of analysis. With a practical run-time limit of a month on a fast personal computer, the Monte Carlo analysis approach needs to be carefully controlled as less than 1000 Monte Carlo parameter combinations are available for the analysis. It should be noted that both geotechnical and geometrical parameters are varied in the analysis. The input parameters whose uncertainty has a significant impact on the numerical model output are first screened out by a one-at-a-time analysis and are then treated as random in a follow-up analysis. All the remaining inputs are assigned nominal mean values. The application of this hybrid technique to an underground coal mine roadway design is introduced in this paper. The form and distribution of the analysis results is shown to provide useful uncertainty information about the potential roof deformation of the roadway with respect to input parameters’ uncertainty.
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