Developing an Applied Method for Determining Geomechanical Parameters of Rock Mass Considering Uncertainty

In analysis and design of rock structures, determination of geomechanical parameters is very important. Discontinuity characteristics severely affect these parameters. But uncertainty in discontinuities and inherent inhomogeneity of rock mass decreases the reliability toward the determined parameters. In this situation, considering a range of parameters leads to more reliable results. In this paper, fuzzy logic and Monte Carlo simulation are developed for considering the uncertainty in rock mass. Hoek and Brown criterion is used as the performance function. For evaluating the efficiency of this method, available data sets in the literature are used. First, by considering the uncertainty in input parameters consist of geological strength index, constant of intact rock (mi) and uniaxial compressive strength of intact rock, sets of fuzzy numbers for S, a, mb  are determined. Latter, utilizing the obtained results, geomechanical parameters of rock mass are obtained as sets of fuzzy numbers. Finally by the Monte Carlo simulation, random data are generated and for each parameter, confidence interval is determined by the 95% of confidence. Results indicate that the proposed method is reliable in problems with uncertainty in parameters and reduces the risk of design and analysis.