Estimating the shear strength parameters of rock mass using Monte Carlo method

The shear strength parameters of rock mass fall among the most important information required for designing and stability analysis of structures excavated in the rocks. Based on this fact، Hoek and Brown suggested a method to estimate the strength and deformability parameters of jointed rock masses. In rock engineering designs، the mean values of Hoek and Brown parameters are often used. In these cases، probability analysis of rock mass properties is highly important. In this paper، based on the results obtained from rock mechanics tests carried out on rock samples of Gol-e-Gohar iron ore mine، the uncertainties in determining the shear strength parameters of the mine rock masses were modeled according to Hoek and Brown failure criteria and using Monte Carlo simulation method. Since determination of shear strength parameters of rock mass based on a specific confidence level results in the required designs of the following steps to be done based on a specific confidence level، the values of these parameters were determined with a specific confidence level. The simulation results showed that the coefficient of variation and consequently، the sparsity of the simulated data can be caused by the equations used for calculating the output parameters. Using the same inputs، higher uncertainties are present in the mathematical model of the equation that produces outputs of greater coefficient of variation compared to other equations. Therefore، the coefficient of variation and thus، the sparsity of the simulated data is smaller for the internal friction angle (due to the trigonometric equation) compared to the cohesion data. Moreover، the advantage of using distribution functions with the limits of 0 to +∞ rather than distribution functions with two infinite limits for fitting the data with small numerical values and high sparsity was shown while applying the Monte Carlo simulation method.