Considering Uncertainty for Estimating Shear Strength Parameters of Intact Rock Using Statistical Methods

Summary

One of the most critical steps in design process of a surface structure by the limit equilibrium method is to determine the shear strength parameters. Because the prediction of these parameters is always accompanied with uncertainty. In such cases, if the range in which the actual shear strength parameters are located is obtained, the results are more reliable. Hence, in this paper an applied technique based on the probabilistic methods is developed. In the first step, by developing an innovative method for two widely used failure criteria, consist of Mohr-Coulomb and Hoek Brown statistical samples of shear strength parameters are generated and latter, using the t distribution in which the shear strength parameters are located with confidence 95% are determined separately for the two failure criteria. The available data from the previous researches are used for case study. The results of the case study indicate that the prediction of shear strength parameters with the presented method is more accurate than the conventional methods.

Introduction

Stability analysis of rock slopes in mining and civil structures such as surface mine walls, dams or rock slopes is very necessary and important. Because the instability of each of them will cause damages and costs. Shear strength parameters are required for stability analysis. Estimation of shear strength parameters is a critical and vital step in the design and analysis of slope stability. In the past decades, some studies reported the determination of the equivalent parameters of shear strength based on the Hoek Brown criterion. According to Brown, determination of exact equivalent shear strength parameters is challenging point due to the inherent uncertainty of rock as well as the failure criterion. Therefore, in this study, to reduce the inherent uncertainty of the rock and increasing the reliability of estimated shear strength parameters of intact rock, a statistical method is developed using statistical approaches.

Methodology and Approaches

The main objective of this study is to estimate the range that consist of the actual shear strength parameters. For this purpose, in the first step, samples of shear strength parameters are generated. Thus, date sets of different triaxial test are generated for the intact rock samples, and then cohesion and internal friction angle for each group are determined. Finally statistical samples of the shear strength parameter are produced and the range in which the actual shear strength parameters are located in is determined using the t distribution.

Results and Conclusions

Reviewing the results of case study indicates that prediction of shear strength parameters with the developed method is more accurate than the conventional methods.