Statistical Analysis of the Q-system in Different Tunnelling Conditions

ABSTRACT: Understanding of the quality of a rock mass is essential in determining the expected mode of failure and the support requirement for tunnel and cavern designs. The Q-system quantifies the quality of a rock mass, but due to the complex and varied mechanisms related to ground structure interaction, a single value is unlikely to classify the variety in a rock mass correctly. Statistical methods can account for uncertainty to select the suitable design value for Q instead of a deterministic value, based on estimated Q input parameters. In this study, the Monte Carlo simulation (MCS) method is used to apply statistical analysis to the Q-system. The paper describes the basis and methodology, in conjunction with a case study, to present the use of MCS analysis, of the Q-system, to associate a quantitative level of risk with determining ground support needs for tunnel and cavern excavations.