ESTIMATION OF THE SPECIFIC ENERGY OF TUNNEL BORING MACHINE USING POST-FAILURE BEHAVIOUR OF ROCK MASS.CASE STUDY: KARAJ-TEHRAN WATER CONVEYANCE TUNNEL IN IRAN

Performance prediction of tunnel boring machines (TBM) is the most important factor for successful tunnel excavation projects. The specific energy (SE) of TBM, defined as the amount of energy required to excavate a unit volume of rock, is one of the critical parameters used for performance prediction of these machines. Estimation of SE is very useful to design the drilling project because it is a function of many parameters such as rock mass behaviour, machine properties and project parameters. Several methods are used to estimate this parameter, such as experimental, empirical and numerical. The aim of this study is to estimate the SE considering the postfailure behaviour of rock mass. For this reason, based on the actual data from Karaj-Tehran water conveyance tunnel, a new empirical method is proposed to estimate the SE using the drop-to-deformation modulus ratio (λ). Based on the statistical analysis, the relation between the SE and λ is estimated. It is clear that the amplitude of λ, is high and to increase the correlation between mentioned parameters, the classification of data is performed. All data is classified in three classes as very weak (GSI75). Also a statistical analysis is performed to estimate the SE using the mentioned parameter (λ) in any class. The result shows that there is a direct relation between both parameters and the best correlation is achieved. So, the best equations are proposed to estimate SE using λ, considering the post failure behaviour of rock mass