Rock mass evaluation for predicting tunnel constructability in the preliminary investigation stage. Part 3. Evaluation of tunneling performance and rock mass properties of discontinuous hard rock based on the borehole core information

A method of evaluating engineering rock mass characteristics has been developed for the purpose to help the adequate selection of the detailed investigation areas, which is an important decision making for the selection of the final disposal site of high level nuclear waste in Japan. The method requires rock mass classification of qu: uniaxial strength of rock core, RQD and Jc: joint condition. Published records of tunnel excavation have been analyzed and relations between the 3 parameters and support and advance rate of excavation have been made clear. Also published in situ rock shear tests and plate jack tests in Japan have been analyzed and relation between the 3 parameter-rock mass description and rock mass properties of strength and Young's modulus have been made clear. Based on the findings, graphs of estimating the engineering rock mass characteristics of shear strength, Young's modulus, support and advance rate have been made. The features of this method are that it uses the 3 dimensional information of qu, RQD and Jc as it is instead of converting the information to one dimensional value as in RMR, and that it is based on Japanese data of in situ rock tests and tunnel excavation. (author)