High-level radioactive waste repositories are to be designed to ensure long-term stability, and it is necessary to consider various effects at deep depth in various aspects. Especially, many uncertainties are involved in characterizing the behavior of deep rock mass in the designing process and interactions among groundwater flow, increased temperature induced by radioactive wastes and stress disturbance due to excavation should be considered. In this study, to investigate the shear characteristics of a saw-cut smooth surface of crystalline rock under various thermal-hydro-mechanical conditions, multistage triaxial tests were conducted on granitic rock. After testing, shear characteristics of the saw-cut surfaces were analyzed based on Mohr- Coulomb failure criterion. From the experimental results, it was observed that the shear characteristics of the granitic rock were sensitive to confining pressure and water pressure but not to temperature variation. Numerical analysis was conducted as well by COMSOL providing with a good agreement with experimental results.

1 Introduction

High-level radioactive waste disposal facilities are usually designed to be stable for an extended period of time as long as 10,000 years. To ensure the mechanical, hydrological and chemical stability of the facilities, long-term performance is assessed with respect to many different variables and their coupled effects. It is well-known that the international cooperative project DECOVALEX has been accumulating lots of information and knowledge of coupled processes in fractured rock masses. In addition many independent studies were carried out to investigate the T-H-M-C coupled effects in numerical and experimental methods. They include the researches by Lockner et al. (1982), Elliott & Brown(1988), Zhao & Brown(1992),Yoon & Jeon (2004) and Wanne & Young (2008).

However, few studies were carried out on the shearing behavior of a shear surface of crystalline rock under various thermal (T), hydro (H) and mechanical (M) conditions. In this study, a series of laboratory scale experiment was carried out to investigate the behavior of smooth shear surface of a crystalline rock under triaxial compression to simulate the stress condition at depth, different water pressure and temperature conditions to simulate the situation at the vicinity of a canister of high-level radioactive waste. The test results were analyzed using Mohr-Coulomb failure criterion. In addition, numerical analysis was carried out using COMSOL Multi physics to simulate the test.

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