This volume of the International Journal of the Japanese Committee for Rock Mechanics presents the papers whose authors were invited to give the main lectures at the 12 ^th Japan Symposium on Rock Mechanics. We express our sincere appreciation to the lecturers for submitting their papers to this special issue. The Japan Symposium on Rock Mechanics (JSRM) has been held every three or four years since 1964 through the collaboration of the Japanese Committee for Rock Mechanics (the Japanese National Group of International Society for Rock Mechanics), the Japan Society of Civil Engineers, the Japanese Geotechnical Society, the Mining and Materials Processing Institute of Japan and the Society of Materials Science, Japan. The 12^th JSRM was held at Yamaguchi University, Ube, Japan from September 2-4, 2008. The themes of the Symposium were “Collaboration in Asia” and “Engineering Education for the Young Generation”. We invited five representative guests from Australia, China, India, Korea and Singapore, and two special guests from Japan. The technical sessions, with presentations in English, were prepared to facilitate research exchange among Japanese and foreign participants. In addition, the Symposium provided a forum for gathering together senior experts and young engineers and students. We announced our plans for the 12^th JSRM to Japanese and foreign students, as well as to former students who are working in their own countries as young engineers and researchers. We were very pleased to have 144 technical papers and seven invited lectures, and eleven exhibitors at the Symposium. The 296 participants came from eight countries. We hope that this special issue can bring back the atmosphere of the Symposium to the readers of the Journal and will lead to the development of activities in the field of Rock Mechanics around the world. Acknowledgements Special thanks are given to the editor and to the reviewers of this special issue of the Journal.

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Mining in Western Australia in the next two decades will be approaching depths and conditions in which the induced stress regimes will approach the strength of the rock masses surrounding the excavations. In such cases, failure may occur violently due to the energy stored within the rock masses. Furthermore, in those highly stressed regions of a rock mass, sudden slip on major structures in the vicinity of the excavations are more likely to occur with an associated release of energy in the form of compressive and shear waves that excite the rock near the boundaries of excavations. In order to be prepared for such scenarios, and to ensure safe and economical excavations in the future, the WA School of Mines (WASM) and a number of sponsoring companies have conceptualized and undertaken a number of research projects in ground support technology. The projects range from static and dynamic laboratory testing of support and reinforcement elements to in-situ assessment of ground support corrosivity. The project background for each of the stabilization research projects at WASM has been summarized together with details of the methodology, current status, applications and future work.

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A new risk analysis system for estimating the risk factors in tunneling is suggested in consideration of the complex effect in tunnel construction. It is verified that various risk factors can be expressed by stability and environment index using numerical and statistical analysis. Stability index includes the factors of safety of ground condition, the amount of ground settlement, condition of inflow and earthquake as a variable, and environment index includes vibration and noise by blasting under construction and train operation. The risk analysis of geotechnical stability factors were performed by classifying the factor of safety calculated SSR method, the damage of neighboring structure due to settlement, the groundwater inflow rate into the tunnel and the potential damage by the certain earthquake. Also, the environmental factors can be grouped into two aspects such as the construction stage and the operation stage; vibration, noise and the drawdown of the groundwater level caused by tunnel construction. Each risk factor was evaluated as a classified term to be the fixed quantity based on various probabilistic and statistic technique, then it was analyzed the distribution characteristic of risk along tunnel line. Then, the impact was evaluated that how much each risk factor influences on the construction cost with a tunnel construction period by analyzing social charge, so it is possible to perform reasonable tunnel design which was capable of minimizing the risk in the construction stage as well as the design stage. Finally, the applicability of quantitative risk assessment method using stability and environment index are evaluated and utilization method in designing tunnels in Korea is reviewed.

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Japan Atomic Energy Agency (JAEA) and its predecessors have been conducting an extensive geoscientific research program since the 1970’s in order to contribute to the formation of a firm scientific and technological basis for the geological disposal of high level radioactive waste in Japan. As a part of this program, in situ experiments have been performed at the Tono Mine in soft sedimentary rocks and at the Kamaishi Mine in hard crystalline rocks. An experiment on excavation disturbance has been one of these experiments and has revealed the extent and properties of the excavation disturbed zone (EDZ) and the applicability of available measurement methods. It is suggested that mechanical excavation and controlled excavation have reduced excavation damage of the rock mass around a drift, although some improvements in the currently available methods for measuring and simulating the EDZ are essential to understand excavation disturbance in more detail. JAEA is now promoting two underground research laboratory projects in Japan; the Mizunami Underground Research Laboratory (MIU) project for crystalline rocks and the Horonobe Underground Research Laboratory (Horonobe URL) project for sedimentary rocks. From a rock mechanical point of view, the major interest in these projects will be paid to failure phenomenon in deep underground, rock stress estimation at larger scales and long-term physical stability of underground structure. These projects are open for international collaboration.

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In the branch of physics called High Energy Physics, the scientists are studying the world of elementary particles. It is the research of what is taking place among these elementary particles in an ultra, ultra small scale of space and time. The knowledge we obtained there has tremendously deepened our understanding of the Nature. It is also expected to serves us as the founding stone of the sciences and technologies both at present and in the future. The High Energy Physicists around the world now have great expectations of the research programs at what is called a linear collider (LC). A linear collider is a new accelerator which provides us with a laboratory to investigate the particle interactions at energies of several hundred Giga-Electron-Volts (GeV) and beyond. The LC is currently being developed through an international collaboration where the scientists and engineers from all corners of the globe, including Asia, America and Europe, are congregated. It is called the International Linear Collider (ILC) collaboration.

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The design of NATM tunnels are often done in two dimensions, even though there are limitations. This paper uses the results from the simulation of a NATM tunnel using finite element method in three dimensions to illustrate a few observations that may aid in practical designs. These observations are three dimensional effects, which will not be apparent in two dimensional analyses. The finite element model was based on the construction of Fort Canning Tunnel, Singapore, which is an approximately 15m wide vehicular tunnel that has been constructed using NATM with applications of steel pipe umbrella method.

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The paper presents summary of the work carried out by the author on the modelling of jointed rock mass with some field applications. The equivalent continuum analyses approach presented attempts to use statistical relations, which are simple and obtained after analyzing a large data from the literature on laboratory test results of jointed rock masses. Systematic investigations were done including laboratory experiments to develop the methodologies to determine the equivalent material properties of rock mass and their stress-strain behaviour, using a hyperbolic approach. Present study covers the development of equivalent continuum model for rock mass, implementation of the model in FLAC3D for 3-dimensional applications and subsequently verification leading to real field application involving jointed rocks. The model was rigorously validated by simulating jointed rock specimens.Element tests were conducted for both uniaxial and triaxial cases and then compared with the respective experimental results. The numerical test program includes laboratory tested cylindrical rock specimens of different rock types, from plaster of Paris representing soft rock to granite representing very hard rock. The results of the equivalent continuum modelling were also compared with explicit modelling results where joints were incorporated in the model as interfaces. Several case studies have been presented with the developed model.

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