Rock Engineering is a broad field that encompasses the design and the construction of structures that will be situated in or on rocks and also the evaluation of the stability of natural slopes. The successful design and construction of man-made structures in or on rocks and also the evaluation of the stability of natural slopes require knowledge of the rock types and characteristics that compose the site and, more importantly, knowledge of the mechanical and hydraulic properties of the rocks, including the presence of any discontinuities such as faults, joints and fractures. Geophysical methods provide tools for mapping and assessing the properties of large volumes of rock in two or three spatial dimensions, as well as over time. The geophysical response of a rock to seismic, electric and electromagnetic is a function of the rock type, fluid-content, and structural features (porosity, cracks, fractures, etc.). Thus, the goal of the application of geophysics to rock engineering is to probe a rock mass to provide the rock engineer with information on the geological, mechanical and hydraulic properties of a proposed site to aid in the design and operation of the proposed structure and also in the evaluation of natural slopes.Based on the background shown above, the Commission on the Application of Geophysics to Rock Engineering was formed in the International Society for Rock Mechanics in 1996. And I was appointed as a president of this commission. At the commission meeting in July 2007 that was held in association with the 11th ISRM Congress in Lisbon I proposed to hand over the commission president to Professor Toshifumi Matsuoka at Kyoto University, Japan. All of the commission members attended the meeting agreed my proposal and Professor Matsuoka accepted to be a president of the commission. One of the main activities of the commission is to organize international workshops, therefore, the 1st International Workshop on the Application of Geophysics to Rock Engineering was held in 1997 in New York. Since then, a series of successful workshops was held continuously, and most recently, the 8th International Workshop on the Application of Geophysics to Rock Engineering was held on June 29th in 2008 in association with the American Rock Mechanics Association San Francisco 2008 Symposium in USA. The 8th International workshop was held under the chairmanship of Professor Matsuoka with strong support by Professor Laura J. Pyrak-Nolte at Purdue University USA.About 100 pages of proceedings were published from all of the 1st to 8th workshops. However the publications of the papers presented at these workshops in the ISRM related journals were not so many. The papers presented at the 1st and the 2nd workshops were published in the special issue of the International Journal of Rock Mechanics and Mining Sciences Volume 38 Number 6 in September 2001. And the keynote lectures presented at the 4th workshop were published in the ISRM News Journal Volume 7 Number 1 in December 2001.Dr. Soichi Tanaka, who is the most active member of the ISRM Commission on the Application of Geophysics to Rock Engineering since establishment of the commission, proposed the publication of the papers presented at the 8th workshop as the special issue of the International Journal of the Japanese Committee for Rock Mechanics. This is an excellent idea and we supported it, and this special issue is going to publish. It is sure that this publication will supply much excellent information to both rock mechanics and exploration geophysics communities.I express my appreciation to all of the authors who made this special issue possible, and I would also like to thank all of the editors for their outstanding effort for the publication of this issue. Thank you.

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We developed several types of MEMS accelerometers using commercial MEMS elements for trial use in seismic surveys. Field experiments and earthquake observations were carried out for investigating the capabilities of the MEMS accelerometers. The results of these experiments and observations show that the properties of these MEMS accelerometers are similar and that they are about 1.5-3.0 times as sensitive as conventional geophones used in seismic surveys. The noise level of the MEMS 3-C accelerometer in natural earthquake observation was about 10^-4kine (cm/s), and the useable frequency band extends to below 1Hz. For future works, we will further investigate the characteristic of MEMS geophones in low frequency band using earthquake records. In addition, we will reexamine the electronic circuit and the MEMS elements in order to attain high sensitivity.

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Rock containing a compliant, fluid-filled fracture can be viewed as one case of heterogeneous poroelastic media. When this fracture is subjected to seismic waves, a strong contrast in the elastic stiffness between the fracture itself and the background can result in enhanced grain-scale local fluid flow. Because this flow—relaxing the pressure building up within the fracture—can increase the dynamic compliance of the fracture and change energy dissipation (attenuation), the scattering of seismic waves can be enhanced. Previously, for a flat, infinite fracture, we derived poroelastic seismic boundary conditions that describe the relationship between a finite jump in the stress and displacement across a fracture, expressed as a function of the stress and displacement at the boundaries. In this paper, we extend these boundary conditions to examine frequency-dependent seismic wave scattering by heterogeneous fractures. Fluid-filled fractures with a range of mechanical and hydraulic properties are examined. From parametric studies, we found that the hydraulic permeability of a fracture fully saturated with water has little impact on seismic wave scattering. In contrast, the seismic response of a partially water-saturated fracture and a heterogeneous fracture filled with compliant liquid (e.g., supercritical CO₂) depended on the fracture permeability.

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An important precondition for underground construction is a detailed knowledge of the soil and/or rock conditions in the area of the construction. In order to overcome existing limitations in classical exploration methods, research and development for exploration ahead of a tunnel face focuses on: hardware development for excavation integrated measurements, modelling and processing of data measured under these specific circumstances, and integrative interpretation of seismic results with other data from the excavation, from geological mapping, and from exploratory drilling, where available. Finite difference modelling of seismic wavefields around tunnels has shown the general feasibility of seismic measurements for imaging structures ahead of a tunnel face. The modelling results were confirmed by field measurements in various tunnel sites. The integrated interpretation of seismic data with all available geological and geotechnical information is currently in the state of development and aims, in the middle to long term perspective, at an “a priori” detection of structures ahead of the face.

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To study the rock physics model for soft sedimentary rocks widely distributed in Japan, the bimodal sand/shale mixture model, which has been proposed for sedimentary rocks, is applied to the seismic P- and S-wave logging velocity, density and porosity data. This model consists of the mixture of two different-size grains. Macroscopic elastic properties are derived from the Hashin-Strikman lower bounds, Hertz-Mindlin contact model and Gassmann’s equation. The changes of P-wave and shear moduli as functions of porosity, clay contents and confining pressure are calculated by the model and compared with the data obtained in three different soft sedimentary rocks in Japan. The model thus obtained is used for predicting porosity and clay content of the soft sedimentary rock using S-wave velocity and density logs. These applications reveal that the model can reproduce the remarkable features of soft sedimentary rocks, in which their elastic properties strongly depend on the grain size distribution and confining pressure.

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In rock engineering, the behavior of solid particles in a fluid flow has become an important topic. This paper demonstrates the effectiveness of a numerical simulation method based on the micro-mechanics of the fluid-solid interaction that couples the lattice-Boltzmann method (LBM) and the discrete element method (DEM). LBM is known to be a suitable technique for simulating fluid flow in complex and time-varying geometries with boundaries. DEM has attracted much attention among rock engineers as a useful simulation technique for large deformation problems. With the coupling of both methods, the complex motions of solid particles in a fluid flow can be simulated. To verify this, the sedimentation behavior of a single circular particle is simulated in a fluid with different Reynolds numbers, and the results are compared with FEM. In addition, the drafting, kissing, and tumbling (DKT) phenomenon between two particles in a fluid is modeled and reasonable results are obtained. The results of these case studies suggest that the method of coupling LBM and DEM can be an effective technique for simulating many kinds of engineering problems.

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A seismic wave propagating in a fluid-saturated porous rock generates relative movement between the rock matrix and the fluid. Because of the electric double layer between fluid and rock, the moving charge produces an electric field. The magnitude of the induced electric field (i. e. seismoelectric conversion) depends on rock and fluid properties, pore geometry, and seismic wave frequency. To study the seismoelectric coupling coefficients, we conducted a series of laboratory experiments in several kinds of rock samples using transient seismic waves and measuring the electric field. Experimental results show that borehole acoustic waves generate seismoelectric fields in fluid-saturated formations. The seismoelectric fields can be detected by an electrode in the borehole. The amplitude of the seismoelectric field is related not only to the seismic wave, but also to the properties of formation such as permeability, conductivity, etc. For example, the seismoelectric conversion increases as the porosity and permeability of the rock samples increase. Seismoelectric and seismomagnetic fields generated by seismic waves in fluid-saturated fractured borehole models are experimentally investigated with an electrode and a Hall-effect sensor. In a borehole with a horizontal fracture, the Stoneley waves induce seismoelectric and seismomagnetic fields in the borehole and an electromagnetic wave propagates at light speed along the borehole.

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Mixed chemical and clastic sedimentary processes form carbonate rock with fine bedding that results in a weakly directed fabric. Laboratory experiments were performed to determine the effect of fabric-controlled layering on compressional and shear wave propagation.X-ray tomographic scans of the sample found a density variation among the layers that ranged from 1700 kg/m³ to 2300 kg/m³ in a cubic sample 100 mm on edge. Wavefront imaging results show that the density contrasts among the layers produced energy confinement. The amplitude and arrival time of the compressional and shear waves are affected by saturation of the sample with water, i.e., by changing the impedance contrast among the layers.Seismic monitoring of the fluid-front during saturation indicates that the fine bedding also affects the hydraulic properties of the sample.

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