A numerical procedure using a crack tensor is one method of analyzing a jointed rock mass. In this study, excavation analyses for a large-scale underground power station cavern are carried out with the finite element analysis modeling of the jointed rock mass by the crack tensors. The purpose of analyses is to investigate the influence of the stress dependency of joint stiffness on the stress and deformation around the cavern. The numerical results reveal that the numerical procedure newly taking into account the stress dependency of joint stiffness can be used to predict the deformation of the jointed rock mass more accurately than the conventional method for approximating the joint stiffness using constant values.

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In order to ensure long-term stability of structures in a rock mass, the study of time-dependent fracturing is essential. We have therefore investigated the effects of relative humidity and temperature on subcritical crack growth in rock experimentally onsamples of Kumamoto andesite, Oshima granite, Berea sandstone, Shirahama sandstone and Kushiro sandstone using the Double Torsion method. All experiments were conducted in moist air. Our results show that, in experiments conducted under the same relative humidity, crack velocity in igneous rocks increased with increasing temperature, in agreement with previous studies. On the other hand, the change of the crack velocity in sandstones at a given stress intensity factor was unclear when the temperature increased under a constant relative humidity in air. Our results also show that, in experiments conducted at the same temperature, crack velocity increased dramatically with increasing relative humidity. This increase is much larger than that expected from the conventional concept based on the theory of stress corrosion. The increase of the crack velocity was larger for sandstone which contained larger amount of clays. We conclude that subcritical crack growth in rock in air is affected remarkably by the relative humidity and the existence of clays.

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Based on the recently developed fully-coupled rigorous mathematical approach (Uenishi (2010)), this paper briefly describes the dynamic effect of multiple interactions between anti-plane shear waves and surface buildings in a town. The study has been motivated by the observation of a unique structural failure pattern caused by the 1976 Friuli, Italy, earthquake: When many structures stand next to each other in a developed area like the Friuli region, the coupling effect between multiple structures and waves propagating in the ground should be included in structural analyses (instead of employing a conventional approach where the mechanical behavior of a structure under dynamic disturbances is usually treated independently for each individual building). Indeed, the two-dimensional anti-plane elastodynamic analysis of the collective behavior of a town consisting of simplified identical buildings has shown that the buildings, standing at regular spatial intervals on a linear elastic half-space, significantly interact with each other through the elastic medium underneath and that the resonant (eigen) frequencies of the collective system (buildings in the town) become lower than that of a single building with the same mechanical characteristics. This “unexpected" phenomenon may be called the "town effect" or "city effect." The failure pattern in Friuli may better be explained by this “town effect." Just as in the 1976 popular song, “Living Next Door to Alice," we may have been living next door to this effect for a number of years (more than “twenty-four years" in the original lyrics) without noticing its cruciality. Now we might have “to get used to not living next door to" (or more exactly, have to avoid living next door to) the town effect.

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Rockburst has been one of major hazards in underground mines, including cut-and-fill mines and it must be properly prevented.The rockburst is characterized by a sudden release of strain energy in the highly stressed pillar that often causes local violent failure of the pillar. An evaluation of rockburst potential based on the ration between stored strain energy and released strain energy has been carried out. It included laboratory work where the specimens were tested in loading-unloading uniaxial compression and numerical analysis of a cut-and-fill mine. The laboratory experiments revealed that the quartz vein samples have very low to high rockburst potential whereas the numerical analysis showed that the crown pillar of quartz vein would have low to moderate rockburst potential.

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Drilling velocity and impact energy are usually used in the exploration drilling system for the geological prediction. The authors, however, propose the new drilling parameter named “Normalized Drilling Velocity Ratio" for evaluation of geological characteristics ahead of the tunnel face, using conversion analysis based on non-core drilling parameters. This new parameter, enable to neglect the change of feed pressure which gives large effect to the evaluation of other drilling parameters, is suitable for engineering classification of tunnel ground and also for detection of fault zone. Additionally, we propose the new calculation method of competence factor in the tunnel ground, which is one of the index for judgement of squeezing ground, using “Normalized Drilling Velocity Ratio". We have already studied the relation between the new drilling parameter and geological condition in Japanese tunnel excavations and close relationship between them. In this paper we show the fundamental concept and outlines of the new analysis system for exploration drilling system.

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