In order to examine the accuracy of stress determination by stress relief of over-core around a strain meter buried into borehole, the authors worked out the axi-symmetrical problem in that far field stress state to be measured is hydrostatic and the closed form solution obtained is shown in this paper.

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It is essential to know the properties of the rock ahead of the face when digging a tunnel. We examined long-hole exploration drilling as a method of determining the rock properties with the objective of establishing an improved procedure for such surveys. This report describes the results of the development of an improved system for exploration drilling. For convenience, the system, including its data-storage package, was designed to be mounted on a drill jumbo. A large-diameter rod was used at the tip of the extension rods to prevent deviation of the hole, after testing had indicated that this was an issue. A rod with an integrated coupling sleeve was employed to reduce the time required for the test. Dedicated software was also developed to enable semi-automated processing of the data. The above features make the system convenient to use, and provide accurate data of the rock properties ahead of the tunnel face.

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This paper describes the results regarding the measurements and analysis to investigate the characteristics of ground surface settlement when a tunnel is advanced through unconsolidated ground. Rokunohe tunnel is a 3,810m long railway tunnel in Hachinohe - Shin-Aomori section of Tohoku Shinkansen. It is located in almost flat diluvial Tableland (Sambongihara plateau) at elevation of 60m above sea level. The tunnel will pass beneath the public facilities such as roads, railways, water channels for agriculture. Hence, measurements of ground subsidence by using the auto tracking level were adopted to monitor the displacement of the ground resulting from the tunneling. 90 % to the total settlement has been occurred due to the excavation of upper and lower section. Shear deformation appears at the side of tunnel due to the invert excavation. These measurement data shows the needs of auxiliary methods with dewatering method to stabilize the tunnel. The numerical simulation was also applied in order to interpret the measurement results. The validation procedure of effective auxiliary methods based on the investigation are described.

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Uniaxial compression tests were performed under various non-atmospheric environments and constant strain rates on Kumamoto andesite. The environments considered were water vapor, organic vapor such as methanol, ethanol and acetone, and inorganic gas such as argon, nitrogen and oxygen. The strength of rock increased in the order of water vapor, methanol, ethanol and acetone vapor, and the stress corrosion index changed with changing environment even for the same rock type. The stress corrosion index was evaluated to be 31 in consideration of the water vapor pressure and strain rate. The stress corrosion index in this research showed good agreement with other researchers' results and it can be concluded that the stress corrosion index is one of the constants representing the mechanical properties of the rock. However, it is an environment-dependent factor and may vary owing to the difference of hydroxyl ion concentrations that may exist in the same rock. Finally, it was shown that the time to failure is delayed by decreasing water vapor pressure in the surrounding environment, and then the long-term strength of rock under water vapor pressure can be estimated, based on sub-critical crack growth due to stress corrosion.

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Hydraulic fracturing is suitable in principle for in-situ stress measurements at deep depths. However, as has been pointed out recently, its current testing systems and procedure involve essential problems which have to be solved before putting the principle into practice. The most serious problem is associated with the hydraulic compliance of fracturing systems. For measuring the reopening pressure, it is necessary to use the fracturing system with sufficiently small compliance. If not, there is no way to estimate the maximum horizontal stress from the reopening pressure assuming a vertical borehole, even though the maximum horizontal stress is the greatest concern in the stress measurement. This limitation makes it difficult to apply hydraulic fracturing for the stress measurement, because the compliance of the conventional system is so large. Taking into account of these facts, we have proposed recently a new method which will allow us to measure both of the maximum and minimum stresses by in-situ tests of hydraulic fracturing at a depth greater than a few km. We have proceeded to test and verify the concept step by step so far through field and laboratory experiments, and we succeeded in applying it to an in-situ test at a depth of 811 m in a vertical borehole drilled from the ground surface.

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Two methods to characterize microscopic fractures occurring in rock due to alteration process were developed.One is fracture-mineral composite analysis, which is useful to characterize relationships among frequency, aperture, orientation of fractures, and minerals adjacent to fractures. This method was applied to hydrothermally altered granite samples. Results showed that fractures adjacent to plagioclase, potassium feldspar, or biotite and fractures with apertures less than or equal to approximately 36 μm were dominant in strongly altered samples. The results of the analysis were consistent with observations by polarization microscopy.The second method is multifractal analysis of standardized images. Standardization of the analyzed images enabled a comparison of the homogeneity of the fracture distribution based on pixel values. An analysis of weathered gabbro samples showed that the fracture distribution in the samples became more heterogeneous with the progress of weathering. The heterogeneity of strongly weathered gabbro was suggested to be caused as many more fractures developed in the plagioclase particles of the gabbro than in amphibole.

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