Japan Atomic Energy Agency has been conducting in-situ stress measurements by hydraulic fracturing method to aiming establish a firm scientific basis for safe geological disposal. Hydraulic fracturing method has many results, but including many errors in data as International Society for Rock Mechanics suggested. This report describes results compared with the data obtained by ordinary system and that of new type of system. Based on the results of 57 hydraulic fracturing tests in Granite at the maximum depth of 1000m, rate of low-quality data obtained by ordinary system was 35%. The quality of data obtained by new type of system improved comparing with the ordinary system, as data of flow rate was measures in borehole. Maximum horizontal stresses calculated using ordinary equation overestimate about 23%.
Fiber reinforced concrete (FRC) is considered to offer improved resistance against crack defects and higher toughness compared to plain concrete. Although knowledge of the durability and service life of FRC is important for a wide range of applications, only limited information is currently available. In the present study, the durability of FRC containing steel or recycled-PET fibers was investigated. In the four-point bending test, specimens were pre-loaded and cracked to reduce the testing time. Specimens for short-term tests were salt sprayed for a period of one week and then placed in a dry air-conditioned room for another week. Specimens for long-term tests were subjected to 15 cycles of salt spraying and air drying. The durability of the FRC was evaluated on the basis of the peak load and toughness index obtained in the four-point bending test. The FRC containing steel fibers suffered severe deterioration in the long-term test but no significant deterioration in the short-term test. The FRC containing PET fibers, on the other hand, suffered only slight deterioration in the long-term test and no deterioration in the short-term test. A simple model was proposed to explain the observed deterioration of FRC.
In recent years, localized torrential rain caused by abnormal weather happened frequently, which induced increasing slop collapses in Japan. Failure could happen in some normally stable slopes due to the seepage of rainwater in the ground. In this study, a model experiment investigating the slope failure caused by water seepage was reproduced in numerical simulation by using the coupled stress-flow method. The failure mechanism of slope induced by the increase of underground water level and decrease of effective stress was investigated through the test and simulation results. Case study was carried out by using numerical simulation to estimate the relation of the variation of pore pressure and the distribution of shear strain. Numerical simulation was furthermore applied to a slope that collapsed on July, 2009 in Kyushu Island during the torrential rain to verify the proposed numerical approach. The numerical simulation results agree well with the model experiment and field investigation results. Based on the results of slope deformation and stability analyses taking into account the change in water pressure and cohesive strength, it shows that the excessive pore pressure increases dramatically especially underneath the surface of slope where failure will happen.
High strength and ultra low permeability concrete (HSULPC) is thought to be an alternative material for a radioactive waste package containing transuranic radionuclides (TRU wastes) for geological disposal. Thus high confining ability is required for HSULPC. In addition, knowledge of time-dependent fracturing and change of permeability due to fracturing is important. For cementitious materials, self sealing of fracture due to the precipitation of calcium compounds can occur in water. This can affect long-term stability and decrease of permeability. In this study, the sealing behavior of macro-fractured HSULPC in water was investigated using micro-focus X-ray CT and image analyses. It was shown that the sealing of fracture by precipitation occurred only near the edge of the specimen. Using the technique of image registration and image subtraction considering the gap between X-ray CT images, the sealed regions in fracture were extracted successfully. The percentage of sealed volume in fracture increased with elapsed time. It is concluded that high confining ability of HSULPC can be maintained due to the self sealing even if fractures are included.
Deformation properties and permeability of sedimentary rock in the compression failure process was numerically studied using the distinct element method. Elastic tensors were estimated using the finite element method (Dfem) and the method assuming the affine deformation (Daffine). Permeabilities were estimated using the effective medium approximation and the fluid flow network. In agreement with the experimental results, the linear stress-strain relation under low differential stress and the nonlinear inelastic stress-strain relation near peak differential stress level were observed in the simulations. The change of Dfem was relatively small in the linear elastic region, then Dfem evidently changed and became anisotropic after the peak strength. On the other hand Daffine didnot varied significantly compared with Dfem but also became anisotropic. After peak strength inelastic deformation was the dominant deformation process. The permeability estimated using the effective medium approximation was increased after the failure. The permeability estimated using the fluid flow network exhibited anisotropy. The anisotropy of the elastic tensors and the permeability estimated from the fluid flow network could be attributed to the structural change of the rock model due to differential stress.
Silicon nitride is a typical engineering ceramics as structural materials for high-temperature or functional applications. However, the fabrication of silicon nitride costs a lot because the densification of silicon nitride needs vast energy to get high-temperature of 2073∼2273 K and special apparatus such as a hot-press. Therefore, it is difficult to use silicon nitride in large amount. Consequently, lowering of the fabrication cost is essential to apply silicon nitride to wider fields. We propose a new process of the liquid phase sintering of silicon nitride using an oxynitride sintering aid which consisted of SiO2, MgO and preliminarily added α-Si3N4 and was fired at temperature up to 2073 K. The α-Si3N4 green compacts with the oxynitride sintering aid were sintered at 1873 K for 64-512 min under 0.1 MPa nitrogen pressure, and fully dense β-Si3N4 ceramic was fabricated after 512 min sintering. This sintering temperature is about 200 K lower than that of a conventional method.