It is essential to investigate the influence of pores and fractures on physical and transport properties of rocks for understanding many key problems in seismology, volcanology and rock engineering. In rocks, water is primarily stored in and migrates through networks of pores and fractures at all scales. It is therefore important to know how fluid flow in such pores and fracture networks responds to the elevated pressures found at depth. Here, we report results from an investigation of changes in fluid permeability, and associated changes in P-wave and S-wave velocities, at elevated effective pressure for both intact and macro-fractured sandstone samples. Specifically, we used two types of sandstone; Clashach sandstone from Scotland and Shirahama sandstone from Japan, which have different porosities and pore size distributions. Wave velocities increased with increasing pressure for all cases. Additionally, wave velocities in macro-fractured samples were lower than those in intact samples. For Shirahama sandstone, permeability decreased with increasing pressure. By contrast, permeability of Clashach sandstone remained essentially constant over the whole pressure range. This lack of change is interpreted as being due to the presence of a well-connected network of large pores with high aspect ratios. It was also found that the difference in permeability between intact and macro-fractured sandstone samples was small. From these results, it is concluded that the networks of pores control the permeability in sandstone.
Survey methods using elastic wave velocity have been performed in order to estimate the pore fluid properties in rock mass, but the viscosity and density of pore fluid have not been estimated quantitatively by the values of velocity or the velocity changes. We describe in this paper whether pore fluid properties can be estimated by using the dispersion of longitudinal elastic waves. We measured the frequency-dependent velocity data of longitudinal elastic waves in porous specimens and the dependence of the velocity dispersion on the kinematic viscosity of pore fluid. Moreover, we try to explain the velocity dispersion shown by the measurement data using the Biot theory. The Biot theory explains that the dispersion phenomenon is caused by the elastic property change in the media with the interaction between the solid phase and liquid phase, so the dispersion is dependent on the properties of liquid phase. The measurement data showed the phase velocities of longitudinal waves increased with an increase of frequencies and the characteristic frequencies which indicate the points of inflection moved to higher frequencies with an increase of kinematic viscosities of pore fluid. We report that we can estimate the kinematic viscosity of pore fluid in rock mass by using the dispersion curves which graphed the relation between the phase velocities and frequencies.
To interpret dynamic and static Young's moduli of soft sedimentary rocks, the Dvorkin-Gutierrez silty shale model, one of granular models is applied to the measured Young's moduli obtained from velocity logging data for the dynamic modulus and from laboratory mechanical test data for the static modulus. The Young's modulus for the rock is calculated by the Hashin-Strikman lower bound, Hertz-Mindlin contact model and Gassmann's equation. For modeling static Young's modulus, in the Hertz-Mindlin contact model, the shear modulus is calculated by incorporating the mixture of frictional and frictionless grain contacts into the model. The calculated dynamic and static Young's moduli are well consistent with the measured data for three different soft sedimentary rocks in Japan. This result demonstrates that the rock physics model can be used to predict the static moduli required in civil engineering applications from dynamic ones obtained from seismic velocities.
In this study the uni-axial compression test using the stress-feedback method was carried out with Inada granite which is a Class II rock. The test was carried out by changing loading direction and water content conditions. A perfect stress-strain curve was measured. The stress-strain curve including the post-failure region was simulated using a spring model. In addition, the effects of anisotropy and water content conditions on the stress strain characterization were examined.
Knowledge of the in-situ stresses is essential for underground excavation design, particularly in evaluating stability of excavation. Acoustic Emission method, which utilizes the Kaiser effect, is one of the simple methods for measuring in-situ stresses. Experiments on the Kaiser effect has been carried out under uniaxial compression and triaxial compression (σ1 > σ2 = σ3), but has not been carried out under the three different principal stresses (σ1 > σ2 > σ3). In this study, we performed two experiments on the Kaiser effect under multiaxial loading, using a hollow cylindrical granite specimen. The rapidly increasing point of cumulative AE event count was determined as the peak point of AE event count rate increment (AERI). The main results are summarized as follows. (1) In the case of the cyclic incremental σ1 loading under σ2≠σ3, the large peak point of AERI appeared just before the pre-stress level. And as more stresses prior to just before the peak point were estimated, the estimated error showed a tendency to increase. (2) In the case of re-loading under the lower σ2 and σ3 more than pre-loading, the estimated stresses using the three peak points of AERI corresponded to the pre-differential stresses (σ1-σ2), (σ1-σ3) and pre-axial stress σ1. The magnitudes of the three principal stresses were estimated under multiaxial loading from the Kaiser effect, using only one specimen.
In this research work, the grout injection model of a single fracture, in which non-Newtonian fluid and the inertia term are considered, has been developed. Then, the grout injection experiments of a single fracture have been conducted and the numerical simulations have been also carried out. As compared our proposed model with past one, the remarkable difference in grout penetration could not be clearly observed, except for the pressure at the aperture entrance and penetration velocity of the grout. Our proposed model could show the practical pressure behavior against previous model. Moreover, it can be also confirmed that the pressure at the fracture entrance had a temporary excess level against a set up level in the only initial time of simulations. And the behavior was considered as a passing phase in relation to the increase of shearing stress at the fracture entrance.
Two types of flow experiments using columns packed with rock fragment and glass beads were performed to examine the deposition and clogging phenomena at high temperatures (180°C at Ogachi HDR site and 70°C at Matsushiro hot spring, respectively) during calcium carbonate water injection. Flow rates of both column tests decreased gradually with decrease of permeability due to mineral precipitation. Deposition of carbonate mineral was found as calcite and aragonite on the surface of rock cuttings and glass beads respectively. In this paper, the numerical simulations using deposition rates provide good agreements with the observed flow rate changes. For the column test at Ogachi, the deposition rate is estimated to be almost constant during the experiment, whereas that at Matsushiro increases with duration time. This result shows that deposition mechanisms of carbonate minerals in both experiments differs each other. At Matsushiro, nucleation of carbonate must be occurred before the injection into the column. The formed fine crystals deposited on the surface of glass beads where precipitation rates were accelerated. This carbonate mineralization on CO2 sequestration will decrease the possibility of CO2 leakage risk at hydrothermal conditions and prevent buoyancy from moving upward.
The seismic response of rock foundation to seismic loads is an important issue to the stability and safety of nuclear power plants. Due to the fact that the discontinuities like joints existing in the rock mass govern principally the deformation and failure behaviors of the rock mass, the influence of discontinuities on the seismic behaviors of rock mass remains as one of the fundamental problems in the safety assessment of nuclear power plants. In this study, the distinct element method (DEM) and finite element method (FEM) were adopted to investigate the seismic responses of rock foundation to a real seismic wave, taking into account the effect of joint dip angle on the deformation and dynamic behaviors of rock foundation. In the DEM simulations, the intact rock has an amplification effect on the amplitudes of seismic waves, while the joints exhibit an attenuation effect on the seismic waves. In the FEM simulations, however, the attenuation effect of joints is not obvious. The dip angle of joints has strong effects on the deformation and dynamic behaviors of rock foundation, in terms that different dip angles lead to obviously different deformation and horizontal stress in the rock foundation when subjected to seismic load. When the dip angle of joints is around 60°, the seismic velocity, displacement and stress reach the maximums. Therefore, attentions need to be paid on this factor during the seismic design of nuclear power plants.
This paper presents compressive and tensile strengths of fly-ash concrete, which is classified as type II in the JIS. Fly-ash concretes were made in different seasons, including summer, autumn and winter. The concretes were made in a ready-mixed concrete plant and were cured in the field to simulate actual construction conditions. To investigate fundamental mechanical properties of the fly-ash concretes, strength tests were conducted at several ages. The paper gives the results of compressive strength, splitting tensile strength and uniaxial tensile strength tests. The study uses the Goral curve for the regression of compressive strength developed with an equivalent age based on the maturity. In the regression result, the coefficient of the Goral curve develops with lower temperatures. The results imply that evaluations using the equivalent age are not always appropriate for predicting the compressive strength of fly-ash concrete. According to comparative results of tensile strengths, the splitting tensile strength of fly-ash concrete can be predicted by using the JSCE design formula. In addition, the results indicate the uniaxial tensile strength of fly-ash concrete is higher than the splitting tensile strength at all test ages. A relationship between splitting strength and uniaxial strength, proposed by Yoshimoto, gives a conservative estimate for the evaluation of fly-ash concrete cracking strength.
In this study, a new surface modification process, an atmospheric-controlled induction-heating multiple-fine-particle peening (AIH-MFPP) using mixed two kinds of shot particles, was proposed. In order to investigate the effects of AIH-MFPP, the surface of carbon steel was modified with mixed shot particles of chromium (Cr) and high speed steel (SKH59) at 900°C in argon atmosphere. The treated surfaces were characterized using a field emission- scanning electron microscope (FE-SEM), an energy dispersive X-ray spectrometer (EDX), an X-ray diffractometer (XRD) and an X-ray photoelectron spectroscope (XPS). In the case of the specimen treated by using mixed shot particles of Cr and SKH59, a relatively thick and uniform Cr rich layer was formed at the surface. The thickness of the Cr rich layer was changed with an increase in peening pressure. In the case of a specific mixed-ratio of shot particles, not only was the thickness of the Cr rich layer changed at the surface, but also the crystal structure was changed. This specimen showed higher corrosion resistance compared to that of the specimen treated by using Cr shot particle only. Moreover, there was the electrical current density of the passive state. This indicates that passive film was generated by AIH-MFPP. This was because the Cr rich layer created by AIH-MFPP was covered with a passive film of FeOOH. These results suggest that a new surface modification process ; AIH-MFPP, is promising for the improvement of the corrosion resistance of carbon steel.
This paper proposed the derivation method of upper and lower bounds for variable piezoresistive coefficients of polycrystalline silicon (polysilicon) films having preferred orientation. Two sets of fundamental piezoresistive coefficients of the polysilicon film were derived from the coefficients of single-crystalline silicon using two approximation models based on assumptions that the stress is uniform and the resistivity change is uniform at any point of the film. The upper and lower bounds for the effective piezoresistive coefficients were mathematically defined using the piezoresistive coefficients obtained from the two approximation models. In order to confirm the validity of this definition, the upper and lower bounds, which are applicable to any polysilicon film, were calculated, and were compared with the measurement results previously reported by some groups. The upper and lower bounds were consistent with the measurement results, which supports the validity of this derivation.
An experimental investigation of fabricating biodegradable composite pipes by filament winding (FW) method using ramie yarn as continuous fibre reinforcements is conducted. Though ramie fibres are discontinuous fibres in origin, ramie yarns can be handled as continuous fibre due to high aspect ratio of the fibre. Influence of use of the yarn on mechanical properties of the FW pipes is also evaluated. Axial and circumferential tensile tests are conducted for the FW pipes fabricated with various winding tensions. Results demonstrate that the winding tension affects not fracture load but only fibre volume fraction of the composites. Furthermore, properties of ramie yarn in FW pipes have been focused on. It has been shown that the elastic modulus of FW pipes using ramie yarns is lower than that of angle-plied laminates while mechanical properties of FW pipes and angle-plied laminates using glass or carbon fibre are comparable. From experimental evidences, it has been found that waviness of the ramie yarns caused by their own large diameter strongly affects the mechanical properties of the FW pipes, and that the ramie yarns do not exert their properties adequately in the FW pipes.
The effects of thermal loading conditions on the mechanical properties of S45C/Cu/Si3N4 composites with brazing filler metals of AgCu and AgCuTi are described. Thermal loading tests were conducted on test samples under various heat conditions, after which the joint parts of the samples were observed with a focus on the Cu interlayers using an optical microscope. Four-point bending tests were conducted on the samples to evaluate the residual strength and stress strain characteristics of the samples. In addition, fracture surfaces and the origins of the fractures were observed using an optical microscope. The results showed that thermal loading of the S45C/Cu/Si3N4 composites caused fatigue damage to the Cu interlayers and its amount increased with increases in the cycle number and temperature range of thermal loading. In the case of relatively-mild thermal loading conditions, fracture initiation regions were observed at the Cu/Si3N4 boundary. In contrast, fracture initiation regions were observed in the Cu interlayer for the samples subjected to relatively-extreme thermal loading conditions. The increases in the cycle number and temperature range of thermal loading promoted reductions of residual strength, resilient modulus and residual fracture ductility for the samples. The reductions of the mechanical properties of the S45C/Cu/Si3N4 composites were affected by the fatigue damage of the Cu interlayers. It was concluded that continuous operation (no start-stop system) is suitable for long-term use of ceramic/metal composites including interlayers in order to minimize reduction of their mechanical strength.
This paper presents a set of the investigation of corrosion of steel bars in autoclaved concrete pile containing γ-2CaO·SiO2 (γ-C2S) with carbonation curing. OPC, γ-C2S, and fine silica powder were used as the binders; the replacement ratio of OPC by γ-C2S was 0%, 40%, and 80% by mass. Autoclaved concrete pile after carbonation was submerged in real marine environment at Kurihama Bay for two years. After immersion, visual observation of steel bars was conducted to confirm the corrosion state of steel inside the concrete pile. Furthermore, to evaluate the corrosion of steel bars - weight loss, corrosion current density, and anodic polarization curve were measured ; various corrosion substances also were measured to evaluate the permeability of corrosion factors. In addition, cement past sample with same mixed proportion and curing condition was made for explaining the permeable characteristics of corrosion substances. As the results, the steel bars in the 80% γ-C2S replacement ratio did not corrode while steel bars in the other mixed proportions had corroded. The weight loss of steel bar in the 80% γ-C2S replacement ratio after carbonation reduced by 39% and corrosion current density reduced more than 95% compared with the 0% γ-C2S replacement ratio. Furthermore, the corrosion substances in concrete pile - carbonation depth, total chloride ion content, and oxygen diffusion rate, reduced significantly at the 80% replacement ratio of γ-C2S. Based on the overall results of this study, we suggest that, when using γ-C2S with an autoclave curing, accelerated carbonation curing is able to do to densify the concrete surface preventing the steel from corrosion for the long-term exposure.