This report explains the present state of in-situ tracer experiment techniques for rock mass and the points to remember when conducting in-situ tests. There are several methods for in-situ tracer experiment. First their principles, advantages and disadvantages and application examples to rock mass are described for typical in-situ tracer testing methods. Point dilution test and single-well injection-withdrawal test are introduced as typical single-hole tracer testing methods. On the other hand, natural gradient test, radially divergent test, radially converging test and dipole test are introduced as typical cross-hole tracer testing methods. A tracer injection system and a recovery system are required to conduct an in-situ tracer experiment. Secondly equipments for in-situ tracer experiment are outlined with testing procedure. And points to remember for test equipments are described. Selection of tracers is one of the most important issues for a successful in-situ tracer experiment. Conservative tracers are used to investigate the phenomena of advection and dispersion, whereas reactive tracers are used to address the phenomena of sorption and matrix diffusion. Thirdly desirable conditions for conservative tracers and generally used conservative tracers are described. And the points to remember for selecting reactive tracers and concentration of injected tracers are outlined. In order to conduct an in-situ tracer experiment successfully and estimate the characteristics of rock mass for solute transport accurately, geological and hydraulical characteristics of rock mass should be investigated closely prior to the in-situ tracer experiment. Finally the procedure for investigating the transport properties of rock mass is outlined including prior geological and hydrological surveys as well as in-situ tracer experiments.
Crack propagations in rock will affect stability of rockmass structures. It is important to predict the crack propagation in rock in order to design the suitable reinforcement or support system. Therefore, authors focus on a distinct element method based on discontinuum mechanics. In this method, a material is expressed as assemblies of rigid circular particles, and input parameters are not mechanical properties of the material, such as Young's modulus and Poisson's ratio, but microscopic parameters related to each particle. This paper firstly describes the numerical simulation using Particle Flow Code (PFC2D) of uniaxial compressive test and Brazilian test so as to determine the proper microscopic parameters of Kimachi sandstone. Stress-strain curves obtained from the uniaxial compressive tests and tensile stress-axial strain curves obtained from the Brazilian tests show that the model can represent not only uniaxial compressive strength, Young's modulus, Poisson's ratio, but also tensile strength, by adopting the clump model. And then numerical simulations of mode I, mode II, and mixed mode fracture toughness testing using Semi-Circular Bend (SCB) specimen are conducted. The results of the simulation are compared with the experimental data. It is found that the differences of the fracture toughness values obtained by the numerical simulation and experiments are within 10%. The locations of the failure plane by the numerical simulation are good agreement with that observed by experiments. In conclusion, the Particle Flow Code can simulate both crack resistance properties and direction of the crack propagation in rock.
In this study, triaxial compression tests were conducted for Toyoura sand containing synthetic methane hydrate at conditions of confining pressure 9 MPa, pore water pressure 8 MPa and temperature 278 K. In the test, strain rate was switched between C1 and C2 (C1 < C2) at every predetermined strain interval, and two stress-strain curves at strain rates of C1 and C2 were estimated from a single specimen. As a result, the peak strength at the faster strain rate C2 was higher than that at the slower strain rate C1. It was also found that strain-rate dependency of peak strength increased with methane hydrate saturation. It can be said that methane hydrate saturation significantly affected to the strain-rate dependency and then failure mechanism of the methane hydrate sediments. Strain-rate dependency of residual strength (stress in the post failure region) was discussed. The ratio, (stress at the strain rate C2 / stress at the strain rate C1), was almost constant in the region. This finding may suggest that the mechanism of strain-rate dependency or time-dependent behavior of methane hydrate sediments does not change in the post-failure region.
The time-dependence of molecular weight of gelatin, the cathode potential and the polarization resistance were investigated during long-term electrolysis of Cu to evaluate the degradation of gelatin and polyethylene glycol (PEG) added to the electrolyte for Cu electrorefining. Gelatin and PEG acted as a polarizer for Cu deposition, shifting the cathode potential to less noble direction. The polarization caused by the additives gradually decreased with increasing the electrolysis duration. The effective duration of additives significantly depended on the molecular weight and was longer in PEG-containing solution than in gelatin-containing solution. The molecular weight of gelatin in electrolyte decreased with increasing the electrolysis duration. Particularly, the molecular weight of gelatin was much more decreased at anode than cathode. Even in the case without electrolysis, the molecular weight and polarization effect of gelatin decreased with increasing the time. The decrease in molecular weight of gelatin brought about the shift of the cathode potential to noble direction, showing that the molecular weight of degraded gelatin had a close relation to the deposition potential of Cu. The Cole-Cole plots obtained by AC impedance techniques showed that the polarization resistance for Cu deposition in PEG-containing solution decreased with increasing the electrolysis duration.
We report our recent results on the photoinduced transient optical absorption measurements of amorphous (a-) As2Se3 and a-As2S3, after the illumination of nanosecond pulsed laser. From the measurements, we have observed a photodarkening in the nanosecond and microsecond domains for the first time. Since the fast photodarkening was also observed in the liquid state, the structural origin of the photodarkening should be different from the conventional metastable photodarkening, which is observed only below the glass transition temperature. We have also examined accumulated photoinduced changes for the stronger repeated pulsed laser illumination. From the measurements, we have found for As2S3 that there exists an accumulated photoinduced absorption in the supercooled liquid state. On the basis of the detailed results of the transient optical absorption measurements, structural origin of the photodarkening is discussed.
For the recovery of nuclear materials from the spent nuclear fuel, the sulfide process which consists of voloxidation of spent fuel and selective sulfurization of fission products has been proposed. In this paper, cerium was used as a stand-in of plutonium as well as one of rare-earth elements of fission products. Sulfurization behavior of cerium dioxide by CS2 was studied by thermogravimetry (TG) and X-ray diffraction (XRD) methods. From the TG results, it was found that the sulfurization reaction begun at temperatures higher than 450°C forming tetravalent cerium oxydisulfide. Then the reduction of cerium from tetravalent to trivalent of occurred forming intermediate oxysulfides such as Ce4O4S3, Ce2O2S and Ce10S14O which were identified by XRD. Finally, Ce2S3 was found to be formed at higher temperatures up to 1000°C. The experimental results were in good agreement with those of thermodynamic consideration.
A new series of chalcogenide glasses in the Cu2S-Sb2S3 system was prepared by a conventional melt-quenching method. The glassy nature of prepared compositions was proved using X-ray diffraction analysis. The homogeneity and microstructure were evaluated using FE-SEM. Physical properties such as glass transition temperature, crystallization temperature, density, optical transmission and electrical resistivity were measured. The results show that the Cu-Sb-S glasses form in the composition region of 21.5 and 24.5 mol% Cu2S. The glass transition temperature is 185°C and the optical transmission window is lying between 0.9 and 15 μm for the representative 22.5Cu2S - 77.5Sb2S3 glass sample. The result of electric resistivity indicates that the change of electric resistivity is about 3 orders by the crystallization of glass.
The pulsed laser deposition of titanium sulfide films was investigated in order to develop new thermoelectric materials. The rutile-type TiO2 powder was first sulfurized with carbon disulfide (CS2) gas. After the sulfurization at 1023 K for 14 h, the resultant powder consisted entirely of the CdI2-type TiS2 phase. The TiS2 target was fabricated by pressing the TiS2 powder under a uniaxial pressure of 20 MPa. The films were prepared on fused quartz substrates by the pulsed laser deposition from the TiS2 target under CS2 pressure. The effects of the CS2 pressure and substrate temperature on the microstructure and composition were investigated. When the film was prepared at room temperature under CS2 pressure of 1.33 Pa, the composition of the film was found to be close to the target composition. The room-temperature electrical resistivity and Seebeck coefficient of this film are 63 μΩ•m and -42 μV/K, respectively.
A sulfur-doped titanium dioxide thin film was prepared by pulsed laser deposition in the atmosphere controlled in carbon disulfide partial pressure. Optical and spectroscopic analyses demonstrated that the doped sulfur atom successfully triggered visible light sensitization by substituting with the lattice oxygen of titanium dioxide, which can absorb ultraviolet light only. As a result, photocatalytic hydrogen evolution activity of sulfur-doped titanium dioxide thin film was remarkably increased, compared with un-doped one. Moreover, an investigation on increase of the substrate temperature during laser ablation revealed that stabilization of sulfur atom in titanium dioxide was attained, resulting in high photocatalytic activity.
Most of waste plaster board, which contains gypsum has been buried in the landfill. However, this treatment of waste gypsum board is becoming a serious problem due to lack of landfill capacity, and secondary pollution by toxic substance. In this study, we focused a recycle of calcium resources as CaO or CaS from the waste gypsum, and developed a reduction process of the gypsum using plastics at high temperature. Reduction behavior of CaSO4 by Polyethylene at temperature from 1273 to 1573K was studied with gravimetry and X-ray diffraction analysis. From the experimental results, we found that increasing CaSO4-CH2 gas interface tend to advance the reduction of CaSO4. Furthermore, direct formation of CaS from CaSO4 was observed only at temperature of 1273K without an intermediate compounds stage, and the reduction sequence was CaSO4→CaO→CaS at temperatures higher than 1373K. Finally, the sequence of reduction process for CaSO4 was discussed on the potential diagram of the Ca-S2-O2 system.