Physical property of molten slag is important to clarify various reaction kinetics and to optimize the metallurgical processes at elevated temperature. In addition, viscosity is also important for understanding the microstructure of the slags. It is well known that most of the metallurgical slags contain the iron oxide. However, the behavior of the iron oxide in the molten slag is still not well understood. Iron oxide has two oxidation states (FeO and Fe2O3) and Fe2O3 is an amphoteric oxide. Therefore, the structural role of the iron oxide could be changed with several factors, such as melting temperature, basicity (chemical composition) and the oxygen partial pressure.In the present review paper, we outlined some of the highlight data of the viscosity and the structural information for iron oxide containing slags, which include calcium ferrite slag and iron oxide containing silicate slags.
Durability evaluation of rocks subjected to freezing-and-thawing is important for stability assessment of a rock fill dam as well as rock slopes, especially in cold weather regions. In this study, freezing-and-thawing tests up to 300 cycles were carried out on twelve kinds of rock samples in order to characterize fracture propagation by freezing-and-thawing and evaluate the durability, and fracture propagation was observed. The fracturing process was characterized by macroscopic observation by digital camera and changes in physical properties. Fracture initiation and propagation in the specimen were also observed by using X-ray CT. It was found that the fracturing process depends on the rock type. For rocks which possess preferred orientation of pre-existing fractures and anisotropy of tensile strength, only one fracture propagated dominantly and split the rock sample in half. On the other hand, for isotropic rock, propagation of several fractures occurred and rock samples were split into several parts. Additionally, spalling continuously progressed once the loss of weight exceeded 5% for isotropic rocks because fractures had developed throughout the specimen. This result indicates that freezing-and-thawing cycles at 5% weight loss is assumed to be the spalling initiation. Therefore, we can conclude that the number of freezing-and-thawing cycles to the spalling initiation is the important indicator of the durability evaluation. It was also pointed out that both supply capacity of water to the crack tip and crack growth resistance affect the durability, because the tensile strength divided by the percentage of water absorption is in good correlation with the number of cycles to the spalling initiation. It is concluded that the durability can be easily evaluated by both tensile strength and the percentage of water absorption.
Drying-induced deformations of porous materials are ubiquitous phenomena, but coupled behaviors of moisture content inside the material and deformation, which are difficult to express the behavior as a physical model. This is partly because multiple mechanisms governing drying-induced deformation are involved so that each mechanism may become dominant by respective situations. This article introduces various activities or efforts in some research fields, and retrieves common results in laboratory experiments and in field observations, mainly for sedimentary rocks. Through these processes, future works to be considered are elucidated.
Measurements of poroelastic coefficients of Horonobe siliceous rock, which constitutes the strata of the JAEA underground research facility, has been conducted using servo-controlled triaxial testing apparatus. The rock specimens were prepared from the cores obtained from the boreholes which penetrate the Koetoi formation and Wakkanai formation. Depth of cores varies from 222 to 599m. Following are the main results: 1) Triaxial testing method, by which the rock test piece is axially loaded under constrained circumferential strain condition, has been developed to determine the poroelastic coefficients. 2) The values of the undrained bulk modulus Ku, which were determined by two different methods, one is direct measurement and another is indirect evaluation using several coefficients, coincides each other for the rock obtained from the Koetoi formation, indicating that the measuring system is reliable. 3) The relationship between poroelastic coefficient and the depth from which the testing sample is obtained has been studied and the results indicate that, the ratio Ku/K varying from 4 to 15 is inversely proportional to the depth. Skempton's coefficient B slightly decreases with depth and Biot-Willis coefficient α exceeding 0.95 is not dependent to depth. 4) Skempton's coefficient B slightly decreases with increase of the confining pressure. On the other hand, undrained bulk modulus Ku increases with confining pressure. 5) Although the poloelasticity theory is well applicable to the rock of Koetoi formation, its applicability is problematic to the rock of Wakkanai formation.
We operated laboratory permeability measurements with Neogene mudstone specimens in order to investigate an applicability of laboratory tests to estimate fracture permeability in depth. We collected rock samples from drill cores of Koetoi Formation diatomaceous mudstone and Wakkanai Formation siliceous mudstone at Horonobe area, northern Hokkaido, Japan. We prepared specimens with a saw-cut discontinuity, simulating a fracture in rock, and measured permeability in the direction parallel to the discontinuity under hydrostatic stress condition up to 80 MPa. The measured permeability of a specimen with a saw-cut discontinuity fracture was larger than that of an intact specimen when confining pressure is less than 1 MPa (comparable to the depth of approximately 150 m) in the case of Koetoi Formation diatomaceous mudstone, but, when confining pressure is 1 MPa or more, the permeability values of a saw-cut specimen and an intact specimen became a similar to each other. On the other hand, in the case of Wakkanai Formation siliceous mudstone, the confining pressure under which the permeability of a saw-cut specimen became similar to the permeability of an intact specimen was close to 80 MPa (comparable to the depth of several km) . These results can explain the difference between Koetoi and Wakkanai Formations on distribution of in situ permeability measurements operated by Japan Atomic Energy Agency. Numerical simulations of a flow through a fracture under normal stress could explain the results of the laboratory test for Koetoi Formation diatomaceous mudstone, by using reasonable mechanical properties. These results support the possibility of estimating stress dependency of fracture permeability from rock mechanical properties and permeability of intact part.
Fluid flow through fractured rock mass is an import issue in the performance and safety assessment of underground rock engineering, such as dam foundation, underground storage system and radioactive waste repository. The coupled shear-flow behavior of rock fractures have received extensive studies in the last few decades, however, some of the key issues such as shear-induced complexity of void space geometry and its influence on fluid flow through a fracture during large shear displacements remain unresolved. In this study, by using a coupled shear-flow apparatus with visualization of fluid flow, flow test on parallel-plates model with circular contacts and shear-flow-tracer test under constant normal load (CNL) boundary condition using artificial rock fracture with natural fracture surface characteristics were carried out. Numerical simulation was then conduced to simulate fluid flow through the fracture with void geometry obtained from coupled shear-flow test. The evolution of mechanical aperture and contact area distribution and their influence on fluid flow during shear process were evaluated. The influence of Reynolds number on the transmissivity of fracture was investigated.
The permeability of Kimachi sandstone in triaxial compression failure process was investigated by laboratory experiments. Tests were carried out under a constant confining pressure of between 5.0 and 15.0 MPa with a constant pore pressure of 2.0 MPa until axial strain reached approximately 5.0%. The stress-strain relation was linear under low differential stress and gradually became nonlinear as peak differential stress approached. In the tests under confining pressure of 5.0 and 7.5 MPa, the permeability decreased in the elastic region and then increased as the peak strength approached. The permeability continued to increase at first in residual strength region, and then it decreased at axial strain of approximately 4.0%. In the tests conducted under higher confining pressure, the variation in the permeability was small until axial strain of 5.0%. It appeared that failure types were different depending on confining pressure from the observation of the thin sections made from the specimens after tests. In the tests under 5.0 MPa confining pressure, a macroscopic fault occurred in the test pieces. On the other hand it did not occur in the tests under higher confining pressures. It was suggested in the elastic FEM analyses that the failure types were influenced by the end constraint.
Evolution of the long-term mechanical, hydraulic, and transport characteristics of rock fractures should be, in advance, predicted in considering an issue on entombment of energy byproducts of high level radioactive wastes. Under stressed and temperature conditions, those behaviors of the rock fractures of interest may be evolved in time and space likely due to the change in topographical aperture distributions. This irreversible process may be induced by pure mechanical and/or chemo-mechanical creeps such as water-rock reactions like stress corrosion and pressure solution, and chemical effects including mineral dissolution and reprecipitation in the free-walls of fractures. Specifically, the chemo-mechanical processes active at the contacting asperities within rock fractures may exert a significant influence on the mechanical, hydraulic, and transport behaviors throughout a long period, and thus, should be vigorously examined theoretically and experimentally. This paper presents the slide-hold-slide shear test results for fully-saturated, single-jointed mortar specimens so as to investigate the effects of load holding on mechanical properties of rock joints. From the test results, it was confirmed that shear strength increased for mortar specimens in both short and long time holding cases. However, the evolution of shear strength recovery in two cases is different. This is because a dominant factor of shear strength recovery during the short time holding may be attributed to a pure mechanical process like creep deformation at contacting asperities, while the one during long time holding is affected by both mechanical and chemical processes like pressure solution. Moreover, to reproduce the shear strength recovery during short time holding we develop a direct shear model by including temporal variation of dilation during holding. The model predictions are in relatively good agreement with the test measurements.
Two effects of clay enrichment in the granite-origin fault zone due to the deformation were studied: (1) it reduces frictional strength and (2) it impedes across-fault fluid flow. We sampled two natural fault rocks located in and out of the aftershock region of 2000 Tottori-ken Seibu Earthquake (Tottori, Japan) , and measured the porosity, permeability and friction coefficient for each gouge zone. Independent of the sampling location and the difference of aftershocks' activities, the deformation concentrated gouge zone showed the lowest porosity in the specimen. The pore in the gouge with the lowest porosity was dominated by smaller sized pore throat (around 10 nm) caused by the enrichment of fine-sized clay minerals, such as smectite. Sliding deformation with permeability monitoring on natural gouges, using the pore pressure oscillation method, were performed along a 30° precut surface of Berea sandstone under 100 MPa of normal stress, 30 MPa of pore water pressure and room temperature condition. The gouges having the lowest porosity showed the lowest friction coefficient and the lowest permeability in the fault rocks. Thus both the frictional and fluid flow properties of natural gouges would be controlled by the clay mineral content. The relationship between the friction coefficient and the permeability on the natural fault gouge draws a similar trend to the previous study on simulated gouges with various mixes of smectite powder and granular quartz, but the trend for the natural fault gouge indicated c.a. 0.1 lower friction than that for the previous study.