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The distribution of cracks strongly affects the hydro-mechanical behavior and strength of soil. In order to characterize the distribution of cracks in undisturbed expansive soil, X-ray computed tomography (X-ray CT) tests were carried out for one type of undisturbed expansive soil from Mile City, China. Seven undisturbed specimens retrieved from depths between 1 and 4.7 m were used to study the evolution of cracks along the drying path. The characteristics of the cracks were quantitatively studied by 3D parameters extracted from CT images by commercial software. The test results suggested that, with an increase in suction, the total volume of the cracks gradually increased, and one large crack formed due to the merging of sub-cracks before the shrinkage limit. When the suction was larger than the suction corresponding to the shrinkage limit, degradation of the cracks caused by the collapse of the soil structure was observed. Meanwhile, due to the development of sub-cracks, the crack anisotropy caused by the typically oriented primary cracks decreased along the drying path. Finally, a conceptual model of crack development for undisturbed Mile clay was proposed based on the evolution of crack volume, number, shape, and orientation.

In the geological disposal of high-level radioactive waste, bentonite buffer materials are required to have self-sealing property, which is the ability to fill gaps by swelling deformation between the buffer material and the waste containment vessel or surrounding bedrock. Self-sealing property was evaluated based on the pressure generated after the gap filling under the assumption of constant dry density and water content in the specimen and buffer material. On the other hand, it takes tens to hundreds of years for the transitional period until the buffer contacts with groundwater, fills the gap, and the internal state converges to a uniform state. To assess changes more accurately in the condition of the buffer material, it is necessary to evaluate time courses in the density and water content of the buffer material because of groundwater infiltration and swelling deformation. From these, the authors developed an experimental apparatus for swelling deformation of bentonite, which consists of a mould with 2 mm-thick stacked rings. It is aimed to evaluate the distribution of dry density, water content, and degree of saturation inside the specimen by cutting the specimen with a 2 mm thick ring after the end of experiment. In this paper, results of preliminary experiments to confirm the applicability of this apparatus to swelling deformation test of bentonite was firstly described. Then, experiments were conducted on compacted bentonite specimens using this apparatus, and changes in the dry density and water content distribution inside the specimens were evaluated in terms of swelling deformation behaviour.

In Japanese project for disposal of high-level radioactive waste, the self-sealing capability of bentonite buffer material, which results from the swelling deformation to fill the gaps between waste container and wall of disposal pit, must be retained thousands of years. However, because of the effect of high pressures, occurrence of cementation and property changes of the buffer material are a concern. Few studies had examined cementation effects because of the difficulties for simulating long-term alteration process experimentally. In this paper, swelling properties of consolidated buffer are regarded as similar as those of naturally consolidated bentonite ore. Therefore, three kinds of bentonite ores were used for experiments to elucidate influences of cementation on self-sealing capabilities. Undisturbed and reconstituted specimens were prepared to assess their swelling pressures after filling a preset gap in a swelling pressure apparatus. Results show that for Japanese ores, the swelling pressure of undisturbed specimens is about half that of reconstituted specimens. For American and Chinese ores, the difference of swelling pressure is greater when the preset gap is smaller. Results imply that effects of cementation on self-sealing capability are smaller when swelling deformation is allowed.

Sand-bentonite mixtures with bentonite content of 10-30% had been planned to handle low-level radioactive waste in Japan, because of its low permeability. Hydraulic conductivity of sand–bentonite mixture depends on the bentonite type, bentonite content, initial water content, and other factors. Given this background, falling head permeability tests were conducted on sand–bentonite mixture by varying the compaction energy for specimen preparation, initial water content (10–20%), and bentonite content (15– 30%). For these tests, the hydraulic gradient of 25-500 was set. Consequently, the hydraulic conductivities were 10-8 – 10-13 m/s for all tested conditions. Correlation between the hydraulic conductivity and the effective montmorillonite dry density (montmorillonite mass divided by the sum of montmorillonite, air, water volume), which is often used to correlate the hydraulic conductivity of bentonite, was found. Correlation was also found between the hydraulic conductivity and a new index designated as the effective montmorillonite wet density (sum of montmorillonite and water mass / sum of montmorillonite, air, water volume). Effective montmorillonite wet density reveals differences in the specimen structural distribution through consideration of the initial water content.

Abstract Background Arterial stiffness is a major contributor to cardiovascular diseases. Because current methods of measuring arterial stiffness are technically demanding, the purpose of this study was to develop a simple method of evaluating arterial stiffness using oscillometric blood pressure measurement. Methods Blood pressure was conventionally measured in the left upper arm of 173 individuals using an inflatable cuff. Using the time series of occlusive cuff pressure and the amplitudes of pulse oscillations, we calculated local slopes of the curve between the decreasing cuff pressure and corresponding arterial volume. Whole pressure-volume curve was derived from numerical integration of the local slopes. The curve was fitted using an equation and we identified a numerical coefficient of the equation as an index of arterial stiffness (Arterial Pressure-volume Index, API). We also measured brachial-ankle (baPWV) PWV and carotid-femoral (cfPWV) PWV using a vascular testing device and compared the values with API. Furthermore, we assessed carotid arterial compliance using ultrasound images to compare with API. Results The slope of the calculated pressure-volume curve was steeper for compliant (low baPWV or cfPWV) than stiff (high baPWV or cfPWV) arteries. API was related to baPWV (r = -0.53, P < 0.05), cfPWV (r = -0.49, P < 0.05), and carotid arterial compliance (r = 0.32, P < 0.05). A stepwise multiple regression analysis demonstrated that baPWV and carotid arterial compliance were the independent determinants of API, and that API was the independent determinant of baPWV and carotid arterial compliance. Conclusions These results suggest that our method can simply and simultaneously evaluate arterial stiffness and blood pressure based on oscillometric measurements of blood pressure.