It is crucial to understand the hydro-mechanical behavior of rock mass to assess the performance of natural barriers. As rock fractures serve as both mechanically weak planes and prominent pathways for hydraulic flow, they significantly influence the hydro-mechanical behavior of the rock mass. Hence, understanding the characteristics of rock fractures is necessary to analyze the long-term behavior of natural barriers. In particular, fracture apertures are crucial parameters directly associated with groundwater flow and consequently hold significant importance in determining the hydro-mechanical behavior of natural barriers. Fracture apertures are defined as mechanical and hydraulic apertures, and various studies have been conducted to measure and analyze them. However, direct measurement of mechanical aperture according to changes in normal stress is known to be a challenging task. For this reason, there has been a scarcity of direct comparative findings between mechanical and hydraulic apertures under various normal stress conditions. This study aims to analyze the characteristics of the mechanical and hydraulic apertures according to changes in normal stress based on experimental results. A digital analysis technique using a pressure film image was applied to analyze the mechanical aperture characteristics of the fracture. This technique can be applied by performing a pressure film compression test and a normal stiffness test on a fracture specimen, and has the advantage of being able to derive mechanical apertures under various normal stress conditions. The hydraulic aperture characteristics of the fracture were analyzed based on Cubic law after measuring the flow rate by performing a constant pressure injection test under triaxial compression conditions. By applying various confining pressures, it was possible to examine the hydraulic apertures according to changes in normal stress conditions. Through the experimental results, the relationship between the mechanical and hydraulic apertures of the fracture was summarized under various normal stress conditions. In addition, the experimental results were used to examine the applicability of various empirical equations for mechanical and hydraulic apertures proposed in previous studies. The characteristics of the fracture aperture resulting from this study are significant because they are required in the hydro-mechanical model of natural barriers. Future studies will entail further experiments, with the objective of establishing novel relationships based on the accumulation of experimental data.

The distribution characteristics of rock fractures determine the hydro-mechanical behavior of natural barriers. Rock fractures are defined by various parameters, which are analyzed as the probability distribution from observation results by surveying the exposed rock surface or borehole. The size is known to have the most uncertainty among the fracture parameters because it cannot be directly measured. Therefore, various estimation methods have been proposed for fracture size distribution using the fracture traces observable on the rock surface. However, most methods are based on a planar survey area, limiting their applicability to the underground research laboratory (URL) excavated in the form of tunnels. This study aims to review a method that can be applied to estimate the size distribution of fractures in deep rock masses at the URL site. The estimation method using the joint center volume (JCV) has recently been extended to be applicable regardless of the geometry of the survey area, which means that it can be applied to the URL site with complex structures. To apply the JCV-based estimation method to non-planar survey areas, JCV calculation using Monte Carlo simulation and estimation of fracture size distribution using the maximum likelihood method are required. In this study, we applied the JCV-based estimation method to a tunnel-shaped survey area to examine its applicability to the URL site. The error rates were analyzed when there were fracture sets with various orientations, size distributions, and maximum fracture sizes in the rock mass, and it was found to be less than 10% in all cases. This result indicates that the JCV-based estimation method can be used to estimate the fracture size distribution of the surrounding rock mass if accompanied by a reliable survey of fracture traces on the tunnel surface inside the URL site. Also, since there are no restrictions on the geometry of the survey area, we can continuously update the estimation results during the URL excavation process to increase reliability. The fracture size distribution is essential for constructing the discrete fracture network (DFN) model of the rock mass units at the URL site. In the future, the uncertainty for the fracture size in the DFN model is expected to be reduced by applying the JCV-based estimation method.

The hydro-mechanical behavior of rock mass in natural barriers is a critical factor of interest, and it is mainly determined by the characteristics of the fractures distributed in the rock mass. In particular, the aperture and contact area of the fractures are important parameters directly related to the fluid flow and significantly influence the hydro-mechanical behavior of natural barriers. Therefore, it is necessary to analyze the aperture and contact area of fractures distributed in potential disposal sites to examine the long-term evolution of the natural barriers. This study aims to propose a new technique for analyzing the aperture and contact area using the natural fractures in KURT (KAERI Underground Research Tunnel), an underground research facility for the deep geological disposal of high-level radioactive waste. The proposed technique consists of a matching algorithm for the three-dimensional point cloud of the upper and lower fracture surfaces and a normal deformation algorithm that considers the fracture normal stiffness. In the matching process of upper and lower fracture surfaces, digital images obtained from compression tests with pressure films are used as input data. First, for the primary matching of the upper and lower fracture surfaces, an iterative closest point (ICP) algorithm is applied in which rotation and translation are performed to minimize the distance error. Second, an algorithm for rotation about the x, y, and z axes and translation in the normal direction is applied so that the contact area of the point cloud is as consistent as possible with the pressure film image. Finally, by applying the normal deformation algorithm considering the fracture normal stiffness, the aperture and contact area of the fracture according to the applied normal stress are derived. The applicability of the proposed technique was validated using 12 natural fractures sampled from KURT, and it was confirmed that the initial apertures were derived similarly to the empirical equation proposed in the previous study. Therefore, it was judged that the distribution of apertures and contact areas according to applied normal stress for laboratory-scale fractures could be derived through the technique proposed in this study.

In this work, highly porous carbons were prepared by chemical activation of carbonized biomass-derived aerogels. These aerogels were synthesized from watermelon flesh using a hydrothermal reaction. After carbonization, chemical activation was conducted using potassium hydroxide to enhance the specific surface area and microporosity. The micro-structural properties and morphologies were measured by X-ray diffraction and scanning electron microscopy, respectively. The specific surface area and microporosity were investigated by N2/77 K adsorption-desorption isotherms using the Brunauer-Emmett-Teller method and Barrett-Joyner-Halenda equation, respectively. Hydrogen storage capacity was dependent on the activation temperature. The highest capacity of 2.7 wt% at 77 K and 1 bar was obtained with an activation temperature of 900°C.

Male crickets (Order Orthoptera), producing sound for courting females and threatening other males, were chosen to perform researches for the better understanding of the microstructures of sound producing organs. It is known that cricket only makes sound for mating-related events. In this research, two patterns out chirping patterns were observed and analyzed. Each chirp was made of several nodes of waves, each node indicates a movement of wings – friction caused by file and plectrum located on wings. Although both wings possess file and plectrum, only the file on right wing and plectrum on left wing are used to produce sound. Each file consists of 126 teeth, where plectrum gets hooked. The teeth located on file have consistent gap between each other, proportional to the wave nodes acquired – except that the gap in the second region among equally divided six regions were shorter. In case of the usage of file, a cricket mostly uses second region to fifth region, since the teeth in first and sixth region are smaller. Since most of the researches made are mainly focused on the correlation between sound production and behavioral pattern, the current research project aims to reveal and provide thorough understanding on the sound producing organs of cricket, to suggest possible biomimetic applications in our daily lives.