Compacted bentonite buffer blocks placed in the engineered barrier system for high-level nuclear waste disposal can undergo swelling, intrusion into rock fractures, and erosion with saturation. Bentonite erosion and intrusion can lead to bentonite mass loss via groundwater flow and can ultimately compromise the overall integrity of the disposal system. To ensure the long-term safety of deep geological disposal, it is essential to assess the hydro-mechanical interactions between the bentonite buffer and surrounding rock. In this study, the impact of bentonite erosion and intrusion on the mechanical properties of the jointed rock mass were assessed via elastic wave propagation measurements using the quasi-static resonant column test. Granite rock discs obtained from the Korea Underground Research Tunnel and Gyeongju bentonite were used to simulate jointed rock specimens with different bentonite intrusion conditions. Different degrees of bentonite intrusion were simulated by mixing bentonite and water to create bentonite paste and gel. The longitudinal and shear wave velocities under different normal stress levels were used to quantify the effects of bentonite intrusion on the mechanical characteristics of the rock joint. Complementary numerical analysis using the three-dimensional distinct element code (3DEC) was conducted to provide improved understanding of wave propagation within bentonite gouge-filled rock mass.

Discontinuities exert great influence on the thermal, hydraulic, and mechanical behavior of rock mass. Rock joint is one of the most frequently encountered discontinuities in many engineering applications, such as tunnel, rock slope and repository for high level radioactive waste. Therefore, the effects of rock joint should be thoroughly investigated in various aspects. Rock joint has gone through many geological processes and its behavior can be characterized by many properties. Among them, geometric properties, such as joint roughness, aperture, and contact area can affect mechanical and hydraulic properties and vice versa. Therefore, accurate understanding and characterization of the geometric properties are of importance. Generally, the geometric properties of a joint are obtained or estimated using the surface height or elevation, which could be measured by various contact or noncontact methods. Then, the coordinates of the surfaces are used to calculate several parameters, for instance roughness indexes and mechanical aperture, in a quantitative manner. This paper is a part of SKB task force project that aims to evaluate the geometric properties of rock joints and to analyze the hydromechanical behavior within a rough joint considering the properties. Four pairs of joint surfaces were laser-scanned in order to obtain coordinates of the surfaces and then the coordinates were used to calculate the roughness, directional roughness, aperture, and spatial correlations. At the same time, fluid flow within a rough joint were simulated by a commercial FEM code, considering the variation of aperture space due to normal load. Flowrate, flow path, and channelization were investigated in an aperture scale. Since rock mass consists of several joints and/or joint sets, characterization of a single rock joint can be utilized for analyzing the behavior of rock mass as a reference.

In KAERI, a site descriptive model for stress field estimation had already been constructed by using integrated field data within KURT site scale. A sub-divided rock block domain containing major fracture zones has spatial rock mass and fault properties. The properties were decided based on the rock classification results of several borehole investigations. Modeling for maximum and minimum horizontal stress field estimation was performed and compared with the in-situ data. As a result, a depth-dependent stress ratio was adopted to obtain numerical results closer to actual in-situ data. Although the results were suitable at a relatively low depth (~500 m), there is still some deviation trend at a deep depth. This study aims to improve these modeling results by incorporating not only depth-dependent stress ratio but also changes in rock mass properties along the depth. The deep borehole of DB2 in the KURT site indicated fracture distribution corresponding to the property changes. Natural fractures are typically randomly oriented, and the fracture frequency decreases with increasing depth. The increase in P-wave velocity log data accompanies these features. A discrete fracture network (DFN) model can be used to simulate fractured rock explicitly, but DFN modeling is not feasible for site scale analysis because of its numerical efficiency. Therefore, as a preliminary model in this study, the effect of fracture distribution was considered by substituting the influence for the depth-dependent property. The properties were estimated from the fracture frequency and P-wave velocity log data. The influence of elastic modulus and density on the site stress field was dominant, with decreasing the deviation trend between modeling and in-situ data at a deep depth. Considering that the depth of the repository construction is within about 500 m, it may not be necessary to consider the change of rock properties with depth. However, it was determined that the rock property effect might need to be considered when the loading conditions change due to subsidence in the long-term evolution scenario. Continuously, this site descriptive modeling will be interdependently conducted with a representative DFN block model for deriving equivalent properties in fractured rock.

Coupled thermo-hydraulic-mechanical (THM) processes are essential for the long-term performance of deep geological disposal of high-level radioactive waste. In this study, a numerical sensitivity analysis was performed to analyze the effect of rock properties on THM responses after the execution of the heater test at the Kamaishi mine in Japan. The TOUGHFLAC simulator was applied for the numerical simulation assuming a continuum model for coupled THM analysis. The rock properties included in the sensitivity study were the Young’s modulus, permeability, thermal conductivity, and thermal expansion coefficients of crystalline rock, rock salt, and clay. The responses, i.e., temperature, water content, displacement, and stress, were measured at monitoring points in the buffer and near-field rock mass during the simulations. The thermal conductivity had an overarching impact on THM responses. The influence of Young’s modulus was evident in the mechanical behavior, whereas that of permeability was noticed through the change in the temperature and water content. The difference in the THM responses of the three rock type models implies the importance of the appropriate characterization of rock mass properties with regard to the performance assessment of the deep geological disposal of high-level radioactive waste.

To decrease area of the repository for high-level radioactive waste, enhancing the disposal efficiency is needed for public acceptance. Previous studies regarding the performance assessment of KRS and KRS+ repository did not consider area-based variations of the geothermal gradient and rock thermal properties in Korea. This research estimated deposition hole spacing based on performance assessment of a repository using the distribution of geothermal gradient and rock thermal properties in Korea to increase disposal efficiency. Distributions of geothermal gradient, rock thermal properties were investigated based on 2019 Korea geothermal atlas published by Korea Institute of Geoscience and Mineral Resources (KIGAM). Effect of thermal performance parameters was analyzed using coupled thermal-hydraulic numerical simulations, and effect of rock thermal conductivity and deposition hole spacing on the maximum temperature of buffer was relatively large. In addition, distribution maps of thermal performance of a repository and deposition hole spacing were plotted using thermal performance parameters-maximum temperature of buffer regression equations and GIS data given by KIGAM. In the regions showing the highest maximum temperature of buffer in Korea, required deposition hole spacings were 10.5 m, 10.0 m, 10.1 m, respectively for KJ-II, MX-80, and FEBEX bentonite cases, and thereby additional disposal area of 40%, 33.3%, and 34.7% were required compared to that of the KRS+ repository. On the other hand, high disposal efficiency can be obtained in the regions showing the low maximum temperature of bentonite buffer. The methodology provided in this research can be used as one of the references for the selection of domestic candidate repository sites. Additional mechanical performance analysis should be conducted using distributions of mechanical properties of rock mass in Korea.

In 1924, natural roack asphalt, which is called Asbuton, was found in South East Sulawesi, Buton Island, Indonesia. Since 2006, Asbuton has been widely applied on national road, provincial road and district roads not only for low volume traffic roads but also for the medium and heavy traffic roads. The use of Asbuton in Indonesian road infrastructure development is increasing because the deposits are estimated to be 677 million tons while current annual production is only approximately 20,000 tons. Asbuton mainly consist of asphalt and mineral like a Trinidad Lake Asphalt. The asphalt content of Asbuton is about 35% or less. Many researchers agreed that pure asphalt binder should be separated from its minerals of Asbuton in order for the conventional asphalt binder to be used widely and economically. Asbuton could replace the conventional asphalt binder. In this study, fundamental and reheological properties of pure asphalt binder extrcted from Asbuton are evauluated to find a possiblity to repalce it as the conventional asphalt binder. The first, pure asphalt binder extrcted from Asbuton through extraction process. Second, penetration test, softening point test, ductility test, and flash point test are conducted to measure physical properties of pure asphalt binder extrcted from Asbuton. Third, dynami shear rheometer (DSR) test, rolling thin film ovens(RTFO) test, pressure aging vessel(PAV) test, and bending beam rheometer(BBR) test are conducted to determine perfoemance grade as a reheological properties. Based on the limited laboratory test results, pure asphalt binder extrcted from would be possibly used as modified additive to improve physical properties and the performance grade at high tempertaure.

본 연구에서는 타당한 지하조건을 모사하기 위한 실험장치를 글로버박스(Glove-box) 내에 설치하고 천연지하수 및 자연균열을 가진 화강암 시추코어를 이용하여 핵종이동 실험을 수행하였다. 암반코어의 균열을 통한 지하수 유동을 해석하기 위하여 비수착성 음이온 핵종인 Br로 지하수 유동실험을 수행하였다. 암반 균열을 통한 우라늄 이동 실험결과에서 유출된 우라늄의 파과곡선이 비수착성 핵종인 Br와 유사한 거동을 보여주었는데, 이는 주어진 지하수 조건에서 우라늄이 주로 탄산염과 결합된 음이온 복합체로 이동하기 때문인 것으로 추정된다. 아울러 균열충전광물에 대한 우라늄의 회분식 수착실험을 수행한 결과, 균열충전광물에 대한 우라늄의 분배계수 는 약 2.7 mL/g로 낮게 나타났다. 이러한 우라늄 수착실험 결과는 빠른 유출을 보인 우라늄 이동실험 결과와 일치한다. 균열암반을 통한 우라늄 이동의 지 연 특성을 보다 자세히 분석하기 위하여 회분식 수착실험으로 부터 구한 값을 이용해 지연인자 값 를 구하고 이동실험 결과로부터 구한 값 과 비교한 결과, 서로 매우 유사한 지연인자 값을 가진다는 것을 알 수 있었다. 이는 화강암 코어의 균열을 통한 우라늄의 이동 지연이 주로 균열충전광물에 의해 이루어지고 있음을 의미하는 것이라고 하겠다.

The vegetation-based spraying method has been used as a revegetation measure for protecting slopes. However, after the method is applied to the fields, the collapse due to deteriorated bond performance of artificial slopes and defective vegetation growth bases prevent it from displaying its proper function. Therefore, research and application technologies for revegetation measures that can achieve both the reinforcement of slopes and the ecological restoration at the same time are necessary. Accordingly, in this study, fundamental research was conducted regarding the bond properties of slopes, according to the addition of additives based on bonding materials for improving bond performance.