Tunnel and Underground SpaceISSN:1225-1275(Print) 2287-1748(Online)한국암반공학회

In order to examine the behavioral characteristics of the fault, scaled model tests were performed using a biaxial compression test apparatus with servo control function. Test specimens were made of a mixture of sand, gypsum, cement and water. The behavior and the failure stress conditions of the faults were investigated by conducting an experiment to pressurize and destroy the fault planes under constant constraint load conditions for 19 model specimens. The strike-slip fault models were displaced along a fault plane that existed in the diagonal direction of the test specimens, and the reverse fault models showed the behavior of the hanging wall riding up the foot wall, so that the fault behavior was empirically identified through physical experiments. The model with a rough and interlocked fault plane had a lower breaking load than the model with a flat fault plane. It was confirmed that the crushed crumbs caused by the wear of the irregularities on the interlocked fault plane acted like a fault gouge to reduce shear resistance.

The effects of blasting vibration on underground structures were numerically analyzed using field-measured data. The research target facility is an open-pit limestone mine. The 3D numerical model for the analysis was constructed using the actual topography based on drone and LiDAR surveying data, and the blasting load which is the main input data in dynamic analysis was determined through back-analysis of the field-measured blasting vibration results. The analysis of the effects of blasting operations revealed that the stability of the underground structures was not significantly compromised when an appropriate maximum charge weight per delay was applied. Also, it was confirmed that the blasting load determined through back-analysis reproduced the blasting vibration regression equation derived from the field-measured data in a highly reasonable manner. Therefore, the back-analysis-based blasting load estimation technique can be effectively utilized as a method to determine input data for dynamic numerical analysis to evaluate blasting vibration impacts on underground structures. Consequently, the methodology proposed in this study is considered appropriate as an approach and analytical procedure for blasting vibration impact assessments.

The access area of a deep geological repository for high-level radioactive waste is a key access facility for the transportation of personnel, equipment, materials, and waste, as well as for ventilation, drainage, emergency evacuation, and maintenance. During the excavation of the access area, typically represented by access ramps and shafts, host rock damage, groundwater inflow, excavation damaged zones (EDZs), and hydro-mechanical disturbances may occur. After closure, the access area may also act as a potential radionuclide flow pathway connecting the surface and the disposal area. Therefore, the design of the access area needs to be carefully reviewed from a proactive regulatory perspective in connection with structural stability, constructability, operational safety, post-closure long-term isolation performance, and quality assurance systems. In this study, domestic and international regulatory requirements and quality management items applicable to the access area were reviewed, and relevant cases from ONKALO in Finland and Forsmark in Sweden were analyzed. The results indicate that the design of the access area should comprehensively consider site conditions, disposal concepts, transportation and ventilation plans, groundwater inflow control, EDZ management, rock support and grouting plans, and post-closure sealing feasibility. Based on these findings, this study proposes a stepwise verification procedure and a design review checklist covering the access route system, access ramp, shafts, and common quality management items. The proposed verification procedure and checklist are expected to serve as basic reference materials for establishing a design suitability verification framework for the access area of future deep geological repositories and underground research facilities in Korea.

The discrete element method (DEM) is widely used to simulate the mechanical behavior of discontinuous rock masses; however, the numerical stability, reproducibility of contact history, and computational efficiency of the analysis can vary depending on the contact calculation method adopted. In this study, two representative DEM contact formulations, the spring model and the impulse-based method, were comparatively analyzed in terms of their numerical response to variations in the timestep under identical simulation conditions. To this end, static contact, quasi-static shear, rotational, and dynamic impact conditions were considered, and the contact force, shear resistance, velocity, position, and energy responses were compared. The results show that the spring model effectively reproduces the gradual mobilization of contact force and shear resistance under static contact and quasi-static shear conditions, but exhibits contact force oscillation, distortion of the energy response, and divergence as the timestep increases. In contrast, the impulse-based method maintains a stable kinematic response even at relatively large timesteps under rotational and dynamic impact conditions, yet shows limitations in reproducing the quasi-static shear behavior that relies on contact history. The difference in the contact calculation schemes of the two methods manifests as a difference in their sensitivity to the timestep, which in turn determines the suitability of each method depending on whether the analysis focuses on contact history or momentum change. These findings suggest that, if future studies address the limitations of the impulse-based method, its application can be extended to jointed rock mass analysis while preserving its computational efficiency.

Currently, deep disposal is being promoted in Korea for the permanent disposal of high-level radioactive waste (HLW) within deep rock formations. The thermal properties of the rock mass are critical factors that determine the spacing between disposal holes and tunnels, as well as the total volume of the disposal facility. Therefore, these properties must be evaluated to ensure the economic feasibility and suitability of a disposal site. However, measured data on the thermal properties of deep rock formations in Korea remain scarce. Crystalline rock considered as a host rock in deep disposal repository includes granite and gneiss. In this study, deep rock samples were collected from Hongcheon and Hadong, which are located in gneiss regions. Thermal properties, including thermal conductivity, specific heat, and thermal diffusivity were determined using the Transient plane source method (TPS), while the coefficient of thermal expansion was measured using strain gauges. Furthermore, X-ray diffraction (XRD) analysis confirmed that rock-forming minerals are key factors influencing thermal conductivity. Both the measured values from this study and the existing literature data exhibited a proportional relationship between thermal conductivity and thermal diffusivity. Furthermore, it was confirmed that the analysis of thermal conductivity based on quartz content yielded the highest accuracy. The findings of this study are expected to serve as significant fundamental data for the site selection and design processes of deep disposal facilities in Korea.

For the safe design and construction of high-level radioactive waste (HLW) disposal facilities, it is essential to accurately characterize the mechanical properties of the rock mass at the disposal site. This study presents methods for estimating and verifying the Uniaxial Compressive Strength (UCS), a key evaluation parameter during the site characterization stage of site selection, to ensure its reliability. We conducted a comparative analysis of domestic and international standard test methods (ASTM, ISRM, KS, KSRM) for UCS and identified quality control factors across the entire process, from specimen preparation and testing to result reporting. Specifically, using granite drill cores from the Wonju area as a case study, we examined error verification of the measurement systems and methods for quantifying natural uncertainties. Furthermore, based on international precedents, we discussed methods for ensuring the representativeness of design parameters by applying statistical techniques, such as calculating 95% confidence intervals using the Central Limit Theorem. The verification methods proposed in this study are expected to serve as a versatile methodology for estimating and validating evaluation parameters in other fields beyond mechanical properties like UCS.