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

The Taebaek Underground Research Laboratory is planned as a large-scale underground facility for validating deep geological disposal technologies, in which access configuration and excavation sequence significantly affect construction duration and cost. This study developed a three-dimensional BIM model using publicly available conceptual planning information and linked the BIM objects with a work breakdown structure, schedule activities, and unit-cost data. Three alternatives were analyzed by varying the shaft excavation sequence and the use of an inclined access tunnel. The estimated construction durations were 37.0, 34.5, and 43.0 months, while the direct construction costs were 72.64, 72.64, and 93.87 billion won, respectively. Alternative 2 reduced the duration by 2.5 months through schedule rearrangement, whereas Alternative 3 increased both duration and direct cost because of the long inclined rampway. The results demonstrate the applicability of 5D BIM to integrated geometry, schedule, and cost evaluation at the planning stage and provide an initial information base for future data integration. It should be noted that construction duration and direct construction cost presented in this study were estimated under general design and construction conditions, and these results may vary depending on site-specific geological and geotechnical environments, detail design specifications, and construction practices.

In long-term safety assessments for deep geological disposal of high-level radioactive waste, the future behavior of the disposal system is represented by scenarios and evaluated quantitatively, and Features, Events and Processes (FEPs) are used in various ways throughout this process. This study compares disposal programs in France, Switzerland, Germany, Japan, Finland, Sweden, and the United States in terms of the starting point, construction process, resulting scenarios, and implementation in quantitative assessment. Recurring procedural characteristics were organized into four types: causal-tracing, FEP grouping-and-integration, framework-first, and evolution-pathway; these are neither official nor mutually exclusive classifications used by the national programs. FEPs are used differently across programs for causal tracing, grouping or integration, evolution analysis, or completeness checking. Under current Korean conditions, where a disposal site has not yet been determined, each method can be conceptually examined using representative geological environments and FEP lists, and geological and rock engineering information can be linked, depending on the method, to FEP causal relationships, state variables, safety-function degradation, or long-term system evolution. As site-specific conditions and data are secured, scenarios and calculation conditions should be specified with traceable documentation of their rationale. This comparison does not identify a preferred method for Korea.

Recently, tunnel collapse accidents have been occurring, raising concerns about tunnel safety. Because tunnels involve ground uncertainty, if they are under-reinforced in poor ground conditions, tunnel collapse accompanied by abnormal displacement may occur. General measurement management standards have been established to verify tunnel stability during construction. However, due to the lack of evaluation standard for signs of tunnel collapse, it is currently difficult to implement collapse response measures, such as additional reinforcement and emergency evacuation. This study developed a tunnel collapse evaluation standard based on abnormal displacement occurring prior to tunnel collapse. Numerical analysis was performed considering parameters such as tunnel cross-section and ground conditions. tunnel displacement and support system were evaluated when the rock strength was downgraded due to ground uncertainty. In some review conditions, it was found that abnormal displacement occurred as the stress of the support system exceeded the allowable standard due to under-reinforcement caused by ground deterioration. Based on abnormal displacements occurring in the tunnel, step-by-step tunnel collapse evaluation standard according to tunnel support patterns were developed. Through the proposed tunnel collapse evaluation standard, it will be possible to identify signs of tunnel collapse in advance and ensure tunnel stability through collapse response measures.

Mechanical excavation is widely used in hard rock excavation because it enables continuous excavation while reducing vibration, noise, and overbreak compared with conventional drilling and blasting. However, in high-strength rocks such as granite, excavation efficiency is often reduced because of high cutting resistance and severe cutter wear. Accordingly, microwave pretreatment has attracted considerable attention as a promising technique for weakening hard rock prior to mechanical excavation. Microwave irradiation induces localized heating and differential thermal expansion among constituent minerals, generating microcracks that degrade the mechanical properties of the rock and improve its cuttability. This study quantitatively investigated the influence of microwave irradiation on the mechanical properties and cutting performance of Pocheon granite. The experimental results showed that microwave irradiation reduced the elastic wave velocities by 23.2% for P-waves and 16.1% for S-waves. The mechanical strength also decreased, with reductions of 35.2% in Brazilian tensile strength and 25.5% in uniaxial compressive strength. In addition, the cutting force and specific energy decreased, while the proportion of fine rock fragments increased. Microwave irradiation significantly reduced the mechanical strength, cutting force, and specific energy while promoting finer fragmentation, demonstrating its potential as a pretreatment technique for improving the efficiency of hard-rock mechanical excavation.

Groundwater flow in crystalline rock masses occurs mainly through joints, making the hydraulic characterization of single joint important for various rock mechanics applications. This study numerically investigated the effects of joint roughness and aperture spatial correlation on linear and nonlinear flow through a single rock joint. Two-dimensional numerical models were constructed using digitized standard JRC profiles, and aperture fields with identical mean and distribution but different correlation lengths were generated. Steady incompressible flow simulations were performed using the Navier-Stokes equations, and the results were analyzed with the Forchheimer and Izbash equations. The results showed that shorter aperture correlation lengths reduced discharge and increased nonlinear flow coefficients under the same mean aperture condition. This is attributed to frequent local aperture variations, which strengthen inertial loss and eddy formation. In addition, the effect was more pronounced for rougher profiles. These findings indicate that both joint roughness and aperture space characteristics should be separately quantified to interpret nonlinear flow through rock joints.

This study quantified the RGB, HSV, and CIELAB color distributions of granite drill-core images and compared the weathering-grade classification performance of support vector machines (SVMs) using quantile-based color features with that of ResNet-18-based deep-learning models. A large image dataset acquired under dry and wet conditions and three illumination levels was used for the color analysis, and the color characteristics associated with imaging conditions and weathering grades were examined using descriptive statistics. The classification experiments used 8,057 images obtained from 2,297 physical cores. The data were group-split into training, validation, and test sets at the physical-core level to ensure that images derived from the same core were not assigned to different subsets. The classification framework consisted of color-feature-based SVMs, a baseline ResNet-18 model using RGB tiles as input (R1), and a fusion model combining the core-level prediction probabilities of R1 with those of the color-feature-based SVM (R2). The fusion coefficient was determined using the validation set only. The test set was not used for model, checkpoint, or fusion-coefficient selection and was reserved for final prediction and a prespecified sensitivity analysis.The results showed that the deep-learning models outperformed the SVM models, with R2, which combined the RGB image model with an SVM incorporating CIELAB features, achieving the highest accuracy of 74.64%. These findings suggest that CIELAB-based color-distribution features may partially complement the predictive information learned by the RGB image model. However, further validation using independent field datasets is required to assess the generalizability and practical applicability of the proposed method.

This study investigated the low-temperature thermal strain and acoustic emission (AE) characteristics of Hwangdeung granite for underground liquid hydrogen storage applications. Granite specimens were cooled stepwise from room temperature to -63°C while their thermal strain and AE activity were monitored. To correct the temperature-dependent effects of the strain gauges and measurement system, the measured strains of copper, borosilicate glass, and titanium alloy were compared with reference data from the National Institute of Standards and Technology (NIST) and the Thermophysical Research Center (TPRC). The calibration curve derived from the copper specimen was then applied to the granite measurements. Before correction, the apparent strain of the granite specimens reached a maximum near -30°C and then decreased. After correction, the thermal strain decreased almost linearly with temperature, reaching approximately -200 με at -63°C. AE activity increased below approximately -20°C and was concentrated between -30 and -50°C, with the highest proportion of AE hits near -40 °C. These results show that AE activity associated with microcracking can be concentrated within a specific temperature range despite continuous macroscopic thermal contraction. The findings provide fundamental experimental data for evaluating the thermal strain and AE characteristics of rock under low-temperature conditions relevant to underground liquid hydrogen storage.

This study evaluated the dynamic compressive behavior of early-age rapid-hardening cement mortar through static compression and split Hopkinson pressure bar (SHPB) tests at curing ages of 1, 3, 7, and 14 days. The dynamic compressive strength and dynamic increase factor (DIF) generally increased with strain rate at all curing ages. The strain-rate sensitivity of the DIF exhibited a non-monotonic trend, reaching its maximum at 3 days and subsequently decreasing at 7 and 14 days. Comparison with previous studies on early-age rapid-hardening cement-based materials showed generally consistent DIF levels and increasing trends within the overlapping test ranges and regression-model comparisons. Based on these results, a unified DIF model incorporating the effects of curing age and strain rate was proposed. The proposed model showed a good fit to the experimental data.