• Tunnel and Underground Space
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• v.31 no.1
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• pp.52-65
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• 2021

In this study, authors analyzed the vapor cloud explosion induced by propane leak at the PEMIX Terminal, which is the propane storage facility outside of Mexico City. TNT equivalence mass for the leaked 4750 kg propane was estimated to be 9398 kg. Blast parameters such as peak overpressure, positive phase duration, and impact at 40-400 (m) away from the center of the explosion were calculated by applying TNT Equivalency Method and Multi-Energy Method. The probability of damage due to lung damage, eardrum rupture, head impact, and whole-body displacement impact by applying the probit function obtained using blast parameters was evaluated. The peak overpressure obtained using Multi-Energy Method was found to be greater than the peak overpressure obtained by applying the TNT Equivalency Method at all distances considered, but it was evaluated that there was no significant difference from the points above 200 m. The peak overpressure obtained by Multi-Energy Method was computed to assess the extent of damage to the structure, and it was shown that structures within 100 m of the explosion center would collapse completely, and that the glasses of the structures 400 m away would be almost broken. The probability of death due to lung damage was shown to vary depending on a human body's position located in the propagating direction of shock wave, and if there is a reflecting surface in the immediate surroundings of a human body, the probability of death was estimated to be the greatest. The impact of shock wave on lung damage, eardrum rupture, head impact, and whole-body displacement impact was evaluated and found to affect whole-body impact < lung damage < eardrum rupture

• Tunnel and Underground Space
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• v.30 no.6
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• pp.509-518
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• 2020

This study constructed a new simulation platform, including mesh generation process, numerical simulation, and post-processing for results analysis based on exploration data to perform real-scale numerical analysis considering the actual geological structure efficiently. To build the simulation platform, we applied for open-source programs. The source code is open to be available for code modification according to the researcher's needs and compatibility with various numerical simulation programs. First, a three-dimensional model(3D) is acquired based on the exploration data obtained using a drone. Then, the domain's mesh density was adjusted to an interpretable level using Blender, the free and open-source 3D creation suite. The next step is to create a 3D numerical model by creating a tetrahedral volume mesh inside the domain using Gmsh, a finite element mesh generation program. To use the mesh information obtained through Gmsh in a numerical simulation program, a converting process to conform to the program's mesh creation protocol is required. We applied a Python code for the procedure. After we completed the stability analysis, we have created various visualization of the study using ParaView, another open-source visualization and data analysis program. We successfully performed a preliminary stability analysis on the full-scale Dokdo model based on drone-acquired data to confirm the usefulness of the proposed platform. The proposed simulation platform in this study can be of various analysis processes in future research.

• Tunnel and Underground Space
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• v.31 no.1
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• pp.41-51
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• 2021

The hydraulic fracturing developed to improve permeability of tight reservoir is one of key stimulation technologies for developing unconventional resources such as shale gas and deep geothermal energy. The experimental study was conducted to improve disadvantage of hydraulic fracturing which has simple fracture pattern and poor fracturing efficiency. The fracturing experiments was conducted for tight rock using various fracturing fluids, water, N2, and CO2 and the created fracture pattern and fracturing efficiency was analyzed depending on fracturing fluids. The borehole pressure increased rapidly and then made fractures for hydraulic fracturing with constant injection rate, however, gas fracturing shows slowly increased pressure and less fracture pressure. The 3D tomography technic was used to generate images of induced fracture using hydraulic and gas fracturing. The stimulated reservoir volume (SRV) was estimated increment of 5.71% (water), 12.72% (N2), and 43.82% (CO2) respectively compared to initial pore volume. In addition, permeability measurement was carried out before and after fracturing experiments and the enhanced permeability by gas fracturing showed higher than hydraulic fracturing. The fracture conductivity was measured by increasing confining stress to consider newly creating fracture and closing induced fracture right after fracturing. When the confining stress was increased from 2MPa to 10MPa, the initial permeability was decreased by 89% (N2) and 50% (CO2) respectively. This study shows that the gas fracturing makes more permeability enhancement and less reduction of induced fracture conductivity than hydraulic fracturing.

• Tunnel and Underground Space
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• v.32 no.2
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• pp.160-172
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• 2022

The design regulations for simple explosive storage in Korea only stipulate standards for the materials and thickness of the wall of the structure because the amount of explosives that can be stored is small. There is concern about secondary damage during an internal explosion in a simple storage facility, and it is necessary to reexamine the current standards. The numerical analysis for the TNT 15 kg explosion inside the simple storage was carried out by setting the factors using the robust experimental design method. The displacement of the structure generated under the same time condition was analyzed, and the contribution was evaluated. The contribution of concrete thickness was the highest, and the contribution of concrete strength and rebar arrangement was lower than that of concrete thickness. The reinforcement diameter contributed extremely little to the displacement. The structural standards of the simple storage that are currently applied are insufficient on blast resistance, and it is necessary to present new design standards. Therefore, the design factor to be applied later analysis and actual experiments were taken into consideration. For the design variables, the thickness of the concrete was 15 cm considering the displacement, the concrete strength was selected as general concrete considering the inlet discharge pressure, the factor with the lowest average displacement was selected for the reinforcement arrangement and the diameter of the reinforcement, the factor with the smallest level was selected in consideration of economic feasibility because the difference in displacement was low.

• Tunnel and Underground Space
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• v.32 no.1
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• pp.78-92
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• 2022

In this study, we proposed a diagnostics and assessment model for mining sites that can evaluate the smart mining technology level in a systematic and structured way. For this, the maturity of the smart mining was defined, and detailed assessment items of the diagnostics and assessment model for smart mining were derived by considering the smart factory diagnostics and assessment model (KS X 9001-3) used in the manufacturing industry. While maintaining the existing system, the existing 46 detailed assessment items were modified to be suitable for mining. As a result, a total of 29 detailed assessment items were derived in the areas of promotion strategy, process, information system and automation, and performance. Based on this, a questionnaire was designed to diagnose the level of smart mining technology, and assessment was performed by applying it to domestic iron mines. The level of smart mining technology in the study area was found to be level 2, and it could be inferred that it was about 40% lower than the average smart level of the general manufacturing industry. In addition, by using the developed model, it was possible to recognize the weak points of the mine at each stage of the introduction, operation, and advancement of smart mining, and to suggest investment and improvement directions.

• Tunnel and Underground Space
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• v.32 no.2
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• pp.120-130
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• 2022

In this study, the applicability of the microseismic monitoring system based on the underground mine communication system has been verified by operation test in the domestic underground mine. The microseismic data consists of wavelet data and meta-data for mine safety management, and both data should be transferred, stored, analyzed and managed with proper method according to the purpose and size of each data. In order to select the optimal communication system for the microseismic monitoring system considering the underground environment as well as properties of data, various types of communication system have been tested and compared during operation test after installing the optical cable communication system, 2.4 GHz and 900 MHz wireless communication system through the underground mine tunnel and overground area of the test site. The integrated microseismic monitoring software, which was developed to secure the stability of data management and ease of use, has been updated according to findings from operation test. Through the operation test of the microseismic monitoring system including the communication system and the monitoring software, the technical basis was established corresponding to various requirements of the domestic mine for adoption of the microseismic monitoring system.

• Tunnel and Underground Space
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• v.32 no.2
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• pp.131-143
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• 2022

The lunar exploration autonomous vehicle operates based on the lunar topography information obtained from real-time image characterization. For highly accurate topography characterization, a large number of training images with various background conditions are required. Since the real lunar topography images are difficult to obtain, it should be helpful to be able to generate mimic lunar image data artificially on the basis of the planetary analogs site images and real lunar images available. In this study, we aim to artificially create lunar topography images by using the location information-based style transfer algorithm known as Wavelet Correct Transform (WCT2). We conducted comparative experiments using lunar analog site images and real lunar topography images taken during China's and America's lunar-exploring projects (i.e., Chang'e and Apollo) to assess the efficacy of our suggested approach. The results show that the proposed techniques can create realistic images, which preserve the topography information of the analog site image while still showing the same condition as an image taken on lunar surface. The proposed algorithm also outperforms a conventional algorithm, Deep Photo Style Transfer (DPST) in terms of temporal and visual aspects. For future work, we intend to use the generated styled image data in combination with real image data for training lunar topography objects to be applied for topographic detection and segmentation. It is expected that this approach can significantly improve the performance of detection and segmentation models on real lunar topography images.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.520-533
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• 2021

It is necessary to increase the blasting efficiency in order to minimize the economic loss caused when the excavation cross section is reduced due to the stability problem of underground mining development, and for this, a new blasting design is proposed. In this study, the blasting efficiency of the general design in the field, the suggestion designI, which added two columns to production blasting, and the suggestion design II, which added one column to create asymmetry, is compared. Advance rate and fragmentation were selected as the evaluation index of the blasting efficiency. In the case of advance rate, compared to the normal, the suggestionI improved by 6.07% and the suggestionII improved by 4.65%. In the case of fragmentation, based on P80, compared to the normal, the suggestionI reduced about 58% and the suggestionII was about 47%. Accoording to the evaluation index, the suggestion designI shows better blasting efficiency than the suggestion designII. But considering the additional work time and cost required for the suggestion designI due to the insignificant difference in the evaluation index results, the asymmetry V-cut, the suggestion designII, is judged to be a more suitable blasting design for the site.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.610-622
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• 2021

The DECOVALEX project is one of the representative international cooperative projects to enhance the understanding of the complex Thermo-Hydro-Mechanical-Chemical(THMC) coupled behavior in the high-level radioactive waste disposal system based on the numerical simulation. DECOVALEX-2023 is the current phase consisting of 7 tasks, and Task C aims to model the THM coupled behavior in the disposal system based on the Full-scale Emplacement (FE) experiment at the Mont-Terri underground rock laboratory. This study performs the numerical simulation based on the OGS-FLAC developed for the current study. In the numerical model, we emplaced the heater with constant power horizontally based on the FE experiment and monitored the pressure development, temperature increase, and mechanical deformation at the specific monitoring points. We monitored the capillary pressure as the primary effect inducing the flow in the buffer system, and thermal stress and pressurization were dominant in the surrounding rocks' area. The results will also be compared and validated with the other participating groups and the experimental data further.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.534-548
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• 2021

In this paper, the feasibility of generating solar power near an abandoned quarry is examined with the objectives of resolving the essential problems that quarries encounter, such as rockfalls and space usage issues. On an abandoned quarry site in Sadang, Seoul, Republic of Korea, two different PV installation methods were analyzed. The first is attaching PV directly on the quarry slope. Since there are no corresponding safety standards and precedents for installing solar panels directly on slopes, the power generation potential was calculated by using topographic data and reasonable assumptions. The surface area of cut slope section was extracted from the Digital Elevation Model(DEM) via ArcGIS and Python programming to calculate the tilt and power capacity of installable panels. The other approach is installing PV as a rockfall barrier, and the power generation potential was analyzed with the assumption that the panel is installed in the direction of facing solar irradiation. For the derivation of power generation, the renewable energy generation analysis program SAM(System Advisor Model) was used for both methods. According to the result, quarries that have terminated resource extraction and remain devastated have the potential to be transformed into renewable energy generation sites.