• Geomechanics and Engineering
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• 제23권2호
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• pp.151-163
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• 2020

Grouting method is an effective way of reinforcing cracked rock masses and plugging water gushing. Current grouting diffusion models are generally developed for horizontal cracks, which is contradictory to the fact that the crack generally occurs in rock masses with irregular spatial distribution characteristics in real underground environments. To solve this problem, this study selected a cement-sodium silicate slurry (C-S slurry) generally used in engineering as a fast-curing grouting material and regarded the C-S slurry as a Bingham fluid with time-varying viscosity for analysis. Based on the theory of fluid mechanics, and by simultaneously considering the deadweight of slurry and characteristics of non-uniform spatial distribution of viscosity of fast-curing grouts, a theoretical model of slurry diffusion in an oblique crack in rock masses at constant grouting rate was established. Moreover, the viscosity and pressure distribution equations in the slurry diffusion zone were deduced, thus quantifying the relationship between grouting pressure, grouting time, and slurry diffusion distance. On this basis, by using a 3-d finite element program in multi-field coupled software Comsol, the numerical simulation results were compared with theoretical calculation values, further verifying the effectiveness of the theoretical model. In addition, through the analysis of two engineering case studies, the theoretical calculations and measured slurry diffusion radius were compared, to evaluate the application effects of the model in engineering practice. Finally, by using the established theoretical model, the influence of cracking in rock masses on the diffusion characteristics of slurry was analysed. The results demonstrate that the inclination angle of the crack in rock masses and azimuth angle of slurry diffusion affect slurry diffusion characteristics. More attention should be paid to the actual grouting process. The results can provide references for determining grouting parameters of fast-curing grouts in engineering practice.

• KIEE International Transactions on Power Engineering
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• 제3A권2호
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• pp.63-69
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• 2003

The necessity of compact high temperature superconducting cables is more keenly felt in densely populated metropolitan areas. Because the compact high-temperature superconducting cables can be installed in ducts and tunnels, thereby reducing construction costs and making the use of underground space more effective, the effect of introducing it to the power system will be huge. Seoul, Korea, is selected as a review model for this paper. The loads are estimated by scenario based on a survey and analysis of 345kV and 154kV power supply networks in this area. Based on this, the following elements for an urban transmission system are examined. (1) A method of constructing a model system to introduce high-temperature superconducting cables to metropolitan areas is presented. (2) A case study is conducted through the analysis of power demand scenarios, and the amount of high-temperature superconducting cable to be introduced by scenario is examined. (3) The economy involved in expanding existing cables and introducing high-temperature superconducting cables(ducts or tunnels) following load increase in urban areas is examined and compared., and standards for current cable ducts are calculated. (4) The voltage level that can be accommodated by existing ducts is examined.

• Tunnel and Underground Space
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• 제18권2호
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• pp.91-97
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• 2008

In this paper, in-situ technique for measuring hydraulic conductivity of Excavation Disturbed Zone (EDZ) in a direct way and its application to an Underground Research Laboratory (URL) site were introduced. It was understood that both the EDZ oriented test equipment as a hardware and analysis/evaluation technique as a software should be integrated for upgrading a quality of estimated EDZ hydraulic conductivity. The well-estimated EDZ hydraulic conductivity is expected to enhance a reliability of stability evaluation for caverns under groundwater table and design of a waterproof or drainage system as well as a grout system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• 제23권5호
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• pp.89-95
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• 2023

The underground utility tunnel is an urban infrastructure that accommodates and manages important facilities such as water and sewage, electricity, and communication in the city, and is a national facility that needs to be protected from disasters such as fire, earthquake, and flooding. In establishing a disaster safety life cycle management system such as prediction, prevention, preparedness, response, and recovery, a disaster safety management platform for underground utility tunnel is being developed by utilizing digital twin technology in which advanced ICT technology and data are converged. In this paper, the maturity model for the disaster safety digital twin was reviewed, and the datasets necessary for implementing the digital twin at each stage were defined.

• Geomechanics and Engineering
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• 제12권3호
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• pp.541-560
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• 2017

In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two non-coplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of $60^{\circ}$, before increasing to the maximum at the ligament angle of $120^{\circ}$, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when ${\alpha}$ < ${\beta}$, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using $PFC^{2D}$ were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.

• Geomechanics and Engineering
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• 제8권5호
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• pp.675-685
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• 2015

Weathering is the breaking/cutting down process of rocks due to physical and chemical processes in natural as well as artificial environment including $CO_2$ injection for storage in the sediment, or natural resource recovery process. This study suggests an alternative method to estimate the degree of weathering for granites. A series of laboratory and field experiments are performed to measure electrical resistivities on various rock samples experienced different degrees of weathering and their residual soils under different saturation conditions. It is found that the normalized electrical resistivity increases with a decrease in water absorption and the saturation. Simple boundaries are suggested to identify the weathering degree of granites, based on limited data. Field test results for three sites confirm that the suggested method could be estimated well the degree of weathering of granites compared with the other methods suggested previously. Although further research is required, this study suggests that an electrical resistivity could be an effective approach to estimate the degree of weathering of granites compared with the other methods suggested previously.

• Journal of Korean Tunnelling and Underground Space Association
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• 제15권2호
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• pp.97-111
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• 2013

It is very important to understand the condition of the surround rock for the successful construction of underground space. Representative methods of estimating the rock mass condition are RMR method and Q-system, and they are applied on design, construction, and maintenance. However, many problems with the accuracy of the measurement method and the subjective viewpoint are questioned continuously, so many researchers have been studied for estimating rock condition from various methods. Most of them show only the local relation and a tendency between site investigation data and rock conditions. In this paper, the relationship between RMR method and electrical resistivity is deducted using the analytical equation derived theoretically from electric field analysis on jointed rock mass. And also, probabilistic relationship between RMR method and electrical resistivity is deducted for the increase of accuracy. If a suggested method is applied with the conventional method for estimating the rock condition, it will be helpful to estimate RMR values on the field.

• Tunnel and Underground Space
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• 제28권6호
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• pp.596-608
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• 2018

As urban infrastructure is aging, the possibility of accidents due to the failures or breakdowns of infrastructure increases. Especially, aging underground infrastructures like sewer pipes, waterworks, and subway have a potential to cause an urban ground sink. Urban ground sink is defined just as a local and erratic collapse occurred by underground cavity due to soil erosion or soil loss, which is separated from a sinkhole in soluble bedrock such as limestone. The conventional measurements such as differential settlement gauge, inclinometer or earth pressure gauge have a shortcoming just to provide point measurements with short coverage. Therefore, these methods are not adequate for monitoring of an erratic subsidence caused by underground cavity due to soil erosion or soil loss which occurring at unspecified time and location. Therefore, an alternative technology is required to detect a change of underground physical condition in real time. In this study, the feasibility of a novel magnetic resonance based monitoring method is investigated through laboratory tests, where the changes of path loss (S21) were measured under various testing conditions: media including air, water, and soil, resonant frequency, impedance, and distances between transmitter (TX) and receiver (RX). Theoretically, the transfer characteristic of magnetic field is known to be independent of the density of the medium. However, the results of the test showed the meaningful differences in the path loss (S21) under the different conditions of medium. And it is found that the reflection coefficient showed the more distinct differences over the testing conditions than the path loss. In particular, input reflection coefficient (S11) is more distinguishable than output reflection coefficient (S22).

• Journal of Korean Tunnelling and Underground Space Association
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• 제12권1호
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• pp.61-73
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• 2010

The cablebolt which secures a workability and stability has been used in foreign countries as one of supporting materials with rebar rockbolt especially in construction of large underground structures. However, only the rebar rockbolt has been applied up to now to all the constructions of underground structures in Korea due to an absence of recognition of cablebolt and large underground structure projects. Consequently, the research for a performance evaluation and verification of cablebolt is very limited and only the proto-type field tests have been conducted. In this study, the cone-shaped button cablebolt is developed by modifying an existing button cablebolt. To evaluate a performance and applicability of cone-shaped button cablebolt, the laboratory pull tests are conducted and bond capacity is analyzed under a various conditions. The rebar rockbolt, plane cablebolt, and bulb cablebolt which has a similar mechanical behavior with cone-shaped button cablebolt, are also tested and their bond capacities are evaluated and compared with cone-shaped button cablebolt under the same condition. The results show that the bond capacity is in the order of (cone-shaped button cablebolt$\approx$bulb cablebolt) > rockbolt > plane cablebolt. It is found that the bond capacity of cone-shaped button cablebolt developed in this study is at least equivalent with an existing high performance cablebolt developed in foreign countries, therefore the cone-shaped button cablebolt could be used as one of supporting materials for underground structures in construction field.

• International conference on construction engineering and project management
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• The 9th International Conference on Construction Engineering and Project Management
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• pp.344-352
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• 2022

Accurate indoor localization of construction workers and mobile assets is essential in safety management. Existing positioning methods based on GPS, wireless, vision, or sensor based RTLS are erroneous or expensive in large-scale indoor environments. Tightly coupled sensor fusion mitigates these limitations. This research paper proposes a state-of-the-art positioning methodology, addressing the existing limitations, by integrating Stereo Visual Inertial Odometry (SVIO) with fiducial landmarks called AprilTags. SVIO determines the relative position of the moving assets or workers from the initial starting point. This relative position is transformed to an absolute position when AprilTag placed at various entry points is decoded. The proposed solution is tested on the NVIDIA ISAAC SIM virtual environment, where the trajectory of the indoor moving forklift is estimated. The results show accurate localization of the moving asset within any indoor or underground environment. The system can be utilized in various use cases to increase productivity and improve safety at construction sites, contributing towards 1) indoor monitoring of man machinery coactivity for collision avoidance and 2) precise real-time knowledge of who is doing what and where.