• Tunnel and Underground Space
• /
• v.16 no.6 s.65
• /
• pp.437-450
• /
• 2006

Failure around an underground opening is a function of in-situ stress magnitudes, intact rock strength and the distribution of fractures in the rock mass. At high in-situ stress, the failure process is affected and eventually dominated by stress-induced fractures preferentially growing parallel to the excavation boundary. This fracturing is often observed in brittle type of failure such as slabbing or spatting. Recent studies dies on the stress-induced damage of rock revealed its importance especially in a highly stressed regime. As the constructions of underground structures at deep depths increased, the cases of the brittle failure also increased and furthermore spalling was occurred in Korea at low depths. To improve the stability of the underground structures at highly stressed regime, the characteristics of brittle failure should be examined, but they have not yet been properly investigated. Therefore in this report the characteristics of brittle failure such as types, failure mechanism and modeling methods etc. were considered in all aspects, based on the previous researches.

• Journal of Environmental Science International
• /
• v.26 no.9
• /
• pp.1013-1021
• /
• 2017

Exposure to Diesel Particulate Matter (DPM) potentially causes adverse health effects (e.g. respiratory symptoms, lung cancer). Due to a lack of data on Elemental Carbon (EC) exposure levels in underground copper ore mining (unlike other underground mining industries such as non-metallic and coal mining), this case study aims to provide individual miners' EC exposure levels, and information on their work practices including use of personal protective equipment. EC measurement was carried out during different work activities (i.e. drilling, driving a loader, plant fitting, plant operation, driving a Specialized Mining Vehicle (SMV)) as per NIOSH Method 5040. The copper miners were working 10 h/day and 5 days/week. This study found that the most significant exposures to EC were reported from driving a loader (range $0.02-0.42mg/m^3$). Even though there were control systems (i.e. water tanks and DPM filters) on the diesel vehicles, around 49.5% of the results were over the adjusted recommendable exposure limit ($0.078mg/m^3$). This was probably due to: (1) driver's frequently getting in and out of the diesel vehicles and opening the windows of the diesel vehicles, and (2) inappropriate maintenance of the diesel vehicles and the DPM control systems. The use of the P2 type respirator provided was less than 19.2%. However, there was no significant difference between the day shift results and the night shift results. In order to prevent or minimize exposure to EC in the copper ore mine, it is recommended that the miners are educated in the need to wear the appropriate respirator provided during their work shifts, and to maintain the diesel engine and emission control systems on a regular basis. Consideration should be given to a specific examination of the diesel vehicles' air-conditioning filters and the air ventilation system to control excessive airborne contaminants in the underground copper mine.

• Proceedings of the KSR Conference
• /
• 2007.11a
• /
• pp.974-981
• /
• 2007

Seoul Metro has operated the air cooling equipment established in a machine room of a station building to improve our services focused on our customers who use Seoul Metro during the summer season. However, a new set of problems has arisen with the cooling tower to support a heat exchange of cooling water. One of them is loss of efficiency in the air conditioner. The leading cause of this problem is that we use an underground type of the cooling tower. As the machine room of a station building is located in the underground of inner city because of the nature of the subway, it is difficult to establish the cooling tower on the ground. The underground structure of the No. $1{\sim}4$ subway line is unsuitable for the location requirements of the underground type of the one because it has a limited space to set up the air cooling equipment, for example, the cooling tower and a ventilating opening. As a result of such an unfavorable condition, the cooling tower doesn't work efficiently and the warmth of cooling water because of insufficiency of a heat exchange and a refrigerator's technical obstacle such as a high-temperature and a high-pressure has arisen. Accordingly, the efficiency of the air conditioning is getting lower and lower. Another problem is too wasteful with water. Each station uses the water over 30 tons every day with waterworks to replenish the cooling tower such as a evaporation, a scattering and a distribution of water. Nevertheless, the more an air conditioner increase, the more the use of water supply increase. For this reason, we can't help wasting an enormous amount of water and discharging the congelation of a low temperature(about $15^{\circ}C$) occurred in a heat exchanger inside an air conditioner. The purpose of this study is to analyze the utility of congealing water to improve efficiency of the air cooling equipment and save energy as a supplementary water for the cooling tower.

• Tunnel and Underground Space
• /
• v.14 no.1
• /
• pp.43-53
• /
• 2004

In this study, scaled-model tests were performed to investigate the effect of underground openings on the stability of surface structure around the abandoned coal mine areas. Four types of test models which had respectively different depths of openings and different ground reinforcement conditions were introduced, where the modelling materials were the mixture of sand, plaster and water. The model with deep openings were turned out more stable to the structure than the model with shallow ones, because the crack-initiating pressure of the former was 2.5 times as much as that of the latter. The models with ground reinforcement were also fumed out more stable than the model without reinforcement, because the crack-initiating pressure of the former was 2.4 times as much as that of the latter. Subsidence profiles were analysed to find the characteristics of slope and curvature, and the model with large reinforcement were turned out the most stable.

• Tunnel and Underground Space
• /
• v.27 no.6
• /
• pp.406-421
• /
• 2017

This study describes a precise numerical analysis process by adopting the real image of mine openings obtained by LIDAR, which can produce a point cloud data by measuring the target surface numerically. Research area is a section of underground limestone mine which is used hybrid room-and-pillar method for improving the production rate. From the application of LIDAR to this section several results were deduced, that is, the central axis of upper and lower vertical safety pillars is distorted to the direction of NW and the section area of lower vertical safety pillar is $34m^2$ smaller than the designed area of $100m^2$. The results of precise measurement in geometrical shape of mine openings and precise simulation in numerical analysis confirms that LIDAR techniques can be suggested as a valuable tool for stability analysis in underground mine by configuring the mine opening shape.

• Journal of the Society of Disaster Information
• /
• v.19 no.3
• /
• pp.665-672
• /
• 2023

Purpose: Underground utility tunnel is facility that is jointly house infrastructure such as electricity, water and gas in city, causing condensation problems due to lack of airflow. This paper aims to prevent electricity leakage fires caused by condensation by detecting whether the control panel door in the underground utility tunnel is open using a deep learning model. Method: YOLO, a deep learning object recognition model, is trained to recognize the opening and closing of the control panel door using video data taken by a robot patrolling the underground utility tunnel. To improve the recognition rate, image augmentation is used. Result: Among the image enhancement techniques, we compared the performance of the YOLO model trained using mosaic with that of the YOLO model without mosaic, and found that the mosaic technique performed better. The mAP for all classes were 0.994, which is high evaluation result. Conclusion: It was able to detect the control panel even when there were lights off or other objects in the underground cavity. This allows you to effectively manage the underground utility tunnel and prevent disasters.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.15 no.3
• /
• pp.3096-3106
• /
• 1973

As a link in the chain of antidrought measure, our attempt is made to obtain basic informations on the construction of an infiltration gallary which can be supplied with irrigation water by catching of underground water in small river beds, which is economical, permanent and efficient. The experiment was made, concerning the structure of catchment conduits, by constructing a model sand tank $1.5m{\times}5m{\times}1.5m$ in dimension made of reinforced concrete. Various kinds of measuring equipment were attached to the model tank which contains a set of catchment conduits, each of them was made 30cm in diameter and 60cm in length with the ratio of sectional area to total area of influx holes 10:1, 20:1, 30:1. The average size of influx holes was fixed from 0mm to 10mm, 20mm and 30mm in diameter respectively. Obtained results are as follow; (a) In view of the water catchment capacity, manufacturing cost and the antipressure strength of the catchment conduits, it is the best method to decide the total number of influx holes 20 per sq. meter of each tile surface, and the size of influx holes 20mm in diameter, when the conduits have diameter less than 1m. (b) The greatest factor of safety against external load is to arrange the influx holes in a zigzag manner on the tile surface. The most effective formula of arrangement is $S{\geqq}\sqrt{2gd}$ where: s : spacing of opening row. g : spacing of opening line. d : diameter of influs hole.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2011.05a
• /
• pp.19-22
• /
• 2011

For underground structures that are exposed to environmental conditions, the declination of the durability of concrete occurs easily because of leakages from high hydraulic pressure and the frequent contact of water due to environmental factors. Therefore this study is to confirm that the leakage reduction of natural inorgnic powder compound applying subsurface structural weak part and make the performance improvement of concrete as an objective. The test was done by making the rebar, flat tie, nail and film infiltration and each of its water tank and cylindrical test body then after pouring water to each of the test body, the test observe the change of the water tank surface absorbed condition and leakage of each specimen with respect to time. As a conclusion, the test was observed that this water proofing admixture has better watertightness from the beginning of the setting time(when it hardens), the ettringite and the thaumasite generates a large quantity of hydration products that controls the formation in a large opening and the CSH produced by pozzolan reaction makes a dent at this opening.

• Tunnel and Underground Space
• /
• v.17 no.5
• /
• pp.389-410
• /
• 2007

For moderately jointed to massive rock masses, the failure and deformation behaviors around an excavated opening are absolutely influenced by the initial rock stress and strength of in-situ rock mass. The localized and progressive brittle failure around an opening does not mean whole collapse of an excavated opening. But, for many cases, it may induce temporary stopping of excavation works and reexamination of the current supporting system, which can result in delay of the entire construction works and additional construction cost. In this paper, the characteristics of the brittle failure around an opening with stress level and tunnel shape was studied by the biaxial compressive test using scaled specimen and by the numerical simulation with $PFC^{2D}$. The biaxial test results were well coincided with the stress induced failure patterns around the excavated openings observed and monitored in the in-situ condition. For the circular part of the opening wall, the stress induced cracks initially occurred at the wall surface in the direction of the minimum principal stress and contributed to the localized notch shaped failure region having a certain range of angle. But for the corner and straight part of the opening wall, the cracks initiated at sharp corners were connected and coalesced each other and with existing micro cracks. Further they resulted in a big notch shaped failure region connecting two sharp corners.

• Economic and Environmental Geology
• /
• v.31 no.6
• /
• pp.527-534
• /
• 1998

Excavation of underground openings changes stress distribution around the opening. The survey of this disturbed zone in excavation is very important to design and construct underground facilities, such as tunnel, gas and oil storage, power plant and disposal site of high- and low-level radioactive wastes. This paper presents a zoning of rock masses with tunnel excavation using PS logging. Compressional and shear wave velocities are measured in boreholes drilled in the tunnel wall, which was constructed with blasting and/or machine excavation. The disturbed zone in excavation can be estimated by comparing PS logging data with a tomographic image of compressional wave velocity and compressional and shear wave velocities of core samples. In the side wall of tunnel, the disturbed zone reaches 1.5 m and 1.0 m in thickness for blocks of blasting and machine excavations, respectively. In the roof of tunnel, however, the disturbed zone is 1.0 m and 0.75 m thick for the two blocks. These results show that the width of the disturbed zone is larger in the side wall of tunnel than in the roof, and 1.3 to 1.5 times larger for the blasting excavation than for the machine excavation.