• Tunnel and Underground Space
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• v.10 no.1
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• pp.80-91
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• 2000

Open cut mining of limestone is generally considered to be more advantageous than underground mining in recovery, grade control, economics, and safety, but it causes substantial environmental pollutants such as ground vibration, noise, dust. It also changes ground surface and may destroy vegetation. The Halla limestone mine which lies adjacent to Baikdu mountains range is selected for a model study. To reduce environmental hazards, and to conserve original surface and woods, both open cut and underground mining methods must be adopted. In case of sub-level sloping. a unit block of 87m high, 70m wide, and 100∼l20m long is suggested with an estimated overall recovery of 42%. Some suggestions to reduce the environmental hazards are also included. The followings must be considered in determining the degree of fragmentation; the discontinuity conditions in the rock mass and the charge concentration both at the bottom and column of the hole. In addition to adopting a barrier wall for reducing environmental hazards, the probable production from underground mining is also discussed.

• Wind and Structures
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• v.26 no.5
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• pp.293-304
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• 2018

A numerical study is conducted on the flow characteristics of a rectangular cylinder (chord-to-width ratio C/W = 2 - 10) mounted close to a rigid wall at gap-to-width ratios G/W = 0.25 - 6.25. The effects of G/W and C/W on the Strouhal number, vortex structure, and time-mean drag and lift forces are examined. The results reveal that both G/W and C/W have strong influences on vortex structure, which significantly affects the forces on the cylinder. An increase in G/W leads to four different flow regimes, namely no vortex street flow (G/W < 0.75), single-row vortex street flow ($0.75{\leq}G/W{\leq}1.25$), inverted two-row vortex street flow ($1.25<G/W{\leq}2.5$), and two-row vortex street flow (G/W > 2.5). Both Strouhal number and time-mean drag are more sensitive to C/W than to G/W. For a given G/W, Strouhal number grows with C/W while time-mean drag decays with C/W, the growth and decay being large between C/W = 2 and 4. The time-mean drag is largest in the single-row vortex street regime, contributed by a large pressure on the front surface, regardless of C/W. A higher C/W, in general, leads to a higher time-mean lift. The maximum time-mean lift occurs for C/W = 10 at G/W = 0.75, while the minimum time-mean lift appears for C/W = 2 at the same G/W. The impact of C/W on the time-mean lift is more substantial in single-row vortex regime. The effect of G/W on the time-mean lift is larger at a larger C/W.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.1
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• pp.1-15
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• 2008

Recently, because of the various factors by uncertainty of underground, the risks in tunnelling have been occurred increasingly. Therefore, it is very important to estimate and control the risks considering geotechnical conditions for tunnel stability and environmental problems by tunnel construction. In this study, the risk analysis for tunnel stability was carried out by classifying the risk factors such as ground support capacity, ground settlement, the inflow of groundwater into the tunnel and the damage by the earthquake. Also, the risk assessment for the environmental problems was performed by calculating the vibration and noise by blasting and the drawdown of the groundwater level caused by tunnel construction. Each risk factor was evaluated quantitatively based on the probabilistic and statistic technique, then it was analyzed the distribution characteristic along overall tunnel site. Finally, it was evaluated that how much each risk factor influences on the construction cost with a period for tunnel construction, so it is possible to perform reasonable tunnel design which was capable of minimizing the risks in the tunnel construction.

• The KSFM Journal of Fluid Machinery
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• v.14 no.3
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• pp.23-27
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• 2011

Due to a roots type medium vacuum pump is operated in condition of $1{\sim}10^{-3}$ torr vacuum, it could be applied for production and process of industrial parts, such as precise processing, vaporization, enrichment, separation, casting, metaling, welding, transportation. Therefore, the demand of this pump is increasing nowadays in our industrial markets of semiconductor, electric, electronic, automobile, material, environmental and transporting industries. However, the pumps are almost imported, because the domestic pumps are inferior in fields of vacuum range as under $10^{-1}$torr, relevant techniques(design, fabrication, casting, test, etc.) to the imported ones. In this study, essential parts of the development pump are designed with using of CFD and 3D decodes, FEM for analysing strength and deformation, generated heat, vibration and noise control, and are casted with using of mechanochemistry techniques for decreasing of weights, increasing of heat resistances and abrasion durability of materials for pump caing and impellers especially. Besides, in order to achieve ultimate vacuum around $10^{-3}$torr, this pump is composed of 6 stages, among which 1st stage is operated separately from remained stages. Additionally, a test rig for prototype pumps(300$m^3/h$ and 2,500$m^3/h$) is designed and procured as to apply for multi-staged rootz type vacuum pump, with modification of the test method recommended by KS B 6314 "Positive-displacement oil-sealed rotary vacuum pumps".

• Wind and Structures
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• v.23 no.2
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• pp.143-155
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• 2016

The interaction between two different shaped structures is very important to be understood. Fluid-structure interactions and aerodynamics of a circular cylinder in the wake of a V-shaped cylinder are examined experimentally, including forces, shedding frequencies, lock-in process, etc., with the V-shaped cylinder width d varying from d/D = 0.6 to 2, where D is the circular cylinder diameter. While the streamwise separation between the circular cylinder and V-shaped cylinder was 10D fixed, the transverse distance T between them was varied from T/D = 0 to 1.5. While fluid force and shedding frequency of the circular cylinder were measured using a load cell installed in the circular cylinder, measurement of shedding frequency of the V-shaped cylinder was done by a hotwire. The major findings are: (i) a larger d begets a larger velocity deficit in the wake; (ii) with increase in d/D, the lock-in between the shedding from the two cylinders is centered at d/D = 1.1, occurring at $d/D{\approx}0.95-1.35$ depending on T/D; (iii) at a given T/D, when d/D is increased, the fluctuating lift grows and reaches a maximum before decaying; the d/D corresponding to the maximum fluctuating lift is dependent on T/D, and the relationship between them is linear, expressed as $d/D=1.2+{\frac{1}{e}}T/D$; that is, a larger d/D corresponds to a greater T/D for the maximum fluctuating lift.

• Explosives and Blasting
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• v.27 no.1
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• pp.47-52
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• 2009

Blasting is necessary for excavation processes since more than 70% of korean land is consist of mountains. The vibration and noise accompanied by blasting processes usually bring about public complaints. Blasting patterns are chosen by economical efficiency, stability and construction conveniency. However, there are many alternatives without control to settle the popular complaint. To prevent those alternatives, standard blasting method for design and construction were suggested by MLTM (Ministry of Land, Transport and Maritime Affairs) in 2006. However, standard blasting pattern of MLTM was designed in a lump irrespective of types of rocks. Economical loss may occur by ignoring the characteristics of rocks for the applications to the rocks with low intensity, such as shale, or containing many joint. We deduced some economical progresses by performing test blasting with adjusted drilling spacing and length of burden considering the characteristics of local rock. This paper suggests the start of case studies for different applications. Economic improvement can be expected by applying those results deduced from case studies to design and construction.

• Journal of the Institute of Convergence Signal Processing
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• v.24 no.2
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• pp.82-89
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• 2023

Due to the characteristics of ship structure, the compartment structure is complicated and narrow, so safety accidents frequently occur during the work process. The main causes of accidents include structural collisions, falling objects, toxic substance leaks, fires, explosions, asphyxiation, and more. Understanding the on-site conditions of workers during accidents is crucial for mitigating damages. In order to ensure safety, the on-site situation is monitored using CCTV in the ship, but it is difficult to prevent accidents with the existing method. To address this issue, a smart safety helmet equipped with location identification and voice/video communication capabilities is being developed as a safety technology. Additionally, the smart safety helmet incorporates environmental sensors for temperature, humidity, vibration, noise, tilt (gyro sensor), and gas detection within the work area. These sensors can notify workers wearing the smart safety helmet of hazardous situations. By utilizing the smart safety helmet and environmental sensors, the safety of workers aboard ships can be enhanced.

• Journal of the Korean GEO-environmental Society
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• v.5 no.3
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• pp.5-15
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• 2004

SIP has been widely used as a low noise and vibration piling method in Korea. But the quality control of SIP was not properly settled down and field workers did not fully understand the principle of SIP method. So not a less troubles were raised at construction site and bearing capacity was not fully mobilized. To settle these problems, Korea National Housing Corporation amended the construction and load test criteria of SIP in 2002. After load tests on the SIPs installed in field according to the new criteria, we found that the bearing capacity in field vs the design load ratio increased and bearing characteristics was enhanced than that installed by the former criteria. To consider the enhanced bearing characteristics in the pile design and determine the adequate design criteria, this paper analyzed the accuracy of design criterion which were commonly used in Korea comparing with the load test results. Analysis result shows that Meyerhof criteria(1976) properly simulates the bearing capacity of SIP installed by the new construction and load test criteria.

• Korean Journal of Construction Engineering and Management
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• v.14 no.2
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• pp.141-149
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• 2013

This paper presents a scheduling technique that reflects various constraints in remodeling project of inhabited condition. The remodeling project of inhabited condition is required more detailed planning and control due to claims by noise, vibration, dust, smells, limited lift capacity, and limited temporary stock area. Because of the constraints, complexity in scheduling is increased and earlier completion is required to reduce the possibility of safety and environment accidents. Especially, in case of inhabited condition, the scheduling should be linked day-time/night-time/weekend work. This paper proposes a structured scheduling technique to incorporate those constraints in remodeling of inhabited condition. This scheduling technique considers not only remodeling process but also dismantling, newly-construction, and residents movement. Process expression method using MS-Project also presented to keep connectivity with existing scheduling system.

• Tunnel and Underground Space
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• v.32 no.6
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• pp.345-352
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• 2022

The existing NATM (New Austrian Tunneling Method) has induced civil compliants due to blasting vibration and noise. Machanized excavation methods such as TBM (Tunnel Boring Machine) are being adopted in the planning and construction of tunneling projects. Shield TBM method is composed of repetition processes of TBM excavation and segment installation, the machine has to be stopped during the later process. Consecutive excavation technology using helical segment is under developing to minimize the stoppage time. The modification of thrust jacks and module are planned to ensure the advance force acting on the inclined surface of helical segment. Also, the integrated system design of hydraulic circuit will be remodeled. This means that the system deactivate the jacks on the installing segment while the others automatically act the thrusting forces on the existing segments. This report briefly introduces the mechanical research part of the current consecutive excavation technological development project of TBM.