• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1518-1525
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• 2008

This paper concerns optimum design of 2-Arch tunnel. A 2-Arch tunnel adopted in a subway tunnel construction site is considered in this study. A calibrated 3D finite element model was adopted to conduct a parametric study on the lagged distance between left and right tunnel faces. The results of analysis were examined to determine optimum lagged distance for minimizing the interaction between the left and right tunnels. The results indicated that the shotcrete lining stress and the center pillar load are more influenced by the second tunnel excavation than the tunnel deformation. Also shown is that a lagged distance of 20m is sufficient to minimize the interaction between two tunnels. Fundamental mechanism of 2-arch tunnel was also investigated based on the results.

• Geomechanics and Engineering
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• v.9 no.3
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• pp.397-414
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• 2015

Three different applications for monitoring displacements in underground structures using a BOTDR-based distributed optical fiber strain sensing system are presented. These applications are related to the strain measurements of (1) instrumented PVC tube designed to be attached to tunnel side wall and ceiling as a sensor; (2) rock bolts for tunnels; and (3) shotcrete lining under loading. The effectiveness of using the proposed strain sensing system is evaluated by carrying out laboratory tests, in-situ measurements, and numerical simulations. The results obtained from this validation process provide confidence that the optical fiber is able to quantify strain fields under a variety of loading conditions and consequently use this information to estimate the behavior of rock mass during mining activity. As the measuring station can be located as far as 1 km of distance, these alternatives presented may increase the safety of the mine during mining process and for the personnel doing the measurements on the field.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.4
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• pp.479-499
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• 2019

State assessment of an operational tunnel is usually done by performing visual inspection and durability tests by following the detailed guideline for safety inspection (SI) and/ or precision inspection for safety and diagnosis (PISD). In this study, 12 NATM tunnels, which have been operational for more than 10 years, were inspected to figure out the cause of longitudinal cracks for the purpose of modifying the scoring items in the state assessment NATM tunnel related to the longitudinal crack and the thickness of concrete lining. All investigated tunnels were classified into four groups depending on the shape and usage of each tunnel. The causes of longitudinal crack occurrence were analyzed by investigating the correlations between the longitudinal crack and the following four factors: the patterns of ground excavation; construction state of primary support system; characteristics of material properties of the concrete lining; and thickness of lining which was obtained by Ground Penetration Radar (GPR) tests. It was found that influencing factors causing longitudinal cracks in the lining were closely related with the construction condition of the primary support system, i.e. shotcrete, rockbolt, and steel-rib; crack occurrences were not much affected by the excavation patterns. As for the properties of concrete lining materials, occurrence of the longitudinal crack was mostly affected by the following three items: w/c ratio; contents of cement; and strength of lining. When estimating the lining thickness of the concrete lining by GPR tests and taking thickness effect into account in the statement assessment, it was concluded that increase of the index score by an average of 0.03 (ranging from 0.01 up to 0.071) is needed; a more realistic way of state assessment should be proposed in which the increased index score caused by lack of lining thickness should be taken into account.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.2
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• pp.307-315
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• 2016

Many countries are trying to reduce a greenhouse gas to step up their fight against climate change. There are many studies related to building only for reducing a greenhouse gas in construction area but studies related to reducing a comprehensive environmental load including various pollutants that affects the global environment are lacking. This study aims to analyse the characteristics of environmental load by work type for tunnel projects. Analysis showed that seven work types, including lining concrete, shotcrete, tunnel portal and open-cut tunnel work, etc., are representative works generated environmental load. These seven works represent 89.22 percent of total environmental load. In addition, comparison results of environmental load per tunnel's length by work type showed that a major factor of environmental load is caused by a tunnel portal and open-cut tunnel work with relatively short length (excavation length). And lining concrete and shotcrete work are larger than any other environmental load with tunnel's total length. It is expected that the result of this study will be used to make a estimation model for environmental load using approximate quantity survey of representative work types in the early stage of tunnel design. And it will be play a considerable role in establishing of environment management plan for sustainable infrastructure construction.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.6
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• pp.675-683
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• 2015

The room-and-pillar construction method for underground space is adopted from the room-and-pillar mining method which is one of the most popular underground mining method in the world. Drainage system in the room-and-pillar underground construction method can be similar with the concept of single shell in tunnel because additional reinforcement except the TSL (thin spray-on liner) is not applied in the room-and-pillar construction method. That is, to decrease groundwater level and maintain safety in tunnel, the drainage pin hole inside lining (shotcrete) can be used. However, if total amount of outflow in the underground structure is relatively small or groundwater is not detected, such drainage system will not be useful and cause additional construction cost. In this study, outflow of conventional tunnels in South Korea was investigated and the criteria to determine whether the drainage pin hole is effective was suggested. And the guided drainage system was suggested when drainage pin hole was not applied in the room-and-pillar construction method.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.1
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• pp.31-40
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• 2016

A new testing equipment is designed to investigate the characteristics of the drainage fabric which is used in the tunnel drain system. The equipment is possible to model the loading as well as boundary conditions of the shotcrete precisely and it follows the general guideline of ASTM D4716 so that the interface between shotcrete and concrete lining retains the real situation in the tunnel site. Using the real loading conditions and surface irregularities, the flow rate and its capacity of the regular fabric has been estimated. A composite drainage fabric having geogrid inside was also used to investigate the flow rate and its efficiency. The advantages of the composite fabric compared with the regular one have been demonstrated using the experimental data and brief outline of the future work is finally proposed.

• The Journal of Engineering Geology
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• v.18 no.1
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• pp.93-102
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• 2008

The use of lattice girder is increased at the tunnel site in Korea because of the several advantages over the traditional H-steel rib. The lattice girder supports the ground with shotcretes, forming a combined support system. Therefore, stress measurements at the lattice girder are necessary to calculated the ground loads. However, field measurements at the lattice girder are rarely performed at the tunnel site. The proper way of stress measurements for the lattice girder is not fully established in Korea. The correction of stress measurements at the shotcretes is often disregarded even though the measured stresses include non-stress related strains. Results of the stress measurements obtained from the lattice girder and non-stress shotcretes are used to improve the credibility of the stress measurements at the primary lining.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.157-169
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• 2007

This study aimed to quantify the deterioration of tunnel structural members such as concrete lining and shotcrete lining after a tunnel fire accident by measuring their mechanical properties between $300^{\circ}C$ and $1,000^{\circ}C$. From the experiments, it was revealed that the critical temperature where mechanical properties start to decrease linearly was approximately $300^{\circ}C$. In addition, the other critical temperature where macro-cracks are induced in specimens was around $600^{\circ}C$. From a series of regression analysis, the optimum regression function with correlation coefficients over 0.99 for mechanical properties at different temperature levels was obtained as the Boltzmann function. Finally, a schematic diagram to estimate temperature distribution inside structural members as well as their mechanical properties at corresponding temperature levels quantitatively was newly proposed for RABT and RWS fire scenarios.

• Journal of the Korean Geotechnical Society
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• v.15 no.3
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• pp.161-176
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• 1999

A powerful numerical method that can be used for modeling rock-structure interaction is the Discontinuous Deformation Analysis (D D A) method developed by Shi in 1988. In this method, rock masses are treated as systems of finite and deformable blocks. Large rock mass deformations and block movements are allowed. Although various extensions of the D D A method have been proposed in the literature, the method is not capable of modeling water-block interaction, sequential loading or unloading and rock reinforcement; three features that are needed when modeling surface or underground excavation in fractured rock. This paper presents three new extensions to the D D A method. The extensions consist of hydro-mechanical coupling between rock blocks and steady water flow in fractures, sequential loading or unloading, and rock reinforcement by rockbolts, shotcrete or concrete lining. Examples of application of the D D A method with the new extensions are presented. Simulations of the underground excavation of the \ulcornerUnju Tunnel\ulcorner in Korea were carried out to evaluate the influence of fracture flow, excavation sequence and reinforcement on the tunnel stability. The results of the present study indicate that fracture flow and improper selection of excavation sequence could have a destabilizing effect on the tunnel stability. On the other hand, reinforcement by rockbolts and shotcrete can stabilize the tunnel. It is found that, in general, the D D A program with the three new extensions can now be used as a practical tool in the design of underground structures. In particular, phases of construction (excavation, reinforcement) can now be simulated more realistically.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.167.2-167.2
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• 2010

본 연구에서는 지열 에너지원으로써 터널 내부 벽면의 항온성을 이용하여 터널 외벽에 텍스타일 형태의 열교환기를 설치하고 열적 거동을 평가하였다. 터널의 라이닝 부분에서는 여러 가지 요인에 의해 지하수가 터널 내부로 유입하게 되므로 지하수의 유무에 대한 열적 거동 및 유동액의 순환 속도에 따른 영향, 열교환 파이프 배열 형태에 따른 영향을 현장 시험 시공과 현장 열응답시험을 통하여 평가하고자 하였다. 또한 3-D 유한체적해석 프로그램(FLUENT)을 이용하여 숏크리트와 라이닝의 열전도도를 고려한 열교환기의 성능을 분석하였다. 수치해석 결과 열교환 파이프 주변에 지하수의 흐름이 존재할 경우 열전달이 상대적으로 더 원활히 이루어졌으며 순환속도가 빠를 때 보다 느릴수록 효율이 높게 나타났다. 또한, 파이프의 간격이 넓을수록, 파이프의 길이가 길수록 효율이 높게 나타났다. 라이닝 및 숏크리트의 열전도도가 증가함에 따라 에너지 텍스타일의 열전달 효율이 높게 나타났다. 현장 시험을 통해 비슷한 길이의 파이프가 사용된 경우, 파이프 배열 형태에 따라 수평형보다는 수직형 배열의 효율이 높게 측정되었다.