• Tunnel and Underground Space
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• v.20 no.5
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• pp.360-368
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• 2010

The paper presents a case study from a surface mine where the controlled augmentation of throw and drop of the blasted muck piles was warranted to spread the muck piles on the lower berm of the bench. While the augmentation of throw increased the lateral spread and the looseness of the broken muck, the augmentation of drop significantly lowered the muck pile height for easy excavation by the excavators. In this light, the present paper highlights and discusses some pertinent changes in the blast design parameters for such specialized application of cast blasting in a surface mine, where a sandstone bench, with average height of 22-24 m was to be made amenable for excavation by 10 m3 rope shovels, which possessed maximum digging capability of up to 14 m. The results of tailoring the blast design parameters for augmentation of throw and drop are compared with the baseline blasts which were earlier practiced on the same bench by dividing the full height of the bench in 2-slices; upper slice (10-14 m high) and lower slice (12-15 m high). Results of fragment size, its distribution and total cycle time of excavator (shovel) are presented, and discussed.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.344-354
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• 2000

The concrete plug in an underground cavern prevents the stored product (oil, gas, etc) from leaking and the excessive inflow of underground water, so it plays an important role in construction and operation of the storage cavern. Additionally, it should maintain its stability under every possible loading condition. Once the plug is constructed, the cavern is isolated from the external access. Therefore, mechanical and hydraulic consideration should be made in construction to fulfill its function. Therefore, in this study, numerical analyses were conducted to study the optimal shape and thickness of the plug with respect to the various conditions of installation depth, the shape of the plug, in-situ stress ratio (K), the condition of rock-plug interface, and the effect of Excavation Damaged Zone (EDZ). This paper also presents the effect of slot depth on the hydraulic behavior of the plug. These analyses were carried out by using the 2-dimensional finite difference code, rm FLAC, and the 3D code, rm FLAC$\^$3D/.

• Tunnel and Underground Space
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• v.29 no.6
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• pp.425-438
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• 2019

A scaled model test was performed to evaluate the stability of subway twin tunnels excavated in the sedimentary rocks with subhorizontal bedding planes. The size of studied tunnel was 6.2 m×6.8 m and pillar width was 4 m. The anisotropic model test specimen was manufactured with the modeling materials suitable for in-situ rocks by way of dimensional analysis. Fracture and deformation behaviors of tunnels according to applied loads were investigated through the biaxial compression test. As the load was increased on the model specimen, the first crack occurred in the middle part of the pillar across twin tunnels and the gradual fractures progressed at crown and floor of twin tunnels. All the cracks in pillar were generated along the existing bedding planes so that they were found to be the main cause of the pillar failure. In addition, the test results were verified by numerical analysis on the experimental conditions using FLAC ubiquitous joint model. The distribution of plastic regions obtained from numerical analysis were in general agreement with test results, confirming the reliability of the scaled model test conducted in this study.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.4
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• pp.303-314
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• 2004

This study is intended to investigate the geotechnical behavior of jointed mass on tunnel excavation experimentally. Laboratory test were conducted in various conditions of distance from joint to tunnel and in-situ stress ratio ($K_0$). In case, the ground around the tunnel that has the joint angle $90^{\circ}$ generate the greatest influence in crown and far shoulder from joint. If the in-situ stress ratio is low, tangential stress of side wall that is opposite side of the joint is increased more than in crown. Otherwise in case, joint angle $45^{\circ}$, the generated compress stress is found out that left side of the tunnel of near the joint has influence on stability of the tunnel about 3 times than non-jointed rock.

• Journal of Korean Society of societal Security
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• v.2 no.4
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• pp.75-81
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• 2009

This paper presents the geotechnical characteristics of tunnel co \l apse based on the case studies. For domestic cases, most collapses are likely to happen along the weakest zone of shear strength due to the change of stresses induced by excavation specially when soft or weathered rock exist in front of a tunnel. In other words, the collapse of a tunnel occurs along the highly weathered fractured zone due to blasting and excavation. In Europe, collapses have been occurred by one joint group even though the ground is relatively fresh and for the rocks of which RQD is over 50%. In addition, the amount of ground water flow does not seem to be seriously affected by the RQD range.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.1062-1066
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• 2004

암반 내에 공동을 굴착하여 LPG 혹은 원유를 저장하는 경우 공동에서의 지하수 유입량은 공동상부의 수압과 공동내의 가스압과의 관계를 파악할 수 있는 정량적인 지표가 된다. 공동내의 유입량은 되도록 일정하게 유지되는 것이 굴착등의 시공단계와 공동 운영 및 유지관리면에서 유리하며, 유입량의 급증 혹은 급감이 일어나는 경우는 그 원인을 조기에 규명하여야 한다. 이를 위해서는 지하수위, 가스저장압, 수막공 주입압 등에 따른 공동주변의 유동장 해석, 공동내로의 지하수 유입량 해석을 실시해야 한다. 지하저장공동의 유입량 해석에 있어서는 공동의 정확한 형상을 반영하기 위해서 유한요소법이 보편적으로 사유되어 왔으나 한번 설정한 유한요소망으로부터 공동의 설계요소를 변경하는 작업은 수원하지 않아 설계전단계에서 공동 및 수막 시설의 다양한 배치에 따른 모의를 수행하는데는 다소 무리가 있다. 이러한 불편함은 경계부의 형상과 조건만으로 내부점에서의 미지변수 계산을 효과적으로 수행할 수 있는 경계요소법을 도입함으로써 극복할 수 있다. 따라서 본 연구에서는 지하공동으로 배수되는 유입량 산정을 위해 경계요소법을 근간으로 한 2차원 지하수 흐름모형을 구성하였고, 이를 지하저장공동이 위치한 A기지에 적용하여 상부경계조건인 지하수위의 변화, 수막공 주입압 등에 따른 공동내의 유입량과 공동저장압과의 관계를 정량적으로 분석하였다. 분석 결과를 지하저장공동의 운영 및 유지관리에 활용될 수 있도록 수식화하여 제시하였다.

• Explosives and Blasting
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• v.22 no.1
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• pp.23-32
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• 2004

터널 발파를 원활히 수행하기 위해서는 암반조건에 적합한 합리적인 설계와 정밀한 천공, 정확한 기폭초시가 기본요소로서 이는 현재 국내 터널 설계.시공 기술 및 기자재의 발달로 만족할 만한 성과를 얻을 수 있다. 특히. 터널발파에서 정확한 기폭초시 부여는 굴진율 및 버럭 파쇄율, 굴착예정선 미려도, 잔여 암반 손상도 등의 시공성에서 뿐만 아니라 소음 및 진동 발생율을 좌우하는 환경적인 측면에서 매우 중요한 요소이다. 기폭요소는 최초 도화선을 활용한 공업뇌관에서 전기뇌관, 비전기식뇌관의 순으로 기폭안전성과 정밀성 면에서 눈부신 성장을 이룩하여 왔으며 특히, 90년대 초에 개발되어 전 세계적으로 최근까지 지속적으로 사용량이 급증하고 있는 전자뇌관은 기폭방식에 일대혁신을 이루었다. 전자기폭 시스템은 기존뇌관의 초시를 결정하는 화약성분의 지연요소 대신에 IC board(전자회로)에 의한 Digital timer로 신호를 발생하여 초시를 결정하는 방식이다. 본 논문에서는 국내 최초로 전자기폭시스템을 활용하여 2003년 9원 23일에서 동년 11월 2일까지 강원도 양구 지역의 $\bigcirc\bigcirc$터널에 전자뇌관을 이용한 시험발파를 실시하였고, 발파에 의한 진동 등을 조사하여 그 효율성을 검토하였다. 이를 위해 전자뇌관의 특성과 장점을 최대한 샅리기 위하여 각공을 발파하는 방식, 즉 1지발에 1공을 발파하는 방식을 채택하고 일반 뇌관과 전자뇌관으로 설계를 하여 각각의 발파효율을 비교하여 보았다. 그 결과 발파진동의 경우 기존뇌관을 이용하여 1공씩을 1지발로 발파를 한 경우에는 18~56%의 진동저감 효과가 있었고. 본선 설계에 의해 진행된 발파에 비하여는 최대 70% 이상의 진동저감 효과가 있는 것으로 나타났다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.3
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• pp.275-283
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• 2010

Recently, the observational design and construction method in tunnels has been becoming important. Rock masses include various discontinuities such as joints, faults, fractures, bedding planes, and, cracks. The behavior of tunnels in hard rocks, therefore, is generally controlled by various discontinuities. In this study, a new key block analysis method for observational design and construction method in tunnels is proposed, and then applied to the actual tunnel with a super-large cross-section. The proposed analysis method considers finite persistence of discontinuities. The new analysis method can handle concave and convex shaped blocks. To demonstrate the applicability of this key block analysis method for observational design and construction method in tunnels, the analysis results are examined and compared with those of the conventional method.

• Journal of the Korean Geotechnical Society
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• v.15 no.5
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• pp.229-240
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• 1999

The groundwater flow and grout flow in individual rock joint and jointed rock mass are studied using various methods of analysis such as (i) the finite difference method, (ii) channel network analysis and (iii) joint network analysis. The flow behaviour is investigated in two distinguishable scales of observation: one for a rough joint of a laboratory scale having variable aperture, and the other for field- scale rock masses having three sets of intermittent joints. In the former case, the aperture-dependent channel flow is identified for both water and grout flows. The comparison of the flow rate in a rough joint is made between the finite difference analysis and existing analytical solution. In the latter case, the effects of increasing number of joints on the groundwater inflow into a circular opening of various diameters are analyzed using both the joint network method and Goodman's analytic solution. Comparisons are made between the two methods. The boundary effects in the joint network method are discussed. The inhomogeneity of joint network and its impacts on the groundwater inflow are also discussed.

• Tunnel and Underground Space
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• v.17 no.1 s.66
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• pp.26-31
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• 2007

The 11 nuclear power plants have been taking charge of more than 40% of the total electrical power development in Korea. In addition to the existing nuclear power plants at Gori, Wolsung, Youngkwang, etc., the 12 nuclear power plants are expected to be newly established until 2006. So, the 23 nuclear power plants will produce the electric power as much as more than 50% of the national gross production. However the nuclear power plants are inevitably generating the detrimental atomic wastes. Therefore the disposal techniques for the nuclear wastes should be ensured considering a very high safety factor. According to the basic researches in KAERI, the underground disposal repositories are reported to be most favorable for Korea. The KBS-3 disposal system has been strongly suggested by KAERI and this system has a deep tunnel with several disposal boreholes in tunnel floor. The nuclear wastes, which are sealed tightly in a canister, will be disposed in these boreholes. Considering the disposal tunnel in a great depth, the in-situ stress regimes will affect severely the tunnel stability. Consequently the effect of the in-situ stresses on the disposal tunnel and the role of the in-situ stresses in tunnel stability analysis are examined by the numerical studies.