Search

Two-arch tunnels require minimal spacing between the 2 tunnels and thus occupy small amount of land compared to parallel tunnels. But it is rather expensive. The parallel tunnel is not as expensive, but it requires more land than 2-arch tunnels. This may cause a problem when there is a land shortage. The new design is to connect these two types of tunnels by another pair of parallel tunnels where the separation distance is gradually increasing. The applicability of this new design to the cases where rock condition is not even fair has to be verified since the width of the pillar between the connecting tunnels can be quite narrow. Therefore both two and three dimensional numerical analyses were conducted and pillar stability was examined for rock classes IV and V in two different ways. Results showed that this new design is still effective for poor rock conditions if central pillar is properly reinforced by tension bolts as long as overburden is less than five times of the tunnel diameter.Key words 2-arch tunnel, Parallel tunnel, Pillar 2-arch varying section tunnel, Tension bolt초 록 2-아치 터널은 터널의 간격이 매우 좁아서 병렬 터널에 비해 점유 면적이 작으나 경제적이지 못하다 . 병렬 터널은 경제적이긴 하지만 2-아치 터널보다 점유 면적이 커서 용지의 매입이 어려운 경우에는 문제가 될 수 있다. 새로운 설계는 이 두 터널을 터널의 간격이 점차 증가하는 제 3의 병렬터널로 연결시키는 것이다. 접속 터널의 필라는 폭이 매우 좁을 수 있기 때문에 이 새로운 설계를 불량한 암반에 적용하려면 검증이 필요하다 . 이에 4등급 및 5등급 암반에 대해 2차원 및 3차원 수치해석을 이용하여 2가지 방법으로 안정성 검토를 수행하였다. 검토 결과, 중앙 필라가 텐션 볼트로 적절히 보강된다면 터널 심도가 직경의 5배 이하인 경우에는 적용이 가능하였다.핵심어 2-아치 터널, 병렬 터널, 2-arch 변단면 터널, 필라, 텐션 볼트

The domestic demand of natural gas has increased continuously due to the sudden rise of oil price and regulations on greenhouse gas to global warming. In order to improve the supply security of natural gas market in Korea, the agreement on supply of pipeline natural gas (PNG) in Russia was signed between Gazprom and Korea Gas Corporation in 2008. If the supply plan of Russian natural gas is realized, underground storage facilities would be required in order to balance supply and demand of natural gas because the gas demand is concentrated in the winter. This study investigated the safety of the storage facility in quantitative way considering several design parameters such as gas pressure, depth of the storage cavern, rock condition and in-situ horizontal stress ratio. Two dimensional stress analyses were conducted using axi- symmetry condition to examine the behavior of cavern depending upon suggested design parameters. Results showed that the factor of safety, defined as the ratio of 'shear strength'/'shear stress', was largely affected by the depth, rock class and gas pressure but was insensitive to the coefficient of lateral pressure(Ko).

This paper describes the design and construction of a 2-arch tunnel with varying section. This new design has advantages of 2-arch tunnels, which is rather expensive, but is still economically competitive compared to parallel tunnels. Economic analysis was also conducted. To secure the stability of the varying section tunnel, excavated part was reinforced by tie-bolts and RRS, and 2-arch part was supported by EPS blocks and concrete walls. Stability of the pillar was theoretically analyzed and also examined by numerical simulations for various widths. Displacement monitoring was conducted and results were compared with numerical results. Economic analysis showed reductions in construction cost and period by 11% and 10 months respectively.

Cablebolts used to be employed as auxiliary supports where long or high capacity bolts are needed, but become competitive by the improvements in supportability and easiness in handling. Based on the test results obtained from various researches, the performance of the cablebolts was analyzed numerically while varying lengths and fixing conditions. The supporting effecte is assessed by monitoring displacements and stress taken place in shotcrete. When cablebolts are grouted without being tensioned, supporting effect was not as good as that of rockbolts. But, their supportability was good enough to substitute rockbolts if tensioned properly. Post grouting right after tensioning of the cablebolts shows reduction in supportability, but long term stability could be achieved without losing supportability if grouted when the bolt is far enough from the face. Further study is necessary including laboratory and in-situ tests under various conditions to use cablebolts as main support in tunnels.

The excavation of rock structures in hard rock involves three safety issues: structural failure such as wedge-type failures, brittle failures such as slabbing and spalling, and a combination of these two. Especially at highly stressed levels, the failure process of rock structures are mainly affected and eventually dominated by stress-induced fractures growing preferentially parallel to the excavation boundary. This brittle failure is usually occurred within very small displacement or strain, and thus it is not easy to determine the precursor and initiation stress level of failure in displacement detection method. To overcome this problem, some researchers have tried to adopt the acoustic emission (AE) detection. This study carried out physical model experiments and determined brittle failure initiation stress and failure grade, which are the two important characteristics of brittle failure. Failure initiation stress and failure grade are determined using AE detection as well as visual observatio...

Background : The aims of this study were to survey the nation-wide susceptibilities of Klebsiella pneumoniae isolates against ceftazidime and cefotaxime and to determine the prevalence of class A extended-spectrum -lactamases (ESBLs). Methods : During the period of February to July 2004, K. pneumoniae isolates intermediate or resistant to ceftazidime and/or cefotaxime were collected from 12 hospitals in Korea. Antimicrobial susceptibilities were determined by the disk diffusion and the agar dilution methods and ESBL-production was by double-disk synergy test. Ceftazidime or cefotaxime-resistance determinants of the ESBL-producers were transfered to Escherichia coli J53 by transconjugation. Searches for class A ESBL genes were performed by PCR amplication. Results : Among 212 clinical K. pneumoniae isolates, 172 (81%) isolates showed positive results in double-disk synergy test; the most prevalent ESBL was SHV-12 (n=104). Genes encoding ESBLs including SHV-2 (n=6), SHV-2a (n=17), CTX-M-3 (n=18), CTX-M-9 (n=6), CTX-M-12 (n=1), CTX-M-14 (n=27), CTX-M-15 (n=3), and a novel CTX-M-type -lactamases were also detected. Conclusions : It is concluded that diversity of ESBLs in K. pneumoniae isolates are increasing in Korea. CTX-M-12 has never been reported in Asia, and a novel CTX-M-type ESBL has emerged.

Rock mass is inhomogeneous in nature. Data for underground structure designs are mainly obtained from site investigations and tests, but they are very limited. For this reason, uncertainty exists in the process of constructing underground structures in a rock mass. In the design a tunnel support pattern, the most important parameters such as advance rate and excavation method must be determined optimally. However, it is difficult to determine these parameters quantitatively. In addition, if these parameters are determined incorrectly, unexpected risk occurs such as the decrease in the tunnel stability or economic loss due to excessive amount of supports. In this study, a methodology to determine an optimal support pattern and advance rate for the design of a tunnel is introduced based on risk analysis. It can be confirmed quantitatively that the more the tunnel is supported, the higher the reliability index becomes and the more stable the tunnel is predicted to be. Also an optimal support pattern and advance rate can be determined quantitatively by performing a risk analysis considering the construction cost and the cost of losses that can occur due to the collapse of a tunnel.

The failure of rock slopes usually occurs along the discontinuities. But for weathered or highly jointed rock mass, failure surface is often curved as in soil slopes. To assess the stability of jointed/weathered rock slopes, shear strength reduction technique is adapted for use with the non-linear Hoek-Brown failure criterion, an empirical approach to estimating rock mass strength. Hoek-Brown strength parameters can be estimated using rock mass classification schemes such as RMR or GSI. Numerical results obtained by strength reduction are compared with limit analysis upper bound solutions derived using a series of linear failure surfaces tangent to the actual non-linear failure surface. Results are presented in graphs of normalized slope height versus RMR that could be used as stability charts.

This paper mainly reports the details of the f rst real test of food storage in the underground food storage cavern in Korea. Pear and apple were selected, and the change of indices such as the rate of soundness, moisture content, total acid, and hardness were monitored with the temperature and humidity in and around cavern. The results showed that the fruits were stored in better quality in the case of underground storage with cooling than natural underground condition or surface storage tank.

This paper reports the background information and the initial results obtained from the pilot underground food storage cavern in Korea, where the seasonal variation of air temperature makes the running of on-ground food storage tanks uneconomical. A pilot cavern has been driven into a granite rock mass which is the typical massive rock in Korea. Basic mechanical properties, including the thermal properties, were measured. The change of rock strengths and the behavior of joints upon the change of temperature, were also identified. A series of monitoring systems have been setup to measure the temperature of the ground, the behavior of the rock mass during excavation and running (i.e. cooling) of the cavern. The results of this paper can provide useful information for the design of future commercial underground food storage caverns in Korea.

Recently, vancomycin-resistant enterococci (VRE) with the vanA genotype that are susceptible to teicoplanin have been described in Japan, Taiwan, and Korea. The investigators suggested three point mutations in the putative sensor domain of vanS or impairment of accessory proteins VanY and VanZ as an explanation for the VanB phenotype-vanA genotype VRE. In this study, we analyzed Tn1546-like elements to determine the molecular mechanisms responsible for the impaired glycopeptide resistance of clinical VRE isolates with VanB phenotype-vanA genotype from Korea.From 2001 to 2004, 28 clinical isolates of Enterococcus faecium with VanB phenotypevanA genotype were collected from 8 different university hospitals in diverse geographic areas in Korea. For structural analysis of Tn1546-like elements, PCR amplifications for internal regions of Tn1546 were performed. The purified PCR products were directly sequenced with an ABI Prism 3100 DNA sequencer.The sequence data of the vanS regulatory gene revealed that none of the isolates had any point mutations in this gene. All 28 isolates had a complete or incomplete deletion of vanY gene. Of these, 13 strains represented a complete deletion of vanZ, and 2 strains showed the deletion of nucleotides near the end point of vanX.The mechanism of VanB phenotype-vanA genotype in VRE isolates from Korea is not point mutations of vanS but the rearrangements of vanX, vanY and vanZ.

This paper describes the use of 3-dimensional displacement monitoring data to predict abrupt change in ground condition ahead of a tunnel face. Displacements were monitored at 3 different tunnelling sites and influence/trend line graphs of roof convergence, L/C ratio and C/C0 ratio were analyzed. In order to verify the estimation technique, Tunnel Seismic Prospecting campaign(TSP) was also conducted. The results showed that the applied technique estimated actual faults or fracture zones ahead of the tunnel face at the accuracy of 80% or higher. Three-dimensional numerical analyses were also performed and the same analysis technique was applied to see the change in influence/trend lines for various weak zones with different orientations and properties. The tendency of the trend lines from the numerical results is helpful in understanding the field data and provides useful ground in predicting the change in ground condition ahead of tunnel face.(A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. "Reprinted with permission from Elsevier".

In a tunnel, failure of its supports can cause collapse of the whole tunnel. Thus, in estimating the safety factor of the tunnel, it is important to take the failure of its supports into account. In previous studies, shotcrete, which is one of the main supports for tunnels, was usually modelled by the elastic beam element which never fails in numerical calculations. According to the Working Stress Design (WSD) concept, the failure of the beam element can be indirectly checked by comparing the allowable stress and the calculated bending stresses inside the beam element. This approach has been also applied in estimating the safety factor of a supported tunnel. However, the calculated safety factors are usually underestimated due to the excessive stress concentration on the shotcrete. In this study, therefore, it is suggested how to properly model shotcrete and consider its failure. To this end, shotcrete was modelled by both the beam (elastic) element and the continuum (elasto-plastic) element in two dimensional numerical analyses. In addition, how the rock mass class, coefficient of lateral pressure, thickness of shotcrete, and excavation method effect the safety factor of a supported tunnel were analyzed. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. "Reprinted with permission from Elsevier".

This paper addresses application of microseismic event monitoring system in excavation of highly stressed rock mass in underground oil storage caverns. The locations and magnitudes of microseismic events were determined using a network of 12 uniaxial sensors. The results indicated that seismic events were frequently induced by blasting activities as the excavation is followed by stress redistribution in the surrounding rock mass. Since the frequency of excavation-induced seismic events usually plateaus and disappears within the first three hours after the blast, special attention should be given to events occurring continuously after the three hours within the excavation damage zone, as well as to those occurring without any specific relation to the blast. Based on the accumulated microseismic event data, evaluation criteria are established for overall stability and integrity of the underground storage caverns. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. "Reprinted with permission from Elsevier".

Joint roughness coefficient, most widely used to express the joint roughness, is known to have some problems such as a possibility to involve subjective judgement of the researcher in determining the value. In this study, to express the joint roughness by the parameters other than JRC, joint specimens were produced artificially by a splitter, and the joint profiles were digitized by a coordinate measuring machine. Six roughness parameters, micro average i -angle, root mean square of i -angle, standard deviation of height, roughness profile index, standard deviation of i -angle and fractal dimension, were computed from the digitized data of the joint profiles and the correlations among the parameters were studied. The influence of sampling interval on the five parameters except for fractal dimension was investigated, and also the regression equations between joint roughness coefficient back-calculated from direct shear test and other roughness parameters were determined.