• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.330-332
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• 2017

본 논문에서는 숏크리트 지보재의 시간 의존적 경화특성을 고려한 터널 지보재의 3차원 유한요소해석을 수행하였다. NATM터널에 대한 기존 숏크리트 지보재 해석방식에 의한 결과화 제안된 시간 의존적 해석방법의 결과를 비교함으로서, 시간의존적 특성이 숏크리트 지보재의 응력 및 내공변위에 미치는 영향을 분석하였다. 시간 의존적 특성을 고려한 3차원 해석방법이 숏크리트 지보재의 변형을 과소평가 할 수 있음을 확인하였다.

• The Journal of Engineering Geology
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• v.22 no.3
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• pp.323-330
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• 2012

The use of lattice girder is increased rapidly as a substitute for H-steel ribs at the tunnel sites in Korea. Ground loads acting on the tunnel are supported by shotcrete and lattice girders. To assess the safety of the tunnel, it is essential to obtain field measurements for the lattice girders; however, lattice girder measurements have rarely been performed at tunnel sites, and the method of measurement is not well established. In the present study we suggest a load cell method for the instrumentation of tunnels with lattice girders. Actual measurements of ground loads acting on lattice girders are presented for a specific tunnel under construction.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.3
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• pp.269-282
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• 2008

In general, the effects of steel ribs are not considered in the numerical analysis of tunnel design. However, attempts have been increased recently to consider these effects in the analysis of shallow tunnels in soft ground, based on the fact that the steel ribs embedded in the shotcrete take a role to support some portion of the redistributed load due to excavation. In such analyses, the steel ribs can be considered in four different methods: (1) a conventional method where the steel ribs are not considered, (2) a method using the equivalent composite cross section in which the bending moment of shotcrete is not considered, (3) a method using the equivalent composite cross section in which both the compressive stress and the bending moment for the shotcrete and steel rib are considered, and (4) a method using beam elements for the shotcrete and the steel rib, respectively. These methods are adopted in the numerical analysis using FLAC 2D to investigate stresses of both the shotcrete and the steel rib. The overall results show that the analyses are more practical and economical when the effects of steel rib are considered fer the methods (2), (3), and (4). Since the results of those analyses considering steel rib capacity may be different according to the ground condition, it will be necessary to consider the appropriate method among them in accordance with design conditions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.2
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• pp.143-153
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• 2002

Convergence Confinement Method (CCM) makes a more simple judgement in a ground-support reaction than numerical method. Also this method is good for the applicability of construction feedback and the analysis of field measurement. However, there has been little research with respect to the application of CCM in tunnel construction. One of the problems in CCM is a decision of the time to support installation. To decide a reasonable supporting installation time, support characteristic curve and displacement characteristic curve considering construction stage are proposed. In addition, to predict displacement distribution ratio and load distribution ratio, the time dependent support reaction curve is used. Finally, through a comparison of the result between CCM and numerical analysis, the trust of this study is proved and the practical application is proposed to control resonable tunnel construction management.

• Tunnel and Underground Space
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• v.8 no.4
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• pp.261-274
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• 1998

The brief results of laboratory and field tests of yieldable steel arches are represented. The test supports were fabricated with three U-sectional beams which are 25.8 kg/m of Glocken profile. The structural analyses of semi-circular and arch supports were conducted to find out shape factor of U beam to be 1.35 and the location of 2nd plastic hinges. Load capacity of arch supports under crown loading were examined as a function of leg length. Yieldable characheristics of test supports were investigated with various bolting torque of connection part. Determination method of bolting torque were also studied. Finally, test supports were installed in-situ with torque of 21 kg .m, which showed a typical yielding procedure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5C
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• pp.221-229
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• 2012

Steel ribs such as H-beam or lattice girder are often reinforced to secure the stability of NATM tunnel when the ground is in the bad condition. When designing, however, steel ribs are not often taken into consideration on the numerical analysis when they are regarded as temporary tunnel supports until shotcrete shows its best performance or if they are, there are various modeling methods. This study shows behavior and loading capacity of steel ribs and shotcrete through the strength test on the bending, pressure and full-scaled. Also, we conducted and analyzed the experiment of composite member consisting of shotcrete and steel ribs under the same condition. Through the result, we can find the fact that shotcrete and steel ribs do not work as one unit because of slipping on the boundary. Also, when numerical analyzing, it was concluded that steel ribs cover all bending moment and shotcrete and steel ribs share with axial force according to the compressive strength.

• Tunnel and Underground Space
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• v.9 no.3
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• pp.204-213
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• 1999

NATM(New Austrian Tunnelling Method) uses a support system of shotcrete, rockbolt and steel support, which are installed after tunnel excavation. Recently, a lattice girder among these support system is used in tunnelling. A lattice girder is a new steel support developed in Europe for the replacement of an existing H-shaped steel set, which is reported to have some problems in installation. This is a triangular shape welded with steel rods and is a light-weight support system which enables fast and easy installation of porepolling. The major advantage of a lattice girder is the good bonding with shotcrete. In this study, to evaluate the applicability of a lattice girder in tunnelling in Korea, field tests were performed at a high speed railway tunnel with a large section. Also, features of lattice girder in field tests were compared with those of a H-shaped steel set respectively. Field tests proved that a lattice girder fully supported the initial earth pressure developed right after excavation and limited ground deformation effectively.

• The Journal of Engineering Geology
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• v.19 no.3
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• pp.269-275
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• 2009

The use of lattice girder is increased at the tunnel site in Korea recently for the substitute of H-steel rib. However, field measurements at the lattice girder are rarely performed at the tunnel site and the method of the measurement is not well established. The use of the vibrating wire strain gauges used for the H-steel rib was proven to be not suitable for the strain measurements of the lattice girder according to the previous research. The credibility of the load cell was investigated using laboratory compression tests for load cells, specially manufactured for the lattice girder far this study, installed at the specimen of the lattice girder. The method of the tunnel instrumentation for the lattice girder using the load cell is given from the interpretation of the compression test results.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.1
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• pp.37-49
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• 2005

In a tunnel, failure of its supports can cause failure of the tunnel. Therefore it is important to estimate safety factor of the tunnel which the failure of its supports is taken into account. In previous studies, supports of tunnels were usually modelled as beam elements. The failure of the supports was decided by comparing the allowable stress and the calculated bending stresses inside the beam elements in estimating safety factor of the tunnel considering the failure of its supports. In this study, it is suggested how to model the supports properly. To this end, supports of a tunnel were modelled by both beam (elastic) elements and continuum (elasto-plastic) elements in two dimensional numerical analyses. Meanwhile, it was analyzed how rock mass class, coefficient of lateral pressure, shotcrete thickness, the existence of rock bolt, and excavation method had an effect on the safety factor of a tunnel.

• Tunnel and Underground Space
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• v.14 no.2
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• pp.154-166
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• 2004

A numerical stability analysis was conducted on the large oil storage caverns excavated in a rock mass under high initial horizonal stress. The behaviors of the surrounding rock mass, rockbolts, and shotcrete were analyzedr and stability of the support members were assessed. For a proper support system design, the effect of the modelling technique, cavern shape and rockbolt length on the stability of the cavern was investigated. Results show that installation timing of supports and the change in cavern shape due to stepwise excavation affect the stress induced in support members. Also found was desperate need for a numerical technique which can properly reflect the behavior of the steel fiber reinforced shotcrete.