• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.839-854
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• 2018

This study was performed to evaluate the performance of GFRP plate reinforced segments for TBM tunnel support. Recently, the SFRC segment has been applied to prevent local damage such as reduction of the amount of reinforcing bars of the segment, crack control and breakage. However, the steel fiber used in the SFRC segment has a problem of durability deterioration due to fiber corrosion. Compared with the RC segment, the maximum flexural load reduction of the SFRC segment hinders the broad application range of the TBM tunnel segment. Therefore, GFRP plate was considered as a stiffener for the maximum load increase of SFRC segment, and structural synthetic fiber without corrosive concern was used as a substitute for steel fiber. The flexural performance of the segment was evaluated by using the type of reinforcing fiber and GFRP plate thickness as the main parameters. As a result, the maximum load and the flexural toughness were increased by 21.78~23.03% and 0.5~7.96%, respectively, as compared with the segments reinforced with reinforcing fiber and GFRP plate of 3 mm thickness.

• Korean Journal of Clinical Laboratory Science
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• v.37 no.3
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• pp.212-215
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• 2005

Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy in clinical practice, with a 0.1% life time risk in the general population. Conventional neurophysiological studies have been useful in the diagnosis of this condition, as have a number of more specialized procedures. Therefore, we evaluated the diagnostic sensitivities of several parameters in nerve conduction technique for CTS patients. We analyzed 100 patients (159 hands) who were diagnosed with CTS clinically and electrophysiolosically. Median motor and sensory nerve conduction velocities (MCV and SCV) with wrist, palm, and finger stimulation were performed in traditional methods. Sensitivities of each test were calculated and compared to normal control data. The sensitivities of existing nerve conduction method were noted in terminal latency on median nerve, 2nd finger-wrist segment, 3rd finger-wrist segment, palm-wrist segment and distoproximal ratio, as 72.96%, 92.45%, 94.34%, 94.97%, and 97.48%, respectively. In the early course of CTS, sensory nerve conductions in the median nerve are more valuable than motor nerve conduction. Sensory nerve conductions are usually affected before motor nerve conductions in CTS. In this study, we detected that slowing of median SCV was the most frequent in the distoproximal ratio.

• Wind and Structures
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• v.37 no.6
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• pp.399-412
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• 2023

Previous studies have shown that the integrated transfer function (ITF) is independent of turbulence characteristics and can be effectively applied to predict the buffeting response of elongated structures, assuming that the strip hypothesis is valid. However, existing research has not effectively identified the ITF through segment model vibration tests, and the influence of the 3D effect on the accuracy of the strip hypothesis and the characteristics of the ITF in wind tunnel tests has not been quantitatively studied. A segment model vibration measurement device that can change a test model's span-width ratio was designed in this study. An airfoil section and a streamlined box girder section structure were taken as the background, and their ITFs were effectively identified under different L/B (L denotes the turbulent integral scale and B denotes the structural width) and model span-width ratios. The influence laws of the 3D effect on the accuracy of the strip hypothesis and ITF identification in wind tunnel tests were systematically investigated. The results showed that L/B and the structural span-width ratio are two significant controlling factors that affect the accuracy of the strip hypothesis and ITF identification. The research provides an effective experimental method for accurately predicting the buffeting response of elongated structures based on ITFs identified through segment model vibration tests.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.99-118
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• 2018

Recently, the limit state design method in the design of the structure is in global trend, but it is limited to a few structures in Korea. Since the introduction of the limit state design method has recently been attempted for tunnels, which are the main underground structures, it is surely necessary to understand the latest limit state design method. Therefore, based on the recently published AASHTO LRFD Road Tunnel Design and Construction Guide Specification (2017), structural load factors and load combinations were reviewed, and various factors which should be applied for the review of structures have been analyzed. In this study, utility tunnel section and subway tunnel sections used in Korea were analyzed by the limit state design method, and we have analyzed the direction of application of limit state design method through studying the tendency of member force by various influential factors such as ground conditions, load modifier and joint stiffness.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.5
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• pp.325-337
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• 2021

On the road and rail tunnels, the evacuation pathway and facilities such as smoke-control and fire suppression system are essential in tunnel fire. In the long twin tunnels, the cross-connection tunnel is usually designed to evacuate from the tunnel where the fire broke out to the other tunnel. In twin shield tunnels, the segment lining has to be demolished to construct the cross-connection tunnel. Considering the modern shield TBM is mostly the closed chamber type, the exposure of underground soil induced by removal of steel segment lining is the most danger construction step in the shield tunnel construction. This case study introduces the excavation method using the thrust of large steel pipe and reviews the measured data after the construction. The large steel pipe thrust method for the cross-connection tunnel can stabilize the excavated face with the two mechanisms. Firstly, the soil in front of excavated face is cylindrically pre-supported by the large steel pipe. Secondly, the excavated face is supported by the plugging effect caused by the soil pressed into the steel pipe. It was reviewed that the large steel pipe thrust method in the cross-connection tunnel is enough to secure the construct ability and stability in soil from the measurement results about the deformation and stress of steel pipe.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.5
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• pp.303-314
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• 2021

With the high quality/high stiffness/high strength of segment lining, segment lining is increasingly used as the final lining of the tunnel. Precast concrete lining has higher quality and strength than field concrete. Paradoxically, this contributes to greater damage to concrete in the event of a fire in a tunnel. In this study, tests were conducted to determine the fire resistance performance of segment linings according to fiber content in fire resistance methods using synthetic fibers such as PP fibers. As a result, it was confirmed that fire resistance performance required by the relevant project can be secured when using 1.5 kg/m³ of PP fiber. In addition, comparison of the results of PP fibers with PET, a similar synthetic fiber, showed better fire resistance performance than when PP fibers were used.

• Smart Structures and Systems
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• v.24 no.6
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• pp.693-707
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• 2019

This paper proposes an integrated safety assessment method that can take multiple sources data into consideration based on a data fusion approach. Data cleaning using the Kalman filter method (KF) was conducted first for monitoring data from each sensor. The inclination data from the four tilt sensors of the same monitoring section have been associated to synchronize in time. Secondly, the finite element method (FEM) model was established to physically correlate the external forces with various structural responses of the shield tunnel, including the measured inclination. Response surface method (RSM) was adopted to express the relationship between external forces and the structural responses. Then, the external forces were updated based on the in situ monitoring data from tilt sensors using the extended Kalman filter method (EKF). Finally, mechanics parameters of the tunnel lining were estimated based on the updated data to make an integrated safety assessment. An application example of the proposed method was presented for an urban tunnel during a nearby deep excavation with multiple source monitoring plans. The change of tunnel convergence, bolt stress and segment internal forces can also be calculated based on the real time deformation monitoring of the shield tunnel. The proposed method was verified by predicting the data using the other three sensors in the same section. The correlation among different monitoring data has been discussed before the conclusion was drawn.

• Geomechanics and Engineering
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• v.30 no.4
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• pp.383-392
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• 2022

Although pipelines are composed of segmental tubes commonly connected by rubber gasket or push-in joints, current studies mainly simplified pipelines as continuous structures. Effects of joints on three-dimensional deformation mechanisms of existing pipelines due to tunnel excavation are not fully understood. By conducting three-dimensional numerical analyses, effects of pipeline burial depth, tunnel burial depth, volume loss, pipeline stiffness and joint stiffness on bending strain and joint rotation of existing pipelines are explored. By increasing pipeline burial depth or decreasing tunnel cover depth, tunneling-induced pipeline deformations are substantially increased. As tunnel volume loss varies from 0.5% to 3%, the maximum bending strains and joint rotation angles of discontinuous pipelines increase by 1.08 and 9.20 times, respectively. By increasing flexural stiffness of pipe segment, a dramatic increase in the maximum joint rotation angles is observed in discontinuous pipelines. Thus, the safety of existing discontinuous pipelines due to tunnel excavation is controlled by joint rotation rather than bending strain. By increasing joint stiffness ratio from 0.0 (i.e., completely flexible joints) to 1.0 (i.e., continuous pipelines), tunneling-induced maximum pipeline settlements decrease by 22.8%-34.7%. If a jointed pipeline is simplified as a continuous structure, tunneling-induced settlement is thus underestimated, but bending strain is grossly overestimated. Thus, joints should be directly simulated in the analysis of tunnel-soil-pipeline interaction.

• Computers and Concrete
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• v.29 no.2
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• pp.69-79
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• 2022

For long underground box utility tunnels, post-tensioned precast concrete is often used. Between precast tunnel segments, sealed waterproof flexible joints are often specified. Fault displacement can lead to excessive deformation of the joints, which can lead to reduction in waterproofing due to diminished contact pressure between the sealant strip and the tunnel segment. This paper authenticates utilization of a finite element model for a prefabricated tunnel fault-crossing founded on ABAQUS software. In addition, material parameter selection, contact setting and boundary condition are reviewed. Analyzed under normal fault action are: the influence of fault displacement; buried depth; soil friction coefficient, and angle of crossing at the fault plane. In addition, distribution characteristics of the utility tunnel structure for vertical and longitudinal/horizontal relative displacement at segmented interface for the top and bottom slab are analyzed. It is found that the effect of increase in fault displacement on the splice joint deformation is significant, whereas the effects of changes in burial depth, pipe-soil friction coefficient and fault-crossing angle on the overall tunnel and joint deformations were not so significant.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.6
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• pp.423-446
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• 2023

Shield TBM tunnel linings are segmented into segments and rings. This study investigates the response characteristics of the stress and displacement of the segment lining under seismic waves through modeling that considers the interface behavior between segments by applying a shell interface element to the contact surface between segments and rings. And there is no management criteria for ovaling deformation of segment linings in Korea. So, this study the ovality criteria and meaning of segment lining. The results of study showed that the distribution patterns of stress and displacement under seismic waves were similar between continuous linings and segment linings. However, the maximum values of stress and displacement showed differences from segment linings. The stress distribution of the continuous lining modeled as a shell type has a stress distribution that has continuity in the 3D cylindrical shape, but the segment lining is concentrated outside the segment, and the largest stress occurs at the location where the contact surface between the segment and the ring is concentrated. This intermittent and localized stress distribution shows an increasing as the ovality of the lining increases at seismic waves. The ovality at which the increase in stress distribution begins to show irregularity and localization is about 150‰. Ovality of 150‰ is an unrealistic value that cannot represent actual lining deformation. Therefore, the ovality of the segment lining increase with depth, but it does not have a significant impact on the stability caused by seismic load.