• Journal of the Korea institute for structural maintenance and inspection
• /
• v.15 no.2
• /
• pp.144-152
• /
• 2011

The existing underground trenchless methods use reinforcing rod in steel tube to obtain structural stiffness. However, there are some problems such as inconvenience of work and expensive material fee which are resulted from limited working space and reinforcing work. To resolve these problems, a new trenchless method, namely P.S.T method (Prestressed Segment Tunnel Method), is developed which uses joint to connect the steel segment and form erection structure in underground construction. Further, installing strands for prestressing. In order to evaluate the flexural capacity of the P.S.T method structure, experiment was conducted. The parameters considered in the experiment are the span-to-depth ratio, diameter of steel tube at corner, prestressing force and welding of joint. Altogether examining the flexural behavior, the effect of deflection in structure according to different parameters has also been analysised.

• Journal of the Korean GEO-environmental Society
• /
• v.15 no.5
• /
• pp.13-21
• /
• 2014

This study analyzed the differences in the analysis techniques through a comparative analysis of the various segment's modeling techniques of Shield TBM method and proposed reasonable modeling techniques. Also, this study suggested reasonable estimating methods of load to be applicable in the field through the load analysis and three-dimensional finite element analysis by estimating model of rock mass relaxation load. Estimating method of relaxation area by rock mass rating makes no odds of output in subgrade with high rock mass rating, but so the difference of output is large, that is judged to set conservative design off. In estimating result of rock mass relaxation area by three-dimensional analysis relaxation area of subgrade with low-grade soil was predicted to be positioned at medium-range of many methods, in case of designing segment in subgrade with low-grade soil it needs to actively review estimation of relaxation area through three-dimensional analysis reflecting mechanical tunnel excavation.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.22 no.3
• /
• pp.311-321
• /
• 2020

In this study, coefficient of variation for the seismic load effect on the segment lining was calculated. The statistical characteristics of the soil property were analyzed for the probability characteristics of domestic soil. In order to calculate the coefficient of variation for the seismic load effect, the MCS technique was applied, and the closed-form equation was applied to calculate the seismic load effect. As a result of calculating the coefficient of variation, the coefficient of variation of the seismic load effect on the weathered soil was analyzed in the range of 0.06~0.15, and the coefficient of variation was judged to be used as basic data for designing the limit state of the shield tunnel on seismic condition.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.20 no.1
• /
• pp.55-72
• /
• 2018

A method that can predict the mixed-ground condition ahead of a TBM tunnel face during tunnel construction utilizing electrical resistivity and induced polarization (IP) was proposed in this study. Effect of TBM advancement approaching the mixed-ground condition (composed of soil layer overlying rock layer) when currently running through soil zone on the electrical resistivity and IP measuring was assessed with laboratory-scale experiments. The resistivity and IP values were measured using four electrodes, by installing two electrodes on the tunnel face (at the cutterhead), and the other two electrodes on the segment lining. The test results showed that both of the measured resistivity and IP values were kept increasing as the TBM is approaching the soil-rock mixed-ground. Also, to get the more reliable results for predicting the mixed-ground condition, it was recommended that the measurement is made at the tunnel face utilizing 4-electrodes installed at the cutterhead as well as it is made utilizing the 2-electrodes installed at the segment lining along with the 2-electrodes installed on the tunnel face (at the cutterhead) so that two measured results are compared each other.

• Journal of Korean Neurosurgical Society
• /
• v.48 no.4
• /
• pp.380-382
• /
• 2010

The authors present an extremely rare case of a pseudoaneurysm of the ulnar artery as a complication of a two-portal endoscopic carpal tunnel release (ECTR). A 70-year-old man with chronic renal failure and on maintenance hemodialysis with a left arteriovenous fistula presented with paresthesia of his right hand. A clinical diagnosis of right carpal tunnel syndrome was confirmed by ultrasonography and an electro physiologic study. He underwent two-portal ECTR, and the paresthesia was much improved. However, he presented to us one month after operation with severe pain, a tender mass distal to the right wrist crease and more aggravation of the paresthesia in the ulnar nerve distribution. Doppler ultrasound was performed and revealed a hypo echoic lesion 20 mm in diameter in the right palm, with arterial Doppler flow inside connected to the palmar segment of the ulnar artery. An ulnar artery pseudoaneurysm was diagnosed and treated by ultrasound-guided percutaneous thrombin injection. Transverse color Doppler ultrasound image showed complete thrombosis of the pseudoaneurysm and flow cessation after a total injection of 500 units of thrombin. The symptoms were also improved.

• Journal of the Korean Society for Railway
• /
• v.12 no.1
• /
• pp.167-174
• /
• 2009

Due to the travelling of the train with high speed the period of maintenance activities of the ballasted track is coming to be short, and more from the residential area of the ballasted track tunnel circumference the civil appeal is increasing with railroad vibration problem. To reduce the vibration problem and a maintenance cost establishes the ballast mat in the tunnel within part segment. In this study, to estimate the vibration reduction effect of the ballast mat we have done a comparative analysis with the vibration field test by the transit train by at the ballasted track with ballast mat and the standard ballasted track without vibration protection in tunnel.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 2008.04a
• /
• pp.624-629
• /
• 2008

When TBM excavates a tunnel, existing concrete lining segments are used as supporting structures for driving force. Axial stress on the lining segments are apt to be large in case of direct driving force. However, it drastically decline as it is farther and father from TBM and later, it tends to converge after a certain point. Such tendencies show similar results of finite element analysis. At the initial intervals, the values of finite element analysis are larger, while at the later intervals, the actual stress values are larger. It concludes that such tendencies are attributable to that the concrete lining segments have partially burst and cracked in the axial direction at the initial intervals. And differences of stresses at the later intervals are created by the changed plasticity of ground and the friction on the external sides of the lining segments.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.25 no.6
• /
• pp.583-603
• /
• 2023

Recently, the advancement of mechanical tunnel boring machine (TBM) technology and the characteristics of subsea railway tunnels subjected to hydrostatic pressure have led to the widespread application of shield TBM methods in the design and construction of subsea railway tunnels. Subsea railway tunnels are exposed in a constant pore water pressure and are influenced by the amplification of seismic waves during earthquake. In particular, seismic loads acting on subsea railway tunnels under various ground conditions such as soft ground, soft soil-rock composite ground, and fractured zones can cause significant changes in tunnel displacement and stress, thereby affecting tunnel safety. Additionally, the dynamic response of the ground and tunnel varies based on seismic load parameters such as frequency characteristics, seismic waveform, and peak acceleration, adding complexity to the behavior of the ground-tunnel structure system. In this study, a finite difference method is employed to model the entire ground-tunnel structure system, considering hydrostatic pressure, for the investigation of dynamic behavior of subsea railway tunnel during earthquake. Since the key factors influencing the dynamic behavior during seismic events are ground conditions and seismic waves, six analysis cases are established based on virtual ground conditions: Case-1 with weathered soil, Case-2 with hard rock, Case-3 with a composite ground of soil and hard rock in the tunnel longitudinal direction, Case-4 with the tunnel passing through a narrow fault zone, Case-5 with a composite ground of soft soil and hard rock in the tunnel longitudinal direction, and Case-6 with the tunnel passing through a wide fractured zone. As a result, horizontal displacements due to earthquakes tend to increase with an increase in ground stiffness, however, the displacements tend to be restrained due to the confining effects of the ground and the rigid shield segments. On the contrary, peak compressive stress of segment significantly increases with weaker ground stiffness and the effects of displacement restrain contribute the increase of peak compressive stress of segment.

• Tunnel and Underground Space
• /
• v.31 no.6
• /
• pp.469-479
• /
• 2021

As a material for preventing spalling of concrete, the effectiveness of PP fiber has already been confirmed. However, it is necessary to consider the maximum temperature that occurs during a fire, and to solve the mixing problem and the strength reduction problem that occur depending on the mixing amount. In this study, the fire resistance performance of tunnel segment linings according to the PP fiber content and air volume under the RABT fire scenario was investigated. As a result, no spalling or cross-sectional loss occurred in all test specimens, and when the PP fiber content was small, the maximum temperature was relatively high and the maximum temperature arrival time was also fast. On the other hand, no trend was found for the maximum temperature and arrival time according to the difference in air volume. In the internal temperature distribution results for the PP fiber mixing amount of 0.75, 1.0, 1.5, and 2.0 kg/m³, the results of 0.75 and 1.0 kg/m³ showed similar temperature distribution, and the results of 1.5 and 2.0 kg/m³ were similar. It was confirmed that the internal temperature distribution tends to decrease at the same depth when the amount of PP fiber mixed is large, and it was confirmed that a remarkable difference occurred from the results of 1.0 kg/m³ and 1.5 kg/m³ of PP fiber mixed amounts.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.17 no.5
• /
• pp.553-561
• /
• 2015

In this study, the performance assessment criterion for reasonable maintenance of shield TBM tunnel was presented. The performance assessment items such as crack, leakage, breakage, spalling, exfoliation/detachment, efflorescence, quality condition, exposure of steel, carbonation, faulting step, bolts condition, drainage condition, ground condition, contact section condition and conduit condition were selected by analyzing domestic and foreign performance assessment criterions and investigating segment lining deterioration cases through the site investigation and in-depth inspection analysis result on the shield TBM tunnel. In addition, the reasonable weight using AHP (Analytic Hierarchy Process) were estimated.