• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.5
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• pp.547-559
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• 2012

The concrete structural design in domestic has based on the allowable stress design (ASD) method and ultimate strength design (USD) method. Recently limit state design (LSD) method has issued and attempted to adopt in geotechnical design. Because ASD method and USD method have restriction in economic design. In this study, the generated member forces were calculated about high strength concrete segment lining based on japanese LSD code. And it compared with domestic USD code for identifying the economic design possibility of LSD and domestic applicability. In analysis results, the aspect of moment had generated similarly each other but the member forces of japanese LSD code were decreased (26.0% of moment and 26.7% of shear force) comparing with USD method. For that reason, possibility of economic segment design with stable condition were identified.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.51-60
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• 2010

Recently, a new type of polyolefin fiber having a good mechanical properties is being developed, and it is necessary to examine a possibility for the new fiber together to be used as a reinforcing fiber with other types of fiber or by itself. The objective of this study is to find flexural toughness and tensile strength of concrete reinforced with steel and polyolefin fibers. Four point beam tests were performed with 324 specimens following two standard tests methods: KS F 2566 and ASTM C 1399-02. From the test results, the effects of volume fraction of fibers, and aspect ratio of steel fiber on the toughness and tensile strength were investigated, and the optimal ratio of steel fiber to polyolefin fiber was suggested.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1907-1914
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• 2013

Textile-type heat exchangers installed on the tunnel walls for facilitating ground source heat pump systems, so called "energy textile", was installed in an abandoned railroad tunnel around Seocheon, South Korea. To evaluate thermal performance of the energy textile, a series of long-term monitoring was performed by artificially applying daily intermittent cooling and heating loads on the energy textile. In the course of the experimental measurement, the inlet and outlet fluid temperatures of the energy textile, pumping rate, temperature distribution in the ground, and air temperature inside the tunnel were continuously measured. From the long-term monitoring, the heat exchange rate was recorded as in the range of 57.6~143.5 W per one unit of the energy textile during heating operation and 362.3~558.4 W per one unit during cooling operation. In addition, the heat exchange rate of energy textile was highly sensitive to a change in air temperature inside the tunnel. The field measurements were verified by a 3D computational fluid dynamics analysis (FLUENT) with the consideration of air temperature variation inside the tunnel. The verified numerical model was used to evaluate parametrically the effect of drainage layer in the energy textile.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.5
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• pp.717-733
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• 2019

In this study, lining thickness distribution and its behind state (particularly, its void state) were analyzed using the GPR survey data performed on three currently operating NATM tunnels. Results of GPR analysis showed that void areas were mostly detected between concrete lining and primary support, particularly, near the crown of the tunnels. The lining thickness in the left-hand side of the tunnel was different from that of the right-hand side by 8.6~253.5 mm when measured in transverse direction. It was also found that longitudinal cracks were prevailed in the area lining thickness was sharply changed. Longitudinal thickness distribution at the crown was also studied and tested by performing 3 goodness-of-fit tests in order to find the most suitable thickness distribution. Normal distribution (or similar distribution) fit most suitably to the measured data if the measured average thickness was larger than designed one; Gamma and/or Inverse Gauss distribution fit to the measured data reasonably well if the measured average thickness was less than the designed value of thickness. Since actual lining thickness can be a potential index when assessing the state and safety of the unreinforced NATM tunnel lining, measuring of the lining thickness with GPR survey might be needed rather than assuming the thickness is always constant and same with the designed value.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.705-708
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• 2008

To obtain tunnel concrete safety in case of fire, this study analyzed fire proof characteristics by fire proof method change, and the results are as follows. As a fire proof characteristics by RABT temperature heating curve, plain concrete experienced severe spalling by initial extremely high temperature. In view of fire proof method, in the cases of organic fiber mixing method and board method, spalling was prevented, and in the case of spray method, severe spalling of over 100mm depth occurred along with exposure of structural concrete including spray coat by heat stress, etc while metal lath, the stiffener, falls off. As for fire proof characteristics by RWS temperature heating curve, in case of organic fiber inclusion, concrete surface experienced fusion of within 5mm, while in the case of spray method, spray coat was severely spalled to a depth of over 100mm causing structural body concrete to expose its reinforcement, and also in the case of board method, board was fused by high temperature, causing structural body concrete be directly exposed to high temperature, which triggered overall fall-off phenomenon, so in such extraordinary high temperature heating condition, establishment of special fire proof measures is needed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.3
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• pp.311-320
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• 2014

High strength concrete is not only vulnerable to the occurrence of spalling which generates the loss of cross-section in concrete structures but produces faster degradation in its mechanical properties than normal strength concrete in the event of fire. This study aims to evaluate fire resistance of high strength segment concrete with PET fibers mixed to prevent spalling under ISO834 (2hr) and RABT fire curve. As results, the samples without PET fibers show the concrete loss up to the depth of about 8 cm and 9.5 cm from the surface exposed to fire under ISO834 and RABT fire curve respectively. The samples mixed with PET fiber of 0.1% show no spalling under ISO834 fire curve and the spalled thickness of 6.5 cm under RABT fire curve after the fire tests. Finally, the sample mixed with PET fiber of 0.2% shows no spalling under RABT fire curve. The results indicate that the suitable amounts of PET fiber for securing fire resistance performance of this high strength segment concrete are 0.1% under ISO834 fire curve and 0.2% under RABT fire curve. However, even though spalling does not occur, it is necessary to repair the deterioration of concrete up to 4 cm from the surface exposed to fire after fire.

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.21-34
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• 2014

This paper studies the time-dependent behaviors of tunnel and surrounding ground due to tunnel deterioration. In the first part, the literature on deterioration characteristics of tunnels was reviewed. In the second part, a numerical analysis was performed to investigate the behavior of concrete lining on the typical section of Korean high-speed rail tunnel (weathered rock) after determination of input variables related to deterioration impact. The result shows that the settlement at the crown of tunnel and surface ground increased up to 7.0% and 30.2% of the total settlements during construction stage, respectively, and the internal convergence reduction of 9.0 mm for concrete linings was generated within 30 years after completion of tunnel construction. Also the loosening height increased up to 2.55 times of tunnel height within 50 years, which is higher than that of Terzaghi's recommendation on ultimate state. Due to this process of extending zones, it is found that additional loads were applied to concrete lining with the axial stress about 3.20~3.66 MPa, which accelerates tunnel deterioration. Finally the quantitative design approach to evaluate time-dependent behavior of lining and surrounding ground due to tunnel deterioration was proposed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.1
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• pp.31-40
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• 2016

A new testing equipment is designed to investigate the characteristics of the drainage fabric which is used in the tunnel drain system. The equipment is possible to model the loading as well as boundary conditions of the shotcrete precisely and it follows the general guideline of ASTM D4716 so that the interface between shotcrete and concrete lining retains the real situation in the tunnel site. Using the real loading conditions and surface irregularities, the flow rate and its capacity of the regular fabric has been estimated. A composite drainage fabric having geogrid inside was also used to investigate the flow rate and its efficiency. The advantages of the composite fabric compared with the regular one have been demonstrated using the experimental data and brief outline of the future work is finally proposed.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.191-194
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• 2008

The cavity behind the tunnel lining, caused by overbrake, might be cause a severe instability during tunnel construction. So backfill grouting is essentially required. GPR(Ground penetrating Radar) is widely used to identify the position and size of the cavity and to verify the effect of the backfill grouting. In this study, GPR survey with 450 MHz antenna was implied to access the effect of the backfill grouting before and after the work to the crown part of ○○ tunnel in Seoul respectively. The result of GPR survey conducted before the backfill, was revealed that cavities behind the lining were existed in the areas of 8 spans. Finally, from the GPR survey implied after backfilling, it was turned out that backfill grouting was successfully carried out. Also, GPR survey was ascertained the better contact between lining and rock base at arrangement of bar span.

• Explosives and Blasting
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• v.25 no.2
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• pp.23-33
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• 2007

It is difficult to measure a blast noise in the vicinity of tunnel blasting works and the effect of lowering noise changes very highly with types of soundproof materials. So, the main interest of this study focuses on the materials of a soundproof facilities and the method of noise forecast in a near distance. 20 types of the soundproof facilities are established and blast noise is generated using firecracker in a Hume concrete pipe. To analyze the variations of magnitudes of noise and frequency with the soundproof materials and types, the noise and frequency is measured in a short distance next to blast area.