• Tunnel and Underground Space
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• v.20 no.6
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• pp.465-474
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• 2010

Although the number of medium-length road tunnels, less than 1 km in length, has increased recently more than 30 percent each year, their ventilation and fire safety system design guidelines have not been established yet. The guidelines for long tunnel design are adopted even for the medium-length road tunnels. Therefore the necessity is brought up to optimize the ventilation and fire safety systems based on their own design guidelines. This study aims at determining the optimal start time of jet fan in case of 20 MW fires by analyzing smoke backlayering range, temperature distribution, range of poor visibility, evacuation time and critical velocity. The CFD study results are expected to contribute to propose the optimal fan operation mode.

• Fire Science and Engineering
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• v.25 no.5
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• pp.119-127
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• 2011

Because of most notably the increase in vehicular traffic in Korea, as measured by highway transport usage, relief is being sought by expanding the construction of highways after 1970s'. These highways have opened up over 70 % of the mountainous areas in Korea's country side which includes the construction of tunnels. Currently there are 607 tunnels installed that are being maintained and by 2015, under the next medium-term plan, Korea will build an additional 440 tunnels. In addition, the use of 1,000m double-pole tunnels is expected to increase significantly in 256 locations. There is no doubt that these tunnels will relieve traffic congestion and aid improved communications, but halfclosed underground highway tunnels in particular are required to reduce tunnel fires caused by poor vehicle maintenance, and other factors such as speeding motorists that increase the number of vehicular accidents. Double-pole tunnels in 1,000m length over require vehicle drivers to be more cautious in terms of the continuous speed limit, judged by how devastating most of car-crash fires within these tunnels can be. In order to prevent these disasters, a full-length tunnel speed enforcement system should be considered mandatorily in legal clauses.

• Geophysics and Geophysical Exploration
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• v.9 no.4
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• pp.279-290
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• 2006

The borehole radar methods used to tunnel detection are mainly classified into borehole radar reflection, directional antenna, crosshole scanning, and radar tomography methods. In this study, we have investigated the feasibility and limitation of each method to tunnel detection through case studies. In the borehole radar reflection data, there were much more clear diffraction signals of the upper wings than lower wings of the hyperbolas reflected from the tunnel, and their upper and lower wings were spreaded out to more than 10m higher and lower traces from the peaks of the hyperbolas. As the ratio of borehole diameter to antenna length increases, the ringing gets stronger on the data due to the increase in the impedance mismatching between antennas and water in the boreholes. It is also found that the reflection signals from the tunnel could be enhanced using the optimal offset distance between transmitter and receiver antennas. Nevertheless, the borehole radar reflection data could not provide directional information of the reflectors in the subsurface. Direction finding antenna system had a advantage to take a three dimensional location of a tunnel with only one borehole survey even though the cost is still very high and it required very high expertise. The data from crosshole scanning could be a good indicator for tunnel detection and it could give more reliable result when the borehole radar reflection survey is carried out together. The images of the subsurface also can be reconstructed using travel time tomography which could provide the physical property of the medium and would be effective for imaging the underground structure such as tunnels. Based on the results described above, we suggest a cost-effective field procedure for detection of a tunnel using borehole radar techniques; borehole radar reflection survey using dipole antenna can firstly be applied to pick up anomalous regions within the borehole, and crosshole scanning or reflection survey using directional antenna can then be applied only to the anomalous regions to detect the tunnel.