• Explosives and Blasting
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• v.23 no.1
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• pp.41-46
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• 2005

Overbreak is an inevitable during tunnel excavation. It significantly affects tunnel construction cost and safety The overbreak occurs due to incorrect expectations to the geologic structures, excessive charge or strength of explosives, etc. This paper introduces multi-hole drilling method to minimize the overbreak in tunnel excavation. Although the drilling cost of the method is more expensive than those of the existing other drilling method, it is expected at that cost will be reduced.

• Explosives and Blasting
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• v.31 no.2
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• pp.14-24
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• 2013

The most effective way of the rock removing works in the downtown area is to removing rocks by splitting the rock by blasting with small amount of explosives in the hole. However environmental factors not only limit the applications but also increase the forbidden area. As this is a distributed multi-stage blasting method and to reduce vibration by applying the optimized precisioncontrol-blasting method, it is applicable in all situations. The process is to fix the stemming-help plastic sheet to the hole entrance when stemming explosives and insert detonator and explosive primer with same delay time, two or three sets. This method is more efficient in the downtown area where claims and dispute from vibration are expected. This method is easily usable by designing blast pattern even in the area where delay time blasting is difficult after multi-stage explosive stemming due to short length of blast hole (1.2~3.0m) and there is no detonator wire shortage or dead-pressure.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.3
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• pp.259-269
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• 2013

In this paper, we propose an SIW(Substrate Integrated Waveguide) multi-section E-plane transformer using air-holes for an SIW system with variable thicknesses. Air-holes are inserted into a SIW E-plane quarter wavelength transformer for matching an E-plane impedance discontinuity. A PSIW(Punched Substrate Integrated Waveguide) consisted of air-holes has an SIW characteristic impedance tunability because of reducing a equivalent shunt capacitance of the SIW. And, a PSIW multi-section E-plane transformer is implemented for improving a matching bandwidth by using the Chebyshev polynomial. The measurement results of PSIW double-section E-plane transformer show that the insertion loss($S_{21}$) is $1.57{\pm}0.11$ dB and input return loss($S_{11}$) is more than 15 dB from 11.45 GHz to 13.6 GHz.

• Proceedings of the KSEE Conference
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• 2007.10a
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• pp.77-85
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• 2007

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.6
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• pp.407-416
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• 2010

A new tunnel auxiliary method is proposed in this paper which utilizes the concept of cavity expansion for tuunel reinforcement by forming an umbrella arch on the roof of tunnel. When an inflatable pipe is inserted and expanded by pressure in the bore hole of umbrella arch, the ground around the bore hole can be compacted so that the stress condition above the tunnel perimeter is favorably changed. In order to verify the reinforcement effect of new concept, pilot-scale chamber test, trapdoor test and numerical analysis were performed and compared. In pilot-scale chamber test, three types of inflatable pipes are tested to verify the capability of expansion, and the results arc compared with analytical results obtained by applying cavity expansion theory and with results obtained from finite clement analysis, and the experimental results showed agreeable matches with analytical and numerical ones. Numerical analysis of a tunnel and trapdoor test applied with the inflatable pipes are also performed to figure out the reinforcement effect of the proposed techniques, and the results implied that the new method with 3 directional inflatable pipe (no pressure to downward direction) can contribute to reduce tunnel convergence and face settlement.

• The Journal of Engineering Geology
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• v.29 no.3
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• pp.201-209
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• 2019

Bottom-up multi-stage pressure grouting is widely applied to domestic slopes and tunnels. It involves injecting earth from the ground to the surface after drilling. Various reports of construction performance have demonstrated its wide applicability. However, little research has studied top-down multi-step pressure grouting in Korea, which involves injection from the surface. This paper compares the grouting effect of both the established bottom-up method and the top-down method in soil box and field tests. The soil box test showed that the bulb volume of the top-down method is ~24% less than that of the bottom-up method. The field test confirmed that the top-down method has a wider grouting range and a higher injection density per area than the bottom-up method.

• Explosives and Blasting
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• v.30 no.2
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• pp.52-58
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• 2012

A TBM launching shaft in DTL2 Contract 915 site is located in a typical hard Bukit Timah granite formation and lots of blasting work is required for shaft sinking. The original blast design used the electric detonator and ANFO blasts consisting of 30 holes per one blast with 1.5 m depth of drilling hole. However, significant delay of work and poor progress were expected due to the limitation of the number of blasting hole and strict vibration regulation on retaining systems. To overcome such constraints, an efficient new blasting method which can improve productivity and satisfy vibration limit was required. The revised blast design, using triple-deck blasts with electronic detonators and cartridge emulsion explosives, gives better construction performance and can reduce construction time. Such a new blasting technique can be effectively used for similar underground projects in the future where the volume of rock blasting is significant.

• Tunnel and Underground Space
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• v.15 no.1 s.54
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• pp.71-79
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• 2005

The stability of the intersection area of two tunnels is analyzed by observational method. The depth from ground surface to the intersected area is shallow and the geology around the area consists of soil and/or weathered rock. The tunnel is supported by reinforced protective umbrella method with 12 m long 3-layer steel-pipes and the intersected area is additionally reinforced with 6 m long rockbolts. The measured displacements are converged and mechanical stability of the intersected area of two tunnels is confirmed; tunnel arch settles to 6-7 mm at the crown and the sidewalls converges to about 5 mm. So based on the displacement measurements, the supporting system for the tunnel intersection proves to be effective to not only reduce the deformation of tunnels but also maintain the stability of tunnels.