• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.231-248
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• 2017

Government plans to construct a double-deck tunnel under a portion of Gyeongbu Expressway that will solve traffic problems and could also be used as a flood storage facility. Divergence tunnels connect the main tunnel to the urban areas and their construction effects on adjacent structures at shallow depth need to be analyzed. This study primarily includes the numerical analysis of construction effects of divergence tunnels on utility tunnels. The utility tunnel was analyzed for three cases of volume loss applied to the divergence tunnel and two cases of the angle between main tunnel and divergence tunnel ($36^{\circ}$ and $45^{\circ}$). The results show that the more the volume loss was applied and the shorter the distance was between utility tunnel and divergence tunnel, the more the utility tunnel was affected in terms of induced displacements, angular displacement and stability. The worst scenario was found out to be the one where the angle between main tunnel and divergence tunnel was $36^{\circ}$ and the distance between divergence tunnel and utility tunnel was 10 m, resulting in the largest displacement and differential settlement at the bottom of the utility tunnel. A relationship between the angular displacement and the distance to diameter ratio was also established.

• Journal of the Society of Disaster Information
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• v.18 no.2
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• pp.261-268
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• 2022

Purpose: In the case of cavity discovered by ground penetrating radar exploration, it is necessary to accurately predict the filling amount in the cavity in advance, fill the cavity sufficiently and exert strength to ensure stability and prevent ground subsidence. Method: The cavity waveform analysis method by GPR exploration and the method using the cavity shape imaging equipment were performed to measure the cavity shape with irregular size and shape of the actual cavity, and the amount of cavity filling of the injection material was calculated during rapid restoration. Results: The expected filling amount was presented by analyzing the correlation between the cavity size and the filling amount of injection material according to the cavity scale and soil depth through the method by GPR exploration and the cavity scale calculation using the cavity shaping equipment. Conclusion: The cavity scale measured by the cavity imaging equipment was found to be in the range of 20% to 40% of the cavity scale by GPR exploration. In addition, the filling amount of injection material compared to the cavity scale predicted by GPR exploration was in the range of about 60% to 140%, and the filling amount of the injection material compared to the cavity size by the cavity shaping equipment was confirmed to be about 260% to 320%.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.425-432
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• 2004

In this paper, the results of the numerical analysis for the minimum depth of soil cover have been compared with those of currently suggested codes. Based on this comparison, the minimum depth of soil cover for the structures with long spans was suggested. Results showed that the actual depth of the soil cover required against soil failure over a circular and low-profile arch structure does not vary significantly with the size of the span and for the circular structure, the minimum depth of the soil cover was about 1.5m, and for the low-profile arch structures, below about 1.6m. And the previously established code in which the minimum depth of soil cover is defined to linearly increase with the increase in the span (CHBDC, 2001) was very conservative. For the structure with the relieving slab, the maximum live load thrust was reduced by about 36 percent and the maximum moment about 81 percent. The numerical analysis gave more conservative estimation of the live-load thrusts than the other design methods.

• Journal of the Korean GEO-environmental Society
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• v.20 no.9
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• pp.5-11
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• 2019

Recently, ground collapse in urban area has been widely paid attention as it frequently happens. To investigate the causes and suggest the measurements, many researches such as ground exploration from GPR, mock test and numerical simulations have been conducted. The proposed risk evaluation chart recently focuses only on the current ground status and is not capable of forecasting the ground collapse. This paper presents the prediction method of ground collapse using the numerical simulations of 30 cases considering void size and ground height as variables. It finally provides the charts that can analyze quantitatively the ground collapse.

• Journal of the Korean Geotechnical Society
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• v.28 no.7
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• pp.17-30
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• 2012

A new trenchless tunneling method using pressurizing support has been developed. As it overcomes shortcomings of conventional methods, it is applied to the field. The main concept of the new method is the pressurization system which, by means of pressurization bag between outer flange of steel ribs and excavated perimeter, applies the pressure corresponding to the magnitude of the relaxed earth pressure caused by excavation to the ground to prevent ground displacement. The stability of the support members and effect of displacement control of the new method were verified through several ways such as numerical tests and various model tests. The new method was applied to the construction of a 10.7 m wide, 7.9 m high and 85 m long road tunnel that passes under Yeongdong Expressway. By applying the new method, the tunnel construction was successfully completed in 13.5 months. It decreases the construction period to 35% compared to that of conventional methods, and ground displacement was almost negligible.

• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.241-249
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• 2017

In a reinforced soil structure, the interaction between soil and an reinforcement occurs due to the frictional resistance on the contact surface between them or the pullout resistance of the reinforcement. Generally, a pullout test is conducted to measure pullout parameters of extensible geogrids. The factors affecting the pullout parameters in a pullout test include a density of backfill, shape of reinforcements, overburden pressure, length of spread reinforcements, and so on. The purpose of this study is to suggest a length of the spreading of an extensible reinforcement that can be used in estimating suitable pullout parameters of a pullout test. To this end, a pullout test was carried out. For the test, the length of spreading of an extensible reinforcement was set as 32 cm, 52 cm, 72 cm, and 100 cm, and effects of the lengths on pullout parameters were analyzed. As a result of the pullout test, it was confirmed that the frictional resistance between the soil and the reinforcement increases with the increase of the length of the reinforcement.

• 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.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.3
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• pp.247-260
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• 2002

This paper presents the design case of the 3-arch tunnel under Daejeon railroad station building. The original construction method was the underpinning method supported by pipe-roof, but it was changed to the mined tunnelling method because of the complex construction condition and the safety problem. This 3-arch tunnel has a width of 28 meters and a height of 10 meters. Overburden is only 23m and the ground around the tunnel is a weathered rock. The allowable settlements for the station building and some railroads are very strict. Accordingly, various measurements for the tunnel stability and the settlement minimization was applied and they were reviewed by 2-D and 3-D numerical analysis.

• Tunnel and Underground Space
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• v.9 no.2
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• pp.114-130
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• 1999

It is very important to study on the structural behaviors of structurally damaged tunnel linings. A series of centrifuge model tests were performed in order to investigate different behaviors of tunnel linings. A 1/100-scaled aluminum horseshoe tunnel linings with a radius 5 cm, height 8 cm were buried in a depth with dry Joomunjin standard sand, the relative density of which was 86%. Such sectional forces as bending moments and thrusts along the tunnel circumference were measured by twelve strain gages. Earth pressures in soil mass and on the outside of lining model were estimated by pressure transducers, ground surface settlements at a center and edges by using LVDTs.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.2
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• pp.197-217
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• 2020

Shield TBM tunneling, used in the construction of Seoul subway line 7 and line 9, has been well known as a very efficient, as well as safe, tunneling method. Although the Shield TBM method has been known to be effectively used in poor ground conditions, a number of troubles have occurred during the use of the shield TBM, due to inappropriate machine selection, machine breakdown, and unpredicted ground conditions etc. In this study, several accidents and trouble cases occurred during excavation by Shield TBM, reported from Japan, were investigated. A series of numerical analysis was then performed to compare with the trouble cases and back-analysis results for the cause analysis. The lessons learned from the case studies are presented at the end.