• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.5-12
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• 2005

In early days, to analyze the behavior of single pile under axial load, many assumptions were made and field tests were performed. But in recent days, the development of computers led the use of the numerical analysis resulting in more realistic and correct results. The numerical methods are classified into Load Transfer Method and Elastic Solid Approach. In this study a numerical program applying t-z model to Load Transfer Method suggested by Coyle & Reese was developed. And another finite difference program using matrix based on this load transfer was developed. As a result, it is found that the values of the F.D.M. were similar to the values measured in-situ.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.536-549
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• 2005

국내 대부분을 차지하고 있는 NATM의 주요원리는 주변지반의 지보효과를 활용하는 터널굴착공법이다. 따라서 실제 지반조건이 원설계조건 보다 역학적으로 불량한 경우 보강공법의 적용은 필수적이라 할 수 있으나, 합리적인 설계변경은 현실적으로 쉽지 않은 실정이다. 또한 현실적인 이유로 양방향으로 터널을 관통하는 설계법과 달리 종종 1방향 굴진으로 터널을 관통하는 경우가 있다. 그러나 이러한 1방향 굴진은 불가분 굴진 종점부에서 저토피 갱구를 향하게 되므로, 지반이 연약한 경ㅇ우 막장 붕괴의 위험이 매우 높은 것으로 알려져 있다. 본 터널은 설계 시 갱구부 지반을 풍화암과 연암으로 보고 설계 하였으나, 실제 굴착 시 확인된 지층은 핵석을 포함한 실트질모래(SP-SM)로 판명되었다. 더구나 터널굴진 방향에 있어서도 양방향 굴착이 아닌 저토피 갱구를 향한 1방향 굴진을 실시하였으며, 이러한 시공 중에 터널관통을 불과 19m 남겨둔 갱구부에서 막장부괴와 동시에 상부사면 함몰이 발생하였다. 본 연구는 토사터널 갱구부 1방향 굴진 시 발생한 막장붕괴 보강사례로서, 지상보강(시멘트밀크 그라우팅)과 갱내보강(방사상 FRP보강그라우팅) 그리고 인버트폐합을 실시하여 성공적으로 터널시공을 완료한 사례연구이다. 본 사례는 향후 토사터널 갱구부의 설계와 시공에 유용한 참고자료가 될 것이다.

• Journal of the Society of Disaster Information
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• v.19 no.3
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• pp.737-746
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• 2023

Purpose: Ground subsidence due to cavity can bring about various problems, such as casualties, decrease of the safety of the structures, and indirect social costs. Therefore, ground subsidence should be prevented through the exploration and recovery of the cavity under the pavements. Method: In this study, GPR exploration method was carried out on both actual roadway and mock-up site to compensate for the problems caused by excavation and restoration process. Result: This study compared the cavity scales obtained from GPR exploration results and the direct excavation of the identified cavity. It was confirmed that the predicted soil depth by GPR exploration was similar to the identified soil depth, but the predicted cavity scale by GPR exploration overestimated the longitudinal and cross-sectional widths compared to the identified cavity scale. Conclusion: Based on the correlation between the predicted cavity scales by GPR exploration, it is possible to qualitatively estimate the cavity scales using the empirical formula proposed in this study.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.141-155
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• 2018

Recently, the number of ground subsidence resulting from underground cavity has been increased. Accordingly, the importance of restoration of stress release zone around the underground cavity has been emphasized. The stress release zone is composed of low density soils having extremely low stiffness and degree of compaction, which can lead to additional cavity expansion and collapse of overlying ground. Therefore, in this study, the suitability of restoration method of underground cavity using expansive material for reinforcement of stress release zone around the cavity is verified. The basic physical properties and expansion characteristics of the expansive material were examined. The experiment equipment capable simulating of stress release zone was developed and is used to investigate the effect of expanding material on stress release zone. The stress release zone was simulated using the spring in numerical analysis. The factors of the volume ratio of the underground cavity to the expansion material, the degree of stress relaxation, and the shape of the cavity were varied in numerical simulations, and the behavior of stress release zone was analyzed based on the numerical analysis results. Analysis variables are factors that affect each other. Also, filling of underground cavity and capacity of restoration of stress release zone were confirmed when the expansive material was inserted into underground cavity.

• Tunnel and Underground Space
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• v.15 no.3 s.56
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• pp.195-212
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• 2005

Surface subsidence which occurs with several reasons, such as collapse of gangway, discharge of groundwater, compaction of weak rock mass, and tunnel excavation in shallow depth, gives rise to a serious problem in national infra-structures. In this study, therefore, the mechanism of subsidence has been examined numerically to overcome the passive approach on subsidence occurrence area. With many kinds of numerical studies, the major geotechnical parameters have been selected and the weighted values have been defined for each parameters. Also the authors developed the numerical program which can estimate the possibility of subsidence occurrence, and proposed the decision method for objective and quantitative guideline. It is anticipated that this research will be helpful to establish the hazard map on subsidence region.

• Journal of the Korean Geotechnical Society
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• v.32 no.2
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• pp.19-30
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• 2016

It is well known that water leakage from decrepit sewer pipe mainly causes frequent occurrence of ground subsidence in urban area. Thus, laboratory model tests were carried out to investigate ground behaviour according to location of sewer fracture and various relative densities of surrounding soil. The portion of fractured pipe was assumed to be 20% compared to the circumference of pipe, and to be positioned at the top and bottom of the pipe. Ground conditions were made as loose sand ($D_r=30%$) and dense sand ($D_r=70%$). In addition, comparison and analysis with results of model tests were carried out by Finite Element analysis. As a result, not only water leakage from the bottom of pipe (scenario 2) caused greater ground behaviour than leakage from the top of pipe (scenario 1), but also much greater surface settlement occurred when the ground condition is loose.

• Journal of the Society of Disaster Information
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• v.13 no.1
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• pp.35-42
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• 2017

In this study, to quantitatively evaluate the strength characteristics of the inflatable liquid used for the recovery of soft ground or partial settlement, the inflatable liquids were prepared by dividing the inflatable capacity and the strength characteristics were analyzed according to the conditions. The experimental group was divided into two groups: relatively high expansion group and low expansion group. The specimens were prepared by controlling the volume of 10 ~ 30% of the maximum expansion volume, and the strength of the specimens were evaluated. The compressive strength of the high expansion group and low expansion group was about 2.1 times.

• The Journal of Engineering Geology
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• v.5 no.1
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• pp.1-20
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• 1995

A train overturn accident occurred on March 1993 in the Gupo area, northern part of Pusan, unfortunately had taken a heavy toll of lives and caused a great loss of property as well. The reasons for the subsidence of the basement under the railroads, which presumed to be the main cause of the accident, have been investigated from many different angles, including conventional geotechnical investigation methods. The deduced nuin reasons of the subsidence were: 1. blasting for tunnel excavation (NATM) at about 39 meter under the railroads, and 2. unexpected change of bedrock conditions along the direction of tunnel. But this accident was derived nrranlv from the lack of geological and geotechnical information under railroad area because it was impossible to drill beneath the railroads. This paper introduces a new geophysical survey techniqueseisrnic geotomography, and shows some results of the method applying to investigate the underground structure of the accident area. This method not only overcomes the unfavourable environment which many conventional investigation methods cannot face, but produces an image of underground structure with high resolution. Furthermore, the outputs from geotomogaphic analysis could provide very valuable in-situ basic parameters (like seismic velocities, elastic moduli, etc.) which is essential to the design and construction.

• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.55-64
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• 2008

When the structure is constructed on the soft ground, the embankment is settleed into the soft ground. At this time, the settlement of the structure is needed to predict. We are using bamboo mats construction only as a way of test construction. Under this circumstance, using the equation of Janbu and Perloff, we calculated the settlement, and analyzed the problem, suggesting proper theoretical equations showing the settlement of soft ground using bamboo mat. Using this equations the settlement was calculated and compared with the result of FEM. The result of the application was very close to the numerical value and the trend of theoretical equations. Using the existing equations, the settlement in Janbu's and Perloff's methods were calculated to be 40% of the actual settlement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.489-501
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• 2017

The collapse accidents during a open ground excavation in urban areas not only lead to human injuries and material damages in the construction site, but also lead to road sinks and damages to the adjacent facilities due to settlement of ground around the construction site. Therefore, during a open ground excavation in the urban areas, it is necessary to thoroughly prepare for prevention of collapse accidents, and consider whole construction stage such as planning, design and construction. In this study, the priorities to be managed mainly were obtained in order to prevent collapse accidents during a open ground excavation. After analyzing results from past accidents cases for open ground excavations, priorities were evaluated regarding collapse-inducing elements using the Delphi technique which is a decision-making method by consensus among experts. As a result, insufficient groundwater treatment, bad geotechnical investigation and instability on construction, etc. were obtained as priorities for prevention of collapse accidents.