• Geomechanics and Engineering
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• v.13 no.2
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• pp.217-235
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• 2017

The stability prediction of shallow buried tunnels is one of the most difficult tasks in civil engineering. The aim of this work is to predict the state of collapse in shallow tunnel in layered soils by employing non-associated flow rule and nonlinear failure criterion within the framework of upper bound theorem. Particular emphasis is first given to consider the effects of dilation on the collapse mechanism of shallow tunnel. Furthermore, the seepage forces and surface settlement are considered to analyze the influence of different dilation coefficients on the collapse shape. Two different curve functions which describe two different soil layers are obtained by virtual work equations under the variational principle. The distinct characteristics of falling blocks up and down the water level are discussed in the present work. According to the numerical results, the potential collapse range decreases with the increase of the dilation coefficient. In layered soils, both of the single layer's dilation coefficient and two layers' dilation coefficients increase, the range of the potential collapse block reduces.

• Journal of the Korean GEO-environmental Society
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• v.15 no.2
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• pp.45-52
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• 2014

The tunnel construction is increasing in order to secure a good driving performance of the car and train. A cases of tunnel collapse and the tunnel excessive displacement are increasing with the increase in tunnel construction. In terms of empirical construction methods using the strength characteristics of soil, it is important for tunnel construction to analyze causes of collapse and displacement. In the paper, it was analyzed the causes of collapse and excessive displacement of tunnel in the fractured ground condition. The results of analysis is that the increase of rainfall and lasting increase of displacement and large scale fractured ground are interconnected.

• Geomechanics and Engineering
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• v.11 no.6
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• pp.867-877
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• 2016

Collapse shape of tunnel roof in layered Hoek-Brown rock media is investigated within the framework of upper bound theorem. The traditional collapse mechanism for homogeneous stratum is no longer suitable for the present analysis of roof stability, and it would be necessary to propose a curve failure mode to describe the velocity discontinuity surface in layered media. What is discussed in the paper is that the failure mechanism of tunnel roofs, consisting of two different functions, is proposed for layered rock media. Then it is employed to investigate the impending roof failure. Based on the nonlinear Hoek-Brown failure criterion, the collapse volume of roof blocks are derived with the upper bound theorem and variational principle. Numerical calculations and parametric analysis are carried out to illustrate the effects of different parameters on the shape of failure mechanism, which is of overriding significance to the stability analysis of tunnel roof in layered rock media.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.323-330
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• 1999

Daylight collapse have been occurred by about 5.0m deep at ground surface and collapse of the crown head part of the tunnel have connected to the ground surface during first step of shotcrete work after blasting of upper half section of the tunnel driving at two-way double track tunnel face section on highway construction. This study is for a successful illustration case for the earth improvement method through applying such strengthening methods as cement milk grouting, S.G.R grouting,, steel pipe reinforced multi-step grouting etc. for the purpose of earth strengthening of loosened earth block occurred by tunnel collapse.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.140-153
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• 2005

During the tunnel construction the major failure mode can be categorized as: tunnel failure just after the tunnel excavation without support, failure after application of shotcrete and finally failure after setting the concrete lining. The failure mode just after the tunnel excavation without support, can be further classified as : bench failure, crown failure, face failure, full face failure, failure due to weak strata and failure due to overburden. Moreover the failure after application of shotcrete is classified as heading face failure, settlement of shotcrete support, local failure of shotcrete lining and invert shotcrete. To find out the major causes of tunnel collapse, the investigation was done in case of the second phase of Seoul subway construction. The investigation results depicted that the major causes of tunnel collapse were due to the weak layer of rock/fault and sudden influx of ground water from the tunnel crown. While the investigation results of the mountain road tunnels construction have shown that the major causes of tunnel failure were inadequate analysis of tunnel face mapping results, intersection of faults and limestone cavities. In this paper some recent measurement in order to mitigate such tunnel collapse are presented

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.117-127
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• 2000

터널 시공과 굴착과정에서 파쇄대, 절리, 연약대, 균열 등 암반에서의 불연속면은 중요한 역할을 한다. 본 연구에서는 지반 고유의 특징인 불확실성에 의한 터널 설계와 시공 과정에서 겪는 많은 시행오차를 최소화하기 위해서 국내의 터널 붕락 현장의 지반조사 자료를 분석하여 터널 붕락 유형 및 규모를 제시할수 있는 Geo-predict 시스템을 개발하였다. Geo-predict 시스템은 총 104개 터널 붕괴/붕락자료(국외84개, 국내20개)를 분석한 자료를 테이터베이스로 인공신경망 학습을 토해서 터널 붕괴 형태와 규모를 추론하는 시스템이다. 본 논문에서는 Geo-predict의 개발과정 및 구성.기능을 소개하였으며 104개 터널 현장 자료를 지반조건별로 분석하고 이를 데이터베이스화하여 인공신경함을 이용한 추론 시스탬을 구축하고, 2개 고속전철 터널현장과 1개 지하철 시공현장에 적용성 평가를 실시하여, 터널의 붕락 가능 및 붕락 규모를 추론하였다.

• Geomechanics and Engineering
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• v.24 no.5
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• pp.491-503
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• 2021

Shallow tunnels are vulnerable to earthquakes, and shallow ground is usually inhomogeneous. Based on the limit equilibrium method and variational principle, a solution for the seismic collapse mechanism of shallow tunnel in inhomogeneous ground is presented. And the finite difference method is employed to compare with the analytical solution. It shows that the analytical results are conservative when the horizontal and vertical stresses equal the static earth pressure and zero at vault section, respectively. The safety factor of shallow tunnel changes greatly during an earthquake. Hence, the cyclic loading characteristics should be considered to evaluate tunnel stability. And the curve sliding surface agrees with the numerical simulation and previous studies. To save time and ensure accuracy, the curve sliding surface with 2 undetermined constants is a good choice to analyze shallow tunnel stability. Parameter analysis demonstrates that the horizontal semiaxis, acceleration, ground cohesion and homogeneity affect tunnel stability greatly, and the horizontal semiaxis, vertical semiaxis, tunnel depth and ground homogeneity have obvious influence on tunnel sliding surface. It concludes that the most applicable approaches to enhance tunnel stability are reducing the horizontal semiaxis, strengthening cohesion and setting the tunnel into good ground.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.6
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• pp.785-791
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• 2023

Risk management is essential for preventing accidents arising from uncertainties in TBM tunnel projects, especially concerning managing the risk of TBM tunnel collapse, which can cause extensive damage from the tunnel face to the ground surface. In addition, prioritizing risks is necessary to allocate resources efficiently within time and cost constraints. Therefore, this study aimed to establish a TBM risk database through case studies of TBM accidents and determine a risk priority for TBM tunnel collapse using the Bayes theorem. The database consisted of 87 cases, dealing with three accidents and five geological sources. Applying the Bayes theorem to the database, it was found that fault zones and weak ground significantly increased the probability of tunnel collapse, while the other sources showed low correlations with collapse. Therefore, the risk priority for TBM tunnel collapse, considering geological sources, is as follows: 1) Fault zone, 2) Weak ground, 3) Mixed ground, 4) High in-situ stress, and 5) Expansive ground. In practice, the derived risk priority can serve as a valuable reference for risk management, enhancing the safety and efficiency of TBM construction. It provides guidance for developing appropriate countermeasure plans and allocating resources effectively to mitigate the risk of TBM tunnel collapse.

• Journal of the Korean GEO-environmental Society
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• v.17 no.4
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• pp.39-46
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• 2016

The final stability analysis of the tunnel structure is generally evaluated by performing site monitoring to determine whether or not the measured value through the convergence after the completion of excavation in the face. When the ground conditions are so poor, the reinforcement around the tunnel was applied for enhancing the stability of tunnels. For the additional tunnel crown collapse or excessive displacement have occurred under construction, correlation analysis were performed for the comparison construction and numeric analyses. In this paper, we investigated the collapse types, tunnel collapse were mostly occurs at the crown and they were analyzed because of the geological conditions in the collapse zone. And also, it was analyzed as being correlated in the crown of tunnel exists a fault fracture zone which extends to the surface part. Thus, in case of ground conditions such as fault fracture zone with a tunnel extending from the crown to the surface, the behavior is larger than the behavior predicted by numerical method.

• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.55-61
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• 2009

Recently, highway tunnel construction has rapidly been increased due to the limited ground usage and geographical characteristic in Korea, i.e. Korea consists of 70% mountains. In this paper, it was analyzed tunnel collapse patterns in the weathered rockmass. Recent tunnel collapse pattern is quite different from that of past ten years. Tunnels in past years have been collapsed at shallow valley area because of shear strength decrease after heavy rain. Tunnels, which have been constructed recently, were collapsed at even the deeper ground position after primary support. Also in the case that proper reinforcement was not applied, it caused excessive crack at shotcrete and local collapse near tunnel face. In this paper, it was analysed the cause of the recent tunnel collapses and proper reinforcement for the collapsed tunnels.