• Title/Summary/Keyword: Shallow failure

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Model Test and Numerical Analysis for Failure Behaviour of Shallow Tunnel Considering Unsupported Tunnel Length (굴진장을 고려한 얕은 터널파괴거동에 대한 모형실험 및 수치해석)

  • Kim, Young-Min
    • Tunnel and Underground Space
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    • v.15 no.6 s.59
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    • pp.400-410
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    • 2005
  • During excavation of shallow tunnels in soft ground, failure mechanism around the tunnel face have major influence on the stability of tunnels. In this paper, a series of laboratory tests under plane strain condition on the small scale of a shallow tunnel considering unsupported tunnel length has been performed. The results have shown that tunnel failure mechanism changes from failure mode 1 to failure mode 2 as unsupported tunnel length increases. By comparing the experimental and the numerical results, the loosening pressure for the shallow tunnel and progressive failure have been investigated.

Characterization of Increases in Volumetric Water Content in Soil Slopes to Predict the Risk of Shallow Failure (토사비탈면 표층붕괴 위험 예측을 위한 체적함수비 증가 특성 연구)

  • Suk, Jae-Wook;Kang, Hyo-Sub;Choi, Sun-Gyu;Jeong, Hyang-Seon;Song, Hyo-Sung
    • The Journal of Engineering Geology
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    • v.30 no.4
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    • pp.485-496
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    • 2020
  • The characteristics of volumetric water content changes in soil slopes were studied here in an effort to identify the signs of heavy rain causing shallow slope failure. Volumetric water contents in cases with and without shallow failure were measured in flume and test-bed experiments. Measurement data from 282 experiments of both types revealed that the volumetric water content gradient in shallow failure events ranged from 0.072 to 0.309. In non-failure cases, the range was 0.01~0.32. Therefore, this one specific value cannot predict shallow slope failure. However, as the volumetric water content gradient increased, there was a clear tendency to shallow failure. By using this trend, criteria for four warning levels are suggested.

Catastrophe analysis of active-passive mechanisms for shallow tunnels with settlement

  • Yang, X.L.;Wang, H.Y.
    • Geomechanics and Engineering
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    • v.15 no.1
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    • pp.621-630
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    • 2018
  • In the note a comprehensive and optimal passive-active mode for describing the limit failure of circular shallow tunnel with settlement is put forward to predict the catastrophic stability during the geotechnical construction. Since the surrounding soil mass around tunnel roof is not homogeneous, with tools of variation calculus, several different curve functions which depict several failure shapes in different soil layers are obtained using virtual work formulae. By making reference to the simple-form of Power-law failure criteria based on numerous experiments, a numerical procedure with consideration of combination of upper bound theorem and stochastic medium theory is applied to the optimal analysis of shallow-buried tunnel failure. With help of functional catastrophe theory, this work presented a more accurate and optimal failure profile compared with previous work. Lastly the note discusses different effects of parameters in new yield rule and soil mechanical coefficients on failure mechanisms. The scope of failure block becomes smaller with increase of the parameter A and the range of failure soil mass tends to decrease with decrease of unit weight of the soil and tunnel radius, which verifies the geomechanics and practical case in engineering.

A Study on Comparison of Finite Element Analysis with Model Test of Shallow Footing Failure for Cohesionless Soil with Non-associated Plasticity and Some Smooth Footing (사질토지반의 지지력분석을 위한 얕은기초의 파괴거동에 대한 모형실험과 유한요소해석 비교 검토)

  • Kim, Young-Min;Kang, Sung-Wi
    • Journal of the Korean Geosynthetics Society
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    • v.9 no.1
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    • pp.13-20
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    • 2010
  • This paper describes the procedure to predict the entire load-displacement curve and the failure mechanism of shallow strip footing for real soil. The presented results show that it is possible to analyze the post peak behavior of shallow strip footing and to give a progressive failure mechanism clearly. Finite element computation of the bearing capacity factor $N_{\gamma}$ have been made for shallow strip footings with friction angles and dilation angle. It is shown that commonly used values of $N_{\gamma}$ which have generally been based on associated plasticity calculations are unconservative for real soil with non-associated plasticity and some smooth footing.

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Shallow Failure Characteristics of Weathered Granite Soil Slope in accordance with the Rainfall Infiltration (강우침투에 따른 화강풍화토 사면의 얕은파괴 특성)

  • Kim, Sun-Hak
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.10 no.10
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    • pp.2810-2818
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    • 2009
  • In order to examine the characteristic of shallow failure in cut slopes composed of weathered granite soil, this study calculated critical permeability coefficient according to rainfall characteristic in Korea, performed stability analysis according to the representative physical properties of weathered granite soil distributed in Korea such as horizontal distance to the failure surface of cut slope, slope inclination, slope height, and the depth of wetting by rainfall, and analyzed the results. In the results of analyzing critical permeability coefficient, when the local rainfall characteristic was considered, the maximum critical permeability coefficient was $7.16{\times}10^{-4}cm/sec$. We judged that shallow failure according to wetting depth should be considered when rainfall below the critical rainfall intensity lasts longer than the minimum rainfall duration in cut slopes composed of weathered granite soil, which had a critical permeability coefficient lower than the maximum critical permeability coefficient. Furthermore, using simulated failure surface, this study could understand the characteristic of shallow failure in cut slopes based on the change in slope safety factor according to horizontal distance, wetting depth, and strength parameter.

Fault Train Construction Based on Shallow Reasoning Strategy (경험기반추론 전략을 이용한 고장트레인 구축)

  • Bae, Yong-Hwan
    • Journal of the Korean Society of Safety
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    • v.20 no.3 s.71
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    • pp.19-26
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    • 2005
  • There are three reasoning method in fault diagnosis process. The shallow reasoning is based on the experiential knowledge and deep reasoning is based on physical model. Hybrid reasoning is mixing two type reasoning. This study describes about fault train embodiment of screw type air compressor that is used widely in industrial facilities by using various experimental method and shallow reasoning. We investigate macroscopic failure cause of air compressor through naked eye observation and then microscopic failure cause by various experimental method. We composed fault train with fault knowledge based on empirical data and scientific data that is acquired through several experiments. It is possible to analysis system reliability and failure rate with these fault train.

A Study on Effects of Failure Behaviour of Tunnel Using A Numerical Analysis (수지해석에 의한 터널의 파괴거동에 미지는 영향분석)

  • 김영민
    • Proceedings of the Korean Geotechical Society Conference
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    • 1999.03a
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    • pp.309-314
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    • 1999
  • In this paper, an application of finite element procedure fur tunnel failure analysis has been studied. The numerical model is applied to the simulation of a series of plane strain laboratory tests on the small scale model of a shallow tunnel. By comparing experimental and numerical results some conclusions are drawn on the effectiveness of the numerical approach. The findings from these numerical experiments show relative differences in the pattern of failure behaviour for shallow tunnels.

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A Study for Characterization on Shallow Behavior of Soil Slope by Flume Experiments (토조실험 장치를 이용한 토사비탈면 표층거동 특성 연구)

  • Suk, Jae-wook;Park, Sung-Yong;Na, Geon-ha;Kang, Hyo-Sub
    • The Journal of Engineering Geology
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    • v.28 no.3
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    • pp.489-499
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    • 2018
  • A flume experiments was used to study the characteristics of the surface displacements and volumetric water contents (VWC) during torrential rain. The surface displacement and VWC of the granite weathered soil were measured for rainfall intensity (100, 200 mm/hr) and initial ground condition (VWC 7, 14, 26%). The test processes were also recorded by video cameras. According to the test results, The shallow failure is classified into three types: retrogressive failure, progressive failure and defined failure. In the case of retrogressive failure and progressive failure, relatively large damage could occur due to the feature that soil is deposited to the bottom of the slope. the shallow failure occurred when the VWC reached a certain value regardless of the initial soil condition. It was found that the shallow failure can be predicted through the increase patton of the VWC under the condition of the ground dry condition (VWC 7%) and the natural condition (VWC 14%). For high rainfall intensity, progressive failure predominated, and rainfall intensity above a certain level did not affect wetting front transition.

Analysis on Bearing Capacity of Eccentrically Loaded Shallow Footing Using Upper Bound Method of Limit Analysis (편심하중 작용시 극한해석 상계법을 이용한 얕은 기초의 지지력 분석)

  • 상현규;최명진;김팔규;권오균
    • Proceedings of the Korean Geotechical Society Conference
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    • 2000.11a
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    • pp.261-268
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    • 2000
  • In this study the bearing capacity of the eccentrically loaded shallow footing is estimated by means of the upper bound method of limit analysis. In the case of applying the upper bound, the results depend on the failure mechanism. So the failure surface is correctly studied through the model test using sand. New method is proposed to estimate the bearing capacity of the eccentrically loaded shallow footing by means of the upper bound method to apply the failure mechanism based on the model test. The propriety of new method is verified by the results of various methods. And the influences of the variables eccentricity, embedment depth, variations of contact width factor by model test using sand are also studied in this paper

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Reliability analysis of shallow tunnel with surface settlement

  • Yang, X.L.;Li, W.T.
    • Geomechanics and Engineering
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    • v.12 no.2
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    • pp.313-326
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    • 2017
  • Based on the reliability theory and limit analysis method, the roof stability of a shallow tunnel is investigated under the condition of surface settlement. Nonlinear Hoek-Brown failure criterion is adopted in the present analysis. With the consideration of surface settlement, the internal energy and external work are calculated. Equating the rate of energy dissipation to the external rate of work, the expression of support pressure is derived. With the help of variational approach, a performance function is proposed to reliability analysis. Improved response surface method is used to calculate the Hasofer-Lind reliability index and the failure probability. In order to assess the validity of the present results, Monte-Carlo simulation is performed to examine the correctness. Sensitivity analysis is used to estimate the influence of different variables on reliability index. Among random variables, the unit weight significantly affects the reliability index. It is found that the greater coefficient of variation of variables lead to the higher failure probability. On the basis of the discussions, the reliability-based design is achieved to calculate the required tunnel support pressure under different situations when the target reliability index is obtained.