• Tunnel and Underground Space
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• v.19 no.2
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• pp.95-106
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• 2009

Numerical analysis of the progressive failure of a rock slope was conducted using a 3-D rock joint element considering fracture mechanics and subcritical crack growth of asperities in the rock joints. Even though the stress state in the rock slope is not changing, the elapse of time causes subcritical crack growth to break asperities in the joints. The increase of broken asperities causes failure of joints in the rock slope and the increase of failed joints results in failure of a jointed rock slope. As a result, the progressive failure of a jointed rock slope due to the gradual breaking of small asperities along joints generated by subcritical crack growth occurs at a lower stress than if rock failure occurred by exceeding the static strength or fracture toughness.

• Geotechnical Engineering
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• v.13 no.6
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• pp.139-146
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• 1997

The failure of footing generally involves the concentration of deformation into one or more narrow bands. With the displacement of the footing, the failure plane will subsequently form The purpose of this paper is to assess the capabilities of numerical techniques to predict bearing capacity and progressive failure of footings. By using the method of large deformation theory and strain softening we have investigated the progressive failure of strip footing on undrained clay. This paper describes the procedure to predict the entire loadfisplacement curve and the failure mechanism of strip footing. The presented results show that it is Possible to analyze the Post Peak behavior of strip footing numerically and to give a progressive failure mechanism clearly.

• Computational Structural Engineering
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• v.9 no.4
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• pp.127-134
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• 1996

This paper is about a progressive fracture analysis of concrete by boundary element method. From both displacement boundary integral equation and traction boundary integral equation of solids with cracks, a boundary integral equation for crack problem is derived. For the analysis of progressive fracture of concrete, fracture process zone is modelled based on Dugdale-Barenblatt model with linear tension-softening curve. By using the boundary element modeling, the progressive fractures of concrete beam and compact-tension specimens with various loading conditions are analyzed and compared with experiments. The analysis results show that the technique in this paper can predict the maximum strength and the nonlinear behavior of concrete including post-peak behavior.

• Journal of the Korean Wood Science and Technology
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• v.24 no.4
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• pp.64-73
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• 1996

고인성 종이의 탄성-소성 파괴를 파괴역학을 이용하여 분석하였다. 탄성-소성 물질의 파괴에 있어서 균열이 언제 진행되기 시작하는지 이론적 판단 기준을 유도하고, mode I 파괴를 linear image strain analysis(LISA)로 관찰한 후, 파괴역학 변수들을 계산하였다. 크랙(crack)이 있는 물질에 외부하중이 작용할 때 변형율 에너지 발산 속도(strain energy release rate)가 그 물질이 견딜 수 있는 파괴저항(fracture resistance)에 도달하면 안정적인 파괴가 진행된다. 이를 이용하여 크랙의 초기 진행시 결점주위의 응력, 파괴저항, 크랙 진행거리, 기하인자(geometry factor) 등을 구하였다. 이 변수들은 종이의 파괴역학적 특성을 정량적으로 나타내므로 유용하게 활용될 수 있을 것이다.

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.205-212
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• 1996

This paper presents progressive fracture analysis of concrete using boundary element method and its stabilizing technique. To determine ultimate strength and to predict nonlinear behavior of concrete during progressive crack growth, the modelling of fracture process zone is done based on Dugdale-Barenblatt model with linear tension-softening curve. We regulate displacement and traction boundary integral equation of solids including crack boundary and analyze progressive fracture of concrete beam and compact tension specimen. Also a numerical technique which considers the growth of stress-free crack of concrete during the analysis and removes snapback of postpeak behavior is proposed.

• Tunnel and Underground Space
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• v.19 no.2
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• pp.86-94
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• 2009

A three dimensional rock joint element was developed considering fracture mechanics and subcritical crack growth to simulate non-linear behavior and the progressive failure of rock joints. Using this 3-D joint element, joint shear tests of rock discontinuities were simulated by a numerical method. The asperities on the joint surface began to fail at stress levels lower than the rock fracture toughness and continued progressively due to subcritical crack growth. As a result of progressive failing in each and every asperity, the joint showed non-linear stress-time behavior including stress hardening/softening and the reaching of a residual stress.

• Geotechnical Engineering
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• v.4 no.2
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• pp.5-14
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• 1988

A probabilistic model for the progressive failure in a homogeneous soil slope consisting of strain-softening material is presented. The local safety margin of any slice above failure surface is assumed to follow a normal distribution. Uncertainties of the shear strength along potential failure surface are expressed by one-dimensional random field models. In this paper, only the case where failure initiates at toe and propagates up to the crest is considerd. The joint distribution of the safety margin of any two adjacent slices above the failure surface is assumed to be bivariate normal. The overall probability of the sliding failure is expressed as a product of probabilities of a series of conditional el.eats. Finally, the developed procedure has been applied in a case study to yield the reliability of a cut slope.

• Journal of the Korean Society for Railway
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• v.12 no.5
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• pp.811-818
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• 2009

An estimation method of the fallout volume of a tunnel under construction is proposed based on an empirical method called bulking factor. For this, the main causes of the tunnel fallout are investigated and the scale of the fallout which is not accessible is considered. The calculated height of the fallout area is compared with borehole core data and the accuracy and efficiency of the proposed method is demonstrated. Another experimental approach on the detection of a progressive cracking around the tunnel fallout is provided based on an acoustic emission method. From the field tests near the tunnel fallout, it is shown that additional progressive cracking of the reinforced area is not foreseen and the effectiveness of the reinforcement is proven.

• 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.

• Magazine of the Korea Concrete Institute
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• v.8 no.1
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• pp.145-153
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• 1996

The fracture process zone in concrete is a region ahead of a traction-free crack, in which two major mechanisms, microcracking and bridging, play important roles. The toughness due to bridging is dominant compared to toughness induced by microcracking, so that the bridging is dominani: mechanism governing the fracture process of concrete. Fracture mechanics does work for concrete provided that the fracture process zone is being considered, so that the development of model for the fracture process zone is most important to describe fracture phenomena in concrete. In this paper the bridging zone, which is a part of extended rnacrocrack with stresses transmitted by aggregates in concrete, is modelled by a Dugdale-Barenblatt type model with linear tension-softening curve. Two finite element techniques are shown for the analysis of progressive cracking in concrete based on the discrete crack approach: one with crack element, the other without crack element. The advantage of the technique with crack element is that it dees not need to update the mesh topology to follow the progressive cracking. Numerical results by the techniques are demonstrated.