• Journal of the Korean Geosynthetics Society
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• v.16 no.4
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• pp.67-74
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• 2017

In order to prevent the ground subsidence accidents caused by the occurrence of underground cavity, it is necessary to evaluate the mechanical characteristics in the relaxation zone of the underground cavity. Also, the relaxation zone including underground cavity be appropriately reinforced. This paper described analysis results based on finite element method that was conducted to analyze the mechanism for occurrence of the relaxation zone around the underground cavity. The finite element analysis applied in forced displacement was carried out to simulate the underground cavity and relaxation zone, and then there were compared with previous research results. The analysis results showed that the void distribution of soil around the underground cavity has figured out. As a result, the area of the relaxation zone could be quantitatively presented by reduction characteristics of the shear stress.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.43-48
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• 2003

The problem of welding stresses and fatigue behavior is the main concerns of welding research fields. The residual stresses and distortion of structures by welding is exert negative effect on the safety of mechanical structures. That is, expansion of material by high temperature and distortion by cooling during welding process is caused of tensile and compressive residual stresses on welding material, and this residual stresses reduce fracture and fatigue strength of welding structures. The accurate prediction of residual stress and relaxation due to loading and post weld heat treatment of weld zone is very important to improve the quality of weldment. In this study, a finite element modeling technique is developed to simulate the relaxation of residual stresses due to loading and post weld heat treatment of weld zone. The accuracy of finite element models is evaluated based on experimental results and the results of the analytical solution.

• Journal of the Korean Geotechnical Society
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• v.35 no.1
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• pp.43-53
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• 2019

This paper described a result of finite element analysis considering sewerage damage scale and soil depth, in order to analyze quantitatively for cavity and relaxation zone of underground due to sewerage damage. The mechanical model, which was verified by previous studies, was applied to the finite element analysis. In addition, the mechanical behavior of the soil around the sewerage damage due to the soil loss was simulated by using the forced displacement. Based on finite element analysis results, characteristics of the void ratio distribution, ground subsidence, and shear stress distribution according to sewerage damage scale and soil depth were analyzed. And then, The boundaries of the underground cavity and relaxation zone were determined by using the shear stress reduction characteristics of the ground. Also, an occurrence scope of the cavity and relaxation zone was quantitatively evaluated by the change of sewerage damage scale and soil depth.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.11-21
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• 2017

Ground subsidence mainly occurs due to the soil wash-away caused by cracked sewer pipes. It is necessary to understand the behavior surrounding soils with the formation of cavity and relaxation zone to set up counterplan. In this paper, a series of laboratory model tests and numerical analyses (Discrete Element Method) were performed to investigate the ground subsidence mechanism due to sewer pipe damage. For model tests, aluminum rod and trap door were used to simulate the behavior of model ground. Test results were compared with the numerical analyses conducted under the same boundary conditions with model tests. From this study, it was investigated the shape and size of cavity and relaxation zone due to the soil wash-away and a void ratio distribution of surrounding soils with relaxation properties.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.5
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• pp.278-286
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• 2020

Reynolds-averaged Navier-Stokes simulations have been performed to investigate an effect of numerical region with high resolution for Kelvin wave around KRISO container ship on its resistance. In the present study, 13 millions cells were used to describe wave profile along the ship hull and Kelvin wave patterns. In order to control a size of numerical region with high resolution for waves around the hull, we employed relaxation zones from a side boundary of numerical domain in which Kelvin wave was suppressed. When the far-field Kelvin wave was not precisely resolved due to the relaxation zone, the instantaneous history of ship resistance was affected although the time average of ship resistance showed -1.15~2.1 % errors. Especially, the damping characteristics of ship resistance in time history was significant when using a large relaxation zone in the side boundary.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.855-867
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• 2018

When a weak zone exists ahead of tunnel face, the stress in the adjacent area would increase due to the longitudinal arching effect and the stability of the tunnel is affected. Therefore, it is critical to prepare a countermeasure through the investigation of the frontal weakness zone of the excavated face. Although there are several researches to predict the existence of weak zone ahead of tunnel face, such as geophysical exploration, numerical analysis and tunnel support, lack of studies on the relaxation zone depending on the width or distance from the vulnerable area. In this study, the impact of the weak zone on the formation of the relaxation zone was investigated. For this purpose, a series of laboratory test were carried out varying the width of the weak zone and the separation distance between tunnel face and weak zone. In the model test, sand with a water content of 3.8% was used to form a model ground. The model weak zone was constructed with dry sand curtains. The tunnel face was adjusted to allow a sequential excavation of upper and lower half part. load cells were installed on the bottom of the foundation and the tunnel face and measuring instruments for displacement were installed on the surface of the model ground to measure the vertical stress and surface displacements due to tunnel excavation respectively. The test results show that the width of weak zone did not affect the ground settlement while the ground subsidence drastically increased within 0.25D. The vertical stress and horizontal stress increased from 0.5D or less. In addition, the longitudinal arching effect is likely within the 1.0D zone ahead of the tunnel face, which may reduce the vertical stress in the ground following tunneling direction.

• Journal of Wetlands Research
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• v.2 no.1
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• pp.11-17
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• 2000

The natural ecology of our coastal zone has been well preserved because of the designation of Han-Ryea national sea park. However, recently, it is being threatened by the frequent request of district regulation of national park and relaxation of green belt, etc. And also, with the reclamation of the foreshore by the development of industrial complex and tourism resource cultivation on a large scale, development pressure for natural coast is increasing. For that reason, preservation of the ecology, organized management and investigation is needed for the islands which scenery is beautiful and rare animals and plants inhabit. And also, it is worried that major habitats of migrants are diminishing because of the district regulation of national park, relaxation of green belt zone and construction of coastal streets. Therefore. on the basis of the through environmental impact assessment, only the business which are aimed at the preservation and restoration of the natural coast should be admitted and the act of eroding must be restricted.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.228-231
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• 1997

A series of load relaxation tests was performed to determine stress-strain rate curves at high temperatures. Constitutive parameters of GBS and GMD were evaluated from the curves using the recently proposed inelastic deformation theory. Tensile tests and Microsturcture investigations showed deformation behavior as the relaxation test results predicted.

• Earthquakes and Structures
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• v.13 no.6
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• pp.519-529
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• 2017

The surrounding rocks of underground openings are natural materials and their mechanical behavior under seismic load is different from traditional man-made materials. This paper proposes a framework to comprehensively model the mechanical behavior of surrounding rocks. Firstly, the effects of seismic load on the surrounding rocks are summarized. Three mechanical effects and the mechanism, including the strengthening effect, the degradation effect, and the relaxation effect, are detailed, respectively. Then, the framework for modelling the mechanical behavior of surrounding rocks are outlined. The strain-dependent characteristics of rocks under seismic load is considered to model the strengthening effect. The damage concept under cyclic load is introduced to model the degradation effect. The quantitative relationship between the damage coefficient and the relaxation zone is established to model the relaxation effect. The major effects caused by seismic load, in this way, are all considered in the proposed framework. Afterwards, an independently developed 3D dynamic FEM analysis code is adopted to include the algorithms and models of the framework. Finally, the proposed framework is illustrated with its application to an underground opening subjected to earthquake impact. The calculation results and post-earthquake survey conclusions are seen to agree well, indicating the effectiveness of the proposed framework. Based on the numerical calculation results, post-earthquake reinforcement measures are suggested.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.872-877
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• 2004

Welding residual stresses are the main topics of welding research fields. The residual stresses and distortion of structures by welding exert negative effect on the safety of mechanical structures. That is, expansion of material by high temperature and distortion by cooling during welding process are caused by tensile and compressive residual stresses in welding material, and this residual stresses can induce fracture and fatigue problems of welding structures. The accurate prediction of residual stress and relaxation due to mechanical loading of weld zone is very important to improve the quality of weldment. In this study, a finite element modeling technique is developed to simulate the relaxation of residual stresses due to mechanical loading. The effects of load ratio for static and cyclic loading are evaluated based on analytical results.