• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.163-174
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• 2007

A New pre-loading system, through which a large pre-load could be charged was developed and applied to the braced wall in order to stabilize the adjacent tunnel. A pre-load larger than the designated axial force of bracing was imposed to prevent the horizontal displacement of the braced wall during the ground excavation. For this purpose, real scale model tests (1/10) were conducted, without and with pre-load on braced wall. And numerical analyses were performed for both the cases without and with pre-load, which were half (50%) and full (100%) respectively, and larger scale of the design axial farce of bracing. FEM program called PLAXIS was used for numerical analysis. As a result, it was found that the stability of the existing tunnel adjacent to the braced wall could be greatly enhanced when the horizontal displacement of braced wall was reduced by applying a pre-load, which was larger than the designated axial force of bracing.

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.19-25
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• 2000

배수성과 인장강성을 가지는 복합 보강재를 사용하여 보강한 포화점성토의 거동에 선행하중이 미치는 영향을 조사하기위하여 평면변형을 시험을 수행하였다. 보강하지 않은 공시체와 보강한 공시체에 대하여 이방압밀(K=0.3, σ3'=50kPa)을 실시하고 비배수 및 배수전단시험을 일정변형율 속도를 실시하였다. 선행하중을 가한 시험의 경우는 이방압밀후 소정의 선행하중을 가하여 크리이프, 제하, 에이징 후에 비배수 전단시험을 실시하였다. 시험결과 분석한 결과 포화전성성토와 같이 연약한 토질이라도 다짐을 잘하고 보강토의 큰 배수압툭강도를 이용하여 큰 배수압축강도를 이용하여 큰 선행하중을 가하여 과압밀 상태로 함으로써 비배수 전단시에 큰 초기강성을 가지는 것을 알수 있었다. 즉, 점성토의 보강토의 경우 보강에 의한 배수강도의 증가는 큰 선행하중을 가하기 위하여 사용하는 것이 가장 효율적인 것으로 판단된다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.4
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• pp.331-341
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• 2007

Pre-loads could be imposed on the braced wall to prevent the horizontal displacements during the ground excavation adjacent to the existing tunnel. For this purpose, new pre-loading system through which large pre-loads could be applied to the braced wall was used in the model tests. Large scale model tests were performed in the real scale test pit which was 2.0 m in width and 6.0 m in hight and 4.0 m in length. Test ground was constructed by sand. Model tunnel in 1.2 m diameter was constructed before test ground excavation. Test ground was excavated adjacent to existing tunnel and was braced. To investigate the effect of pre-loading, tests without pre-load were also performed. During the ground excavation were the behavior of braced wall, test tunnel, and ground measured. Model tests were also numerically analysed and their results were compared to that of the real scale tests. As a result, it was found that the stability of the existing tunnel was greatly enhanced when the horizontal displacements of braced wall was reduced by applying pre-load larger than the design load.

• 기술발표회
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• s.2006
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• pp.193-198
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• 2006

서울지하철 0호선 000 공구 000 정거장 구간은 버팀보 7단, 어스앵커 2단, 그리고 록볼트 3단의 개착식 가시설로 설계되어 있다. 버팀보 및 앵커 축력 계측을 위해 변형률계 및 하중계를 설치하고 연속계측 중, 4~6단 버팀보 수 개소에서 5월부터 하중이 급격히 증가하엿다. 따라서 굴착작업을 즉시 중단하고 관리기준치를 초과하는 하중이 계측된 STA.9k+750~800 구간의 5, 6단 버팀보 위치에 격간으로 총 20본(10본${\times}$2단), 그리고 STA.9k+900~920 구간의 7단 버팀보 위치에 격간으로 총 9본(9본${\times}$1단)의 버팀보를 추가적으로 설치 완료하였다. 이 때, 추가 버팀보는 선행하중잭을 이용하여 10ton의 선행하중을 재하하였으며, 향후 추가 보강 필요시 재하하중 증가가 가능하도록 조치하였다. 또한, 추가 설치된 버팀보, 그리고 이상하중이 발생된 버팀보에 계측기를 추가 설치하여 지속적으로 계측중이며, 띠장의 변위발생 구간은 스티프너 및 앵글 등을 응급조치하였다. 본 사례 연구에서는 보강 전.후의 계측결과 및 수치해석적 분석을 이용하여 가시설 굴착시 버팀보의 하중증가 원인 및 보강 효과를 규명하고, 향후 추가 굴착시의 안정성 여부를 검토해 보고자 하였다. 계측값 분석 결과, 추가버팀보 보강 후의 기존버팀보 축력 계측 결과 보강 직후 기존버팀보의 축력이 어느정도 감소하였으며, 이후 시간이 지남에 따라 축력이 더 이상 증가하지 않고 일정한 값에 수렴하는 경향을 보였다. 또한 수치해석 결과 온도 증가가 버팀보 축력증가에 미치는 영향은 버팀보 위치의 지반강성이 클수록 크며, 축력증가는 온도증가에 대체적으로 비례하였고, 추가버팀보의 보강 효과는 선행하중의 크기에 비례하는 것으로 나타났으며, 잔여굴착은 전반적으로 기존 버팀보의 축력 증가에 영향을 미치는 것으로 나타났다. 따라서 추가굴착시 지속적인 계측을 수행하며, 급격한 축력증가가 관찰될 경우 현재 보강된 버팀보의 선행하중 추가 재하, 굴착에 가장 큰 영향을 받는 최하단 버팀보의 추가보강 등의 대책방안을 제시하였다.

• Journal of the Korean Geosynthetics Society
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• v.20 no.2
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• pp.45-56
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• 2021

As the utilization of the underground space is activated, deep excavation of ground has been conducted for the installation of underground structures, the earth retaining wall has widely used to minimize deformation of the excavated ground. In particular, as deep excavation is actively progressing in an urban area where structures are concentrated, methods to minimize the deformation of wall have been devised to prevent damage to the structure adjacent to the wall, and one of these methods is the pre-loading method. This method is a method of suppressing the deformation of wall by actively applying a load on the strut to be installed in wall, and research on this method has been conducted recently. However, although related studies have been actively conducted, the management standard for the pre-loading of bracing has not been clearly presented until now. In addition, since the working force in the strut may increase depending on the depth of excavation or the soil condition of the backfill, the magnitude of the pre-loading that can be applied to the brace may decrease. Nevertheless, the magnitude of the pre-loading (more than 50% of the working load) proposed by the previous research results has been uniformly applied to the strut. In this study, 3D finite element analysis was performed to evaluate the application range of the pre-loading of H-beam strut according to the soil conditions of backfill. As a result of the analysis, it was found that there is a very high possibility that a problem may occur in the stability of the structure of strut due to the earth pressure and the pre-loading when the soil condition is weak and deep excavation proceeds. And it was found that the application range of the pre-loading was 5%~70% of the working load in strut.

• Journal of the Korean Geotechnical Society
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• v.15 no.1
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• pp.31-40
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• 1999

The bracing system using screw jack is not effective for the restraining of adjacent ground displacement. since the screw jack dose not induce sufficient preloading on struts. In order to protect excessive displacement of adjacent ground at braced excavation, new preloading jack was developed in the country. In this paper, the new preloading jack and the measurement results of the lateral displacement of braced wall at three deep excavation sites in Seoul city are introduced. The measurement results showed that the maximum displacements of braced wall are smaller than 0.15% of excavation depth, therefore the wall displacements can be minimized by preloading which is acted on bracing. If the bracing system with new preloading jack is used in braced excavation, it is effective for reducing the cost and period of construction.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.3
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• pp.87-92
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• 2005

The permeability of concrete affects largely on the durability of concrete, therefore it is required that the correct assessment and improvement of permeability. Therefore it is rational method that the permeability of concrete structures is estimated in the common use states under loading than in the early sound conditions. In this study, to improve the permeable efficiency of concrete, some kinds of fiber and resin are mixed in making of concrete specimens. And also, for the reasonable assessment of permeability, after 50% and 70% pre-loadings of its compressive strength were acted on the specimens, the tests were executed. From the results of this study, in the case of 50% pre-loading coefficients of permeability were increased about 1.4times against the nonpre-loading specimens and in the case of 70% pre-loading they were increased about 17.8times. And it turned out that hybrid steel fiber reinforcement is most effective for the improvement of permeable efficiency of concrete.

• Tunnel and Underground Space
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• v.20 no.5
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• pp.369-377
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• 2010

Applied to the braced wall in order to stabilize the adjacent tunnel. A pre-load of bracing was imposed to prevent the horizontal displacement of the braced wall during the ground excavation. For this purpose, real scale model tests were conducted, without and with pre-load on braced wall. Real scale model tests were conducted, without and with building load (0 m, 1D, 2D) on ground surface. As a result, it was found that the stability of the existing tunnel adjacent to the braced wall could be greatly enhanced when the horizontal displacement of the braced wall was reduced by applying a pre-load, which was larger than the designated axial force of bracing. In this paper, the behaviors of braced wall and adjacent tunnel was studied. Model tests in 1:10 scale were performed in real construction sequences. Adjacent tunnel was 12 m in diameter and the size of test pit was 2.0 m (width) ${\times}$ 6.0 m (height) ${\times}$ 4.0 m (length) in dimension.

• Journal of the Korean GEO-environmental Society
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• v.13 no.5
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• pp.25-33
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• 2012

In this study, gathered measuring data at fields constructed by IPS(Innovative Prestressed Support) system controls the ground displacement and improves the constructability of earth work and structure work greatly, and compared with horizontal displacement calculated by Elasto-plastic analysis program(EXCAV/W). As the result, displacement of calculated by pre-loading data is reduced 13.2% average of general method, and measuring displacement is also reduced 26.7% average of general method. Therefore that IPS system is more safe than conventional strut method in contrast to displacement of underground wall. In addition, horizontal displacement is reduced through the pre-loading effect used by IPS system.

• Journal of the Korean Geotechnical Society
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• v.24 no.6
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• pp.101-116
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• 2008

The use of reinforced earth walls id permanent structures is getting its popularity. Despite a number of advantages of reinforced earth walls over conventional concrete retaining walls, there exists concerns over long-term residual deformations when subjected to repeated and/or cyclic loads, during their service period. In this investigation, the effects of pre-loading in reducing long term residual deformation of reinforced soil structures under sustained and/or repeated loading environment are investigated using a series of reduced-scale model tests. A model pier and a back-to-back (BTB) reinforced soil structures were constructed and tested under various loading and backfilling conditions. The results indicate that the pre-loading technique can be an effective means of controlling residual deformations of reinforced soils under various loading conditions.