• Geomechanics and Engineering
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• 제24권5호
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• pp.457-470
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• 2021

In this study, the pull-out behavior of a tunnel-type anchorage for suspension bridges was investigated using experimental tests and image processing analyses. The study focused on evaluating the initial failure behavior and failure mode of the tunnel-type anchorage. In order to evaluate the failure mode of tunnel-type anchorage, a series of scaled model tests were conducted based on the prototype anchorage of the Ulsan Grand Bridge. In the model tests, the anchorage body and surrounding rocks were fabricated using a gypsum mixture. The pull-out behavior was investigated under plane strain conditions. The results of the model tests demonstrate that the tunnel-type anchorage underwent a wedge-shaped failure. In addition, the failure mode changed according to the differences in the physical properties of the surrounding rock and the anchorage body and the size of the anchor plate. The size of the anchor plate was found to be an important parameter that determines the failure mode. However, the difference in physical properties between the surrounding rock and the anchorage body did not affect its size. In addition, this study analyzed the initial failure behavior of the tunnel-type anchorage through image analysis and confirmed that the failure was sequentially transferred from the inside of the tunnel to the surrounding rock according to the image analysis. The reasonable failure mode for the design of the tunnel-type anchorage should be wedge-type rather than pull-out type.

• Geomechanics and Engineering
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• 제36권1호
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• pp.71-81
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• 2024

This study analyzes the pull-out behavior of tunnel-type anchorage under various joint conditions, including joint direction, spacing, and position, using a finite element analysis. The validity of the numerical model was evaluated by comparing the results with a small-scaled model test, and the results of the numerical analysis and the small-scaled model test agree very well. The parametric study evaluated the quantitative effects of each influencing factor, such as joint direction, spacing, and position, on the behavior of tunnel-type anchorage using pull-out resistance-displacement curves. The study found that joint direction had a significant effect on the behavior of tunnel-type anchorage, and the pull-out resistance decreased as the displacement level increased from 0.002L to 0.006L (L: anchorage length). It was confirmed that the reduction in pull-out resistance increased as the number of joints in contact with the anchorage body increased and the spacing between the joints decreased. The pull-out behavior of tunnel-type anchorage was thus shown to be significantly influenced by the position and spacing of the rock joints. In addition, it is found that the number of joints through which the anchorage passes, the wider the area where the plastic point occurs, which leads to a decrease in the resistance of the anchorage.

• 한국지반공학회논문집
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• 제34권10호
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• pp.61-74
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• 2018

본 연구에서는 케이블 인발하중이 작용하는 현수교의 앵커리지 종류 중 터널식 앵커리지의 인발거동 특성을 축소모형실험과 수치해석을 통하여 분석하였다. 터널식 앵커리지는 국내외 적용사례가 적고 파괴형태 및 안전율 등 설계기법이 명확히 정립되어 있지 않아 설계기법 개선과 관련한 연구가 필요한 실정이다. 이에 국내 최초로 터널식 앵커리지가 적용된 울산대교를 대상으로 형상 및 구조를 단순화하여 축소모형실험을 수행하였다. 모형실험에서 앵커리지 구체와 주변 암반을 석고혼합물로 구현하였고, 평면 변형률 조건에서 인발 거동 특성을 조사하였다. 모형실험결과 터널식 앵커리지의 최종 인발 파괴모드는 울산대교의 설계시 가정한 바와 달리 쐐기(wedge)형태로 나타났다. 이를 검증하기 위해 유한요소해석 프로그램인 ABAQUS를 사용하여 수치해석을 시행하였고, 모형실험결과와 동일한 인발 파괴 거동을 확인할 수 있었다. 수치해석에서는 추가적으로 모형재료의 포아송비 및 주변암반의 강도 변화에 따른 영향을 조사하였다. 그 결과 극한 인발상태까지는 포아송비에 따른 영향이 적은 것으로 나타났고, 주변암반의 강도가 앵커리지 구체의 강도보다 10배 이상 큰 특수한 경우에 한하여 앵커리지가 주변 암반의 경계면을 따라 빠져나오는 소위 플러그(plug)형태의 파괴모드가 발생할 수 있음을 확인하였다.

• Geomechanics and Engineering
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• 제12권1호
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• pp.139-160
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• 2017

The bearing mechanism of tunnel-type anchorage (TTA) for suspension bridges is studied. Model tests are conducted using different shapes of plug bodies, which are circular column shape and circular truncated cone shape. The results show that the plug body of the latter shape possesses much larger bearing capacity, namely 4.48 times at elastic deformation stage and 4.54 times at failure stage compared to the former shape. Numerical simulation is then conducted to understand the mechanical and structural responses of plug body and surrounding rock mass. The mechanical parameters of the surrounding rock mass are firstly back-analyzed based on the monitoring data. The calculation laws of deformation and equivalent plastic strain show that the numerical simulation results are rational and provide subsequent mechanism analysis with an established basis. Afterwards, the bearing mechanism of TTA is studied. It is concluded that the plug body of circular truncated cone shape is able to take advantage of the material strength of the surrounding rock mass, which greatly enhances its bearing capacity. The ultimate bearing capacity of TTA, therefore, is concluded to be determined by the material strength of surrounding rock mass. Finally, recommendations for TTA design are proposed and discussed.

• 한국지반공학회논문집
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• 제37권2호
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• pp.33-48
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• 2021

현수교의 지중정착식 앵커리지는 기초 암반이 신선할 경우에 적용될 수 있는 형식으로, 앵커리지 형식 중 환경성과 경제성 측면에서 뚜렷한 장점이 있다. 그러나 케이블 하중 재하시 암반의 거동특성이 아직 명확하게 규명되지 않았고 설계기법이 정립되어 있지 않아, 실무자들이 구조물 계획을 수립하는데 많은 어려움을 겪고 있다. 본 연구에서는 국내 도서지역의 경암 지반에 계획된 지중정착식 앵커리지를 대상으로 모형실험과 수치해석을 수행하고 지지암반의 거동 특성을 평가하였으며, 자중과 전단력으로 케이블 하중에 저항하는 비대칭 형태의 암반 쐐기 블록을 제안하였다. 또한 경암 지반에서 강연선 홀 설치를 위한 실규모 시험천공을 실시하고, 경사 천공의 정밀도를 확인하여 지중정착식 앵커리지의 적용 가능성을 평가하였다.

• Geomechanics and Engineering
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• 제15권3호
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• pp.841-849
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• 2018

The purpose of a rock bolt is to improve the mechanical performance of a jointed-rock mass. The performance of a rock bolt is generally evaluated by conducting a field pullout test, as the analytical or numerical evaluation of the rock bolt behavior still remains difficult. In this study, wide range of field test was performed to investigate the pullout resistance of rock bolts considering influencing factors such as the rock type, water bearing conditions, rock bolt type and length. The test results showed that the fully grouted rock bolt (FGR) in water-bearing rocks can be inadequate to provide the required pullout resistance, meanwhile the inflated steel tube rock bolt (ISR) satisfied required pullout resistance, even immediately after installation in water-bearing conditions. The ISR was particularly effective when the water inflow into a drill hole is greater than 1.0 l/min. The effect of the rock bolt failure on the tunnel stability was investigated through numerical analysis. The results show that the contribution of the rock bolt to the overall stability of the tunnel was not significant. However, it is found that the rock bolt can effectively reinforce the jointed-rock mass and reduce the possibility of local collapses of rocks, thus the importance of the rock bolt should not be overlooked, regardless of the overall stability.