• Journal of Korean Society of Coastal and Ocean Engineers
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• v.27 no.2
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• pp.135-141
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• 2015

In this study, two different uniform placement methods are proposed for each of Tetrapod, Rakuna-IV, and Dimple armoring a rubble mound breakwater, and the corresponding stability coefficients are determined by hydraulic experiments. The Tetrapod and Rakuna-IV show similar stability coefficients regardless of the placement methods, whereas the Dimple shows somewhat different stability coefficients depending on the placement methods. It is shown that the Dimple gives the largest stability coefficient, whereas the Tatrapod gives the smallest value. The uniform placement methods of Tatrapod and Rakuna-IV give slightly larger stability coefficients than the random placement, whereas the uniform placements of Dimple give much larger stability coefficients than the random placement. However, the small void ratio of uniform placements of Dimple requires attention because the blocks would behave like single layer system blocks so that brittle failure could occur.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.5
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• pp.345-356
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• 2009

Tetrapod has been used as the armor blocks of most rubble mound breakwaters constructed in Korea. The Hudson formula has been widely used in the design of breakwater armor blocks in Korea. In the present study, we calculate the load and resistance partial safety factors of the Hudson formula for Tetrapod armors. The partial safety factors were calculated for the typical breakwater cross-sections of 12 trade harbors and 8 coastal harbors in Korea. The mean and standard deviation of them were also calculated. The mean values were compared with the partial safety factors of US Army (2006). The load and resistance factors are slightly smaller and larger, respectively, than the US Army values. However, the overall safety factors obtained by multiplying the load and resistance factors are close to the US Army values. The result of the present study could be used as the basic data to propose authorized partial safety factors in the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1B
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• pp.59-69
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• 2012

Probabilistic design is required to effectively consider the coastal environment of great uncertainty. However, designers who are familiar with the deterministic design method prefer a method which is similar to the existing method but is based on the probabilistic concept. Therefore, the partial safety factor method has been adopted as a new design method over the world. In Korea, Tetrapod is widely used for armoring rubble mound breakwaters. Even though the partial safety factor method developed in the United States and Europe covers Tetrapods, the limited wave and structure conditions in its development make the engineers hesitate about its use in practical breakwater design. In this study, partial safety factors for Tetrapod armor blocks have been developed by analyzing 116 breakwater cross-sections and wave conditions in 16 trade harbors and 15 coastal harbors with the FORM and optimal code calibration approach. Especially, partial safety factors have been proposed depending on the shape parameter of the Weibull extreme wave height distribution. For other types of extreme distributions, it is possible to apply the proposed partial safety factors using the relationship between skewness coefficient and shape parameter. Finally, the proposed partial safety factors have been applied to existing structures to show that they better satisfy the target reliability of the structures than previous partial safety factors.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.109-117
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• 2011

It was calculated using empirical formulas for the weight of Tetrapod, which was a representative armor unit in the rubble mound breakwater in Korea. As the formulas were evaluated from a curve-fitting with the result of hydraulic test, the uncertainty of experimental error was included. Therefore, the neural network and M5' model tree were used to minimize the uncertainty and predicted the stability number of armor block. The index of agreement between the predicted and measured stability number was calculated to assess the degree of uncertainty for each model. While the neural network with the highest index of agreement have an excellent prediction capability, a significant disadvantage exists that general designers can not easily handle the method. However, although M5' model tree has a lower prediction capability than the neural network, the model tree is easily used by the designers because it has a good prediction capability compared with the existing empirical formula and can be used to propose the formulas like an empirical formula.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.6
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• pp.516-523
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• 2020

Since the aging of coastal structures have been increased, the researches about the reinforcements of the existing aged structures are needed. Especially, the existing armor units placed on rubble mound structures should satisfy the stability against the increased design wave conditions. However the researches about these design problems have not been performed. In this study, the hydraulic model tests to investigate the stability number about the additionally placed armor unit were conducted. The main armor unit is a Tetrapod. The test results showed that the stability number (Kd) for additionally placed armor units(Tetrapod) increased up to maximum 10% comparing with that for 2 layers tetrapod (Kd = 8) within these test conditions with the pattern placing for existing armor layers and the stable armor layer slope for the non overtopping condition.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.303-303
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• 2020

국내의 주요 외곽시설은 대수심화 및 설계외력의 증대 등으로 경제성 및 안정성 등의 확보를 위해 혼성제 형식의 구조물을 적용하는 사례가 주를 이루고 있다. 혼성제 근고부 안정성과 관련해서는, 설계파에 대한 안정적인 피복재 중량을 구하는 것이 설계상 중요하다. 기존의 직각 입사파에 대한 연구는 많이 수행되어 왔으나, 경사 입사파 조건에 대한 검토 사례는 미미한 실정이다. 또한 직각입사 뿐만 아니라 경사 입사파에 대한 근고부 중량산정식으로 확장된 Tanimoto식을 적용하고 있으나, 수리실험과 중량산정식에 대한 오차가 발생하고 있어 수리실험을 통해 기존의 산정식에 대한 검토가 필요하다. 따라서 본 연구에서는 경사입사파 조건에 따른 혼성제 제두부 구간의 피복재 안정성에 대하여 실험을 수행하였다. 설치수심은 0.3m 수심으로 고정하고, 입사각도를 0°, 30°, 45°, 60° 및 75°로 변화시켜 실험을 수행하였다. 전체 연장 10m의 모형에서 종점부 1m 구간을 실험구간으로 설정하고, 피복재의 종류는 피복석(50g), 콘크리트 피복블록(Tetrapod, Tripod)를 사용하였으며, 파랑조건은 불규칙파를 적용하였다. 주기 및 파고를 변화시켜 수리실험을 수행하였다. 실험결과는 제두부 구간에 피복된 피복재의 구간별 피해율을 분석하기 위해 구역분할도 적용하였으며, 확장된 Tanimoto식과 비교분석하여 중량산정식의 타당성을 검토하였다.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.777-782
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• 2001

Occurrence of crack in the Half-loc of rubble mound breakwater under T.T.P (Tetrapod) can cause serious problems in structural safety. There, probing of such cracks in marine structures is an important process in evaluating the overall integrity of structures. Ultrasonic, SASW(Spectral-Analysis-of-Surface-Waves)and Impect-Echo methods were used for the inspection of pilot concrete and SFC (Steel Fiber Concrete) block in this study. The advantage and limitations of these methods for non-destructive inspection in concrete blocks are investigated. As a result, it has been verified that these methods proved to present effective solution for detecting the crack of the pilot concrete block.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.1
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• pp.11-19
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• 2024

In this study, the program was modified by adding the empirical formula of EurOtop (2018) to enable calculation of wave overtopping on armoured slope structures in the FUNWAVE-TVD model using the fully nonlinear Boussinesq equation. The validity of the modified numerical model was verified by comparing it with CLASH data and experiment data for the rubble mound structure. This model accurately reproduced the change in wave overtopping rate according to the difference in the roughness factor of the armoured block, and well reproduced the rate of decrease in wave overtopping rate due to the increase in relative freeboard. The overtopping rate of the armoured slope structures showed significant differences depending on the positioning condition of the armoured blocks. When Tetrapods were placed with regular positioning, the overtopping rate increased significantly compared to when they were placed with random positioning, and it was consistent with when they were placed with Rocks. Meanwhile, when rocks were placed in one row, the wave overtopping rate was greater than when rocks were placed in two rows, which is believed to be due to the influence of the roughness and permeability of the structure's surface.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.5
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• pp.277-283
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• 2016

Tetrapod is one of the most widely used concrete armor units for rubble mound breakwaters. The calculation of the stability number of Tetrapods is necessary to determine the optimal weight of Tetrapods. Many empirical formulas have been developed to calculate the stability number of Tetrapods, from the Hudson formula in 1950s to the recent one developed by Suh and Kang. They were developed by using the regression analysis to determine the coefficients of an assumed formula using the experimental data. Recently, software engineering (or machine learning) methods are introduced as a large amount of experimental data becomes available, e.g. artificial neural network (ANN) models for rock armors. However, these methods are seldom used probably because they did not significantly improve the accuracy compared with the empirical formula and/or the engineers are not familiar with them. In this study, we propose an explicit method to calculate the stability number of Tetrapods using the weights and biases of an ANN model. This method can be used by an engineer who has basic knowledge of matrix operation without requiring knowledge of ANN, and it is more accurate than previous empirical formulas.