Nishimatsu Construction Co., Ltd., Technical Research Institute Yamato, Kanagawa, JAPAN

tadashi_fukumoto@nishimatsu.co.jp

　

To protect the coastline from wind waves and beach erosion, subaerial offshore breakwaters were constructed in Japan and other countries. It has become equally important to utilize the developed coastal area in harmony with the natural environment. Submerged artificial reef breakwaters are more aesthetic than subaerial offshore breakwaters. However, the crest width of a conventional submerged breakwater must be very wide to reduce wave transmission sufficiently. To dissipate wave energy more efficiently than traditional trapezoidal reef breakwaters, Yasuda et al. (1996) proposed a new concrete reef structure composed of two layers. Experiments were conducted in a wave flume to show the effectiveness of the perforated concrete reef in increasing wave energy dissipation. However, this reef was unrealistic for practical applications because of its crest width extending all the way to the shoreline.

　

A wave trapping artificial reef (WATAR) is a submerged concrete structure placed on a rubble mound or jacket. The concrete structure is perforated in such a way as to trap and break incident waves on the structure and cause effective wave energy dissipation and return flow in the structure. Regular wave experiments were conducted in a wave flume to evaluate the effectiveness of WATAR in reducing wave transmission and reflection. The cross-shore variations of the measured wave heights are indeed encouraging.

　

　

¹School of Construction and Environmental System Engineering Kyongju University Kyongbnk-Pref. Kyongju, KOREA

hmkweon@kyongju.ac.kr

　

²Division of Architecture, Urban, Civil & Environmental Engineering Wongkwang University Jeonbuk-Pref. Iksan, KOREA

stjeong@mail.wonkwang.ac.kr

　

For the construction of under layer of the breakwater against a big wave, Kweon Lee (2000) had developed new shape of the artificial armor unit which could replace the natural stone as a filtered layer. The new shape unit was named as Half-loc because of its half inter-locking characteristics. However, the hydraulic investigation is not sufficient for design information because under layer of Half-loc is subject to loading by upper layer materials. In this study, the field experiment of load effect and placement of Half-loc has been conducted.

　

In order to estimate the loading effect, about 7 times heavier weight of Tetrapod relative to Half-loc is loaded on a single layer Half-loc slope and loaded weight is measured. With the 30 times placements of 2 layers system of Tetrapod of model type respectively, fundamental data are collected and analyzed. The results show the weights on a Half-loc follow the normal distribution and the weight of accumulated probability of 90% is corresponding to that of a Tetrapod. Referencing the result, the effect of the point load of 40 ton on a Half-loc of 5-ton type is investigated by the elasto-plastic analysis. The analysis shows a part of the loading point has a plastic behavior.

　

Another estimation in a field is conducted with Tetrapod of 40 ton type (actual weight of 36.80 ton) and Half-loc of 5 ton type (actual weight of 4.94 ton). Photo 1 shows the field experiment conditions. The lower part of 4 lags of Half-loc are supported on plate ground and Tetrapod of 40 ton type hanging on two strings controlled is loaded on a Half-loc. Non destructive inspection by ultrasonic method is applied for detection of crack inside Half-loc. The inspection indicates there is no crack inside the concrete block. The concrete has specific weight of 2.3 ton/m³ and design strength of 210 kg/cm². The load effect on a Half-loc has been investigated in a field. The result shows about up to the 8 times heavier weight than that of a Half-loc could be loaded as the upper layer. Combined with the result of hydraulic experiment (Kweon Lee 2000), the combination slope with Tetrapod and Half-loc would be stable if the weight ratio on per one unit is less than 8.0.

　

　

¹Civil Engineering Research Institute of Hokkaido Toyohiro, Sapporo, JAPAN

99258@ceri.go.jp

　

²Muroran Institute of Technology Mizumoto-cho, Muroran, JAPAN

　

The Civil Engineering Research Institute of Hokkaido is developing a high-mound composite seawall with slit crown wall, which is aimed at cost reduction and environmental enhancement. The structure of this seawall allows a high rubble mound, whose mound slope negates the force of most waves by its wave-breaking action. Employment of the slit structure in the superstructure of this seawall enables reduction of wave forces acting on the seawall. The mound slope provides an optimal living environment for seaweed where sunlight abounds.

　

To clarify the hydraulic characteristics of the high-mount composite seawall with slit crown wall, wave forces characteristics and wave-overtopping characteristics have been studied. These studies revealed that the hydraulic characteristics superior to the conventional wave-absorbing seawall. However, sufficient examination has not been conducted on the stability of the armor units of the rubble mound. Therefore, it is not possible to calculate the stable mass of the armor units. We report the results of 2-D and 3-D hydraulic model experiments on the stability of the armor units for high-mound composite seawall with slit crown wall.

　

　

¹Taisei Corporation, Yokohama, JAPAN

otas@pub.taisei.co.jp

　

²Ceramic House Ltd., Funabashi, JAPAN

0e8pw@polka.plala.or.jp

　

³Dept. of Oceanic Architecture & Engineering College of Science & Technology Nihon University, Funabashi, JAPAN

sanwa@ocean.cst.nihon-u.ac.jp

adachi@ocean.cst.nihon-u.ac.jp

　

The offshore oil development has been expanded to activities in the ice-covered seas. In the northern part of Okhotsk Sea the oil production projects are now proceeded. In such ice-covered seas the ice load is generally significant design condition for offshore platforms.

　

In our study the interactions between various offshore structures and floating ice were investigated. We have carried out the many model tests in ice model basin to study the ice load when ice fails by crushing or bending in front of cylindrical or conical shaped structures. In addition to the above the theoretical analysis methods were proposed to investigate the earthquake response by considering the interaction between ice floes and structures.

　

In this paper we present the results of study for modeling dynamic ice-structure interaction regarding a conical shaped structure. Firstly an analytical model of hysteretic curve was proposed for the interaction based on the cyclic indentation results of conical-shaped structures in an ice model basin. Then the seismic response analysis was performed. The result shows the maximum response shear force on the column was larger than the maximum ice force acting on the structure by the bending ice failure mode by unidirectional indentation. We also examined the dynamic behavior of structures in the earthquake event by performing the pseudo dynamic tests of structural models based on the sub-structure method in an ice model basin. The results of this pseudo dynamic test were used to confirm the validity of the proposed analytical hysteretic model.