ABSTRACT

The suction bucket foundation is installed on the seabed under combined self-weight and under-pressure. In this case study, four submersible monitoring structures for the active sensors were constructed on the ultra-soft seabed using suction bucket foundations. After construction, the excessive displacements of the column top due to the external excitation were measured. The cause analysis of the problem carried out and the reinforcement method to reduce the excessive displacement were applied. As the review results, the excessive displacements were developed for the connection rigidity problem between suction foundation and upper part column. Adopted reinforcing method was additional bettered stiffener mounting. Finally, the angular displacements at the same underwater excitation test after the reinforcement were reduced nearly designed value.

INTRODUCTION

The suction bucket foundation is different from both driving pile and traditional bored pile foundation. The suction bucket foundation method utilizes suction pressure. Suction pressure discharges the water from inside the bucket foundation. It is used as both ocean structure foundation and anchor. It is easy to construct and remove because it uses only a pump to build large sea-floor foundations. It is adaptable to water depths between approximately 10 to 2,500 meters. This method has been used to construct harbor structures, mooring anchor and substructures for wind turbines in Korea.

This project was planned to construct the substructure for underwater active sonar, and suction foundation system was applied. There were 4 construction positions (zone a, zone b, zone c and zone d) and water depth of installation positions was about 12.0m which were some differences depending on the location. Suction foundation structures with 5m length column were fully fabricated on land and were constructed under water at all time. The specific construction position and details were not open for the security problems

SITE CONDITIONS AND INVESTIGATION

The construction site is near shore of jinhae port located in south coast of Korea (see fig. 1). To get the geotechnical properties, the seabed type offshore CPT(cone penetration test) were performed 4 times at each construction point. Fig. 2~5 shows the measured tip resistances of soil in depth. As the CPT Result, the seabed ground is very soft and the strengths are increased in depth.

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