• Journal of the Korean Geotechnical Society
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• v.36 no.1
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• pp.29-38
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• 2020

These days the circular cross section cofferdam has been frequently used for the earth retaining structures or cut off wall such as ventilating opening, intake tower in cofferdam, shaft for emergency. By the arching effect, the circular cross section type cofferdam has more advantage than a polygon cofferdam in terms of the structural forces and moment. This paper shows the proper approach to analyze the circular cross section cofferdam using 2D Finite Element Method (FEM) for the circular stiffener (ring beam) evaluation. Besides, the various shapes of cofferdam indluding circular cross section have modeled the 3D Finite Element Mothod (FEM). The circular cross section cofferdam shows the minimum reaction force compared with the other shapes of cofferdam.

• Journal of the Korean Geotechnical Society
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• v.36 no.10
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• pp.5-19
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• 2020

With increasing demand for offshore structures, the demand for temporary structures to help the offshore construction work has increased. A cofferdam is a temporary barrier to stop the inflow of water in the construction site and allows working in the dry condition when the construction is done within the water. However, it is a major cause of construction delays and increased costs because additional works are required to block the water inflow. Recently, in order to overcome the limitations of the conventional cofferdam methods and to increase economic efficiency, a large-diameter steel cofferdam method has been proposed which can be installed quickly in the seabed by using the suction pressure. In this circular steel cofferdam method, the top side of the cofferdam including the top-lid is always exposed above the sea level in order to use it as a water barrier, unlike the conventional suction bucket foundation. After installation, the top-lid of the cofferdam is removed and the water filled inside the cofferdam is discharged to make the interior dry condition. In this study, the circular steel cofferdam with a 5 m inner diameter was fabricated and the installation tests were conducted at the Saemaguem test site. During the experiment, variation of suction pressure, leakage between connections, structure deformation, and inclination of the steel cofferdam were measured and post-analyzed. This study verified the new circular steel cofferdam method and confirmed that the suction installation method can be successfully used for various purposes on offshore structures.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.35-43
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• 2020

Currently, cofferdams of circular cross section are widely applied as temporary facilities for the installation of bridge foundations in river/sea bridge construction in Korea. Existing caisson, sheet pile, and cell type cofferdam are widely used, but these methods take a lot of time and cost for installation and dismantling. In the case of the existing sheet pile construction method, attention is needed to secure internal and external stability because of the damage to the sheet pile due to ground penetration and difficulty in connecting element members. In this study, penetration design of circular steel pipes using suction pressure was performed on the soft ground of the west coast, and it was confirmed that penetration construction using suction pressure was possible through field tests. It was confirmed that applying the ground analysis results using the cone penetration test (CPT) to the design rather than the standard penetration test (N value) results more similar to the field test results. In addition, it was confirmed that local failure of the inside of the cofferdam was induced when a suction pressure higher than the upper limit suction pressure was applied in the silty sand.

• Journal of the Korean Geotechnical Society
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• v.35 no.12
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• pp.123-134
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• 2019

This study presents dynamic responses of circular pipe models as a part of fundamental studies on dynamic stability monitoring of the large circular steel pipe cofferdam with the ship collision. Small-scaled laboratory experiments are performed with a single and bolted circular steel pipes with a diameter, thickness, and height of 30, 0.4, 90 cm, respectively. The bolted circular steel pipe is configured with three segments of 30 cm in height. Circular steel pipe models are embedded in a soil tank, all 1 m in length, width, and height. The thickness of soil in the soil tank is set at 23 cm. The ship collision is simulated with a hammer impacting. The dynamic responses are investigated with different water levels of 25, 40, 55, and 70 cm. Experimental results show that a signal energy decreases with increasing water level. More sensitive reduction in the energy appears for the bolted circular steel pipe. A predominant frequency decreases with increasing water level for both single and bolted steel pipes. The minor reduction in the frequency appears for the bolted circular steel pipe under the water level of 70 cm. This study suggests that the signal energy and frequency response is useful for the dynamic stability monitoring of the large circular steel pipe cofferdam.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2006.09a
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• pp.125-128
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• 2006

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2004.08a
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• pp.18-24
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• 2004

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• autumn
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• pp.255-266
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• 2000

Since 1993, Seohae grand bridge has been continued construction for 7 years and will be completed late this year. The bridge is a part of west sea castal highway and consists of 3 types of bridge including precast segmental method, free cantilever method and cable stayed bridge. A cable stayed bridge is the core of this bridge and it consists of 5 span, symetrical cable-stayed bridge with a total length of 990 m. The main span between two H-shaped pylons extending approximately 180 M above massive foundation of a cable stayed bridge is 470 m long and an approach span of that is 260 m long respectively. The circular cofferdam with 16 ea of 25 m diameter flat type sheet pile had been applied to construct foundation. The slipform method had been applied for forming of con'c of two H-shaped pylons with 3 cross beams respectively which is varied horizontally and vertically. The deck has been erected with balanced cantilever method using movable derrick crane. The stay cables is a bundle of parallel individually protected, 7 wire high tensile strands. The strands is hot deep galvanized and sheathed with a tight high density polyethylene coating. A petroleum wax fills all the inter-wire voids. The bundle of strands to prevent from deterioration due to the ambient problem covered with high density polyethylene pipe. The Isotension method has been applied for the stressing of cable strands to ensure uniformity of force in all the strands of a syay and such works has been performed on the stay specially provided in the pylon.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.71-81
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• 2020

The large circular steel pipe for a marine bridge foundation has been developed as a construction method capable of performing the role of the working platform and cofferdam. The objective of this study is to demonstrate the wireless remote sensing system for monitoring the stability of the large circular steel pipe during construction and operation through field tests. The artificial seabed ground with an water level of 4 m is constructed for field tests. The large circular steel pipe with a diameter of 5 m and height of 9.5 m is installed into the ground by suction, and the embedded depth is 5 m. The inclinometer and strain gauges are installed on different surfaces of the upper module, and the tilt angle and stress are monitored throughout the entire construction process. As results, tilt angles are measured to be constant during the suction penetration. However, the tilt angle is larger in the x-axis direction. In addition, even when installed on different surfaces, the tilt angle in the same axial direction is measured to be almost the same. The stresses measured by strain gauges increase during suction penetration and decrease during pull-out. Based on measured stresses, it is found that the eccentricity is acting on the large circular steel pipe. This study shows that a wireless remote sensing system built with an inclinometer and strain gauge can be a useful tool for the stability monitoring of the large circular steel pipe.