Engineering Behavior Artificial Benthic Habitats And Analysis and Design Anchoring Design Devices for Farming Cages

• Main Authors: Rong-Chang Ou, 歐榮昌
• Other Authors: Wen-Miin Tian
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/31268036400110609906

碩士 === 國立中山大學 === 海洋環境及工程學系研究所 === 90 === The purpose of this investigation was to integrate the knowledge and techniques of marine geotechnical engineering, underwater acoustic and optical observation into studying the engineering problems of artificial reefs off south-western coast of Taiwan (Fang-Liau ,Lin-Yang, Yung-An artificial reefs etc.) and the destruction of mooring system on farming cages caused by the interaction of wave-current system. The ultimate goal of this investigation was to understand the scouring activities of loosely and closely spaced artificial reefs; as well as, to evaluate the feasibility of using artificial reefs as deadweight anchoring devices for farming cages at Fang-Liau reef site. The results of this research were as follows: Fang-Liau artificial reef site: The maximum scouring depth can reach as deep as 2.2m around closely distributed reefs at this site. Only a few loosely deployed reefs were buried there, and the scouring depressions around these buried reefs had been filled up completely. To sum up, the behavior of scouring produced by the action of wave, current and typhoon around this site, merely limited to loosely distributed reefs, and the rim of closely distributed reefs. With the scouring time increasing, there were no obvious evidences for the burial of artificial reefs at this site. Lin-Yang artificial reef site: The scouring depressions around part of loosely deployed reefs expand as typhoons attacking at this site. The horizontal range of the scouring depressions can reach 92.3m in length, and parts of the reefs were buried during the process of scouring. Besides, as time went on, part of closely distributed reefs illustrated periodic variations of being buried by sediments with ripple marks, then shown up with evident height, and then buried again. To sum up, the behavior of scouring produced by the action of wave, current and typhoon around this site could cause the complete burial of the reefs. The possible procedures for the burial of reefs in the scouring depression were the actions of backfill of sandy sediments at this site. Yung-An artificial reef site: During summer time, especially with typhoons passed by, surficial sediments at this site were evident with mega ripple marks. The effects of scouring at this site were prominent than those at Fang-Liau reef site. The textures of surficial sediments were the major factor which induced this difference. Based on the considerations of safety of sliding, bearing capacity and overturning, the usage of artificial reefs as anchoring devices for farming cages could not satisfy the basic engineering requirements under the action of extreme wave and current. This research suggested the usage of cubical concrete block with shear keys for anchoring devices on farming cages. The minimum buoyant weight of this block should reach 28.8 to 38.7ton. The problem regarding construction and deployment techniques of this block need further considerations.