A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile Foundation
Offshore wind power is a new trend in renewable energy development. However, during the operation of offshore wind turbines, the rock-socketed monopile foundation is subjected to long-term cyclic loads, which will cause the seawater to erode the rock around the monopile foundation and reduce the ult...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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MDPI AG
2023-12-01
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| Series: | Journal of Marine Science and Engineering |
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| Online Access: | https://www.mdpi.com/2077-1312/11/12/2310 |
| _version_ | 1827574489597083648 |
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| author | Qi Zhang Yixin Shen Xiaokang Guo Chenhao Zhang Yifeng Lin Xiaojun Wang |
| author_facet | Qi Zhang Yixin Shen Xiaokang Guo Chenhao Zhang Yifeng Lin Xiaojun Wang |
| author_sort | Qi Zhang |
| collection | DOAJ |
| description | Offshore wind power is a new trend in renewable energy development. However, during the operation of offshore wind turbines, the rock-socketed monopile foundation is subjected to long-term cyclic loads, which will cause the seawater to erode the rock around the monopile foundation and reduce the ultimate end-bearing capacity. There is no suitable rock mass classification for evaluating the quality of marine bedrock and no theoretical method for accurately calculating the ultimate end-bearing capacity of the monopile foundation. Therefore, based on the existing rock mass classification, an ocean rock mass classification (OMR) that is applicable to marine bedrock is proposed. The ratings of four geological indices (<i>R</i><sub>1</sub>, <i>R</i><sub>2</sub>, <i>R</i><sub>3</sub>, and <i>R</i><sub>4</sub>) in the OMR classification are reset by the analysis hierarchy process and modified according to the geological conditions of marine bedrock. Then, an accelerated test of seawater erosion is used over 60 days to simulate seawater erosion for up to 12 years to determine the adjustment factor for the effect of time, <i>F<sub>t</sub></i>, in the OMR classification. Based on the OMR classification, a theoretical calculation method of the ultimate end-bearing capacity of the offshore wind monopile foundation under the overall sliding failure mode of rock mass is proposed. The theoretical calculation method was employed for offshore wind engineering, and the reliability of the theoretical calculation and three-dimensional numerical simulation was validated. The results show that the theoretical and numerical results for the ultimate end-bearing capacity without seawater erosion are similar to the measured results, with a relative error of less than 9%. The theoretical results are always larger than the numerical results, with a relative error of less than 7%. Finally, the theoretical and numerical results were used to guide the design and construction of an offshore wind turbine. The offshore wind turbine has been operating for 8 years, and its displacement is 15.3 mm, which is less than the numerical result of 16.94 mm. |
| first_indexed | 2024-03-08T20:37:51Z |
| format | Article |
| id | doaj.art-72789c77ffa4424aa628014502d3fa9b |
| institution | Directory Open Access Journal |
| issn | 2077-1312 |
| language | English |
| last_indexed | 2024-03-08T20:37:51Z |
| publishDate | 2023-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Journal of Marine Science and Engineering |
| spelling | doaj.art-72789c77ffa4424aa628014502d3fa9b2023-12-22T14:18:53ZengMDPI AGJournal of Marine Science and Engineering2077-13122023-12-011112231010.3390/jmse11122310A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile FoundationQi Zhang0Yixin Shen1Xiaokang Guo2Chenhao Zhang3Yifeng Lin4Xiaojun Wang5School of Civil Engineering, Southeast University, Nanjing 211189, ChinaSchool of Civil Engineering, Southeast University, Nanjing 211189, ChinaSchool of Civil Engineering, Southeast University, Nanjing 211189, ChinaDepartment of Architecture and Civil Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong 999077, ChinaShanghai Investigation, Design & Research Institute Co., Ltd., Shanghai 200434, ChinaDepartment of Geotechnical Engineering, College of Civil Engineering, Tongji University, Shanghai 200092, ChinaOffshore wind power is a new trend in renewable energy development. However, during the operation of offshore wind turbines, the rock-socketed monopile foundation is subjected to long-term cyclic loads, which will cause the seawater to erode the rock around the monopile foundation and reduce the ultimate end-bearing capacity. There is no suitable rock mass classification for evaluating the quality of marine bedrock and no theoretical method for accurately calculating the ultimate end-bearing capacity of the monopile foundation. Therefore, based on the existing rock mass classification, an ocean rock mass classification (OMR) that is applicable to marine bedrock is proposed. The ratings of four geological indices (<i>R</i><sub>1</sub>, <i>R</i><sub>2</sub>, <i>R</i><sub>3</sub>, and <i>R</i><sub>4</sub>) in the OMR classification are reset by the analysis hierarchy process and modified according to the geological conditions of marine bedrock. Then, an accelerated test of seawater erosion is used over 60 days to simulate seawater erosion for up to 12 years to determine the adjustment factor for the effect of time, <i>F<sub>t</sub></i>, in the OMR classification. Based on the OMR classification, a theoretical calculation method of the ultimate end-bearing capacity of the offshore wind monopile foundation under the overall sliding failure mode of rock mass is proposed. The theoretical calculation method was employed for offshore wind engineering, and the reliability of the theoretical calculation and three-dimensional numerical simulation was validated. The results show that the theoretical and numerical results for the ultimate end-bearing capacity without seawater erosion are similar to the measured results, with a relative error of less than 9%. The theoretical results are always larger than the numerical results, with a relative error of less than 7%. Finally, the theoretical and numerical results were used to guide the design and construction of an offshore wind turbine. The offshore wind turbine has been operating for 8 years, and its displacement is 15.3 mm, which is less than the numerical result of 16.94 mm.https://www.mdpi.com/2077-1312/11/12/2310ocean rock mass (OMR) classificationultimate end-bearing capacityoffshore wind turbinemonopile foundationaccelerated test of seawater erosion |
| spellingShingle | Qi Zhang Yixin Shen Xiaokang Guo Chenhao Zhang Yifeng Lin Xiaojun Wang A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile Foundation Journal of Marine Science and Engineering ocean rock mass (OMR) classification ultimate end-bearing capacity offshore wind turbine monopile foundation accelerated test of seawater erosion |
| title | A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile Foundation |
| title_full | A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile Foundation |
| title_fullStr | A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile Foundation |
| title_full_unstemmed | A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile Foundation |
| title_short | A New Ocean Rock Mass Rating and Its Application to Determine the Ultimate Bearing Capacity of an Offshore Wind Monopile Foundation |
| title_sort | new ocean rock mass rating and its application to determine the ultimate bearing capacity of an offshore wind monopile foundation |
| topic | ocean rock mass (OMR) classification ultimate end-bearing capacity offshore wind turbine monopile foundation accelerated test of seawater erosion |
| url | https://www.mdpi.com/2077-1312/11/12/2310 |
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