Abstract
A safety assessment framework based on the concept of load utilization (LU) ratio is used to evaluate the resistance capacity of monopile-supported offshore wind turbines (MOWTs) in liquefiable soil under combined seismic and environmental loads. A modification strategy of soil parameters based on the degree of soil degradation is proposed to account for the weakening effects of soil in the assessment. The LU ratios of monopiles corresponding to various offshore wind turbine (OWT) states are obtained through three distinct methods, including simplified method, API-based method and advanced method. The proposed framework is validated through a case study of a Siemens SWT-4.0-130 wind turbine located offshore of eastern China, which combines both prototype simulation and scaled model shaking table tests. The results indicate that the LU ratio-based safety assessment framework is applicable to earthquake-induced liquefaction problems. The advanced method that incorporates soil weakening effects can accurately reflect the reduction in the resistance capacity of monopiles in degraded or liquefied soil. The LU ratios corresponding to the liquefied scenarios range from 0.29 to 0.93 for the prototype and from 0.93 to 1.69 for the scaled test model. The LU ratio-based safety assessment framework can accurately identify MOWT failures caused by soil liquefaction, which is expected to provide methodological guidance for the safety assessment and practical design of OWTs in seismic regions.
•An integrated safety assessment framework is proposed to evaluate the resistance capacity of MOWTs in liquefiable soil.•A modification strategy of soil parameters based on the degree of soil degradation is considered in the assessment.•The LU ratios of monopiles corresponding to various OWT states are obtained through three distinct methods.•The proposed framework is verified by both the prototype simulation and scaled model shaking table tests.