Numerical Investigation on Repowering Aging Onshore Wind Turbine Foundations Through a Reuse Strategy: An Engineering Case Study

For the repowering of aging onshore wind foundations, a reuse-oriented strengthening scheme that does not require demolition of the existing foundation is proposed based on the retrofit project of an octagonal extended foundation at a wind farm in Shandong Province, China. Through structural measures such as connecting the foundation ring with high-strength threaded rebars and underpinning the existing foundation with a new foundation, the new and existing foundations are integrated into a composite foundation system with coordinated load-bearing behavior. To ensure a sufficient safety margin, the structural bearing contribution of the existing foundation is conservatively neglected, and only its counterweight effect is considered. Based on code-based methods, the foundation bearing capacity is used for structural design and verification, and a three-dimensional finite element model of the new foundation-existing foundation–soil interaction is established in ABAQUS to analyze the mechanical performance of the overall structure and key local regions. The results show that the reuse-oriented scheme can reduce concrete consumption and earthwork excavation, while significantly lowering solid waste generation and construction disturbance caused by demolition of the existing foundation. Under both normal and extreme loading conditions, all design criteria satisfy the code requirements, and the finite element results show good consistency with the code-based calculations. In addition, significant stress concentration is likely to occur at the corners of the octagonal underpinning region. Optimizing it into a circular underpinning configuration can effectively alleviate the stress peaks induced by geometric discontinuities, reducing the maximum tensile stress by approximately 27%. Further CDP analysis indicates that relatively high tensile stresses occur in the foundation base slab and underpinning regions, suggesting a risk of local cracking. Therefore, local strengthening measures are recommended for these critical regions. The findings of this study can provide a reference for reducing material consumption, construction disturbance, and potential environmental impacts in the repowering of onshore wind foundations.