Abstract: The bottom-supported platform for offshore wind power, suitable for soft soil areas of the sea, has gained popularity with increasing total installed capacity of offshore wind power. The platform is anchored on a mat foundation through a supporting structure, which evenly distributes the concentrated load into the seabed foundation, providing essential support for the offshore wind installation platform. Due to long-term bottom-sitting, the soil beneath the foundation consolidates, increasing the difficulty of foundation recovery or relocation. Therefore, a new hollow square-shaped mat foundation structure is proposed. To investigate the vertical bearing capacity characteristics of this new type mat foundation in saturated soft clay, centrifuge vertical bearing capacity tests were conducted. Additionally, finite element numerical analysis was employed to study the effects of open porosity and normalized strength on vertical ultimate bearing capacity. The results indicate that the American Petroleum Institute (API) standards underestimate the vertical bearing capacity of foundations when the normalized strength of soil is less than 2, and overestimate it when it exceeds 2. Furthermore, the vertical ultimate bearing capacity gradually decreases as the open porosity increases. However, linearly reducing the effective area according to API standards is inappropriate. A formula considering the open porosity and normalized strength as variables is presented for calculating the vertical ultimate bearing capacity of hollow square-shaped mat foundation, serving as a reference for practical engineering.

Key words: mat foundation, vertical bearing capacity, open porosity, centrifuge test