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Based on the unified strength theory and the Terzaghi limit equilibrium theory, the ultimate bearing capacity of screw pile has been deduced. The method to determine the critical pitch and calculate the ultimate bearing capacity of the screw pile in two failure modes including the independent bearing failure mode and the cylinder shear failure mode has been proposed. The influence of the unified strength theoretical parameter b and the key parameters of concrete screw pile on the ultimate bearing capacity has been analyzed. The results show that the ultimate bearing capacity of the screw pile is 1.5—2 times that of the round pile with the same outer diameter. The ultimate bearing capacity of the screw teeth is mainly determined by the cohesion, the internal friction angle, and the buried depth of the soil. As b increases from 0 to 1, the theoretical value of the ultimate bearing capacity of the screw pile increases by nearly 48%. As the influence of the medium principal stress on the soil strength is considered, the theoretical calculation results of the bearing capacity of the concrete screw pile will be more accurate. Of the parameters of the concrete screw pile, the screw height bh has the greatest influence on the ultimate bearing capacity, while the screw thickness t has little influence on the bearing capacity. When designing threaded pile, the height of screw can be increased to some extent to improve the ultimate bearing capacity of the screw pile.

Zhanjiang City, with an area of 37 000 hm² of mariculture, is an important production and processing base for aquatic products in Guangdong Province and even in the whole country. Conducting carbon sink accounting for mariculture bivalve and seaweed is of great significance, as it will provide data support for Zhanjiang City to conduct fishery carbon sink trading in the future and meet the national carbon neutral demand. Based on the field surveys and laboratory analysis, the key basic data of carbon sink accounting of native bivalve and seaweed in Zhanjiang was obtained in this study. And the carbon sink capacity of mariculture in Zhanjiang based on the whole life cycle carbon emissions of bivalve and seaweed were also evaluated. The results showed that the total carbon sink (measured in CO2) of mariculture bivalve and seaweed in Zhanjiang was 155 436 t in 2021, with bivalve accounting for 155 359 t and seaweed accounting for 77 t. According to the current CO2 trading price in China's blue carbon market, the economic value created by the carbon sinks of bivalve and seaweed in Zhanjiang was 16.48 million RMB. Using the comprehensive method of carbon emission in the whole life cycle assessment, the net carbon sink of the bivalve in Zhanjiang City was 135 176 t, and the seaweed was 39 t. It is evident that Zhanjiang City has a high carbon sequestration capacity in marine bivalve cultivation, which can bring significant economic benefits through emission reduction, and making an important contribution to China's climate change solutions and achieving the "dual carbon" goals. [ABSTRACT FROM AUTHOR]