A case study on the mechanical behavior analysis of ultra-long (over 1000 m) U-shaped underwater steel pipeline during immersion construction

The directional control of complex configurations and the safety challenges posed by multi-body coupling effects during the immersion of ultra-long (over 1000 m) underwater steel pipelines are critical issues that require resolution. Previous studies have primarily focused on short underwater steel pipelines (less than 1000 m). This paper presents a case study analyzing the mechanical behavior of an ultra-long (over 1000 m) U-shaped underwater steel pipeline during immersion construction. The mechanical behavior of the immersion system and the sensitivity of key parameters are systematically analyzed. The results indicate that the maximum total load on the cables is only 30.8% of their bearing capacity, and the peak von Mises stress in the steel pipeline is only 43.9% of the material's yield strength. By optimizing the number of cables and the configuration of steel floats, the uneven distribution of cable forces can be significantly reduced, with the maximum difference decreasing from 28.6% to 9.3%. Additionally, a cable release speed of 0.42 m/s achieves the optimal balance between load distribution and motion response. This study provides a theoretical foundation for ensuring the safe immersion construction of ultra-long underwater steel pipelines.