Abstract: The uneven settlement of an immersed tunnel can be reduced by improving the foundation treatment precision and bearing capacity of an offshore immersed tunnel. In this study, the underwater leveling system of a shipframe separationtype leveling ship used in the immersed tunnel of the ShenzhenZhongshan link is introduced in terms of the system composition, working principle, and applicable conditions. The two factors affecting the leveling precision are the elevation changes of the hopper mouth and the height control of gravel material in the hopper during underwater construction. Moreover, the precision control technology of a gravel leveling system that controls the foundation deformation induced by rails under selfweight and various combinations of base frame is proposed based on the ANSYS numerical calculation method. In addition, a sensor system is employed for continuous realtime and multipoint monitoring of the gravel height in the hopper. The proposed underwater gravel leveling system has been successfully applied in the laying and leveling of the gravel foundations in the E32E24 immersed tunnel pipes of the ShenzhenZhongshan link. The average deviation of foundation leveling was 15.3 mm, which is within the design requirements of a deviation of ±40 mm. Thus, foundation laying precision can be improved by applying a shipframe separationtype leveling ship.

Key words: Shenzhenzhongshan link, immersed tunnel, gravel foundation laying, underwater gravel leveling system, leveling precision, elevation control, height monitoring