Abstract: The utilization of offshore composite foundations with deep cement mixing(DCM) piles in immersed tunnels lacks precedence in China. Further exploration of the adaptability, stress characteristics, and layout forms of DCM piles in immersed tunnels is crucial. Therefore, a case study is conducted on the ShenzhenZhongshan link immersed tunnel. A threedimensional finite element model is employed to assess four distinct layout forms of DCM piles. A rational layout form for DCM piles is indentified and validated through field load plate tests. Key findings include: (1) DCM piles with shallow cover exhibit subpar quality and low strength, while the quality of the short pile section under the bracket layout form cannot be guaranteed. (2) Under similar replacement rates, the simulated settlement of piles with a singlepile layout is smaller than that with a bracket layout. Therefore the singlepile layout is superior for DCM piles. (3) The allowable bearing capacities of the composite foundation, with pile spacings of 3 m × 4 m and 3 m × 3 m, are not less than 158.3 and 211.1 kPa, respectively. These values align well with the calculated results. (4) Considering the foundation load distribution pattern and load plate test results, a variable space DCM pile layout of 3~5 m is preferred for the ShenzhenZhongshan link immersed tunnel.

Key words: ShenzhenZhongshan link, immersed tunnel, composite foundation of deep cement mixing pile, finite element, load plate test