Abstract: A case study is conducted on a sludge solidification project of Bid 3 of a publicprivate partnership project of the Lianghu tunnel (Nanhu section), and adaptability tests of a lakephase silt solidification agent are conducted to investigate the composition ratio, dosage, spraying, and stirring process of the solidification agent, to provide launching conditions for ultralargediameter shields in urban lake island building cofferdams. Furthermore, the solidification effect of sludge is clarified through light dynamic penetration tests and thickness tests of the solidification slurry layer to obtain the optimal amount of curing agent and process. The experimental research results suggest the following: (1) The curing agent adaptation and onsite insitu solidification tests demonstrate that the technology is feasible for lakephase sludge and meets the requirements of construction bearing capacity and other indicators. (2) A solidified agent with a mass ratio between cement and industrial waste of 6∶4, solidified admixture dosage of 1‰, and geopolymer solidified dosage of 10.5% exhibits a good treatment effect, considering the strength and uniformity of the solidified soil of the sludge in the Nanhu section. (3) A solidification process with four stirring and spraying cycles is more conducive to ensuring the demand for a unit volume of curing agent dosage, reducing slurry waste, and uniformly strengthening the silt layer. A reasonable amount and solidification process of silt solidification are proposed, which successfully improves the solidification strength uniformity of sludge by evaluating the solidification effect of silt in the experimental field of building an island cofferdam under different working conditions.

Key words: ultralarge diameter shield, island building cofferdam, lakephase silt, insitu solidification of sludge, light dynamic penetration, thickness of churning layer