Abstract: Inadequate soil conditioning poses substantial challenges for earth pressure balance shields operating in water-rich sandy strata, including mucking obstruction, muck spewing, accelerated cutterhead tool wear, and difficulties in regulating tunnel face pressure. To address these challenges, a comprehensive evaluation system for soil conditioning is established. This system integrates the plasticity, impermeability, friction, and pressure transmission characteristics of conditioned muck, enabling the rapid, quantitative assessment and parameter optimization of soil conditioning performance. After soil conditioning using foam, bentonite slurry, and sand mixtures, a series of laboratory tests is conducted, including slump, pressurized permeability, vane shear, and pressure transmission characteristic tests using a shield model soil chamber. Key parameters of ideal conditioned muck, including the slump value, fine particle content, undrained shear strength, and pressure transmission coefficient, are determined. The reliability of these indices is further verified through field measurements and model experiments using a shield soil chamber. The results indicate that ideal conditioned muck should satisfy the following criteria: (1) a slump value S of 150－200 mm to ensure excellent flowability and smooth muck discharge; (2) a fine particle content exceeding 10% to enhance impermeability under high hydraulic pressure and effectively prevent spewing; (3) an undrained shear strength S_u of 3－7 kPa to balance low friction with favorable pressure transmission properties; and (4) a pressure transmission coefficient K₀ of 0.70－0.85 to ensure effective transfer of shield thrust to the tunnel face and over-excavation zones, thereby maintaining pressure equilibrium and preventing tunnel face instability or excessive ground settlement.

Key words: earth pressure balance shield, water-rich sandy strata, soil conditioning, comprehensive evaluation indicators, experiment