Based on the Mohr-Coulomb strength criterion and uncorrelated flow rule, Abaqus is used to simulate the passive failure of the excavation surface of underwater shield tunnel in sandy soil layer, and influences of the buried depth ratio C/D, height of overlying water level H and friction angle φ in sandy soil on the surface displacement are analyzed. The failure mode of the soil in front of the excavation face is also discussed. The results show that the support pressure of standard excavation face is related to C/D, sand φ, and there is a positive correlation between them; the surface displacement is greatly affected by the change of C/D, and when C/D increases from 0.8 to 1.5, the maximum longitudinal and transverse displacement decrease by 80% and 86% respectively; hydrostatic pressure will only limit the development of lateral surface displacement and has little effect on longitudinal surface displacement; when C/D is small, the passive failure mode presents an inverted pyramid shape extending to the surface, which belongs to overall failure; when C/D increases to 4.3, the soil arch cannot reach the ground surface, which belongs to local damage.

Aiming at the problem that the backfill grouting of the shield project must have a short setting time and maintain good fluidity, Rapid hardening sulfoaluminate cement (R·SAC) and triethanolamine (TEA) are used as external accelerated setting materials, Analysis of the influence law and microscopic mechanism of the two on grout properties. The results show that with the increase of R·SAC, the setting time of the grout decreases from 9.5 h to 2.0 h, but the fluidity loss at 150 min is about 50%; With 0.6% dosage of TEA as the inflection point, the setting time and fluidity of the grout both increased first and then decreased; In compound blending, The two have a synergistic effect on grout hydration, rapid hydration in the initial stage, shortened setting time, and TEA deflocculation improves grout fluidity and slows down the loss of fluidity over time; By adding 15% R·SAC and 0.05% TEA, a fast-setting and high-fluidity backfill with a setting time of 6 h and a fluidity of 250 mm in 150 min can be prepared.