Abstract: To study the variations and distribution characteristics of excess pore water pressure during shield tunneling in waterrich silty fine sandy stratum and explore the influence of excess pore water pressure on the limit support pressure of excavation face, the constrained nonlinear function is calculated using the limit equilibrium method, and a modified formula for calculating the limit support pressure is proposed based on field test data of a largediameter rivercrossing shield tunnel project. The study shows the following: (1) During shield tunneling, the disturbance area of pore water pressure is roughly twice the excavation diameter ahead of the excavation face and 1.5 times the excavation diameter on both sides of the excavation face; the closer to the excavation face, the greater the disturbance degree. (2) The excess pore water pressure has a great impact on active failure limit support pressure of excavation face, thus, the slurry pressure should be appropriately increased, or the whole slurry balance mode should be adopted to maintain the stability of the excavation face and reduce the disturbance range and degree of pore water pressure.

Key words: shield tunnel, waterrich sandy stratum, excess pore water pressure, limit support pressure