Abstract: To explore the evolution patterns of pore pressure during the excavation of a deep tunnel and determine the longitudinal value of a threedimensional seepage calculation model, a threedimensional finite element model of a deepburied long tunnel is established with the monitoring section as the center. First, a scheme, in which the tunnel is excavated through one time, is adopted and the timehistory of pore pressure dissipation during excavation is studied. Then, the drawdown of the water table and the evolution of pore water pressure are investigated with excavation process. To construct an entire curve of pore water pressure evolution on the monitoring section, the influence scope of the tunnel face in the process of excavation is explored. Finally, the suggestions for the longitudinal value in threedimensional seepage numerical model and the setting of monitoring section are given. The results show the following: (1) The stepped excavation method can better reflect the mechanism of pore water pressure evolution than the onetime excavation method. (2) When the excavation distance is 22.5〖WT〗D, where refers to the tunnel diameter, the forward influence scope of the tunnel face gradually reaches 〖WT〗80D. 〖WT5《TNR》〗(3) When the tunnel face goes across the monitoring section and the excavation distance reaches 〖WT〗155D, 〖WT5《TNR》〗the backward influence scope of the tunnel face gradually reaches 〖WT〗72D. Therefore, a large longitudinal model range is required, and the monitoring section should be outside the forward and backward influence scope of tunnel face, which should be more than 〖WT〗174.5D.

Key words: deepburied long tunnel, excavation of water conveyance tunnel, seepage pore water pressure, influence scope of tunnel face, model longitudinal range