Abstract: To investigate the impact of riverbed scouring and silting on the long-term service performance of underwater shield tunnels, the authors analyze the transverse and longitudinal relationships among historical riverbed elevation changes, water level variations, and tunnel structural responses. The analysis is based on measured data collation and numerical simulations using operational monitoring data from a Yangtze river-crossing tunnel. The main findings are as follows: (1) Overburden thickness is the critical factor influencing structural responses during riverbed scouring and silting, significantly affecting settlement trends of tunnel cross-sections. (2) Segment joint deformations exhibit distinct positive and negative correlations with overburden thickness and water level, respectively. Longitudinal joint dislocations are particularly sensitive to uneven scouring and silting along the tunnel axis. (3) Numerical simulations at a specific cross-section on the river′s right line show that the regression coefficients of joint deformation with water level and overburden thickness range from －0.000 4 to －0.004 mm/m and 0.003 to 0.03 mm/m, respectively, indicating that scouring and silting exert insufficient disturbance on tunnel joints to directly compromise waterproofing performance. (4) Changes in overburden thickness significantly alter the soil pressure distribution around the tunnel, with regression coefficients of joint deformation with riverbed elevation notably exceeding those associated with water level variation.

Key words: riverbed scouring and silting, underwater large-diameter shield tunnel in operational period, joint deformation, monitoring, numerical simulation