Inversion Analysis of Shield Tunnel Load in Composite Strata Based on Field Tests

［Objective］Due to the unclear load pattern, the final internal force design value often deviates from the actual value when a tunnel crosses transverse composite strata. Therefore, it is necessary to study the interaction between the metro shield tunnel segments and the soil in composite strata with soft upper layers and hard lower layers. ［Method］Taking the Liuxiandong Station to Baiwang HKU Station shield tunnel crossing the mixed granite interval on Shenzhen Metro Line 13 as an example, the internal force situation of the main structure is analyzed. Based on the field-measured values after the segment internal force stabilizes, parameters for the inversion analysis are selected, and an optimization objective function is defined. The QPSO (quantum particle swarm optimization) algorithm is used to optimize the load parameters, and the reasonable parameter values and specific loading conditions in the upper-soft and lower-hard strata are obtained through inversion analysis. ［Result & Conclusion］Compared with the values in TB 10003-2016 Code for Design of Railway Tunnels, the load parameters obtained through QPSO algorithm inversion calculation are more suitable for the upper-soft and lower-hard strata. The calculated internal force distribution is more similar to the actual situation, verifying the feasibility and rationality of the proposed analysis method. For composite strata with upper-soft and lower-hard layers, the tunnel overburden load can be calculated using the collapse arch height, and the lateral pressure coefficient of the lower hard rock section should be appropriately amplified for geological survey values.