Development and demonstration of prototype test platform for shield tunnel linings under complex loading scenarios

During the entire life cycle of shield tunnel structures, there will always be various complex loading scenarios, including asymmetric and unfavorable conditions like grouting, eccentric loading, or rolling. The prototype structural tests are the most effective means to verify the applicability of the structures under such scenarios. However, the existing prototype tests predominantly focus on the mechanical behavior of tunnel structures under simple symmetric loading, while complex asymmetric loading scenarios are rarely addressed. To expand the application of the prototype tests, a prototype test platform suitable for the tunnel structures with any cross-sections is established. Additionally, a corresponding test load design method simulating the complex scenarios is also proposed, which is applicable to loading systems with any arrangement of loading points and hydraulic stations. To demonstrate the effectiveness of the test platform, the Quasi-rectangular tunnel, DOT (double circular) tunnel, and circular tunnel under the eccentric loading scenario are taken as examples. Further analysis of key test parameters reveals that the weight coefficients of control targets can be adjusted to meet different simulation requirements. The proposed test load design method allows for iterative modifications, effectively considering the nonlinearity of the model or boundary support conditions. By combining the hoop strand with the hydraulic jacks in the loading mode, the fitting error level can be reduced to 1/5 compared to the jacks-only loading mode, where some loading points need to be cancelled to make the design test load reasonable and applicable. For the accurate simulation of structural behavior under different loading scenarios, the structures with greater complexity and loading scenarios require a higher number of independent loading groups and more stringent requirements for the test platform.