Deformation characteristics and support force determination method during shield tunnelling near through river channels

The construction of shield tunnelling under river channels at short range faces risks of excavation face instability and stratum settlement. This paper systematically investigates the influence of river channel geometric parameters on stratum deformation and face stability, combining theoretical derivation with laboratory model tests. A parameterized formula considering slope ratio and depth is established to transform non-uniform overlying-soil loads. Based on a three-dimensional wedge instability model, a calculation method is proposed to dynamically update the ultimate support force according to tunnelling distance. The response relationship of support force to river channel parameters, geotechnical parameters and tunnel dimensions is analyzed. Model tests were conducted to monitor surface, subsurface and river channel settlement of different sections, as well as earth pressure. Results show that settlement above the shield axis is greatest, followed by the river slope. The settlement disturbance range increases with tunnelling distance. The support force exhibits phased variation: earth pressure rises as the cutterhead approaches, then decreases after passage due to stress release. This research provides theoretical and experimental support for optimizing support force and stability control during shield tunnelling under river channels.