Study on lateral grouting repair of shield tunnel deformation using bamboo fiber-polyurethane cementitious composites

Urban shield tunnels frequently deform due to geological shifts and operational loads. Conventional cement-based grouting materials suffer from brittleness and poor crack resistance in tunnel rehabilitation. This study develops a sustainable bamboo fiber-waterborne polyurethane cementitious composite (BF/WPU) for lateral grouting repair. The optimal composite with 6% WPU improves flexural toughness by 20% and reduces pore fractal dimension by 9%, suppressing microcracks through fiber bridging and interfacial bonding, enhancing microstructural integrity. Scaled model tests quantified the deformation recovery and stress redistribution during BF/WPU grouting. Grouting induced a “vertical ellipse” convergence pattern due to radial stress redistribution caused by BF/WPU from the grouting hole. The tunnel and soil parameters play a crucial regulatory role in the grouting effect of BF/WPU. Arch crown deformation exhibits extreme sensitivity to all parameters, while tunnel diameter has the greatest impact on the hoop deformation of the arch crown, and the 1% change in tunnel diameter results in a 16.32% increase in hoop deformation. The soil water content dominates the longitudinal strain response with a normalized effect size ( NES ) of 29.20. These validate BF/WPU as an efficient grouting material for tunnel deformation repair, and the established parameter-response relationships provide actionable guidance for optimizing grouting practices in urban tunnel rehabilitation.