Investigation on tunnel stability considering pipe‐roof support with transparent soil technology

Pipe‐roof support serves as a critical prereinforcement technique for ensuring face stability and controlling surface settlement in shallow tunneling through soft ground. However, existing numerical simulations and monitoring techniques often fail to adequately capture the complex three‐dimensional internal response of pipe‐roof‐reinforced soil. Capturing this internal behavior is essential for elucidating the invisible failure mechanisms and the spatial interaction between the support structure and the surrounding soil. To address this limitation, this study develops an integrated research framework utilizing fused quartz sand and pore fluid with matching refractive indices to synthesize transparent soil. A reduced‐scale shield tunneling model test was conducted, combining digital image correlation, 3D reconstruction algorithms, and comparative finite element analysis. This framework enables full‐field visualization and quantitative analysis of pipe‐soil interaction mechanisms under varying burial depths. The results reveal that face instability follows a deformation evolution pattern characterized by distinct zones and stages. The strengthening effect of pipe‐roof in tunneling is attributed to the “soil‐arching barrier effect,” as the pipe‐roof would restrain failure wedge development by extending the stress transfer path. Unlike previous studies, this work captures the spatial characteristics of the deformation field and provides direct visual evidence of the support mechanism. These findings hold significant implications for safe construction practices in urban tunneling.