Deformation evolution characterization of shallow-buried asymmetrically loaded twin-arch tunnels under long-term rainfall

Abstract

The rapid development of global transportation infrastructure has led to increasing applications of large-span shallow-buried tunnels in complex geological conditions. Shallow-buried twin-arch tunnels with asymmetric overburden are prone to deformation and instability under long-term rainfall, particularly in soft clayey strata. This study investigates the rainfall-induced deformation behavior of such tunnels through a combined physical modeling and numerical simulation approach, based on the Wulongshan Tunnel in Nanjing. Results show that rainfall primarily affects shallow slopes within the first 3 d, with delayed seepage responses and infiltration depths up to twice the tunnel diameter. Under sustained torrential rainfall, crown settlement increases by 50% compared to dry conditions, while surface deformation exceeds twice the dry-state value and surpasses crown settlement. A coupled seepage–deformation model incorporating strength softening captures a “slow–rapid–slow” settlement pattern with increasing rainfall and highlights elevated deep-seated sliding risk under extreme conditions. The findings clarify the deformation mechanisms of twin-arch tunnels under rainfall and provide a basis for support design, construction timing, and risk control in similar geotechnical environments.

Graphical abstract

Keywords

deformation evolution / physical model test / twin-arch tunnel / silty clay / shallow-buried asymmetrical loading

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