Rethinking tunnel-soil relative stiffness: insights from interactions between tunnels and strata subjected to ground surcharge

The stiffness difference between tunnels and surrounding strata can lead to relative deformations when subjected to factors such as ground surcharge, significantly influencing the earth pressure on tunnel linings. To address this, the concept of tunnel-soil relative stiffness has been introduced to evaluate these pressures. Existing methods, however, often treat tunnels and surrounding strata as independent entities, thus overlooking their complex interactions. Drawing insights from a recorded experiment, this paper redefines tunnel-soil relative stiffness, now conceptualized as the ratio of natural ground deformation to tunnel deformation subsequent to their interactions. Based on this definition, an analytical formula is derived to calculate the defined relative stiffness. A numerical case study is subsequently conducted to verify and evaluate the effectiveness of the proposed methods. It is found that traditional methods lead to a notable underestimation of tunnel-soil relative stiffness and consequently, the earth pressures on the tunnel linings; in contrast, the proposed method exhibits relatively better accuracy. The intrinsic physical reasons for the enhanced accuracy of the proposed method are discussed. Finally, leveraging the proposed method, insights on enhancing the load-bearing performance of tunnel linings in soft soils are presented, which may provide a valuable reference for the design and maintenance of tunnel linings in soft soil regions. © 2025 Informa UK Limited, trading as Taylor & Francis Group.