Analysis of the Deformation Response of Existing Tunnels Induced by Adjacent Surcharge Load

[Objective] Surcharge load easily causes settlement and deformation of the surrounding soil, which may further threaten the safety of the underlying existing tunnel. However, most of the theories in this regard mainly focus on the mechanical equilibrium of the tunnel, neglecting the energy changes in the tunnel system during tunnel deformation. Therefore, it is necessary to start from the perspective of energy, and obtain the theoretical analytical solution to the stress and deformation response of the existing tunnel under adjacent surcharge load through theoretical calculations. [Method] The tunnel deformation theory is introduced. The Boussinesq solution is used to obtain the additional load at the axis of the existing tunnel caused by adjacent surcharge load, and an energy equation of the tunnel under surcharge load is established based on the two-parameter Vlasov foundation model. The stress and deformation response of the existing tunnel is obtained by using the energy variational theory. [Result & Conclusion] The proposed calculation method is compared with the measured data of engineering cases in existing literature, verifying the accuracy of the proposed calculation method. Compared with the calculation results of the Winkler foundation model, the calculation results of the proposed method are closer to the measured data. The results of parameter studies show that an increase in the distance between the tunnel and the center of the surcharge load will cause a decrease in the longitudinal displacement and internal forces of the tunnel; an increase in the surcharge load and the tunnel diameter will lead to an increase in the stress, deformation and bending moment of the tunnel under surcharge load; increasing the elastic modulus of the soil can effectively reduce the impact of adjacent surcharge load on the existing tunnel.