Study of longitudinal deformation of existing tunnel due to above excavation unloading

The effect of above deep excavation on existing tunnel is of great concern because the excavation unloading can induce longitudinal deformation of existing tunnels. A prediction model based on the method of beam on Kerr elastic foundation is proposed. The existing tunnel is simplified as Euler-Bernoulli beam and Timoshenko beam, respectively, to consider the effect of the tunnel shear stiffness on the longitudinal uplift caused by the above excavation. The impact of unloading on the existing tunnel can be obtained based on the Mindlin Solution. The effect of tunnel shear stiffness on the longitudinal uplift of existing tunnel cause by above excavation is investigated. The results of Timoshenko beam are consistent with those of Euler-Bernoulli beam when the tunnel shear stiffness is big enough. The effect of tunnel shear stiffness is very significant when the equivalent shear stiffness ratio is less than 1/4. Based on the proposed method, cement-soil effective coefficient of unloading is proved to be 0.22 through the measured data analysis. The ribbon-unloading method of rapid excavation and equivalent load quickly is assuming to be equal to the accumulation of relatively independent excavation. The proposed method is finally validated using the field monitoring in Zhengzhou.