Settlement of an Existing Tunnel Induced by Crossing Shield Tunneling Involving Residual Jacking Force

An analytical formulation involving residual force is proposed to predict the displacement of an existing structure by simplifying the tunnel as an infinite Euler-Bernoulli beam resting on a two-parameter Pasternak foundation. The feasibility is confirmed by two actual measurements at sites in the published literature. Parametric studies-including consideration of jacking force alone, jacking force and ground loss, and jacking force and equivalent bending stiffness-are carried out to study the influence on the deformation of the existing tunnel. The results show that the residual jacking force can decrease the settlement of the existing tunnel, but the significance of its effect varies under different engineering conditions. With the increase in ground loss, the beneficial effect of jacking force in preventing further aggravation of tunnel settlement gradually becomes obvious, and the jacking force can reduce the deformation more effectively when the tunnel has lower bending stiffness. As a result, it is recommended that some effective measures should be adopted to maintain sufficient residual jacking force in the segments, so as to prolong the life of the tunnel.