Investigation On The Response And Control Index Of Existing River-crossing Tunnel Due To Subway Shield Tunneling Above Or Below

With the development and utilization of underground space in Shanghai, more and more subway tunnels are inevitably constructed adjacent to existing infrastructures. As a typical case, this study considers a scenario, in which a new subway shield tunnel is perpendicularly constructed over or underneath a river-crossing tunnel. A centrifuge model test, numerical analysis and theoretical analysis were carried out to investigate the response of the river-crossing tunnel due to tunneling above or below. Furthermore, values of governing indexes of river-crossing tunnels with longitudinal uneven displacement were assessed. The gist and primary new findings of this dissertation include:1) The construction process of the new shield tunnel, which is just over the river-crossing tunnel, was simulated by the centrifuge model test. Moreover, the rebound displacement and the longitudinal stress of the river-crossing tunnel, as well as the pore water pressure at its spring line, were measured. Furthermore, the changes of the rebound displacement and the longitudinal internal force of the river-crossing tunnel along with the increases in ground loss ratio and grouting ratio during the construction process of the new shield tunnel were quantitatively investigated. Test results show that: i) the rebound displacement and the longitudinal stress of the river-crossing tunnel increase as excavation of the new tunnel occurs, while they decrease as grouting of the new tunnel occurs; ii) the rebound displacement and the longitudinal stress exhibit an approximately linear change with increases in ground loss ratio and grouting ratio of the new shield tunnel; iii) the heave zone of the river-crossing tunnel is within the horizontal offset of 3 D(D represents the diameter of the river-crossing tunnel) from the axis of the new shield tunnel; iv) the variation in pore water pressure of the soil around the river-crossing tunnel is low during the construction process of the new shield tunnel.2) The validity of the numerical analysis was verified by the centrifuge test data, and then, parametric study was conducted by finite element method. Special attention was paid to the influences of longitudinal bending stiffness of the river-crossing tunnel, vertical clearance between the two tunnels, and Young’s modulus of the soil on the vertical displacement and the curvature radius of the river-crossing tunnel. Results show that: i) the maximum rebound displacement decreases and the minimum curvature radius increases with the increases of the three aforementioned influential parameters; ii) for the rebound displacement, the influence scope induced by the change of Young’s modulus of the soil is comparatively wider than that induced by the change of longitudinal bending stiffness of the river-crossing tunnel and the change of vertical clearance between two tunnels; iii) the rebound displacement is more sensitive to Young’s modulus of the soil, while the curvature radius is more sensitive to longitudinal bending stiffness of the river-crossing tunnel.3) By modeling the river-crossing tunnel as a Timoshenko beam resting on a Winkler foundation, the governing differential equation for the response of the river-crossing tunnel due to tunneling beneath was derived, and the analytical solution for the governing differential equation was presented. The validity of the analytical solution is verified by a centrifuge test, and the merit of this analytical method is confirmed by comparison with the conventional Euler-Bernoulli beam model. Then, parametric study was conducted. Results show that: i) the settlement based on the Timoshenko model is greater than that based on the Euler-Bernoulli model; ii) the proposed Timoshenko beam solution can degrade into the Euler-Bernoulli beam solution by ignoring the effect of shear deformation on the total deflection of the river-crossing tunnel; iii) the relative settlement and the relative longitudinal bending moment of the river-crossing tunnel decrease along with the increase of relative tunnel-soil stiffness.4) Based on an equivalent continuous model, the longitudinal curvature radii of river-crossing tunnels with uneven displacements caused by longitudinal bending were studied. Moreover, for the uneven displacements of river-crossing tunnels caused by transverse dislocations, the relative bending of river-crossing tunnels was studied. Results show that: i) when longitudinal curvature radii are equal, the crack width of a river-crossing tunnel segment joint is bigger than that of a subway tunnel segment joint; ii) under the condition of a same crack width, the longitudinal curvature radius of a river-crossing tunnel approximately linearly increases with the increase of its diameter; iii) when the values of relative bending are equal, the dislocation amount of a river-crossing tunnel is 1.5 to 2 times as large as that of a subway tunnel; iv) compared with subway tunnels, larger longitudinal curvature radius and smaller relative bending are suitable values to confine longitudinal uneven displacements of river-crossing tunnels.