Short-Distance Undercrossing of Shield Tunneling on Existent Tunnel in Soft Soil Area

Abstract

In urban environment, short-distance undercrossing of shield tunneling to an existent tunnel is an unloading process and can cause adverse effect on the existent tunnel. This kind of effect should be controlled. To analysis and control this effect, numerical simulation, field monitoring and optimization of construction parameter are used. To get reasonable calculation parameters for numerical models, field monitoring is conducted. The numerical simulation is utilized to study the process of short-distance undercrossing. The simulation result revealed that the deformation of the existent tunnel can be beyond the tolerable value unless some measure is adopted, but the deformation can be reduced significantly by improving the ground under the existent tunnel with cement deep mixing method. Construction measures are adopted, such as the strict controlling of synchronized grouting, secondary grouting, rotation speed of cutter head and driving speed. As a result, the deformation of the existent tunnel is controlled in the tolerable value.