Multistage regulation strategy as a tool to control the vertical displacement of railway tracks placed over the building site of two overlapped shield tunnels

摘要

Constructing a tunnel by means of an Earth Pressure-Balanced Machine (EPBM) requires an appropriate definition of the relevant variables to minimize the environmental impact. Because of the complexities and uncertainties of underground engineering, however, the values of the EPBM variables assumed in the design stage are often inappropriate, and adjustments are required based onin situobservations. In this paper, the Multistage Regulation Strategy is applied to the displacement control during the construction of two overlapped tunnels in Tianjin Metro line 5 underneath a pre-existing railway line, and the EPBM variables are continuously adjusted based on works in progress. The core of the Multistage Regulation Strategy is the so-called target decomposition (as each tunnelling stage requires its control target), which is accomplished based on the tunnelling work at a nearby site (test zone, beside the railway line), whose instrumentation is presented in detail. By rigorously applying MRS, the surface settlements along the railway line passing over the two metro tunnels can be successfully controlled through a step-by-step adjustment of EPBM variables, and the requirements concerning the accumulated surface settlements specified by the current design standards can easily be fulfilled.