Field instrumentation of ground responses during tunnel excavation plays a most important role in the so called New Austrian Tunnelling Method(NATM). With the tunnelling method, field measurement data are continuously fed back into the tunnel design and field construction operation as tunnelling proceeds.
An extensive program of tunnel instrumentation has been implemented in the construction of the Seoul Subway Line 3 and 4, in which the NATM has been adopted as a main tunnelling technique. Particularly, the downtown section of the subway has been heavily instrumented to ensure the safety during tunnel construction and the proper performance of tunnel during subway operation. The instrumentation includes measurements of surface settlement, crown settlement, ground deformation around tunnel, convergency and shotcrete stresses, etc.
This thesis describes the instrumentation program implemented throughout the construction of the Seoul subway system, and presents the results from the field measurement. Among more than ten instrumented sections in the downtown area, five representative test sections were selected for analysis in this study, with emphasis on the surface settlement and the crown settlement.
Both transverse distributions and longitudinal profiles of the settlement were analysed using the Gaussian probability curve and error function to achieve empirical rationality in assessing the effects of each parameters influencing the settlement. The analysis indicate that the governing factors of ground settlement during tunnel construction can be largely grouped into three categories such as ground conditions, tunnel geometry and construction conditions.
The variations of the settlement with these governing factors are described in this study. Subsequently possible mechanisms for ground deformation occurring at different stages of tunnel construction are formulated based on a overall interpretation of the field observations and analyzed data. Finally this thesis summaries the measurement results from a view point of their practical application to design, construction control and field instrumentation of tunnel.
