Design of tunnels constructed using pressurized shield methods.

摘要

Pressurized tunnelling methods have reached a satisfactory degree of achievement as they provide a support to all the boundaries of the excavation during the entire construction process. Three methods constitute the main branches of the pressurized tunnelling technology: the compressed air method, the betonite slurry shield method, and the earth pressure balanced shield method.;The applicability of these methods extends over a wide range of construction conditions. Through various site conditions, the objectives of pressurized tunnelling methods are to provide adequate control of the displacement at the ground surface, to maintain the integrity of the excavation boundaries, and to select the lining system adequate for the loading conditions imposed on it.;In general, the control over ground conditions during excavation is achieved through two phases: the stability of the face of the excavation, and the ground control behind the shield. A finite element analysis is carried out to assess the required pressure to be applied at the face for different mechanical properties of the ground. Three-dimensional and axisymmteric schemes are used in the study. The results of the analysis are compared, with satisfactory degree of agreement, with experimental studies, with other similar numerical analyses, and with actual case histories.;The stress-strain field related to the construction process is analyzed using three-dimensional finite element analysis. Along with parameters affecting soil behaviour, two main straining actions are related to the construction process: the grout pressure and the liner pressure. The purpose of the grout pressure is to fill the void behind the tail of the shield. The liner pressure is the longitudinal pressure applied by the shield on the liner as a reaction to the advance of the excavation. While the liner pressure enhances the face stability, high liner pressure may result in an excessive ground movement behind the shield tail.;The results of the two analyses are presented in a generalized form using the framework previously established by Eisenstein-Negro's method of tunnel design. The proposed design method is compared to an actual case history in Edmonton.