Assessment of retaining system in bored tunnels lining with finite element method

One of the most important problems in tunnel analysis and design is the deformations established in tunnel linings. So tunnels type, kind of linings and retaining systems and alsotechnique of tunnel excavation will have important effects on deformation of tunnel lining. In these days one of the conventional methods of tunnel drilling is excavation with the use of T.B.M boring machines. Nowadays, because of better efficiency and more advantages, thisdrilling method is considered preferable to others; most urban tunnels in different countries of the world are built in this way. One of the advantages of these machines is they establish the tunnel retention system simultaneously. In this method, tunnel retention is accomplished byconcrete prefabricated parts (segments). These parts are erected simultaneous with drilling and progress in the tunnel, and they are installed by the machine itself. The considerable point about these parts is the method of connection between them; since resistance rates betweenthese parts has a considerable effect in creating deformations and forces in tunnel lining. This essay evaluates the modeling of tunnels and segments considering restraint conditions, andpresents the most desired connection-state between segments. For this purpose, at first two tunnels are modeled simultaneously and the restraint conditions between the segments of these tunnels are evaluated. Therefore, a complete hinge state and a complete restrained state are considered between segments and these states are analyzed and compared. Then, other models with different restraints are modeled between two hinge and restrained states and the restraint conditions between these segments are evaluated. According to the obtained results, it seems that created deformations and forces in the tunnel lining are influenced by the restraint between segments and this factor can be considered as a determinative parameter in the design.

Keywords:

tunnel , retention system , segment , restraint , hinged connection