3-Dimensional Structural Modelling of Segmental Tunnel Lining Using Finite Element Software > 기술자료실

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3-Dimensional Structural Modelling of Segmental Tunnel Lining Using Finite Element Software

R. Mahajan (rmahajan@pb.com.au) 

Parsons Brinckerhoff, Sydney 

ABSTRACT 

Closed-face shielded TBM driven tunnels are supported using precast concrete segmental linings. In the past these types of lining have been assessed without consideration being given to the coupling action along circumferential joints of adjacent rings or the true behaviour of joints along longitudinal joints, especially where these have a taper. The mechanical and geometrical characteristics of these joints strongly affect the structural behaviour of tunnel lining. The current practice is to use closed form solutions or adopt two-dimensional ‘beam-spring’ modelling techniques to assess the structural behaviour of segmental linings when loaded. However, it can be argued that this simple two-dimensional approach do not fully take account of the coupling action or joint behaviour and so will not provide accurate results. Particularly with respect to: the structural behaviour of the tunnel lining in longitudinal direction; the deformation of the lining due to the rotation along longitudinal joints; and the relative displacement in the circumferential joints. 

It is suggested that a more comprehensive three dimensional finite element method (FEM) is required to more accurately explore the coupling action and joint behaviour. The paper aims to show how the behaviour of the rings and joints can be modelled in an appropriate way. The paper describes an  approach that uses the Strand7 structural software to develop a three dimensional model. A description is given of how loading assumptions have been derived. Comparisons are made with the results from traditional two-dimensional beam spring models. 

1. Introduction 

The behaviour of a segmental tunnel lining under applied loading is very different to that of a monolithic cast-in-place concrete lining. For precast segments, the stiffness and resistance to deformation of rings depends on many factors. These factors include: the number of segments in each ring; anticipated joints rotation under load; the joint profile; the amount of force applied between segments in each ring; the quality of the ring build geometry; and the interaction between the relative rings. 

The squatting of precast rings under load is generally a consequence of non-uniform applied ground pressures, where vertical applied pressures are either greater or less than horizontal pressures. This imbalance will cause rings to deform. Depending of the ring rotation of adjacent rings and the staggering of joints, this relative deformation may differ. This change in deformation profile will have an impact on the imposed structural actions on each ring. Relative ring behaviour is to a large degree dictated by the behaviour of joints, as the segments rotate about these points. Where longitudinal joints are tapered this rotation is complex and requires special attention, given the tendency for local torsional stresses to develop. Therefore, the behaviour of the joints needs to be considered in the design of the segments and in this paper it is shown how these joints can be modelled by using a three dimensional FEM approach.