Study on Design Properties of Segmental Lining by 3DFEM Model
Analysis methods for shield tunnel lining design can be classified to beam-spring model and continuum model. The beam-spring model has the advantage in calculating the force acting on the lining reasonably. However, this model cannot take account of the stress redistribution due to ground and cannot calculate the ground surface settlement. On the other hand, continuum model has the advantage in calculating the ground surface settlement and being adopted to a three-dimensional analysis, which has a problem that the results depend on stress release ratio and analysis region. In previous study, a three-dimensional continuum FEM model including ground model had been developed, and the validity of the analysis model was confirmed by parameter studies.
In FEM model, constant on the characteristics of ground deformation is Young°«s modulus of the ground Es. On the other hand, in beam-spring model, that is coefficient of ground reaction k. Currently, for the conversion of the two constants, some experience formula has been used. However, their reliability is not high. Then this study aims to derive a conversion formula so that displacement and sectional force by FEM model and beam-spring model coincide. Then the followings are carried out:
1) The conversion formula between Es and k was derived for stiff ground so that the oblateness of lining by the both models coincides;
2) A correction formula of the above conversion formula at soft ground was derived, based on the same concept; and
3) The validity of the conversion formula was examined using the normalized bending moment by tunnel radius.
As a result, we found the followings:
1) The proposed conversion formula derived in this study can make the deformation and sectional force of the lining by the both models agree more, compared with the empirical formula; and
2) The proposed conversion formula can provide the bending moment obtained by beam-spring model at safety side.
As a future research, it is recommended to apply this model to NATM, and to validate the FEM model by comparing with the site data.
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