Dynamic analysis of urban circular tunnels and the influences of infrastructure factors on their behavior

Circular Tunnels are used in urban transportation these days. One of the major applicable is metro tunnel which is built by T. B. M. an investigation of these structures during an earthquake should be considered in design of these structures.

for studying on dynamic behavior of tunnel under earthquake motion، PLAXIS software which is based on finite element code is used. In this study، the method of seismic analysis of tunnel with PLAXIS is explained. For more accuracy the data are used based on Tabriz tunnel properties. The dynamic properties of soil and also the method of iterative process for finding acceptable shear strain are obtained from previous study and also result of some dynamic tests. Numerical analyses are performed in both linear and Mohr-Culomb model for soil. Approaches: In order to investigation the effect of tunnel on earthquake motion، the diametric deflection of final lining is calculated on each analysis. The major forces such as bending moments and axial forces are happen in maximum deflection in diameter. For finding the effective parameter on dynamic behavior of tunnel، sensitive analyses are performed. In these analysis variation of dynamic parameter such as maximum acceleration، damping and shear modulus of soil are mentioned. Moreover، other mechanical properties of medium like friction angel of soil are selected for sensitive analysis. Geometrical properties of final lining such as thickness and diameter of lining are also used to calculate the flexibility ratio. Allowable stress and strain is also calculated and compare with existence result.

the results show that stress and strain are not different on acceleration blow 0. 5g but the different in result are more mentioned for acceleration more than 0. 5g. In addition on sensitive analysis in friction angle of soil، the rate of dynamic forces is decrees up to 30 degree and after that، the results showing no variation. These effects are more significant for tunnel with high depth. Investigation on variation of dynamic results versus fallibility ration show that with increasing this ratio، the rate of degradation of dynamic forces are decrees and in F=25 and for more، these variation is disappear and the results are independent of diameter of tunnel.