Parameter identification of concrete lining for a subway tunnel

The key factor in filling the gap between the real and predicted behaviour of structures is the use of field measurements not only to monitor the stability of structures, but also to re-evaluate the input data of the parameters used in the numerical analysis. Based on this re-evaluation of the input data, the original model is continuously modified to achieve minimum discrepancy between the behaviour of the model and the real structure. This can be done by using the back analysis procedures. Till now most of the researchers concentrate on the parameter identification of the soil constants only and consider the constants of the supporting elements (concrete or shotcrete) as fixed known values although the true constants of the supporting elements may be different than their assumed values. In a previous paper, the parameter identification of the concrete constants has been done and checked with some theoretical examples. In this study, the parameter identification of the constants of the tunnel concrete lining had been achieved. A two-dimensional element, called BEAM 6 element, is used to simulate the tunnel concrete lining while another element, called, LST element (Linearly Varying Strain Triangular element), is used to simulate the surrounding soil. The back analysis was done based on the dual boundary control method. The parameter identification has been applied on two real tunnels. The first application has been done for the soil constants only while the identification of the constants of the tunnel shotcrete lining simultaneously with the soil parameters had been applied on the second tunnel. Although more than one region of concrete are used, the parameters of the concrete lining have been identified simultaneously with the soil parameters. The obtained displacements are compared with the measured ones and the obtained results have been discussed. The main points can be summarized as: Although only parts of the measurements were used, satisfactory results were obtained at most measuring points. The calculated curve of displacements matches the measured curve very well, except for the lower region of measurements and some points in the middle part. The difference between the measured and the calculated displacements for the lower region may be due to unknown loading conditions of air pressure and water level. Another reason of this difference may be due to the accuracy of the sliding micrometers in this region because the measurements are very small. The forces of shotcrete lining in cases of identification of shotcrete parameters simultaneously with the soil parameters are higher than those in cases of identification of soil parameters with fixed shotcrete parameters. Therefore, it is preferable to identify the shotcrete parameters simultaneously with the soil parameters to ensure the safety in tunnelling process. Although the tunnel is still safe, the predicted factor of safety is reduced. Hence, the back analysis helps in making a reliable assessment of tunnelling safety. The identification of soil parameters only and considering the shotcrete parameters as constant parameters gives displacements far from the observed displacements while the identification of all soil layers simultaneously with the shotcrete parameters has a big effect on the calculated displacements. This application can be considered as a successful application of the parameter identification of shotcrete lining although the poor available measurements data. (A). "Reprinted with permission from Elsevier". For the covering abstract see ITRD E124500.

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  • Authors:
    • SWOBODA, G
    • MANSOUR, M H
    • ABD EL SHAFY, A G
  • Publication Date: 2004-7

Language

  • English

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Filing Info

  • Accession Number: 01011678
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Dec 19 2005 3:24PM