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EVALUATION OF CONFINEMENT CHANGES AROUND SHIELD TUNNELS CONSTRUCTED IN LIQUEFIABLE SOIL

The liqnefaction phenomenon is the cause of many effects on underground structures constructed at shallow depth. The shield tunnels of subways arid underground routes are the most common types of these structures. Oue of the main effects of soil liquefaction around these kinds of structure is the variation of confinement, which occurs during earthquake loadings. In this paper, the changes in the circumferential condition of a shield tunnel, due to liqnefaction, are presented. In this study, the influence of changes in shield forces and the uplifting of the tunnel due to liquefactiou are investigated, using an appropriate model for soil liquefaction. For this reason, the FLAC package, which is capable of undertaking this type of modeling, is used. These are two main parts in this paper. In the first part, a reference model is defined and the ways of evaluating the influences of soil liquefaction are discussed. In the second part, the induced forces in the tunnel shield, due to liquefaction, are estimated, considering the appropriate changes in the circumferential condition of the tunnel. Research has been carried out on the assessment of the effect of different parameters on the variation of forces and the deformation of the lining.