Investigation on earth pressure on urban NATM tunnels

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A nonlinear finite element analysis procedure was proposed for modeling a deformational behavior, which is unique to tunnels with shallow depth. An objective was to point out the importance of modeling a nonline ar nature of the deformational mechanism for obtaining a better understanding of design load on tunnel linings and its relation to kinematics of the surrounding ground. The results obtained showed that modeling of a ground behavior, which is essentially of nonlinear nature, by an elastic or elastic-perfectly plastic approach, leads to incorrect understanding of the deformational mechanism. The proposed approach produced strain distribution, deformational mechanism, surface settlement profile, ground reaction curve, which were in good agreement with the results of the model test. Use of the proposed approach would enable a better understanding of deformational characteristics of the ground medium not only in identifying local plastic zones, but also in revealing kinematics of movement of blocks formed between slip planes, or shear bands. This make s a good starting point for optimizing ground support for reducing surface settlement, considering a particular nature of the deformational mechanism of shallow tunnels.