A New Procedure for Calculation of Ground Response Curve of a Circular Tunnel Considering the Influence of Young’s Modulus Variation and the Plastic Weight Loading

In this paper, an analytical–numerical solution is presented for a circular tunnel in the hydrostatic condition using a generalized nonlinear Hoek–Brown failure criterion. To a deep insight into the problem, the influence of the plastic zone weight, and the Young's modulus on the ground response curve of a deep tunnel in a strain-softening media is highlighted. Experimental results show that the magnitude of the confined stress can have a direct effect on the critical softening parameter. Thus, a variable critical softening parameter is also assumed. That is, as the radial stress magnitude increases, the critical softening parameter is enhanced. The equations are derived for different directions (e.g. crown, floor, and sidewall) around the circular tunnel. The accuracy of the proposed method is validated by some examples. The results show that assuming a constant Young's modulus in the plastic zone imposes a significant error in the predicting of the tunnel convergence.