Reliability Analysis of Shield Tunnel in Twolayered Ground

Abstract eng:
Both physical modeling and analytical studies have shown that the non-homogeneous ground has a significant impact on the magnitude and distribution of lining stress. Besides, the uncertainty in the soil parameters has further complicated the structure properties. In this paper, this impact was assessed based on the reliability analysis using an analytical model for non-homogeneous ground. The non-homogeneous ground was represented by two-layers here. The cohesions c, friction angles φ and the modulus of subgrade reaction k were selected as the random variables because of their sensitivity and uncertainty to the tunnel design. Besides, the interface of the two layers also randomly located. Monte-Carlo simulation was adopted to evaluate the reliability of maximum of positive, negative bending moment. Then the reliability was compared between the homogeneous and two-layered ground conditions considering the influence of the correlation of the parameters. It indicated that using the equivalent homogeneous model can underestimate the reliability of the maximum positive bending moment, however, overestimate the reliability of the maximum negative bending moment. The impact of the relative modulus of subgrade reaction and the spatial correlation of these two ks were further discussed. It was shown that the reliability of positive moment would increase with the relative k. On the other hand, the negative bending moment would have a peak reliability index and then would drop as the relative k increases. But the spatial correlation of the two formations had little influence on the structure properties.

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