Seismic Design of Tunnels - Parsons Brinckerhoff

frame analysis models shown in Figures 38A and 38B are considered to comprise an
adequate and reasonable design approach to the complex problem.
5.7 Summary of Racking Design Approaches
In summary, four different approaches to analyzing the seismic racking effect on twodimensional
cut-and-cover tunnel section have been presented in this chapter. Table 7
summarizes the advantages, disadvantages and applicability of these four approaches.
Based on the comparisons made in Table 7, it can be concluded that:
• The simplified frame analysis procedure recommended in Section 5.6 should be used
in most cases.
• The complex soil-structure interaction finite-element analysis is warranted only when
highly variable ground conditions exist at the site and other methods using
conservative assumptions would yield results that are too conservative.
• The dynamic earth pressure methods (e.g., the Mononobe-Okabe method) should be
used to double check the structure’s capacity for tunnels with small soil burial and
with soil-structure characteristics similar to those of aboveground retaining structures
(e.g., a depressed U-section).
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