Document: NUREG-0800
Document ID: 73747cf4-ff95-449b-b6b0-53dc0755b9e0
Document Type: srp
Title: OTHER SEISMIC CATEGORY I STRUCTURES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1235/ML12353A382.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.8.4
CFR Part: 
CFR Title: 

Content:
The governing pressures of the three methods should be considered in the design. The governing pressures should also be determined based on the pressure distribution that generates the maximum member forces used for design of the foundation walls. The first two methods are based on linear or equivalent-linear elastic assumptions, while the third method is based on the passive pressure and accounts for inelastic strains, albeit in a simplified manner. A clarification is also made relative to the passive pressure; the intent is to ensure that all or part of the passive pressure is incorporated in the design regardless of whether the maximum passive state condition has been reached in the soil (as indicated above, the latter is rarely the case for embedded walls in NPP structures). The displacement-dependent fraction of the passive pressure that is effectively mobilized can be determined from nonlinear FEM computations or from experimental results. The proposed enhancement also emphasizes the review of the analysis assumptions. This is important because soil pressures can vary substantially depending on the different factors identified above. Conservative assumptions are thus critical. The second method has been added to the SRP in light of recent NPP designs, in which seismic soil pressures have been computed using an embedded SSI/FEM analysis model. This is a general approach that is appropriate under the linear elastic or equivalent-linear elastic strain assumption and may address some of the issues discussed above. However, a careful review is still needed to ensure the validity of the modeling for this type of application. For example, the computed pressures may be overestimated in the upper soil layers near the surface. Also, the strain iterated soil profiles utilized in typical SSI analysis may not be consistent with the range of strains expected in the backfill soil adjacent to the walls. 3.8.4-41 Draft Revision 4 – December 2012 Best estimate, lower bound,