Document: NUREG-0800
Document ID: 73dc4705-6dff-4f44-87ee-2a6f76cc6536
Document Type: srp
Title: OTHER SEISMIC CATEGORY I STRUCTURES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1319/ML13198A258.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.8.4
CFR Part: 
CFR Title: 

Content:
tial upper bound that would correspond to the walls being pushed into the soil by the overall motion of the structure. However, the magnitude of soil deformations/strains computed from typical seismic SSI analysis indicates that this magnitude is much smaller than what is required to fully develop the maximum passive state. As a result, seismic design practice in the past has been based on methods that assume linear elastic or equivalent-linear elastic soil stresses/strains. It is clear that the true stress/strain state in the soil under seismic conditions is likely to deviate from the inelastic limit states discussed above. Important additional factors to consider are: • Kinematics of the problem. Significant differences in the pressure distribution profile and the stress/strain state in the soil could occur depending on whether the embedded walls are assumed rigid or flexible, whether the base of the walls are allowed to rotate or slide relative to the soil, whether the structure is supported on stiff or flexible soil, and whether the overall motion of the structure includes a significant rocking component or not. 3.8.4-40 Revision 4 – September 2013 • Heterogeneity of the soil mass. An additional complication occurs if there is significant difference in stiffness between different backfill and in situ soil layers, and especially if the structure is partially embedded in rock. In the latter case, a large stress discontinuity is expected in the interface region between soil and rock. • In typical NPP configurations, linear or equivalent-linear strains would tend to produce conservative estimates of pressures; however, there may be specific configurations for which the opposite occurs. • Separation of the soil from the wall. • Structure-soil-structure interactions between structures. • Effects of groundwater on static and dynamic soil pressure. Field measurements and experimental investigations confirm the wide variation in soil pressures depending on