Document: NUREG-0800
Document ID: 8160c1fd-7cef-4c93-8e12-456019f2cfd2
Document Type: srp
Title: FOUNDATIONS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML1319/ML13198A267.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.8.5
CFR Part: 
CFR Title: 

Content:
e construction sequence of the mat foundation and walls, as well as the potential for loss of subgrade contact (e.g., because of loss of cement from a mud mat) that may lead to a differential pressure distribution on the mat. K. An essential aspect of the design and analysis procedures for seismic Category I foundations is the stiffness modeling of the soil material under and to the sides of the structures. Soil stiffness can be represented by means of analytical or 3.8.5-12 Revision 4 – September 2013 numerical (e.g., solid finite elements, distributed springs) formulations that are appropriate for the loading conditions as well as for the soil type, foundation type and size, and time scale being considered. In the case of seismic dynamic loads, the soil stiffness parameters should be consistent with the magnitude of soil strains assumed in the SSI analysis described in SRP Section 3.7.2, which are associated with the relatively short time scale of the seismic input. The distribution of toe bearing pressures used in foundation design should be consistent with the distribution of toe bearing pressures obtained from the SSI analysis. In the case of gravity loads and basemat foundations, the soil stiffness parameters should be consistent with: (a) dishing or Boussinesq effects (if uncoupled distributed springs are used then it may be necessary for the stiffness to be increased at the edges and reduced at the center of the basemat footprint); (b) basemat size (subgrade modulus could be highly dependent on basemat dimensions); (c) time scale of the loads (i.e., short term construction loads vs. long term loads present throughout the life of the structure); and (d) soil type (i.e., granular vs. cohesive soils). Appropriate stiffness parameters are particularly important when evaluating loads induced by the construction process and by differential settlements, as described in items E and J above. Additional guidance to consider in the review of DC and COL applications