Document: NRC Regulatory Guide
Document ID: a094549d-8685-4dad-b90f-c28c7d279a53
Document Type: regulatory_guide
Title: Geologic and Geotechnical Site Characterization Investigations for Nuclear Power Plants + HISTORY – HISTORY 08/2021 – DG-1392 , Proposed Revision 3 07/2014 – Periodic Review of Revision 2 – Reviewed with no issues identified 02/2001 – DG-1101 , Proposed Revision 2 (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2119/ML21194A176.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.132
CFR Part: 
CFR Title: 

Content:
this guide reproduces a table from NUREG/CR-5738 showing widely used techniques for subsurface investigations and describing the applicability and limitations of the techniques. Appendix D to this RG contains general guidelines for spacing and depth of borings. 4.4.1 Spacing and Depth Spacing, depth, and the number of borings for safety-related structures should be chosen and justified based on foundation requirements and the complexity of anticipated subsurface conditions. Appendix D provides general guidelines on this topic. Spacing of borings for a deeply embedded structure with smaller foundation dimensions should be reduced, and additional boreholes should be located outside the foundation footprint to obtain detailed geologic and geotechnical information about the surrounding materials. This information will provide pertinent data for the analysis of soil-structure interactions and determination of lateral earth pressures. Uniform subsurface conditions permit the maximum spacing of borings in a regular grid for adequate definition of those conditions. Subsurface conditions can be considered uniform if the geologic characteristics and features to be defined can be correlated from one boring location to the next with relatively smooth variations in thicknesses and properties of the geologic units. An occasional anomaly or a limited number of unexpected lateral variations might occur. If subsurface conditions are not uniform, a regular grid might not provide the most effective distribution of boreholes. Soil deposits or rock units could be encountered in which the geologic characteristics are so complex that only the major rock unit contacts are correlated. Material types and properties might also vary within major geologic units in an apparently random manner from one boring to another. The number and distribution of borings needed for such nonuniform conditions are determined by the degree of resolution needed to define geotechnical properties required for