Document: NUREG-0800
Document ID: 9cdf4eb8-90c4-435e-84a4-d23c09056921
Document Type: srp
Title: STABILITY OF SUBSURFACE MATERIALS AND FOUNDATIONS
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070268.pdf
Revision Date: 2023-06
Chapter: 2
Section ID: 2.5.4
CFR Part: 
CFR Title: 

Content:
and that the design analyses contain adequate margins of safety for construction and operation of the subject nuclear power plant. Staff reservations about any portion of the applicant's analyses will be stated in sufficient detail to make clear the precise nature of the staff concern. A typical staff SER finding follows: The site is located in the Piedmont at an average elevation of +120 meters (395 feet)58 mean sea level (msl). Exploratory borings have been made and refraction and reflection seismic surveys conducted to establish the stratigraphy of the site. Additionally, undisturbed samples of representative soils and core borings have been obtained to evaluate the characteristics of the foundation materials; close-centered cross-hole seismic tests have been conducted to determine the elastic properties of these materials. Ground-water at the site varies from +114 to 116 meters (+375 to 380 feet) msl. 59 The area has been exposed to subaerial weathering and erosion since middle Mesozoic time, and a deep weathering profile has developed. The depth of weathering depends on the location and degree of jointing, orientation of schistosity, and composition of the parent rock. The applicant has categorized the foundation material into three zones according to the degree of weathering: (a) Zone 1 contains residual soil derived from severely weathered slate. The soil is a sandy, silty clay containing slate and quartz fragments. Decomposed to severely 2.5.4-17 DRAFT Rev. 3 - April 1996 weathered slate is also present. The slate still retains the original rock structure, although it is soft and partly friable. Quartz veins within the slate are extremely fractured. Seismic compression (P) and shear (S) wave velocities exceed 1200 m/sec (4000 ft/sec) and 500 m/sec (1800 ft/sec), respectively. Zone 1 60 61 ranges in thickness from less than 6 meters (20 feet) to more than 15 meters 62 (50 feet).63 (b) Zone 2 consists of moderately weathered slate and varies from 5 to 18