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:
een estimated to be less than 2.5 centimeters (1 inch).74 The applicant states that severely weathered or soft zones of rock will be excavated and replaced with lean concrete. This procedure will also be followed wherever severe weathering extends along joints, schistosity, etc. Below the base of the foundations, this material will be excavated to a depth 1-½ times the width of the zone and backfilled with concrete. Category I structural backfill under structures will either be concrete or compacted granular backfill. If granular backfill is used, it will be compacted to at least 85 percent relative density or to 95 percent of the maximum density determined by the Modified Proctor test. These backfill criteria are acceptable criteria for soil pressures on foundations and buried pipes and are suitable and conservative for both static and dynamic conditions. Suitable borrow material for dikes, dams and impervious linings are available for the ultimate heat sink ponds. The applicant's tests on these materials and the construction criteria to be followed ensure that leakage, piping and cracking hazards of these vital earthworks are minimal. Filters, blanket drains, relief wells, piezometers and settlement monuments will assureensure the reliable performance of the ultimate heat sink water-retention facilities. DRAFT Rev. 3 - April 1996 2.5.4-18 The applicant has shown that the appropriate acceleration level on sound rock is 0.12 g for the safe shutdown earthquake (SSE). The operating bases earthquake (OBE) value is taken as 0.06g. The applicant has performed a site-dependent analysis to estimate the site amplification effects and found that the weathered rock or structural backfill would amplify the rock motion. An acceleration level of 0.17 g for the SSE will be used for those structures founded on weathered rock or structural backfill over weathered rock. The time history used for seismic design of Category I earth dams and for liquefaction assessment envelopes the