ML19221A979
| ML19221A979 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-02.5.5, NUREG-75-87, NUREG-75-87-2.5.5, SRP-02.05.05, SRP-2.05.05, NUDOCS 7907120120 | |
| Download: ML19221A979 (9) | |
Text
NU REG 75.'087 pa atcg%
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U.S. NUCLEAR REGULATORY COMMISSION
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i g WQj STANDARD REVIEW PLAN OFFICE OF NUCLEAR REACTOR REGULATION SECTICN 2.5.5 STABILITY OF SLOPES REVIEW RESPONSIBILITIES Primary - Geosciences Branch (GB)
I second3ry - Structural Engineering Branch (SEB) l I.
AREAS OF REVIEW Information, including analyses and substantiation, must be presented in the applicant's safety analysis report (SAR) and reviewed by the staff concerning the stability of all earth a.,d rock slopes both natural and man-made (cuts, fills, embaakments, dams, etc.)
whose failure, under any of the conditions to which they could be exposed during the life of the plant, could adversely affect the safety of the plant. The following subjects must be evaluated using the applicant's data in the SAR and information avail-able from other sources: slope characteristics (Subsection 2.5.5.1); design criteria and design analyses (Subsection 2.5.5.2); results of the investigations including borings, chafts, pits, trenches, and laboratory tests (Subsection 2.5.5.3); properties of borrcw material, compaction and excavation specifications (Subsection 2.5.5.4).
The results of the Aability of slopes evalu3tions are revie-ea by SEB to assure that displace-eents cr failure of site slopes as indicated in tha SAR do not have an adverse irpact on l
structural components.
f II.
ACCEPTANCE CRITERIA The information in the SAR ' rust be in compliance with the Standard Format (Ref. 2) and tre Seismic and Geologic Siting Criteria (Ref. 1).
This section of the SAR is judged acceptable if the information presented is tufficient to demonstrate the dynamic and static stability of all slopes whose failure could adversely af fect, directly or in-directly, safety-re'ated structures of the nuclear plant or pose a hazard to the public.
The emergency cooling water source is of particular interest with regard to slope stability. The secondary source of energency cooling water should survive the operat-ing basis earthquake (CBE) and design basis flood. Completeness is determined by the ability to make an independent evaluation on *.he basis of information provided by the applicant.
Subsection 2.5.5.l.
The discussion of slope characteristics is acceptable if the subsection includes:
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a.
Cross sections and profiles of the slope in sufficient quantity and detail to represent the slope and foundation conditions.
b.
A summary and description of static ind dynamic properties of the soil and rock comprising seismic Category I embankment dams and their foundations, natural and cut slopes, and all soil or rocn sicpes whose stability would directly or indirectly affect safety-related and Category I facilities. The text should include a complete discussion of procedures used to estimate, from the available field and laboratory data, conservative soil properties and profiles to be used in the analysis.
c.
A summary and description of groundwater, seepage, and high and low groundwater conditions.
Subsection 2.5.5.2.
The discussion of design criteria and analyses is acceptable if the criteria for the stability and design of all seismic Category I slopes are described and valid static and dynamic analyses have been presented to demonstrate that there is an adequate margin of safety. A number of different methods of analysis are available in the literature. Computer analyses should be verified by manual methods.
To be acceptable, the static analyses should include calculations with different assump-tions and methods of analysis to assess the following factors:
1.
The uncertainties with regard to the snape of the slope, boundaries of the several typ?s of soil within the slopo and the properties, the forces acting on the slope, and pore pressures acting within the slope.
2.
Failure surfaces corresponding to the lowest actor of safety.
.i.
The effect of the assumptions inherent in the method of analysis used.
4.
Adverse conditions such as high water levels due to the probable maximum flood (PMF), sudden drawdown, or steady seepage at various levels. In general, safety factors related to the slope hazard are needed; however, actual values depend somewhat on the method of analysis, on the assumptions concerning the soil proper-ties, on construction techniques, and on the range of material parameters.
To be acceptable, the dynamic analyses must account for the effect of cyclic motion of the parthquake on soil strength properties. Actual test data are needed for both the in situ soils as well as for any materials used in the construction of dams or embank ~
ments. As discussed above, the various parameters, such as geometry, soil strength, modeling method (location and number of elements (mesh) if a finite-element analysis is used), and hydrodynamic and pore pressure forces, should be varied to show that there is an adequate margin of safety (Refs. 16 and 17). Where liquefaction is possible, l
major dam foundation slopes and embankments should be analyzed by state-of-the-art finite-element or finite-difference methods of analysis. Where there are liquefiable Rev. 1 2.5.5-2 146 044
soils, changes in pore pressure due to cyclic loading must be considered in the analysis to assess not only the potential for liquefaction but also the effect of pore pressure increase on the stress-strain characteristic of the soil and the post earthquake sta-bility of the slopes.
Subsection 2.5.5.3.
In discussing the soil investigations, the applicant should describe the borings and soil testing that was carried out for slope stability studies and dam and dike analyses. The test data, which must meet the criteria set forth in Sections 2.5.1 and 2.5.4, could be presented ia those sections and referenced in this subsection.
Because dams, dikes, and natural or cut slopes are often remote from the main plant area, additional exploration, tests, and analyses for these areas should be presented in this subsection.
Subsection 2.5.5.4 Compaction specifications should be discussed in this section.
The applicant should describe the excavation, backfill, and borrow material planned for any dams, dikes, and embankment slopes. Planned construction procedures and control of earthworks should be described. To be acceptable, the information must be given as discussed in Subsection 2.5.4.5.
Some of this information could be presented in Subsection 2.5.4.5.
Because dams, dikes, and other earthworks are often remote from the main seismic Category I structures, it is necessary to complete this information in this subsection. Quality control techniques and requirements during and following construction must also be discussed and referenced to quality assurance sections of the SAR.
III. DEVIEW PROCEDURES The review process is conducted in a similar manner and concurrent wIth that described in Standard Review Plans (SRP) 2.5.1, 2.5.2, and 2.5.4.
The Corps of Engineers is the principal advisor to the staff regarding foundation engineering and slope stability analyses, particularly in the evaluation of safety-related and seismic Category I earthworks, earth and rock-fill dams, dikes, and reservoirs. Standard references ur:d by the staff are listed in Section V of this SRP.
An acceptance review is conducted to determine if the Standard Format (Ref. 2) has been adhered to and to judge whether or not the information presented is sufficient to permit an independent in-depth review and analysis of the safety of the proposed f acility. l After acceptance of the SAR, the results of site investigations such as borings, maps, logs of trenches, permeability test records, results of seismic investigations, labora-tory test results, profiles, plot plans, and stability analyses are studied and cross-checked in considerable detail to determine whether or not the assurrptions and analyses used in the design are conservative. The degree of conservatism required depends upon the type of analysis used, the reliability of parameters considered in the slope sta-bility analysis, the number of borings, the sampling program, the extent of the labora-tory test program, and the resultant safety factor. In general, the applicable soil strength data should be conservatively selected for the various possible soil profiles and slope conditions. For lower safety factors, several soil profiles should be analyzed 146 Re.45 1
2.5.5-3
to insure that reasonable ranges of soil properties have been considered. Other factors such as flood conditions, pore pressure effects, possible erosion of soils, and pos-sible seismic amplification effects should De conservatively assessed.
The design criteria and analyses are reviewed to ascertain that the techniques employed ar appropriate and represent the present state of-the-art.
Staff ccmments and ques-e tions at this phase of the review, corcerning the information ir the SAR, are sent to the applicant as first round questions (Q-1).
An independent analysis of the design of safety related earth or rock-fill embankments is performed by the staff's advisors, the Corps of Engineers, or by the staff as deemed recessary. The Corps also evaluates natural or cut slopes, as required, on a case-by-case basis. The evaluations conducted by the staf f and its advisors may identify additional unresolved items or reveal that the applicant's analyses are not conservative. Additional information is then requested in a second round of questions (Q-2), or a staff position is taken requiring conformance to more conservative approach.
After completing the review, if the staff's conclusions are consistent with those reached by the applicant, these conclusions are summarized in the safety evaluation report (SER) or in a supplement to the SER.
In the event that the applicant's investi-gation and design are not judged to be ruf ficiently conservative, a staf f position is stattd and the applicant is asked to further substantiate his position by additional inveL+irations or monitoring to demonstrate that a failure of the slopes in question will not harm the safety functions of the plant, or to concur in the staff position.
The data needed to satisfy the requirements of this section are often incomplete in the early stages. However, sufficient field and laboratory data should be presented and conservatively interpreted to allow a realistic assessment of the safety of proposed slopes and supporting 'oundations. Detailed design investigations are usually still in progress and final design conclusions have of ten not been made. Because of this, the question and answer exchange is not generally complete at the Q-2 stage. Most of the open items of Section 2.5 remaining at the time that the safety evaluation report (SER) input is required are in the foundation engineering and slope stability areas because actual conditions may not be revealed until excavations are opened; site visits corducted af ter construction permit (CP) issuance are therefore necessary.
All natural safety related slopes are examined during at least one of the twc site visits required of the staff. Because excavated slopes or embankments are not usually constructed until after a construction permit has been granted, detailed as-built documentation of these slopes and embankments, as well as complete stability and safety analyses, are necessary in the FSAR.
Following is a brief description of the review procedures conducted by the staff in evaluating the slope stability aspects of nuclear power plant sites.
2.5.5-4 146 046
Subsection 2.5.5.1.
Plot plans, cross sections, and profiles of all safety-related slopes in relation to the topography and physical properties of the underlying materials are reviewed and Compared with exploratory records to ascertain that the most critical conditions have been addressed and that the characteristics of all slopes have been defined. The soil and rock test data are reviewed to insure that there is suf ficient relevant test data to verify the soil strength characteristics assumed for the slopes, dikes, and dams under analysis. Tv evaluation is to some extent a matter of engineer-ing judgment; however, if the safety factors resulting from the analysis are not appro-priate to the hazards posed by a slope failure and other than clearly conservative soil properties and profiles were used, the applicant is required to obtain additional data to verify his assumptions, or to show that, even if the worst possible conditions are assumed, there is an adeouate margin of safety. With respect to seismic analysis, this subsection and Subsection 2.5.5.2 are reviewed concurrently because different methods of analysis may involse different approximations, assumptions, and soil properties.
In additien to generic state-of-the-art literature, other potential sources of informa-tion are those c m iining design, construction, and performance records of natural slopes, excavation slopes, and dams that may have been constructed in the general vicinity of the nuclear power plant. Examples of such documents are design memoranda and construction reports regarding nearby projects of public agencies such as the Corps nf Engineers, the Tennessee Valley Authority, the Bureau of Reclamation, and private construction contractors or architect-engineers.
Subsection 2.5.5.2.
The criteria, design techniques, and analyses are evaluated by the staf f to ascertain that:
1.
Appropriate stcte-of-the-art methods have been employed.
2.
Conservative assumptions regarding soil and rock properties have been used in the design and analysis of slopes and embankments as discussed above in Subsection 2.5.5.1.
3.
Appropriately conservative margins of safety have oeen incorporated in the cesign.
The criteria and design methods used by the applicant are reviewed to ascertain that state-of-the-art techniques are being employed. The oesign analyses are reviewed to be sure that the most conservative failure approach has been used and that all adverse conditions to which the slope might be subjected have been considered. Such conditions include ground motions from the safe shutdown earthquake, settlement, cracking, flood or low-water steadystate seepage, sudden drawdown of an adjacent reservoir, or a reason-able assumption of the possible simultaneous occurrence of two natural events such as an earthquake and flood. The review is also concerned with determining whether or not the soil and rock characteristics derived from the investigations described in Subsection 2.5.5.3 have been completely and conservatively incorporated into the design.
When marginal factors of safety are indicated by the independent analyses performed by 2.5.5-5 Rev. 1 146 047
the staff and its consultants, additional substantiation and refinement is required or the applicant must use more conservative assumptions.
No single method of analysis is ent: rely acceptable for all stability assessments; thus, no single inetnod of analysis can be recommended. Relevant manuals issued by public agencies (such as the U.S. Navy Department, U.S. Army Corps of Engineers, and U.S. Bureau of Reclamation) are often used in reviews to ascertain whether the analyses performed by the applicant are reasonable. Many of the important interaction effects cannot be included in current analyses and must be treated in some approximate fashion.
Engineering judgment is an important factor in the stLff's review of the analyses and in assessing the adequacy of the resulting safety factors.
If the staff review indicates that questionable assumptions have been made by the applicant or some non-standard or inappropriate method of analysis has been used, then the staf f or its consultant may model the dam or slope in a manner which it feels is more consistent with the data and perform an independent analysis.
During the operating license review, all open items requiring resolution, including construction data and as-built analyses, settlement records, piezameter records, and absence of seepage, that support the adequacy and safety of the design, are reviewed by the staff.
Subsection 2.5.5.3.
A comprehensive program of site investigations including borings, sampling, geophysical surveys, test pits, trenches, and laboratory and field testing must be carried out by the applicant to define the physical characteristics of all soil and rock beneath safety-related and seismic Category I slopes, and borrow mater' d that is to be used to construct safety-related dams, fills, and embankments. The staff reviews these investigatinns to ascertain that the program has been adeouate to define the in situ and earthwork soil and rock characteristics. The cecision as to the adequacy of the ilvestigation program is based on the methods discussed in Section 2.5.4.
Suhsection 2.5.5.4.
The preliminary specifications and quality centrol techniques to be used during construction are reviewed by the staff to ascertain that all design conditions are likely to te met.
During this part of the review the following are among those subjects reviewad for adequacy:
1.
Proposed construction dewatering plan to ensure that it will not result in damage either to the natural or engineered foundation materials or to the structural foundation.
2.
The excavation plan to remove all unsuitable materials from beneath the founda-tions and the quality control procedures which establish suitable materials.
3.
The techniques and equipment to be used in compacting foundation and embankment A
materials.
Rev. 1 2.5.5-6 146 048
4.
The quality control and testing program to provide a high level of assurance that:
The selected borrow material is as good and as relatively homogeneous as a.
anticipated from the investigation program.
b.
The compacted foundation soil meets design specifications.
5.
The techniques for improving the stability of natural slopes such as drainage, grouting, rock bolting, and applying gunite.
6.
The plans for monitoring during and after construction t0 detect occurrences that could detrimentally affect the facility. Such monitoring includes periodic examina-tion of slopes, survey of settlement monuments, and measurements of local wells and piezometers.
IV.
EVALUATION FINDINGS The staff's conclusions regarding the stability of slopes are summarized in the safety evaluaticn report (StR) ur in a supplement to the SER. The following is an example:
"Both natural and man-made slopes exist at the site. At the plant site, which is located several hundred feet from the Green Valley and about 280 feet above the level of Jones Pond, the slope is relatively gentle for about 250 feet west of the westernmast Category I structures, then steepens, att?ining an angle of more than 45 near the bottcm of the valley wall. Major structural trends, schistosity, and one of the pre-dominant joint trend; are nearly perpendicular to the slope. A second predominant joint set is nearly parallel to the river and dips to the southwest, but no slope movements have apparently affacted the valley walls in the vicinity of the site. Seven other joint trends were detected by the applicant. These joint sets are reported to be moderately spaced and discontinuous. The applicant has drilled several exploratory holes and cored others to assess the natural slope characteristics and groundwater regime. Even though the natural slopes are some distance from safety-related plant facilities and slope failures are not obvious safety hazards, the applicant has performed stability analyses of these slopes under safe shutdown earthquake (SSE) co-ditions.
The minimum computed safety factor was 1.6 using conservative slope and material parameters.
" Man made earth slopes related to the safety of the plant include excavation cuts for tha ultimate heat sink canal and dams and dikes for the ultimate heat sink storage pond. An extensive investigation and test prog'3m has determined all the 3ignificant characteristics and properties of cut slopes and fill embankments. Earthwork compac-tion criteria, construction control, and select fill materials are censistent with high quality water retention facilities. Conservative stability analyses of these slopes under SSE conditions indicated minimum safety factors of 1.5.
9 146 049 2.5.5-7 Rev. 1
" Based on the results of the applicant's investigations, laboratory and field tests, analyses, and criteria for design and construction, we and our consultants conclude that natural and man-made sicpes will remain stable under SSE conditions and that safety-related earthworks will function reliably."
V.
REFERENCES 1.
10 CFR Fart 100, Appendix A, " Seismic and Geologic Siting Criteria for Nuclear Power Plante."
2.
Regulatory Guide 1.70, " Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants," Revision 2.
3.
"ASCE Soil Mechani s and Foundation Division Conference on Stability and Perform-ance of Slopes and Embankments, Augtst 22-26, 1966."
Published in J. Soil Mech.
and Found., ASCE, Vol. 93 (1967).
4.
P. Chakrabarti and A. K. Chopra, "A Computer Program for Earthquake Analysis of Gravity Dams Including Hydrodynamic Interaction," Report No. EERC 73-7, Earthquake Engineering Research Center, Univ. of California, Berkeley (1973).
5.
I. M.
Idriss, J. Lysmer, R. Hwang, and H. B. Seed, " Quad-4 a Computer Program for Evaluating the beismic Response of Soil Structures by Variable Damping Finite Element Procedures," Report No. EERC 73-16, Earthquake Engineering Recearch Center, Univ. of California, Berkeley (1973).
6.
Bureau of Reclamation, " Earth Manual," First Edition, U. S. Dept. of Interior (1968).
7.
K. Stagg and O. Zienkiewicz, " Rock Mechanics in Engineering Practice," John Wiley
& Sons (1968).
8.
Shannon & Wilson, Inc. and Agbabian-Jacobsen Associates, " Soil Behavior Under Earthquake loading Conditions - State-of-the-Art Evaluation of Soil Character-istics for Seismic Response /.nalyses," U. S. Atomic Energy Commission Contract W-7405-eng-26, January 1972.
9.
F. H. Kulhawy, J. M. Cuncan, and H. B. Seed, " Finite Element Analysis of Stresses and Movements in Embankments During Construction," Report No. TE-69-4, U. S. Army Engineers Waterways Experiment Station, Vicksburg (1969).
10.
K.
ferzaghi and R. B. Peck, " Soil Mechanics in Engineering Practice," 2nd ed.,
John Wiley & Sons (1967).
11.
Corps of Engineers, " Engineering and Design Stability of Earth and Rock-Fill Dams," Manual N. EM 1110-2-1902, Office of the Chief of Engineers, Dept. of the Army (1970).
Rev. 1 2.5.5-8 146 050
12.
J. W.
Snyder, " Pore Pressures in Embankment Foundations," Report 5-28-2, U. 5.
Army Engineers Waterways Experiment Station, Vicksburg (1968).
13.
Corps of Engineers, " Procedures for Foundation Design of Buildings and Other Structures (Except HydraJliC Structures)," Tech. Report TM 5-818-1 (formerly EM 1110-345-147), Office of the Chirf of Engineers, Cept. of the Army (1965) 14.
GEODEX, INTERNATIONAL, Soil hechanics Information Service, Sonoma, California.
15.
Department of the Navy, " Soil Mechanics, Foundations, and Earth Struttures,"
NAVFAC DM-7, March 1971.
16.
H. Bolton Seed, K.
L. Lee, I. M.
Idriss, and F. Makdisi, " Analysis of the Slides in the San Fernando Dams During the Earthquake of February 9, 1971," Report No. EERC 73-2, Earthquake Engineering Research Center, University of California, Berkeley (1973).
17.
N. M. Newmark, " Effects of Earthquakes on Dams and Embankments' Geotechnique, 15: 140-141; 156, 1969.
146 05i 2.5.5-9 Rev. 1