ML20094B569
| ML20094B569 | |
| Person / Time | |
|---|---|
| Issue date: | 11/24/1975 |
| 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 9511010137 | |
| Download: ML20094B569 (9) | |
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U.S. NUCLEAR REGULATORY COMMISSION p
1 STANDARD REVIEW PLAN OFFICE OF NUCLEAR REACTOR REGULATION
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o c SECTION 2.5.5 STABILITY OF SLOPES 1
REVIEW RESPONSIBILITIES Primary - Site Analysis Branen (SAB)
Secondary - None 1.
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 and rock slopes both natural and man-made (cuts, fills, embankments, 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 sui,jects must be evaluated using the applicant's data in the SAR and information available 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, shaf ts, pits, trenches, and laboratory tests (Subsection 2.5.5.3); properties of borrow material, compaction and ex-cavation specifications (Subsection 2.5.5.4).
II. ACCEPTANCE CRITERIA The information in the SAR must be in compliance with the Standard Format (Ref. 2) and the Seismic and Geologic Siting Criteria (Ref.1). This section of the SAR is judged acceptable if the infomation presented is sufficient to demonstrate the dynamic and static stability of all slopes whose failure could adversely affects directly or indirectly, safety-related structures of the nuclear plant or pose a hazard to the public. The emergency cooling water j
source is of particular interest with regard to slope stability. The secondary source of emergency cooling water should survive the operating basis earthquake (OBE) and design basis flood. Completeness is determined by the ability to make an independent evaluation on the basis of infonnation provided by the applicant.
Subsection 2.5.5.1.
The discussion of slope characteristics is acceptable if the subsection includes:
a.
Cross sections and profiles of the slope in sufficient quantity and detail to represent the slope and foundation conditions.
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A sumary and d;scription f.f static and dynamic properties of the soil and rock comprising seismic Category I embankment dams and their foundations, natural and cut slopes, and all soil or rock slopes whose stability would directly or indirectly affect safety-related and Category I facilities. The text should include a complete i
discussion of procedures used to estimate, from the available field and laboratory data, conservative soil properties and profiles to be used in the analysis, v
c.
A sunwry and description of groundwater, seepage, and high and low groundwater con-ditions.
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l Subsection 2.5.5.2.
The discussion of design criteria anc analyses is acceptable if the j
l criteria for the stability and design of all seismic Category I slopes are described and l
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 assumptions and Methods of analysis to assess the following factors:
1.
Th 'Jncertainties with regard to the shape of the slope, boundaries of the several types of soil within the slope and their properties, the forces acting on the slope, and pore pressures acting within the slope.
2.
Failure surfaces corresponding to the lowest factor of safety.
3.
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 re-lated to the slope hazard are needed; however, actual values depend somewhat on the method of analysis, on the assumptions concerning the soil properties, on constru: tion techniques, and on the range of material parameters.
To be acceptable, the dynamic analyses must account for the effect of cyclic motion of the earthquake 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 embankments. 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 hydro-dynamic and pore pressure forces, should be varied to show that there is an adequate margin of safety. Where liquefaction is possible, 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 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 stability of th'e slopes.
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l Subsection 2.5.5.3 In discussing the soil investigations, the applicant should dsscribe th2 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 in 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 earth-works 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 infonnation in this subsection. Quality control techniques and requirements during and following construction must also be dis-cussed and referenced to quality assurance sections of the SAR.
III. REVIEW 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 used 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 in-depth review of the safety of the proposed facility. After acceptance of the SAR, the results of site investigations such as borings, maps, logs of trenches, permeability test records, results of seismic investigations, laboratory test results, profiles, plot plans, and stability analyses are studied and cross-checked in considerable detail to determine whether or not the assumptions 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 stability analysis, the number of borings, the sampling program, the extent of the laboratory 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 Inalyzed to insure that reasonable ranges of soil prop-erties have been considered. Other factors such as flood conditions, pore pressure effects, possible erosion of soils, and possible seismic amplification effects should be conservatively assessed.
The design criteria and analyses are reviewed to ascertain that the techniques employed are appropriate and represent the present state-of-the-art. Staff comments and questions at this phase of the review, concerning the information in the SAR, are sent to the appli-cant as first-round questions (Q-1). An independent analysis of the design of safety-related 2.5.5-3 l
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earth or rock-fill embankments is perfomed by the staff's advisors, the Corps of Enginnrs, or by the staff as deemed n;cessary. The Corps also evaluates natural or cut slopes, as required, on a case-by-case basis. The evaluations conducted by the staff 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 a more conservative approach.
After completing the review, if the staff's conclusions are consistent with those reached by the applicant, these conclusions are suunarized in the safety evaluation report (SER) or in a supplement to the SER. In the event that the applicant's investigation and design are not judged to be sufficiently conservative, a staff position is stated and the applicant is asked to further substantiate his position by additional investigations or monitoring, to demonstrato 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 con-servatively interpreted to allow a realistic assessment of the safety of proposed slopes and supporting foundations. Detailed design investigations are usually still in progress and final design conclusions have often 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 tne 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 conducted after construction permit (CP)issuancearethereforenecessary.
All natural safety-related slopes are examined during at least one of the two site visits required of the staff. Because excavated slopes or embankments are not usually constructed until after a construction pemit 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 eval-uating the slope stability aspects of nuclear power plant sites.
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 re-viewed 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 sufficient relevant test data to verify the soil strength characteristics assumed for the slopes, dikes, and dams under analysis. The evaluation is to some extent a matter of engineering judgment; however, if the safety factors resulting from the analysis are not appropriate 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 worse possible conditions are assumed, there is an adequate margin of 2.5.5-4 11/24/75
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safety. With respect 80 seismic analysis this subsection and Subsection 2.5.5.2 are reviewed concurrently because different methods of analysis may involve different approxi-mations, assumptions, and soil properties.
In addition to generic state-of-the-art literature, other potential sources of information are those containing design, construction, and performance records of natural slopes, ex-cavation 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 of Engineers, the Tennessee Valley Authority, the Bureau of Reclamation, and private' construction con-tractors or architect-engineers.
Subsection 2.5.5.2.
The criteria, design techniques, and analyses are evaluated by the staff to ascertain that:
1.
Appropriate state-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 been incorporated in the design.
The criteria and design methods used by the applicant are reviewed to ascertain that state-of-the-art techniques are being employed. The design 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 steady-state seepage, sudden drawdown of an adjacent reservoir, or a reasonable 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 characteris-tics 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 the staff and its consultants, additional sub-stantiation and refinement is required or the applicant must use more conservative assumptions.
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No single method of analysis is entirely acceptable for all stability assessments; thus.
I no single method of analysis can be recommended. Relevant manuals issued by public agencies (such as the U.S. Navy Department U.S. Anny Corps of Engineers, and U.S. Bureau of Recla-mation) are often used in reviews to ascertain whether the analyses performed by the appli-cant 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 staff's review of the analyses and in assessing the adequacy of the resulting safety factors.
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If th) staff review indicates that questionable assumptions have bein made by the applicant or some non-standard or inappropriate method of analysis has beIn ussd, then the staff 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 con.
y struction data and as-built analyses, settlement records, piezometer records, and absence of seepage. that support the adequacy and safety of the design is 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 j
beneath safety-related and seismic Category I slopes, and borrow material that is to be used to construct safety-related dams, fills, and embankments. The staff reviews these in-vestigations to ascertain that the program has been adequate to define the in situ and earth-work soil and rock characteristics. The decision as to the adequacy of the investigation program is based on the methods discussed in Section 2.5.4.
Subsection 2.5.5.4 The preliminary specifications and quality control techniques to be used during construction are reviewed by the staff to ascertain that all design conditions are likely to be met. During this part of the review the following are among those sub-jects reviewed 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 foundations and the quality control procedures which establish suitable materials.
3.
The techniques and equipment to be used in compacting foundation and embankment materials.
4.
The quality control and testing program to provide a high level of assurance that:
a.
The selected borrow material is as good and as relatively homogeneous as antici-pated 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 to detect occurrences that could detrimentally affect the facility. Such monitoring includes periodic examination of slopes, survey of settlement monuments, and measurements of local wells and piezometers.
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IV. EVALUATION FINDINGS I
Th2 staff's conclusions regarding the stability of slopes are suninarind in the safety evaluation report (SER) or 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 westernmost v
j Category I structures, then steepens, attaining an angle of more than 45" near the bottom of the valley wall. Major structural trends, schistocity, and one of the pre-dominant joint trends 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 affected 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) conditions. The minimum computed safety factor was 1.6 using conservative slope and material parameters.
3
" Man-made earth slopes related to the safety of the plant include excavation cuts for the ultimate heat sink canal and dams and dikes for the ultimate heat sink storage j
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pond. An extensive investigation and test program has determined all the significant l
characteristics and properties of cut slopes and fill embankments. Earthwork com-paction criteria, construction control, and select fill materials are consistent with high-quality water-retention facilities. Conservative stability analyses of these l
slopes under SSE conditions indicated minimum safety factors of 1.5.
" 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 slopes will remain stable under SSE conditions and that safety-related earthworks will function reliably."
4 V.
REFERENCES 1.
10 CFR Part 100. Appendix A. " Seismic and Geologic Siting Criteria for Nuclear Power
(
Plants."
l 2.
Regulatory Guide 1.70, " Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants," Revision 2.
i l
3.
"ASCE Soil Mechanics and Foundation Division Conference on Stability and Performance of Slopes and Embankments. August 22-26, 1966." Published in J. Soil Mech. and Found.,
ASCE, Vol. 93(1967).
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4.
P. Chakrabarti and A. K. Chopra, "A Computer Program for Earthquaks Analysis of Gravity Dams including Hydrodynamic Interaction," Rep;rt No. EERC 73-7. Earthquake Engineering Research Center, Univ. of California, Berkeley (1973).
.5.
- 1. M. Idress,.J. Lysmer, R. Hwang, and H. B. Seed. " Quad-4 a Computer Program for Evaluating the Seismic Response of Soil Structures by Variable Damping Finite Element Procedures," Report No. EERC 73-16. Earthquake Engineering Research 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).
I 8
Shannon & Wilson, Inc. and Agbabian-Jacobsen Associates, " Soil Behavior Under Earth-quake Loading Conditions - State-of-the-Art Evaluation of Soil Characteristics for Seismic Response Analyses," U. S. Atomic Energy Connission Contract W-7405-eng-26, January 1972.
9.
F. H. Kulhawy, J. M. Duncan, and H. B. Seed. " Finite Element Analysis of Stresses and Movements in Embankments During Construction," Report No. TE-69-4, U. S. Anny Engineers Waterways Experiment Station Vicksburg (1969).
10.
K. Terzaghi and R. B. Peck. " Soil Mechanics in Engineering Practice " 2nd ed.,
JohnWiley& 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).
- 12.. J. W. Snyder, " Pore Pressures in Embankment Foundations," Report S-28-2, U. S. Anny Engineers Waterways Experiment Station, Vicksburg (1968).
13.
Corps of Engineers, " Procedures for Foundation Design of Buildings and Other Structures (Except Hydraulic Structures)." Tech. Report TM 5-818-1 (formerly EM 1110-345-147), Office of the Chief of Engineers, Dept. of the Army (1965).
14 GEODEX, INTERNATIONAL, Soil Mechanics Information Servio anoma, California.
15.
Department of the Navy, " Soil Mechanics Foundations, and Earth Structures,"
NAVFAC DM-7, March 1971.
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