ML19221A978
| ML19221A978 | |
| Person / Time | |
|---|---|
| Issue date: | 03/31/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-02.5.4, NUREG-75-87, NUREG-75-87-2.5.4, SRP-02.05.04, SRP-2.05.04, NUDOCS 7907120117 | |
| Download: ML19221A978 (15) | |
Text
NUR EG 75/087 fp Recg%
U.S. NUCLEAR REGULATORY COMMISSION N;L' 'e i
g'>,'i
- g
\\,~Q' /
OFFICE OF NUCLEAR REACTOR REGULATION 1
STANDARD REVIEW PLAN
+
SECTICN 2.5.4 STABILITY OF SUBSURFACE MATERIALS AND FOUNDATIGNS REVIEW RESPONSIBILITIES Primary - Geosciences Branch (GB)
Secondary - Structural Engineering Branch (SEB)
I.
AREAS OF REVIEW Information must te presented by the applicant concerning the properties and stability of all soils and rock which may af fect the neclear power plant facilities, under both static and dynamic conditior.s including the vibratory ground moth >ns associated with the safe shutdowq earthquake. Stability of these matcrials, as they influence the safety of seismic Category I facilities, must be demonstrated In addition ai, assess-ment of the properties and stability of these materials should be corsistent with SRP Sections 3.7 and 3.S.
Much o' the information discussed in this section may be pre-sented in other secticns, in which case it may be cross referenced rather than repeated here.
The results of the stability evaluations of subsurface materials and foundations are reviewed by SEB to assure that the loads and deflections including any reduction in support capability of subsurface materials can safely be accommodated by structural components.
The staff review covers the following specific areas:
1.
Geologic features (Subsection 2.5.4.1) in the vicinity of the site:
a.
Are3s of actual or potential surface or subsurf ace subsidence, solution activity, uplift, or collapse.
b.
Zones of alteration or irregular weathering profiles, nd zones of structural weakness.
c.
Unrelieved stresses in t'edrock and their potential for creep and rebound
- effects, d.
Rocks ir soils that might be unstable because of their mineralogy, lack of consolidation, water content, or potentially undesirable response to seismic or other events.
USNRC STAND ARO REVIEW PLAN standerd.e ew p,.n.. e p<.pa,ed +o, th. go,de-e o the on,ce., wo.e, Reactor negoier on
,se, compons,bie eo, the,ew e.
..ppi., e..on s to c onst oct.nd e
operete nucleat Dower plent e these documeras are made evadable to the publ.c es part of the Commesseon a po6er.y to mform he ow(leer endustry and the generai puche of eegulato<y proceduces ar.d pas.c es Standeed rev.ew plane e e not out>et tutes f oe requietoev gu den or the Come soon s requise r s and compbance with them is not required The standerd rovsom plan socirone *-e hoved to Revie on 2 of the S'endard f ormat and Content of Safet y Anary, P oport o toe %ueer Power P' ente Not oss sections #>tthe Sesadeed Formet have e correspondmg review pl Pubitshed stenoord coview plans mile be sed periodicotty as appropreste to occorrimndete commeate and to eenec t new.o f ormation and emper'**se
- Commente end suggesteone for empeevement avH be consedered and should t*e sent to the U $ Nudear Regulatory Commiseson Off.co of Nucteer R iactor Regu sesion Weeniegten D C 20666 ao 7007120111 I,A t' 818' v
a
e.
History of deposition and erosion, including glacial and otner preloading influunce on soil deposits.
f.
Estimates of consolidation and preconsolidation pressures and trethods used to estimate these values.
2.
The static and dynamic engineering properties of soil and rock strata underlying the site (Subsection 2.5.4.2) as supported by representative field and laboratory data provided by the applicant.
3.
The relationship of the foundations for safety-related facilities and the engineer-ing properties of underlying materials as itiustrated on plot plans and profiles (Subsection 2.5.4.3) providea by the applicant.
4 The results of seismic refraction and reflection surveys, including in-hole and cross-hole explorations, as presented in the safety analysis report (SM) ty discussions, plot plans, boring logs, tables, and profiles to support t-ssumed dynamic soil or rock characteristics (fubsection 2.5.4.4) and stratigraphy.
5.
Safety-related excavation and backfill plans and engir.eered earthwork analyses and criteria (Subsection 2.5.4.5) as illustrated on plot plans and profiles, discussed in the text, and supported by explorations for bcrrow material, test fills and l
adequate representative laboratory test records.
G 6.
Groundw3ter conditions and piezametric pressure in all critical strata (Subsection 2.5.4.6) as they affect the loading and stability of foundation materials. This part of the staff review also includes an evaluation of the applicant's plans for dewatering during construction as well as groundwater control throughout the life of the plant.
7.
The responses of site sofls or rocks to dynamic loading (Subsection 2.5.4.7),
including appropriate laboratory and field test records in sufficient number and detail adequate to support conclusions derived from the analyses. Soil-structure interaction analyses are reviewed to evaluate stability and to provide input to SEB regarding the validity of the soil profile model used in the analyses.
8.
The liquefaction potential (Subsection 2.5.4.8) and consequences of liquefaction l
of all subsurface soils, including the settlement of foundations. These analyses are based on soil properties obtained by state-of-the-art laboratory and 1ield tests.
9.
The earthquake design bases (Subsection 2.'.4.9) are evaluated in detail in l
Section 2.5.2.
These are summari??d and cross-referenced in this subsection. The safe shutdown earthquake (SSE) and the operating basis earthquake (0BE) are evalu-l ated in this subsection in combination with other haards (floods, etc.) to assess the adequacy of the site materials under dynamic conditions.
{ Q2h Rev. 1 2.5.4-2
10.
The results of investigations and analyses conducted to determine foundation material stability, deformation and settlement under static conditions l
(Subsection 2.5.4.10).
11.
Criteria, references, and design methods ($Lbsection 2.5.4.11) used in static and seismic analyses of foundation materials, including an explanation of computer programs used in the analyses and soil loads en subsurf ace f acilities.
12.
Techniques and specificatio.s to improve subsurface conditions ($ubsection 2.5.4.12),
which are to be used at the site to provide suitable foundation conditions.
l 13.
Add:tional information on foundations is covered in SRP Sections 3.8.5 and should be cross-referenced to this section.
II.
ACCEPTANCE CRITERIA A thorough evaluation of the geotechnical engineering aspects of the nuclear ;Gant site l
as described in the following subsections must be presented along with the basic data supporting all conclusions. Sufficient information must be provided to allow the staff and its advisors to conduct independent analyses. The site investigations must be adequate in scope and in technique to p. ovide the necessary data. Guidelines for site investigations are given in Regulatory Gui1e 1.132.
Subsection 2.5.4.1.
The section defining geologic features is acceptable if the dis as-sions, maps, and profiles of the site stratigraphy, lithology, structural geology, geologic history, and engineering geology are complete and are supported by site investi-gations sufficiently detailed to obtain an unambiguous representation of the geology.
The information must be presented in this subsection or cross-referenced to the appro-priate subsection in Section 2.5.1.
Subsection 2.5.4.2.
The description of properties of underlying materials is considered acceptable if state-of-the-art trethods are used to determine the static and dynamit engineering properties of all foundation soils and rocks in the site area. These methods are described, for example, in geotechnical journals published by the American Society of C hil Engineers (Ref. 3), applicable standards published by the American Society for Testing and Materials (Ref. 4), publications of the Institution of Civil Engineers (Ref. 5), and various research reports prepared by universities (Ref. 6).
The properties of foundation material must be supported by field (Ref. 10 and 11) and laboratory (Ref. 12) test records.
Normally, a complete field investigation and sampling program must be performed to define the occurrence and properties of underlying materials at a given site (Ref. 7).
Summary tables must be provided which catalog the important test results; test results should be plotted when appropriate. Also, a detailed discussion of laboratory sample
. reparation must be given when applicable. For critical laboratory tests, full details must be given, e.g.,
how saturation of the sample was determined and maintained during testing, how the pore pressures changed.
146 030 2.5.4 -3 Rev. 1
ine applicant should provide a detailed and quantitative discussion of the criteria used to determine that the samples were properly taken and tested in sufficient number to define all the critical soil parameters for the tite.
For sites that are underlain by saturated soils and sensitive clays, it should be shown that all zones which could become unstable due to liquefaction or strain softening phenomena have been adequately sampled and tested. The relative density of the soils at the site should be determined.
The applicant must also show that he has acequately defined the consolidation behavior of the soils as well as their static and dynamic strength. The discussion should explain how the develcped data is used in the safety analyses, how the test data is enveloped for design, and why the design envelc.pe is conservative.
Subsection 2.5.4.3.
The discussion of the relation; hip of foundations and underlying materials is acceptable if it includes:
1.
A plot plan or plans showing the locations of all site explorations, such as borings, trenches, seismic lines, piezometers, geologic profi!es, and excavations with the locations cf the safety related facilities superimposed trereon.
2.
Profiles illustrating the detailed relationship of the foundations of all seismic Category I and other safety-related facilities to the subsurface materials.
3.
Logs of core borings and test pits.
4.
Logs and maps of explora", y trenches in the preliminary safety analysis report (PSAR), and geologic maps and photographs of the excavations for the facilities of the nuclear pcwer plant in the final safety analysis report (f 5AR).
Subsection 2.5.4.4 The presentation of the dynamic characteristics of soil or rock is acceptable if qeophysical investigations have been performed at the site and the results obtained therefrom are presented in detail. Completeness of the presentation is judged by whether or not the exploratory techniques used by the applicant yield unambiguous and useful information, whether they represent state-of-the art exploration methods (Refs. 3, 4, 7, 9), and whether the applicant's interpretations are supported b, ade-l quate field records in the SAR.
See also Subsection 2.5.2.3.
Subsection 2.5.4.5.
The presentation of the data concerning excavation, backfill, and earthwork analyses is acceptable if:
1.
The sources and quantities of backfill and borrow are icentified and are shown to have been adequately investigated by borings, pits, and laboratory property and strength testing (dynamic and static) and these data are ir.cluded, interpreted, and sumarized.
2.
The extent (horizontally and vertically) of all Lategory I excavations, fills, and slopes are clearly shown on plot plans and profiles.
146 031 Rev. 1 2.5.4-4
3.
Compaction specifications and embankment and foundation designs are justified by field and laboratory tests and analyses to assure stability and reliable performance.
4.
Quality control methods are discussed and the quality assurance program described and referenced.
5.
Centrol of graundwater during excavation to preclude degradation of foundation materials is described and referenced.
Subsection 2.5.4.6.
The analysis of groundwater conoitions is acceptable if the follow-ing are included in this subsection or cross-referenced to the appropriate subsections in Section 2.4:
1.
Discussion of critical cases of groundwater conditions relative to the foundation stability of the safety-related facilities of the nuclear pcwer plant.
2.
Plans for dewatering during construction.
3.
Analysis and interpretation of seepagt and potential piping conditions during l
construction.
4.
Records of field and laboratory permeability tests.
5.
History of groundwater fluctuations as determined by periodic monitoring of local wells and piezometers. Flcod conditions should also be considered.
Subsection 2.5.4.7 Descriptions of the response of soil and rock to dynamic INJing are acceptable if:
1.
An investigation has been conducted and discussed to determine the effects of prior earthquakes on the soils and rocks in the vicinity of the site. Evidence of liquefaction and sand cone formation should be included.
2.
Field seismic surveys (surface refract.on and ref%ction and in-bole and cross-hole seismic explorations) have been accomplished and the data presented and interpreted to develop P and 5 wave velocity profiles.
3.
Dynamic tests have been performed in the laboratory on samples of the foundation soil and rock and the results included. The sec+ ion should be cross referenced with Subsection 2.5.2.5.
The soil-structure interaction analysis should be described in SRP Sections 3.7.1 and 3.7.2 and cross-referenced to this subsection. In the soil-structure interaction analysis, the following parameters are reviewed:
146 032 2.5.4-5 Pev. I
1.
The static and dynamic properties of the soil supporting the structure are properly determined and compatible with the characteristics of the analytical moael used to eva!uate soil-structure interaction effects.
2.
The soil profile has been properly modeled when a two-dimensional finite-element analysis is used, or if a half-space analysis method is used, when foundation moduli and damping are consistent with soil properties and soil profiles at the l
site.
3.
The sta'ic and dynamic loads, and tne stresses and strains induced in the soil surrounding and underlying the structure are adequately and realistically evaluated. l 4.
The consequences of the induced soil stresses and strains, as they influence the surrouncing and underlying the structure, have been conservatively assessed.
I Subsection 7.5.4.8.
If the foundation materials at the site adjacent to and under Category I structures and facilities are saturated soils and the water table is above l
bedrock, then an analysis of the liquefaction potential at the site is required. The need for a detailed analysis is determined by a study on a case by case basis of the l
site stratigraphy, critical soil parameters, and the location of safety-related founda-tions. Undisturbed samples obtained at the site and appropriate laboratory tests are required to show if the soils are likely to liquefy.
l When the need for an in-depth analysis is %dicated, it may be Dased on cyclic triaxial l
,est data obtained from undisturbed soil samples taken from the critical zones in the site area. T5e shear stresses induced in the soil by the postulated earthquake should be determined in a manner that is consistent with Standard Review Plan (SRP)
Section 2.5.2.
The criterion that should be used to determine when the soil e. miles tested " liquefied" should br taken as La onset of liquefaction (defined as the cycle when the pore pressure first equals tne confining pressure)
Test data showing the rate of pore pressure increase with number of load cycles should be presented. If the behavior of the pore pressure is such that peak to peak axidi strains greater than a few percent occur before liquef action, then the applicant must include the ef fects of these strains in his assessment of the potential ha7ards that complete or partial liquef action could have on the stability c.nd settlement of any Category I structures.
Nonseismic liquefaction (such as that induced by ercsion, floods, wind loads on struc-tures and wave action) should be analyzed using state-of-the-art soil mechanics principles.
Subsection 2.5.4.9.
The earthquake design basis analysis is acceptable if a brief summary of the derivation of the safe shutdown and oper ?ing basis earthquakes (SSE and OBE) is presented and references are included to Subsections 2.5.2.6 and 2.5.2.7.
Rev. 1 2.5.4-6 146 C33
Subsection 2.5.4.10.
The discussions of static calvses are acceptable if the stability of all safety-related facilities has been analyzed from a static stability standpoint including bearing capacity, rebound, settlement and differential settlements under deadloads of fills and plant facilities, and lateral loading conditions. Field and laboratory test procedures and results must be included to document soil and rock properties used in the analyses. The applicant must snow that the methods of analysis used are appropriate for the c. soil conditions and the function of the facility.
l Subsection 2.5.4.11.
The Jiscussion of criteria and design methods is acceptable if the criteria used for the design, the design methodt employed, and the factors of safety obtained in the design analyses are described and a list of ref?rences presented.
An explanation and verification of the computer analyses used and source references should be included.
Subsection 2.5.4.1,7 The discussion of techniques to improve subsurface conditions is acceptable if plans, summaries of specifications, and methods of quality control are described for all techniques to be used to improve foundation conditions (such as grouting, vibraflotation, dental w rk, rock bolting, or anchors).
III. REVIEW PROCEDURES The review process is conducted in a similar manner and concurrent with that described in SRP 2.5.1.
The services of the Corps of Engineers are used on selected sites to aid the staff in evaluating the geotechnical engineering aspects of particular sites.
l After acceptance of the SAR, the results of site investigations (such as borings, geologic maps, logs of trenches and pits, permeability test records, results of seismic investigations, laboratory test results, profiles, and plot plans) are studied and cross-checked in considerable detail to determine whether or not, the assumptions used in the evaluation are conservative. The design criteria are reviewed to ascertain that l
they are within 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 applicant as first round questions (Q-1).
For *. hose facilities that have complex subsurface conditiens, where marginal safety has been achieved, or where the applicant proposes to construct a seismic Category I earth or rockfill dam, an independent anaiysis of the design is performed by the staff or its advisors, the Corps of Engineers. The evalua-tions conducted by the staff and its advisors may identify additional unresolved ums,
or reveal that the applicant's investigations and analyses are not complete or suf-ficiently conservative. Additional information is then requested in a second round of questions (Q-2), or a staff position is taken requiring adoption of a more conservative approach.
The data needed to satisfy the requirements of this section are not usually complete in the early stages. Detailed design investigations are usually still in progress and final conclusions have often not been made. Because of this, the question and answer exchange may not be complete at the Q-2 stage. Most of the open items of Section 2.5 4
034 2.5.4-7 "e"- '
remaining at the time that the safety evaluation report (SER) input is required are in the geotechnical engineering area because actual site conditions may not be fully l
revealed until excavations are opened and const.'uction has begun.
Thus, a site visit, in addition to that noted in Section 2.5.1, " Basic oeu W ic and Seismic Information,"
is necessary during the oost-CP period to examine the foundation materials exposed in excavations during construction. Inforration and final designs, including confirming tests and revised analyses, are to be submitted in the FSAR.
Generc.lly, the staff is guided by the Seismic and Geologic Siting Criteria (Ref. 1) and the Standard format (Ref. 2) in reviewing Section
'E 4 Following is a brief description of the review procedures conducted by the staff in evaluating the geotechnical engineering upcct5 uf nuclear power plant sites.
l Subsection 2.5.4.1.
Geolcgic features are evaluated by condu aing an independent l
literm.ure search and comparing these results with the informition included in the applicant's SAR.
References used in reviewing thic subsM tton include published or unpublished reports, maps, geophysical data, constructirn records, etc., by the USG$,
other Federal agencies, State agencies, 3nd private companies (suct as oil Corporations and architect engineering firms). In conjunction with the literature search, 'he staff and its USGS advisors review the geological investigations conducted by the app,. cant.
Using the references listed at the end of this section and other sources, the following questions ara considered n detail:
O 1.
Are the exploratory techniques used by the site investigator representative of the present state-of-the-art? Do the samples rep esent the in situ scil conditions?
2.
Do the applicant's investigations rovide adequate coverage of the site are, ind r
in sufficient detail to define the specific subsurface conditions with a high degree of confidence?
3.
Have all areas or zones of actual or potential surface or subsurface subsidence, uplift or collapse, deformation, alternatiori, solution cavities or structural l
weakness, unrelieved stresses in bedrock, or rocks or soils ; hat might be unstable because of their physical or chemical properties been identified and adequately evaluated?
Su0section 2.5.4.2.
Properties of underlying materials are evaluated to determine whether or not the investigations performed (includirg laboratory and field testing) were sufficient to justify the soil and rock properties used in the foundation analyses. l To determine whether sufficient investigations were performed, the staff carefully reviews the criteria developed and used by the applicant in laying out the boring, l
sampling and testing program and evaluates the effectiveness of the program in defining y
the specific foundation iitions at the site to assure that all critical conditions
[
1 16 5
Rev. 1 2.E.4-8 7
have been adequately sampled and tested. If suitable criteria have not been developed and used by the applicant, tne staf f develops appropriate criteria, using Regulatory Guide 1.132 and the data given in the SAR, and determines if sufficient investigation l
and testing have been carried out.
If criteria are given, the staff reviews them to determine if they are appropriate and have been implementad.
If it is the staff's judgment that the applicant's investigations or testing are inappro-priate or insufficient, additional investigations will be required. The final conclusion is based on professional judgment, considering the complexity of the site subsurface conditions. As part of the review, the staff must ascertain, often with the help of the Corps of Engineers, that state-of-the-art laboratory and field techniques and equipment are employed in determining the material properties.
Subsection 2.5.4.3.
Plot plans and profiles are reviewed by comparing the subsurface materials with the,aroposed locations (horizontal and vertical) cf foundations and
. alls of all seismic Category I facilities. The profiles and plot plans are cross-checked in detail with the results Cf all subsurface investigations conducted at the site to ascertain that sufficient exploration has been carried out and to determine whether or not the interpretations made by the investigators are valid and the founda-tion design assumptions contain adequate margins of safety.
Subsection 2.5.4.4.
Staff evaluation consists of a detailed review of all geophysical explorations conducted at the site, including seismic refraction, reflection, and in-hole surveys anu ma n d -
...a,rav:2.y surveys. Expertise within the USGS recarding specific techniques is drawn wpon i this review.
8.ogs of core borings, trenches, and test pits are reviewed and comparcd with data from the seismic surveys and other geo-physical explorations. Results must be consistent or additional investigations are required, or the applicant must use the most conservative values. Following the PSAR review and during the FSAR review the staff compares conditions as mapped in the open excavations with interpretations and assumptions derived during the investigation program.
Subsection 2.5.4.5.
Excavations, backfill, and (arthwork are evaluated by the staf f as follows:
1.
The investigations for borrow material, including boring and test pit logs, and compaction test data are reviewed ar.d judged as tc their adequacy.
2.
Laboratory dynamic and static records of tests performed an samples ccmpacted to the design specifications are reviewed to ascertain that state of-the-art criteria are met.
3.
Analyses and interpretations are reviewed to assure that static and dynamic sta-bility requirements are met.
2.5.4-9 Rev. 1 146 036
4 Excavation and compaction specifications and ouality control procedures are reviewed to ascertain conformance to state-of-tne art conservative standards.
Subsection 2.5.4.6.
Groundwater conditions as they af fect foundation stability are evaluated by studying the applicant's records of the historic fluctuations of ground-water at the site as obtained by monitoring local wells and springs and by analysis of piezometer and permeability data from tests conducted at the site.
The 3rplicant's dewatering plans during and following construction are also reviewed. Adequacy of thsse plans is evaluated by comparing with the results of the groundwater investigations and by professional judgment of ground ater and soil conditions at the site.
Sub action 2.5.4.7.
Response of soil and rock to dynamic loading and soil-structure i teraction is evaluated by a detailed study of the results of the investigations and n
analyses performed. Specifically, the effects of past earthquakes on site soils or rocks (a requirement in SRP 2.5.2) are determined. The data from core borings, from geophysical investigations, and f rom dynamic laboratory tests such as sonic and cyclic triaxial tests on undisturbed samples are evaluated. The object of the staff review is to ascertain that reasonably conservative dynamic soil and rock characteristics are used in the design and analyses and that all the significant soil and rock strata nave been considered in the analyses. In some cases, independent analyses and interpreta-tions are carried out as outlined in SRP 2.5.2, or as required to verify the liquefac-tion analysis discussed in Subsection 2.5.4.8.
Subsection 2.S.4.8.
Liquefaction poiential
's reviewed by a study of the results of geotechnical investigations includir g boring logs, laboratory classification test data and soil profiles to determine if any of t'
,ite soils could be susceptible to liquefac-tion.
The results of in-situ tests such as the standard penetration tests and the den-sity and strength data cbtained from undisturbed samples cutained in exploration borings are examined and, when appropriate, related to the liquefaction potential of in situ soils.
If it is determined that there may be liquefaction-susceptible soils beneath the site, l
the applicant's site exploration methods, laboratory test prcgram, and analyses are reviewed for adequacy and reasonableness. The analysis submitted by the applicant is l
reviewed in detail and compared to an independent study performed by the staff. As a minimum, the staff study consists of:
1.
A review of appropriate Standard Penetration test results, other in-situ test data and groundwater conditions to assess liquefaction potential.
2.
A careful review of conventional laboratory and cyclic triaxial test data to insure that appropriate samples were obtained and tested from critical, liquefiable zones.
Rev. I 2.5.4-10 146 037
3.
Confirmation that an adequate number of samples were properly tested and that the test rtiults account for the natural variation in different samples as well as define the cyclic resistance to liquefaction of the soils.
4.
An i it ^f the liquefaction potential using a conservative envelope of the t.e s
- at a s us '.t ed.
A calculation of the stress induced by the earthquake that has been arrived at by
,o envelnpe of critical conditions calculated for the site based on variations in l
the croperties of the soil strata.
6.
Assurance that onservative ranges f relative density of the soils are estimated.
The applicant's estimates of the " safety factor" obtained from his analysis is compared to the safety margins estimated by the staff. (The applicant's plans to
" eliminate" the liquefaction condition, usually by excavation and backfill, vibro-flotation, or chemical grouting is evaluated as discussed in Subsections 2.5.4.5 and 2.5.4.12.)
7.
An assessrent of pos+-aarthquake stability and settlements due to partial liquefac-l tion using state-of-the art techniques.
8.
Ar, assessment of nonseismic liquefaction based on state-of-the art techniques.
Subsection 2.5.4.9.
The in-depth staff evaluation of the safe shutdown and operating basis earthquakes is contained in SRP 2.5.2.
The staff's evaluation of the amplifica-tion characteristics of specific soils and rocks Deneath the site as determined ty procedures discussed in that section and in Suu: Actions 2.5.4.2, 2.5.4.4, and 2.5.4.7 are summarized and cross-referenced herein.
The review of Subsection 2.5.4.9 concentrates on determining its consistency or incon-sistency with other subsections. Cross referencing with other sections is expected.
Subsection 2.5.4.10.
Static analyses of the bearing capacity and settlement of the supporting soils under the loads of fills, embankrents, and foundations are evaluated by conventional, state-of-the-art methods (Ref 8).
In general, the evaluation pro-cedure includes:
1.
Determining whether or not the soil and rock properties used in the analyses represent the actual site conditions beneath the plant facilities. The site investigation, sampling, and laboratory test programs must be adequate for this evaluation.
2.
Determining whether or not the methods of analysis are appropriate for the earth-works, foundatians, and soil conditions at the site.
2.5.4-11 Rev. 1 146 038
3.
Coordinate with SEB to determine whether or not the bearing capacity, settlement, l
differential settlement, and tilt estimates indicate conservative and tolerable behavior of the plant foundations when these values are compared to design criteria and quality assurance specifications.
4.
Evaluation of particularly complex cases on the basis of accepted principles and techniques as supplemented by case histories and confirmatory measurement and analysis programs (Ref. 8).
Subsection 2.5.4.11.
Criteria and design methods, including construction control and monitoring systems, are evaluated on the basis of conservative accepted practice for similar facilities. Site exploration, sampling, testing, and interpretation are judged wi'h respect to completeness, care and technique, meaningful documentation, performance records for similar projects, published guidelines, and state-of-the-art practice.
However, unconventional or research-oriented tests and interpretations are encouraged whenever such work aids or supplements conventional practices. Design criteria and methods ?re compared to similar standards published or utilized by public agencies such as the U. S. o v Department, U. S. Army Engineers, and U. 5. Department of the Interior.
Design safety featu.<. the applicant's proposed confirmatory tests and measurements, and monitoring of performa ~e for safety-related foundations and earthworks are reviewed and evaluated on a case-by-case basis.
Subsection 2.5.4.12.
Techniques to improve subsurface conditions are evaluated by reviewing the applicant's specifications and techniques for performance and quality control for such activities as grouting, excavation and backfill, vibroflotation, rock bolting, and anchoring. Confirmatory data should be contained in the FSAR.
IV.
EVALUATIDN FINDINGS If the evaluation by the staff, on completion of the review of geotechnical engineering l
aspects of the plant site, confirms that of the applicant, the conclusion in the SER states that the investigations performed at the site are adequate to justify the soil and rock characteristics used in the design, 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 are 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 +395 feet mean sea l
level (msl). Exploratory bor ngs have been made anJ refraction and reflection i
s ei srai m 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. Groundwater at the site varies from +375 to +380 feet ms1.
Rev. 1 2.5.4-12 146 039
"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 e
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 weathere'1 slate is also present. The slate still retains the original rock structure, although it is sof t and partly friable. Quartz veins within the slate are extremely fractured. Seismic compression (P) and shear (S) wa.e velocities exceed 4000 f t/sec and 1800 f t/sec, respectively.
Zone l ranges in thickness from less than 20 feet to more than 50 feet.
(b) Zone 2 consists of moderately weathered slate and varies from 15 to 60 feet thick. P and S wave velocities generally exceed 6500 ft/sec and 2500 ft/sec, respectively.
(c) Zone 3 contains slightly weathered to unweathered slate and is encountered at depths of 60 to 90 ft below ground surface.
"The site area will be leveled to about elevation +390 feet msl, and containments will be founded on a 10 foot thick, reinforced concrete mat an slightly weathered slate or fill concrete over slightly weathered slate. The reactor service building between the reactors and the control building will be on mats at elevation v385 feet msl on compacted structural fill resting on slightly to moderately weathered rock.
The turbine generators will be founded on compacted structural fill over moderately weathered rock at elevation +380 feet msl.
The diesel generator build-ing, reactor plant component air-cooled hcat exchanger enclosures, and the CACS air-cooled heat exchanger will be founded on either individual concrete footings or continuous footings (grade beams) at +385 feet msl, on compacted structural fill over moderately weathered slate. Allowable bearing capacities f-om laboratory tests and field plate tests for Zone 1, Zone 2, and Zone 3 materials are 4,10, and 25 tons per square foot, respectively. All piping will be entrenched and bedded in moderately to severely weathered slate.
" Settlement and differential settlement of safety-related facilities has been estimated to be less than one inch.
"The applicant states that severely weatilered or sof t zones of rock will be exca-l vated 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 1-1/2 times the width of the zone and backfilled with concrete.
2.5.4-13 Rev. I 146 040
Category I structural backfill under structures will either De concrete or compacted granular backfill. It 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 dyramic conditions.
" Suitable borrow material for dikes, dams and impervious linings are available for the ultimate heat sink ponds. The applicant'; tests on these materials and the construction criteria to be followed ensure that ieakage, piping and cracking hazards of these vital earthworks are minimal. Filters, blar. at drains, relief wells, piezameters and settlement monuments will assure the reliable performance of the ultimate heat sink water-retention facilities.
"The applicant has shown that the appropriate acceleralion level on sound rock is l
0.12g for the safe shutdown earthquake (SSE). The cperating bases earthquake (OBE) value is taken as 0.06g.
The applicant has performed a site-d> pendent analysis to estimate the site amplification effects and found that the weatherea rock or structural backfill would amplify the rock motion. An acceleration level of 0.17g 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 j
design of Category I earth dams and for liquefaction assessment envelopes the response spectra for the site and has a conservative duration.
I O
" Based on the results of the applicant's investigations, laboratory and field tests, analyses, and criteria for design and construction, we conclude that the l
site and the plant foundations will be adequate to safely support the planned nuclear power plar.t and that safety-related earthworks will perform their functions reliably."
V.
REFERENCES 1
10 CFR Part 100, Appendix A, " Seismic and Geologic Siting Criteria for Nuclear Power Plants."
2.
Regulatory Guide 1.70, " Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants," Revision 2.
3.
Journal of tne Geotechnical Engineering Division, Proceedings of the American Society of Civil Engir.eers.
4.
B iak of ASTM Standards and Special Technical Publications, \\merican Society for Testing and Ma+erials.
Rev. 1 2.5.4-14 146 041
5.
Geotechnique, The Institution of Civil Engineers, London.
6.
Earthquake Engineering Research Center, University of California, Berkeley.
7.
M. Juul Hvorslev, " Subsurface Exploration and Sampling of Soils for Civil Engineer-ing Purposes," Waterways Evperiment Station, U.
S. Army Corps of Engineers, November 1949.
t.
aE0DEX INTERNATIONAL, Soil Mechanics Information Service: Sonoma, California.
9.
Regulatory Guide 1.132, " Site Investigations for Foundations of Nuclear Power Plants."
10.
Engineering Manual EMl!10-2-1907, " Soil Sampling," U.S. Army Corps of Engineers, March 1972.
11.
Engineering Manual EM110-2-1908, " Instrumentation of Earth and Rock Fill Dams,"
U.S. Army Corps of Engineers, August 1971.
12.
Engineering Manual EM1110-2-1906, " Laboratory Soil Testing," U.S. Army Corps of Engineers, November 1970.
2.5.4-15 j
R. 1