ML19321A037
| ML19321A037 | |
| Person / Time | |
|---|---|
| Site: | Vallecitos File:GEH Hitachi icon.png |
| Issue date: | 06/27/1980 |
| From: | ENGINEERING DECISION ANALYSIS CO., INC. |
| To: | |
| Shared Package | |
| ML19321A022 | List: |
| References | |
| EDAC-117-253.01, EDAC-117-253.01-R1-S, NUDOCS 8007220362 | |
| Download: ML19321A037 (24) | |
Text
.
EDAC-117-253.01, Revision 1 Supplement 1
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EXPANDED DESCRIPTION OF S0IL PRESSURE ANALYSES SUPPLEMENT NO. 1 TO ADDITIONAL INVESTIGATIONS TO DETERMINE THE EFFECTS OF COMBINED VIBRATORY MOTIONS AND SURFACE RUPTlRE OFFSET DUE TO AN EARTHQUAKE ON THE POSTULATED VERONA FAULT 4
prepared for GENERAL ELECTRIC COMPANY Vallecitos, California 27 June 1980 dF
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480 CALIFORNIA AVE., SUITE 301 BURNITZSTRASSE 34 PALO ALTO CALIF. 94306 6 FRANKFURT 70. W. GERMANY I
8 0 0 7 220 36R
1 TABLE OF CONTENTS Pag,e
-INTRODUCTION..............................
1 S0IL PROPERTIES............................
1 S0IL PRESSURE ANALYSES.........................
2 CONCLUSIONS..............................
3 4
REFERENCES l
APPENDICES A - Properties of Foundation Soils B - Discussion of Founda' ion Soils Properties C - Evaluation of Bear'.g Pressures at Footing Bases r
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EXPANDED DESCRIPTION OF S0IL PRESSURE ANALYSES SUPPLEMENT NO. 1 TO ADDITIONAL INVESTIGATIONS TO DETERMINE THE EFFECTS 0,F COMBINED VIBRATORY MOTIONS AND SURFACE RUPTURE OFFSET DUE TO AN EARTHOUAKE ON THE POSTULATED VERONA FAULT INTRODUCTION This report presents an expanded discussion of the soil pressure analyses described on pages 2 and 3 of Reference 1, and has been prepared in response to a request received from the USNRC (Reference 2). The soil pressure analyses were performed to determine the physical load limits on the combined load case comprised of a ground acceleration vibratory motion and a surf ace rupture offset, the latter represented analytically as an
" unsupported length" of the building (see Figure 1). Note that in Figure 1, and in subsequent figures, the plane of the offset has been shown as being vertical for illustration purposes only. Per Reference 5, the postulated dip angle varies from 10 to 45 degrees.
SOIL PROPERTIES Properties of the foundation soils beneath the GETR reactor Building have been described previously in Reference 3 (Page 3-6, Table 3-1, and Figure 3-4).
Table 3-1 and Figure 3-4 are reproduced in Appendix A of this report for easy reference. Based on these properties, an ultimate bearir.g capacity of'20ksf was developed as described in Appendix B.
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S0IL PRESSURE ANALYSES A series of analyses of soil pressures under the Reactor Building was performed for different combinations of one component of horizontal ground acceleration and " unsupported length". These soil pressures are produced by the vertical weight of the structure and the overturning moment produced by horizontal seismic forces. Effects of other ground motion components are discussed near the end of this section.
Soil cessures in the region of the edge of the supporting soil (Figure 1) we examined due to the application of vertical dead load and static lateral inertial forces. The inertial forces were determined from the previously performed linear dynamic analyses. To simplify the computational process, the foundation was assumed to be an equivalent rectangular plate (in plan). The procedures used to calculate the soil pressure distribution were the conventional methods for foundation design as described in Reference 4 relevant excerpts of which are reproduced in Appendix C.
In these analyses, " incipient local yielding" was defined as the loading combination which produces bearing pressure at the edge of the supporting soil equal to the ultimate bearing capacity (20 ksf).
The soil pressure diagram for this situation is illustrated in Figure 2a for the example case of an unsupported length, Lc, of 13 ft. For this example, yielding in the soil begins at a horizontil ground acceleration of about 0.269 The local mode of failure of the soil at the edge of the offset is shown schematically in Figure 3.
In this case, rapid loading which produces a soil pressure slightly less than the ultimate bearing capacity will cause the soil to deform n snown. Analyses were also performed for several other cases of unsupported length, and the horizontal earthquake accelerations at which incipient yielding in the soil occurs were plotted versus unsupported lengths as the lower edge of the band in Figure 4.
Thus, loading combinations of horizontal earthquake, gravity load, and unsupported length at which incipient local soil yielding will occur are shown grapnically by the lower edge of the band in Figure 4.
Load combinations greater than those at the lower edge of the band will induce additional soil yielding at the edge of the offset, which will result in j
the structure settling so as to be supported continuously or simply supported by the soil to the left of the offset zone in Figure 1. EDAC
3 As the horizontal ground acceleration, and thus the over-turning moment caused by the lateral force, increases above the value at which incipient local yielding occurs, the region of local soil yielding will be represented by a pressure diagram as shown in Figure 2b. Finally, an upper limit on local soil pressures can be represented as shown in Figure 2c.
For.the selected example of 13 ft. unsuppported length in Figure 2c, the maximum ground acceleration is about 0.38g. For this case, the mode of deformation of the soil in the region of the edge of the offset is shown schematically in Figure 5.
Rapid loading of the soil at pressures equal to the ultimate bearing capacity will induce movement of the soil as shown.
Analyses were also performed for other cases of unsupported length, and the resulting horizontal accelerations at complete local soil yielding were plotted versus unsupported length as the upper edge of the band in Figure 4.
The upper edge of the band in Figure 4 is a conservative estimate 'of the bound on cmplete local soil yielding in the region of the edge of the offset, at which point the structure will have completely settled down and be supported by the undisturbed soil to the left of the offset zone in Figure 1.
As discussed in the beginning of the text of this section, for simplicity in the calculations, the soil pressure analyses were performed for one component of horizontal ground acceleration. Subsequent analyses showed that inclusion of the vertical acceleration component will change the vertical amplitude of the band (ground acceleration) in Figure 4 by less than plus or minus five percent.
In addition, inclusion of the second horizontal component will lower the band in Figure 4 by about 7 percent.
CONCLUSIONS The soil pressure analyses described in this report demonstrated that there are physical limits on the cabined loading of vibratory motion and
" unsupported length", the latter of which is the selected analytical
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representation of the postulates. surf ace rupture offset.
Based on these soil pressure analyses, it was concluded that the structure will settle down for all load combinations above the band on Figure 4 Partial or
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complete settling down of the structure are conditions which can be easily tolerated without distress in either the soil or the structure. Only those load combinations which are below the band of Figure 4 actually nad be considered in the structural evaluations.
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SOIL PRESSURE DISTRIBUTIONS (For Example Case of 13hgtscLLaosth. k Ab
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DEFORMATION OF FOUNDATION SOILS
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REFERENCES 1.
Engineering Decision Analysis Company, Inc., " Additional Investigations to Determine the Effects of Combined Vibratory Motions and Surface Rupture Offset Due to an Earthquake on the Postulated Verona Fault,"
EDAC-ll7-253.01, Revision 1, prepared for General Electric Company, 8 May 1980.
2.
USNRC (R. A. Clark) Letter to General Electric Company (R. W. Darmitzel) 10 June 1980.
3.
Engineering Decision Analysis Company, Inc., " Seismic Analysis of Reactor Building, General Electric Test Reactor - Phase 2,"
EDAC-117-217.03, prepared for General Electric Company, 1 June 1978.
4.
Kramrisch, F., "Handbood of Concrete Engineering, Chapter 5 Footings,"
Ed. by M. Fintel, Van Nostrand Reinhold Co., 1974.
5.
USNRC (D. G. Eisenhut) Letter to General Electric Company (R. W. Darmitzel) 23 May 1980.
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APPENDIX A PROPERTIES OF FOUNDATICN S0ILS (Reproduced From Refe-e 4)
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TABLE 3-1 STRUCTURAL AND FOUNDATION MATERIAL PROPERTIES
- Structural Concrete Type 1 Concrete Type 2 Concrete Type 3 Concrete Prooerties (Ordinary)
(Macnetite)
(Ferrochocohorus)
Unit weight Y 150 lb/ft3 225 lb/ft3 230 lb/ft3 Modulus of clasticity, E
3.83x106 p3j 7,04 x 106 psi 9.78 x 106 psi Ccmpressive strength, f'
5,400 psi 3,400 psi 5,000 psi c
Soil Properties Beneath Reactor Buildinq*
Soil Tvoe 1 Soil Tyne 2 Moisture content, w
- 13. percent 15 percent Dry unit weight, Y 120 p;f 117 pcf d
Average total unit weight, Y 135 pcf 135 pcf T
Standard penetration resistance, N 50 - 100 blows /ft 50 - 100 blows /ft Shear modulus, G 1.1 x lo psf **
2.4 x 106 s
psf **
Shear velocity, V 500 fps **
750 fps **
3 Percent critical damping, A 11 percent **
11 percent **
- Soil properties are averages based on Shannon and Wilson 1973 data (Ref.10) and published correlations.
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APPENDIX B DISCUSSION OF FOUNDATION S0IL PROPERTIES (Prepared by Richard L. Meehan, Earth Sciences Associates)
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B-1 DISCUSSION OF FOUNDATION S0Il PROPERTIES INTRODUCTION Postulated simultaneous or near-simultaneous fault rupture and seismic ground shaking could cause relatively high local pressures on soils benheath the foundation slab of the GETR Reactor Building structure.
Because the underlying soils are weaker than the concrete of the slab, yielding of the soils will occur when the pressures reach a certain limiting value. This limiting value then provides an upper bound on the pressures which may exist beneath the slab.
If the structure imposes greater loads on the foundation, plastic yielding of the underlying soil will occur until the supporting soil area increases sufficiently so as to reduce the pressures to the limiting value. The point at which plastic yielding occurs depends upon the type of soil beneath the slab and the manner in which the load is applied (rapidly or slowly, locally or over a broad area).
50Il CONDITIONS BENEATH GETR Knowledge of soil characteristics ' eneath GETR comes from three sources:
o
- 1.. General knowledge of the characteristics of Livermore Formation soils, known from recent trenches, borings, and geologic mapping in the general vicinity of GETR.
2.
The following reports:
a.
Shannon and Wilson, Inc.,1973, Investigations of Foundation Conditions, G.E. Test Reactor. This investigation included two 70-ft. borings drilled near the reactor, various laboratory tests including triaxial strength tests, and an evaluation of bearing capacity under cyclic loadings.
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Dames and Moore,1960, Foundation I :vestigation Proposed Boiling Water Reactor, Vallecitos Atomic Laboratory. This report presents results of borings and tests for a different facility near the GETR site. Earth Sciences Associates (ESA) geologists believe that geological foundation conditions are similar at this other site, and that test data are generally applicable to the GETR foundation.
The 70-ft. diameter GETR foundation slab is founded about 20 ft. below grade, and rests on very dense clayey sand and gravel with the following trypical properties:
Water Content:
13 percent Dry Density:
120 pcf Standard Peletration N: 50-100 blows /ft.
Below a depth of about 50 ft., very stiff to hard gravelly clay is encoun tered. According to the Shannon and Wilson report, the water table is at or near foundation level, 20 ft. below ground surface.
LOADING CONDITIONS The following sequence of loading conditions is postulated:
1.
Approximately 1 meter of fault rupture occurs beneath the reactor.
Most of this movement is postulated to occur in several seconds, with perhaps the last few centimeters extending over a period of minutes.
2.
Nearly simultaneously, shaking of the ground occurs which causes vibration and cyclic loading of the reactor structure and foundation soils. These vibratory loadings are superimposed on the f ault rupture condition.
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B-3 This suggests that the peak loads of concern from a structural standpoint will be applied within a few seconds, rapidly enough so that pore pressures within the soil volume beneath the slab affected by high foundation loads - a volume with dimensions of tens of feet - will not dissipate by drainage. Thus, the soil loading will be in an undrained condition.
S0IL STRENGTH The following strength parameters are from the Shannon and Wilson report:
4 Minimum strength:
Ccu - 1000 psf deu - 16.5*
Maximum strength:
Ccu - 1400 psf deu = 31.5*
Plots of.the Dames and Moore data yield the following average results:
Ccu - 200 psf dcu - 22*
The shear strength at a confining pressure of 4500 psf (the piessure on the soil beneath the slab before the f ault or shaking loads occur) is as follows for the three sets of strength parameters:
1 S (S+W minimum):
2332 psf l
5 (S+W maximum): 4157 psf S (D+M)
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1 B-4 ULTIMATE BEARING CAPACITY Shannon and Wilson conclude that for earthquake-induced pressure concentrations beneath the foundation mat, the ultimate bearing capacity is controlled by the soils at shallow depth beneath the mat. Based on their minimum value of C = 0.5 psf and d = 16.5 degrees, they compute a bearing capacity from the Terzaghi formula of 20,000 psf. The loading condition they visualized is basically similar to the loading condition under consideration here.
Alternatively, ESA has considered the problem as one of rapid loading of soil, initially confined to a pressure of 4500 psf, whicn has a mean shear strength of 3300 psf, a value intermediate between Shannon and Wilson's minimum and maximum values.
For this approach, the Terzaghi bearing equation simplifies to:
Oult = sNc With Nc = 6, ultimate bearing capacity is 20,000 psf.
ESA therefore recommends use of the value of 20,000 psf as suitable for the loading and soil deformation condition shown on Figures 3 and 5 in the main body of this report.
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APPENDIX C EVALUATION OF BEARING PRESSURES AT FOOTING BASES (Reproduction from Reference 5) 1 4
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112 MANOSOOK CP CONCIETt ENGINEEmNG sgsrstructure; he must assume the appropriate sa y p
fac to arrive at the a!!owable bearing press
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'de on the most economical type o undation g
o*4 to be used.
this reason it is essential a foundation engineer to posse good knowleds the problems that
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are involved in the ign and chaviour of the super-structure, a certain familia with the basic principles of l
fe soil mechanics, and a go un anding of the interaction between both.
A detailed tre ent of above topics not fall within the scope is handbook; however, a short
- cussion of the footing base (reaction), must be of equal intensity and the bas' onsiderations affecting the evaluation and ribu-opposite direction.as the resultant of all loads andfor tio f the bearing pressures under footing bases is 31 vertical effects due to moments and lateral forces, acting on
- clow, the footing element (action).
- 2. The location where the resultant vector of the reac-5.2 EVAL.UATION OF BEARING PRESSURFS AT tinn intersects the footing base must coincide with the loca-FOOTING BASES ti n where the resultant c qtor of the action is applied.
Action and reaction are as c.efined under (I) above.
5.2.1 General Principles
- * ' * " " " ' " E" ' Y the most severe combmation of service loads must he The distribution of the bearing pressures under h concen.
smaller than, or equal to, the maximum beart gressure trict.llyloaded, infinitely stiff footing, with frictionless base, allowed for this kind of loading and type of soil, as deter-resting on an ideal, cohesionless or cohesive subsoil,8*2 is mined by principles of soil mechanics.
generally known, and shown in Fig. 51. Under ordinary
- 4. The resultant vector of the least favorable combination conditions few soils will exhibit such a behavior; no footing of vertical loads, horizontal shears, and hending moments could be considered to be infinitely stiff. The distribution that may occur under service load conditions, including of the bearing pressure under somewhat flexible footings wind or earthquake, must intersect the footing base within and ordinary soil conditions will be similar to those shown a maximum eccentricity that will provide safety against in Fig. 5-2; or it may assume any intermediate distributhn.
overturning.
The assumption of a uniform bearing pressure over the The method most commonly used for the design of entire base area of a concentrically loaded footing, as sh, wn footings and related elements for ordinary building construc-in Fig. 5-3, seems to be justified, therefore, for reasons of tion, is the one where static equilibrium is obtained by simplicity, and is common design practice.This assumption bearing pressures against the footing base only. This method not only represents an average condition, but is usually on is also the standard method that has been included in the the safe side because most of the common soil types will
" Building Code Requirements for Reinforced Concrcte" produce bearing pressure distributions similar to that shown ACI 318-71.
in Fig. 5 2a. The foundation designer, however, shall keep For zero eccentricities, the bearing pressures will be in mind that the assumption of e uniform bearing pressure uniformly distributed over the entire base area of the distribution was primarily made for reasons of simplicity footing as shown in Fig. 5-3 and will have the intensity and may, in special cases, require adjustment.
of q = P/Ag, Any footing Jhat is held in static equilibrium solely by lf the footing shall restrain the column base, i.e., if a beartng pressures acting against its base has to satisfy the bending moment has to be resisted by the subsoil alongsid following basic requirements regard!ers of whether it is an with a concentric load, or if the column load is applico iso ated or a combined footing:
outside of the centroid of the base area of the footing, the L The resultant of all bearing pressures, acting against bearing pressure distribution will vary depending on the magnitude of the eccentricity and its relationship to the p
p kern distance ck. The kern distance can generaily be evaluated as shown in Fig. 5 4 g
g When the eccentricity is equal to, or sma!!er than, the 1
kern distance c, the extreme (maximum or minimum) a l
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I beanng pressures q"*n' can be found by superposing the
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flexu 1 bearing pressures over the axial bearing pressures, q
g When the eccentricity becomes greater than the kern dis-Fig. 51 8 earing pressure distribution for a s'aff footing with fric-tance superposition cannot be applied anymore, because it tioniess base on ident sod. (a) on cohesionless sod (send); and would result in tensile stresses between soil and footing tb) on coheswe sod (ctay)*
near the lifted edge of the base. Equilibrium can, however, be attained by resisting the load resultant by a bearing P
pressure resultant of equal magnitude and location. In this case' the extreme bearing pressures at the edge of the base l
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can be evaluated as shown in Fig. 5-5b.The maximum edge pressure 4 man must, under all conditions, be smal!er or equal than the maximum allowable sad pressure, go.-
Q.
This condition applies until the excentricity, e, of the load, P, reaches the edge of the footing base. Any greater (a)
(b) eccentricity will result in overturning. Such a condition, Fig. 5 2 Beoring pressure distribution for a flexible footing oa however, can only occur on rock or on very hard, stiff soils.
ordinary sod. (a) on grenular soit; and tb) on clevey sod.
For most practical cases, edge-yielding can make a footing OFFICIAL EbAL VmtMA C. CMOUEIRO SM g@M93 - u-u-wmm comn f
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FOOTIN ~ S 113 tricity. Unless actual test results are available, the failure l,
condition in the beadne capacity of the soil, qf, can he assumed with about 2.5 times the allowable, bearing capac-ity, 4,; the minimum safety factor against overturning is i,
\\l usually specified as 1.50; although somewhat greater safety factors are sometimes desirable. Introducing these ity,"e max, that can safely be utilized. Ilow far the design to--- - *'
engineer will take advantage of this condition will depend on his judgment of the soil and on the sensitivity of the j
superstructure to tolerate lateral tilting that may occurif a loading, causing such an eccentricity,is applied for a longer l
period.5-3 1
M ments occurring alongside with concentric loads, raay Fig.5 4 Kern distance. (a) eks = /p:/Apa a: (bl /pg = moment be u iaxial or biaxial. If they occur in oblique directio it r
cf inertie of footing base about neutral axis 11; (c) : = distance is mo t practical to have their influence divided into wo (f extreme fiber et opposite side of cesired kern distance: (d) for perpen icular components, each of them parallel t the strips.cn = 1/6.
main a s of the footing mat, and superpose the r Iting f
hearing ressures. Such conditions occur not on with isolated s. read footings, but also with strip fru ings of limited ten th, as in the case of shear walls and si lar, Combine-footings, (i.e., footings supporting ore than q,,
one column ad, such as exterior double-colu footings),
strip footings s prorting spaced column loads, fts, or mats N
can be designe as described above, as long at the entire
- "--]I}--
foundation can e considered as infinitely s ff. In this case e
/,
the resultant of 11 bearing pressures must e equal to the
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resultant of allloa s, and its location must nincide with the w
T'l-k ' %h '..
. }. 'l ",,-..,. y,,..";;.
I eccentricity f th resultant. This app ach is statically
.b.
correct,but not nec ssarily close to the tual condition.
I I
N in certain cases i, may be advisa e to consider the I *
D'
',',,.'.,
- d, (' ' h footing as a beam on n elastic foun tion and utilize the n.
Elasticity of the footin mat as wel as that of the soil in the evaluation of the bearing essures. The bearing y
pressures obtainec by t is meth d no longer follow a straight line distribution a oss th contact area. They show g
maximum accumulsWns i mer' ately below, and in the
{'*iT l/,,
vicinity of, concentrat., lo ds nd greatly reduced inten-sities betwr-en a*,now n Fig. 5-6. Such a pressure
[
i distributior educe the m imum design moments of a 9 "11 T
c.
. i'e t
foundation.,siderably an therefore in many cases sl
quite economical. This ma od, in addition, intriguing in its setup and appealing e mecial to the mathematically s s
- - so, inclined engineer.5d e,42
'6f Q uee, p
p p
/
I
'/
l figs
!._., _J i-lllll}ll llllllllllllb llllll
d i
- / e, i
,, = h a,
- ,
- h, 7
i 3
' deformat line
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l s
9- -
y
._.. ;;. i,s. e t
v r e,. 2 Sa and sF a i s 7
l e,i2-a
.,.h.
actual simplified bearing pressure i
destribution
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Fig.5 5 Bearing pressure distribution under eccentric loading.
r, ex, M
A
/
unusable and produce a condition that is equivalent to V
V V
overturning. Edge-yielding will occur when the extreme bearing pressure at the pressed edge will cause failure in the moment distribution bearing capacity of the subsoil. The eccentricity causing this i. 51 GyeraQonditions for a beam on an elastic foundation.
condition will, therefore, limit the m2ximit% useful eccen 9
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