ML13310B091
| ML13310B091 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/28/1983 |
| From: | Medford M Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-02-04.F, TASK-2-4.F, TASK-RR NUDOCS 8311300170 | |
| Download: ML13310B091 (21) | |
Text
{{#Wiki_filter:Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE
- ROSEMEAD, CALIFORNIA 91770 M.O. MEDFORD TELEPHONE MANAGER, NUCLEAR LICENSING November 28, 1983 (213) 572-1749 Director, Office of Nuclear Reactor Regulation Attention: D. M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 SEP Topic II-4.F San Onofre Nuclear Generating Station Unit 1 By letters dated April 18, September 1 and September 20, 1983 we submitted our revised report concerning backfill soil conditions at San Onofre Unit 1 as well as Addenda 1 and 2 to this report. In response to subsequent questions from the NRC, provided as an enclosure to this letter is Addendum 3 to that report. Addendum 3 describes the methodology for calculation of shear modulus values at San Onofre Unit 1 and presents the modulus values used for each structure. If you have any question on this information, please let us know. Sincerely, Enclosure 8311300170 831128 PDR ADOCK 05000206 PPDR
ADDENDUM 3 TO REPORT ON SOIL BACKFILL CONDITIONS SAN ONOFRE NUCLEAR GENERATING STATION UNIT 1
ADDENDUM 3 SHEAR MODULUS VALUES USED IN SOIL STRUCTURE INTERACTION STUDIES SONGS 1
1.0 INTRODUCTION
This addendum describes the calculation of shear modulus values used for determining spring constants for soil structure interaction studies at SONGS 1. Specifically, Section 2 describes the general process for calculating shear modulus and spring constants used for soil-structure interaction analyses and the sensitivity to soil conditions and Section 3 presents the modulus values used for each structure. 2.0 METHOD OF CALCULATION OF SPRING CONSTANTS AND SENSITIVITY TO SOIL CONDITIONS All soil at the site is either native San Mateo Sand to a depth of 1,000 feet or recompacted San Mateo sand backfill overlying the native soils. The distribution and density of the backfills at the site have been discussed in detail in the soil backfill conditions report (Ref. 1). The shear modulus values for this material are dependent on confining pressures, seismic input (strain level) and density (rela tive compaction) as shown in Figure 1 (Ref. 1 and Ref. 2). In the SONGS Unit 1 seismic reevaluation, the initial spring constants for foundations were calculated assuming that the foundations were founded in native San Mateo Sand or fill compacted to 95 percent relative compaction (Ref. 1). As the reevaluation progressed, it was noted based on field observations that in some cases backfill was compacted to less than 95 percent relative compaction. The lowest average relative compaction for backfills was determined to
-2 be 85 percent (Addendum 1). The effects of lowering the density of the backfill on the spring constants are two fold: (1) As shown in Figure 1, at 85 percent relative compac tion (50 percent relative density) the modulus would be computed by multiplying the modulus at 95 percent relative compaction for Design Basis Earthquake level excitation (2/3 g) by a reduction factor (Rf) of 0.79.. Because the spring constant is proportional to the shear modulus (Ref. 3), the difference between the spring constant for a surface foundation on soil compacted to 95 percent relative compaction and a soil compacted to 85 percent relative compaction would be in direct proportion to the difference in shear moduli. (2) For embedded foundations, the degree of compaction can also effect the contact efficiency of the embed ment stiffness. For example, for the San Mateo Sand the contact efficiency of backfill compacted to 85 percent relative compaction is taken to be half that of a backfill compacted to 95 percent or higher relative compaction. To demonstrate the sensitivity of the spring constant to the relative compaction, three cases have been defined as shown in Figure 2. Case 1 shows a foundation supported completely in native San Mateo Sand. As indicated in Reference 2, the shear modulus for use in computing a spring constant would be calculated at a depth of one half radius below the foundation. The overburden pressure in the shear modulus equation in Figure 1 would be based on 0.9 times the total bearing pressure of the foundation plus the pressure imposed
-3 by the weight of soil between the base of the foundation and point A. In all
- cases, effective parameters should be considered to account for the water table.
For the case 1 footing in Figure 2 the total spring constant Kl' would be calculated by: Kl' = KlC 2 = Kl + AK 1 where C2 is the embedment correction factor, K1 = the unembedded stiffness for vertical, horizon tal, rocking, or twisting response, and AK 1 = the corresponding portion of stiffness attributed to embedment. For purposes of this example, C2 is assumed to be 1.5 for case 1 in Figure 2; therefore, Kl' = 1.5K 1 and AK 1 = 0.5K 1. Because K1 is directly proportional to G calculated below the base of the foundation and Kl' is directly proportional to Kl (Ref. 2 and 3), it follows that Kl' and AK1 are directly proportional to G calculated below the base of the foundation. Therefore, for case 1 in Figure 2, K1 ' can be calculated knowing the size and bearing pressure for the foundation. For the same foundation with the case 2 soil condition, K 2 ' would be: K 2 ' = K2 + AK 2 Because K2 = K, and AK2 = 0.79 (0.5) AK 1 (i.e., Rf = 0.79 and contact efficiency factor = 0.5), it follows that: K 2 ' = Kl + 0.4 AKi Because AK 1 = 0.5K 1, it follows that: K 2 ' = Kl + 0.2 K1 = 1.2 K1 and in terms of.Kl', K 2 ' would be:
-4 K2' =1.2 =0.8 Kl 1.5 Therefore, for the example given above, the spring constant for case 2 would be 20 percent lower than for case 1 even though the footing was still founded on native soil. For the same foundation with the case 3 soil conditions, K3 ' would be: K3' =K3 + AK 3 Because K3 = 0.79 K1 and AK 3 = 0.79 (0.5) AK1, it follows that: K3' = 0.79 (Kl + 0.5 AK l ) Because AK1 = 0.5K1, it follows that: K3' = 0.79 (K1 + 0.25 Kl) = 0.99 Kl and in terms of Kl', K3 ' would be: K 3 ' = .99 0.66 K1 ' 1.5 Therefore, for the foregoing example the spring constant for case 3 would be 34 percent lower than for case 1 even though the shear modulus for the supporting soil was only 21 percent lower. Based on the examples described above, it can be seen that the embedment effects are significant in developing the reduction factors to be applied to case 1 conditions to obtain the spring constants for case 2 and 3 conditions. These reduction factors have been documented for each structure.in Reference 1, Sections 4 and 5.
-5 3.0 MODULUS VALUES USED IN SPRING CONSTANT CALCULATIONS Table, 1 tabulates the value of shear modulus or the range of shear moduli calculated for structures. Where a single value is used for a specific structure or significant element of a structure, like the turbine pedestal, it is shown as one value. If, however, the shear modulus values were for spring constants for nodal points on a structure or small elements of a structure, the maximum and minimum values are presented. Also, Figures 3 through 8 (cross referenced to structure in Table
- 1) show plan and cross section views of the foundations, the soil condition adjacent to and beneath the foundations and the values of shear moduli used in the analyses.
In the case of the Turbine Building, the 480 Volt Room and the Control Building
- footings, typical examples of moduli are shown in the figures.
As indicated in Section 2 above, the backfill conditions are also significant.
- However, the modulus of the backfill is not shown in Figures 3 through 8, because all calculations -of spring constant-are expressed in terms of the modulus of soil beneath the foundation as discussed in the preceeding section (References 2 and 3).
In addition to the foregoing discussion, the calculation of the vertical spring constant for the Fuel Pool is provided in Attachment A as a detailed example of the procedure.
REFERENCES
- 1. "Soil Backfill Conditions" enclosure to letters K.
P. Baskin (SCE) to D. M. Crutchfield (NRC) dated April 18, 1983 and September 1, 1983.
- 2.
"Material Property Studies, San Onofre Nuclear Gener ating Station," San Onofre Nuclear Generating Station Units 2 and 3
- PSAR, Amendment 11, Attachment A3 to Appendix 2E, March 13, 1972.
- 3.
"Balance of Plant (BOP) SONGS Unit 1, Soil-Structure Interaction Methodology Report", Revision 1, Woodward Clyde Consultants, Orange, California, July 1978.
TABLE 1
SUMMARY
OF SHEAR MODULUS VALUES USED FOR SSI PARAMETERS Figure Showing Range of Shear Typical Structure Modulus Values (ksf) Value of G Turbine Building Pedestal 1189 3 Extension footings 298-822 4 Fuel Storage Building Fuel pool 1244 5 480V Room footings 210-992 6 Ventilation Building 274-364 7 Control Building 296-1167 8a, 8b
600 G (psf) = 100 Km(am 2/3 Native San Mateo Sand am =2/3 ao 500 -= effective overburden pressure (psf) 1/100 g Dashed curves are based on response analyses with the indicated acceleration 400 giving the peak ground acceleration used in analysis. 300 K 95%+ Relative Compaction 1 /20 g* 200 1 / 0 g 2 / 1 0 g
- 85% Relative Compaction 100 1/3 g*
100 -2/3 g 1-4 10-3 10-2 10-1 100 Shear Strain,7 % Project: SONGS UNIT 1 SEISMIC RE-EVALUATION MODULUS AS A FUNCTION OF STRAIN AND Fig. Project No. 413521 PEAK GROUND ACCELERATION WOODWARD-CLYDE CONSULTANTS
CASE 1 ~N /Foundation Native San Mateo Sand r/2
- A Backfill compacted to 85%
relative compaction CASE 2 Native San Mateo Sand r/2 A CASE 3 Foundation Backfill compacted to 85% relative compaction SCHEMATIC DIAGRAM (CROSS SECTIONS) OF 3 CHARACTERISTIC FOUNDATION SUPPORT CONDITIONS FIGURE 2
Anchor Block 2 Turbine Pedestal Mat Foundation ] H H Anchor Block 1 I 2 0 10 20 30 Feet Backfil 20-85% R.C. Backfill LU L10 0 > r/2=24.25 LU -J LU 20-G=1189 ksf -20 Backfill Backfill 20 92% R.C. SECTION 1-1 90% R.C. O 0Anchor Block 1 TubnAnchor Block 2 Generator r/2=24.25 -Pedestal Native San Mateo Sand G=1189 ksf SECTION 2-2 SHEAR MODULUS FOR TURBINE BUILDING PEDESTAL FIGURE 3
2 Native San Mateo Sand Backfill 85% R.C. O 10 20 Feet (Column loads = 180.20 kips) UJ 1 +20 LL O +10 S+0Native San Mateo Sand u-- o L -r/2=9' 0
- SECTION 1-1 G=584 ksf u
(Column loads = 180.20 kips) ua +20 Z 85% R.C. z O +10 Native San Mateo Sand ui Lr/2=9' -j 0 SECTION 2-2 Native San Mateo Sand G=584 ksf TYPICAL SHEAR MODULUS FOR TURBINE BUILDING EXTENSION EAST FOOTING A FIGURE 4
WT El. +5.0 ft 20 Wall J (Col. load = 3.43 kips/ft) Wall L (load 1.78 kips/ft) Wall( Slab 480 V Switch Gear Room W r/2=0425
- 2.
A1.5' -Walls z G=40 ksfG=328 ksf / G k85% R.C. Fuel -W Backfill Pool Area 2 2 L -20 SECTION 1-1 / -480 V Switch Gear Room Wall 480 V Switch 1.5' Gear Room 20 -Wall K1 (load = 3.43 kips/ft) El. -2.8 ft WalO H Fuel r/2=0.425' E+-fW 10-Storage Building Native San Mateo Sand z 1 0 85% R.C. G=646 ksf Backfill -J -10 tu 0 10-20 Feet -20 SECTION 2.2 TYPICAL SHEAR MODULUS FOR 480 VOLT ROOM FIGURE 5
2 North Footing Fuel Pool 480 V Switch Gear Room -2 0 10 20 Feet 20 - North Footing I L 10 - Fuel Pool 00 Concrete Backfill O 0 Backfi! 271, 85 R.C. r/2=13.70' Native San Mateo Sand -G=1244 ksf -20 20 - 480 V Switch Fuel Pool Gear Room (Total Bearing u 10 -Pressure=
- u.
5.43 ksf) z z 0 Backfill 85% R.C. 0 Backfill 85% R.C. S r/2= 13.70' m Native San Mateo Sand G=1244 ksf -20 L-SHEAR MODULUS FOR FUEL POOL FIGURE 6
2 B=1.5 2 0 10 20 Feet Ventilation Building +20 - r/2=0.45' r/2=0.45' Fuel G=364 ksf Lu +10 - G=274 ksf Storage UL Building O 0 Native San Mateo Sand Backfill 85% R.C. LUj -j -10 LU -20 SECTION 1-1 Pipe Ventilation +20 Tunnel Building Reactor Ptr/2=0.45 r/2=0.45' Auxiliary Building G-274 ksf Backfill 85% R.C. LL u.G= 274 ksf 0 0 Native San Mateo Sand Backfill 85% R.C. u -10 LU TYPICAL SHEAR MODULUS FOR SECTION 2-2 VENTILATION BUILDING FIGURE 7
222 I El. 17.5' El. 18.5 112 21 El. 17.5 E.\\ 161El.5'. 2E .l 1 0.5 ' E10. E2 16l.105 L~ Soil Compacted to 85% Relative Compaction El. 10' 0 10 20 Feet SHEAR MODULUS FOR CONTROL BUILDING FIGURE 8a
load = 8.2 kips/ft 20 -Control Building Backfill 85% R.C. LuI u 10 - r/2=0.76' G=801 ksf z 0 Native San Mateo Sand 0 0 Lu -J -10 LU -20 L SECTION 1-1 (from Figure 9a) load 7.7 kips/ft Control Building 85% R.C. Backfill 20 r/2=0.47' U 10 G=756 ksf Native San Mateo Sand z O 0 -10 LU -20 SECTION 2-2 (from Figure 9a) SHEAR MODULUS FOR CONTROL BUILDING FIGURE 8b
ATTACHMENT A EXAMPLE OF VERTICAL SPRING CONSTANT CALCULATION FOR FUEL POOL Calculation of Vertical Spring Constant Step 1 - Calculate G From Figure 1, G = 100 Km (am)2/3 where Km = strain dependent factor = 50 for 2/3 g earthquake as shown in Figure 1 am = mean confining pressure = 2/3 overburden pressure am = 2/3 [os + 0.9 Gb) where as = pressure due to soil between structure and point r/2 below the structure (note r = 27.4 feet and is average radius for all modes of vibration) buoyant unit weight of soil = 138-65 = 73 pcf Gb = total bearing presure = 5430 psf Gin =2/3 [73 (13.7) + 0.9 (5430)] = 3925 psf G = 50 (100) [3925]2/3 = 1.244 x 106 psf = 1244 ksf Step 2 - Calculate Kl' for 95 percent compacted backfill or better Kl' =[-f-vv -LWj Cl C2 = vertical spring constant (kips/ft) where G = shear modulus = 1244 ksf v = Poissons Ratio = 0.35 v = shape factor dependent on L and W W and L = the width and length of the structure, respectively Cl = stress distribution factor = 0.81 C2 = embedment factor = function of h/r where h = depth of embedment and r = effective radius LW
W 73.3 (30) r
= 26.5 feet (note: the 27.4 feet in Figure 6 represents the average for all modes) Average embedment = h = 16.8 feet h/r = 16.8/26.5 = 0.61 2.0 CN a 1.5 -1.45 1.0I 0 0.5 1.0 1.5 2.0 h/r
-2 For W/L = 0.4m v= 2.3 from reference 3 K =r1244 K' [1-0.35 (2.3) 73.3 (30)] 0.81 (1.45) = 2.4 x 105 k/ft Step 3 - Calculate portion of spring constant due to embed ment, AK 2 For this case: the north, south, and west sides have 85 percent relative compaction backfill and the east side has concrete backfill transferring load to native soil. Therefore: AK 2 = AK 1 Al + Rf A 2 A where subscripts 1 and 2 refer to cases 1 and 2 in Figure 2, A = total side wall area, Al = total side wall area in contact with native soil, A 2 = total side wall area in contact with 85 percent compacted soil Also, using a contact efficiency factor of 0.50 for the 85 percent compacted soil, the stiffness is further reduced as follows: AK 2 = AK1 [Al + 0.50 Rf A 2 ] A In addition, 7.75 feet of the soil backfill is below the water table and is susceptible to the effects of liquefaction which further reduces the stiffness by 90 percent, i.e.. to 10 percent of where it was without liquefaction. Therefore, an additional reduction factor should be applied to the A 2 in proportion to the depth of soil below the water table. This factor is taken to be: [0.1 hw + (h-hw)] where h = total embedded height of wall hw = embedded height of wall below the water table
-3 Therefore AK 2 AK1 Al + 0.50 Rf A 2 0.1 h + (h-hw) A h For constant embedded height, h, the area, A, can be substi tuted by perimeter length, P, as follows: AK2 AK1 [P + 0.50 Rf P2 (h-.9 hw)1 A P h h For P = 2 (30) + 2 (73.3) = 206.6 feet Pl = 30 feet P2 = 206.6-30 = 176.6 feet h = 16.75 feet hw = 7.75 feet Rf = 0.79 AK 2 = AK [30 + 0.5 (0.79) (176.6) (16.75-6.98)] 206.6167 AK 2 = 0.34 AK 1 Step 4 - Calculate K 2 ' for all embedded soil conditions K 2' K + AK 2 K + 0.34 AK 1 C2 C 2 = Kl' + 0.34 K1' (C2-1) C2 C2 K1 [1 + 0.34 (C2 -1)] C2 K1 [1 + 0.34 (1.45-1)] 1.45 = 0.80 K1 ' Because Kl' = 2.4 x 105 k/ft K2.= 0.8 (2.4 x 105) = 1.9 x 105 k/ft}}