ML19345B774
| ML19345B774 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 11/25/1980 |
| From: | Frederick Brown ARMY, DEPT. OF, CORPS OF ENGINEERS |
| To: | Knight J Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8012020490 | |
| Download: ML19345B774 (3) | |
Text
--
O'g, DEPARTMENT OF THE ARMY WATERWAYS EXPERIMENT STATION. CORPS OF ENGINEERS P. O. BOX 631 VICKSBURG, MISSISSIPPI 39180 WF.SGH 2 5 i:i, ;.,
.. n o,.u.,..
Mr. J. P. Knight Site Analysis Branch Directorate of Licensing Regulation Nuclear Regulatory Co= mission Washington, DC 20555 i
Dear Mr. Knight:
As requested, we are sending you a review of Dames and Moore's report entitled " Liquefaction Potential Under Genoa-3 Stack Adjacent to Lacrosse Boiling Water Reactor (LACBWR) Near Genoa, Vernon County Wisconsin," dated October 1980 (Incl 1).
If you have any questions concerning this reviev, please call Dr. W. F.
Marcuson, III, at FTS Sk2-2217 Sincerely, (fI l
1 Incl F. R. BROWN As stated Engineer Acting Director
- 4
/00f S
//
80120204')0 f
1
Review of
" Liquefaction Potential Under Genoa-3 Stack Adjacent to Lacrosse Boiling Water Reactor (LACBWR) Near Genoa, Vernon County Wisconsin" By W. F. Marcuson, III I have reviewed the above-mentioned report prepared by Dames and Moore and, in general, agree with their conclusion that the soils at the Genoa-3 Stack site probably vill not liquefy under the safe shutdown earthquake (S3E) producing a peak acceleration of 0.12 g at the ground surface or at the foundation level. This analysis assumes that these motions are generated by a magnitude 5.6 seismic event.
As a result of my review, some specific questions and cc=ments arise, as follows:
a.
Page 2, paragraph 3.
Dames and Moore state " Occasionally at greater depths some isolated pockets of organic materials, compressible clays, and loose shells were encountered." Da=es and Moore should provide the data which indicate these, in fact, are isolated pockets instead of continuous layers of loose materials, b.
Pacas 5 and 6.
Dames and Moore state that "the water table was assumed 10 ft belev grade." How many days a year is the water table above this elevation?
c.
Page 8, first paragraph. Dames and Moore state "The lower bound of the cyclic shear strength is considered as the design cyclic shear strength for both the hydraulic fill and the natural material at G-3 site.
This assumption is ecnservative." On Figure 18, the hydraulic fill shows lower strength (one value shown) than the lover bcund of the other test data. Why shouldn't the data from the hydraulic fill material be extrapolated and used if a conservative cyclic strength is desired? Hydraulic fill strength should be used for soils above 30 ft, according to Figure 17 d.
Tables 2 4.
Seed's information concerning r as a function of d
depth show that there is a considerable range of possible r values belcw d
a depth of h0 ft.
Average values may not be conservative.
I would recommend using correction factors (r ) of no less than 0.85 for depths lesc than 60 to 65 ft.
This vill charge some of the factors of safety presented in the report.
e.
Table 5 A spot check of calculations shown in this table indicates that the effect of the soil surrounding the stack foundation above a depth of 7 ft on both the total and effective stresses beneath the stack has been neglected. The effect of this en factor of safety is most pronounced beneath the edge of the stack.
If the effect of this neglected soil layer
is taken into account, the cyclic shear stresses as shown in Teble 8 vill be increased. For exa=ple, at a depth of 30 ft below the edge of the foundation, the stress level vill be increased frem 282 to 328 psf.
f.
Figures 15 and 16. The points plotted in these figures that fall nearest to the liquefaction threshold curve appear to represent soils in the i
depth interval of 20 to 30 ft in borings DM-16 and DM-18, both at the edge of the stack. This suggests that the factor of safety against liquefaction for soils in that interval is consistently marginal.
It is ny opinion that liquefaction is improbable at the site, as concluded by Dames and Moore, because of the relatively small SSE otions assumed, the fact that the stack places relatively large consolidation pressures on the underlying soil, and the fact that the SPT N values under the stack are slightly greater than the SPT N values obtained in the Lacrosse free field.
However, it is my opinion that the margin of safety is less than resuired te give complete confidence in the safety of the stack.
Therefore, I r>eonmend that the stack be assumed to fail and measures be taken to prevent it from interfering with Lacrosse.
2