ML20244A471

Comments on Subj Facil Soil Study of Category I Struc. Studies 1-4 Conclude That Liquefaction Should Not Occur During the Simultaneous Occurrence of the SSE & the 25 Year Flood.Agrees W/Studies & Suggests a Portion Be Amplified

ML20244A471
Person / Time
Site:	Beaver Valley
Issue date:	07/15/1978
From:	Richart F AFFILIATION NOT ASSIGNED
To:	Fraley R Advisory Committee on Reactor Safeguards
References
TAC-6605, NUDOCS 7810030040
Download: ML20244A471 (3)

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• JUL 191973 f.] ,

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Ib S. ,, PROF. OF civil ENG.

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July 15, 1978 Mr. R.F.- Fraley, Executive Secretary Advisory Committee on Reactor Safeguards U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Re: Beaver Valley Power Station-Unit No.1-Soil Study, Category I Structures

Dear Mr. Fraley:

In his letter of March 24, 1978, Mr. Ragnwald Muller forwarded a. request from Dr. W. Kerr that I review papers No. (1) , (2) , and (3), noted below, and return my comments on NRC Staff actions thereon. In reviewing these papers, I noted that a report of laboratory tests was anticipated on April 1, 1978, and I requested this report. -The paper j covering laboratory soil tests, noted as (4) below, was j j sent to me on June 5, 1978. }

(1) Summary of Meeting with Dusquesne Light Company on Nov.

15, 1977, to discuss the Soil Study Program at Beaver j Valley' Power Station-Unit No.1 (U.S. NRC letter,12/22/77) i (2) Soils Study-Category I Structures (Response to NRC l' l letter of 11/17/76) Beaver Valley Power Station- Unit No.1. Duquesne Light Company, Feb.,1977.  !

j (3) Supplement to Soil Study dategory I Structures (Response l to NRC Meeting of 11/15/77) Beaver Valley Power Station- l Unit No.l. Shippingport, Pa.,Jan.13,1978.

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(4) Supplement No.2 to Soil Study-Category I Structures (Re- ,

sponse to NRC Meeting on 11/15/77) , Beaver Valley Power  !

Station-Unit No.1, Shippingport, Pa., May 1, 1978.

1 The procedures described in paper (3) represent the l .' l present state-of-the-art for evaluating the liquefaction ]

potential of soils, based on observations from previous j j earthquakes. The improvements to include the effect of l gravel on the observed blow count and the reanalysis of Ny l values, based on recently published Cg curves were needed to -

l update the previous study. From this study it appears that j

-i liquefaction should not occur during the simultaneous occur- l

'l rence of the SSE and the 25-year flood. I agree with this I

- i presentation.

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I The NRC staff request for a check on potential lique-faction based on laboratory t'est data seems reasonable.

Paper (4)' describes -the tests, briefly, and gives most of

(. the test data. The results of the laboratory tests also indicate that liquefaction should not occur during the simul-taneous occurrence of the SSE and the 25-year flood. However, some details of the testing program are not adequately de-scribed in the. paper (4), and it would assist evaluation: of the presentation if information could be obtained from Duquesne Light Company (or Stone & Webster) concerning the following points.

(a) In the triaxial tests it is indicated that the reconsbi-tuted samples were "anisotropically consolidated and test-ed isotopically ". The Summary Sheet in Appendix A of paper (4) gives 5-c which should~be the isotropic effect-ive confining pressure. However, I find no indication of the anisotropic consolidation.pressurcs.

(b) The cyclic triaxial test data have the usual appearance, but the' stress history applied to each sample is not

. clearly identified. For example, from p.5," Initially a sample (Test No.1) was anisotropically consolidated, backed off to isotropic conditions and statically tested by increasing the pore pressure to approximately 85 per-cent of the chamber' pressure. The pore pressure was then gradually released and the change in volume recorded as the' pore pressure dissipated. The sample was then cycli-cally loaded for 10 cycles at a stress ratio of 0.09."

Then, apparently after all pore pressures had dissipated, the sample was tested in the undrained condition at B- =

39.6 psi.and ( c' = 11.2 psi. until liquefaction occurredataboub46- c3 )cY cycles. It would be useful to have the stress histories defined for each sample.

(c) The dynamic settlement analysis described on p.5 of paper (4) was based on the average of the pore pressures devel-oped in the three samples after 8 cycles, as noted in Appendix D. I do not find numerical identification of B-applied to these samples, but the text, p.5, states, "A c stress ratio of 0.09 corresponds to the applied shear stress during the SSE for the deepest sample of interest."

The value of c'c is 46.8 psi (from Summary Sheet) for the deepest sample. Then the stress ratio of 0.09 requires that a1 - c3 = 0.42 psi, which checks with the value scaled from the Test #1 and Test #3, Cyclic Stress, Strain, and Pore-Water Pressure Time History plots in Appendix B.

! The stress ratio of 0.12 gives c1 - c3= 11.2 psi, which also checks with the diagram. At 0 cycles the A U/5-c values scaled from the diagram are about 0.11 and 0.09 for Tests #1 and #3, and 0.24 for Test #2. An average of those three values is less than the O.16 noted on p.6.

There is no indication of how the value for Test #2 was e

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' corrected to correspond to a stress ratio of 0.09, the maximum value from the three tests was not used..or why' -

ri The section.in paperJ (4) covering Dynamic Settlement $

l Analysis should be amplified to include a complete descrip- {

tion of.the tests and method of analysis. j

Conclusions:

From a review of the papers -(l) through (4) , I am satis-fied that the present state-of-the-ar,t has boon followed to evaluate the liquefaction potential of the . loose soils below Beaver: Valley Power Station-Unit No.l.

lagainst suggest that liquefaction is calculated to be adequate.'The factor

.Iofdosafety paper (4) the section on Dynamic Settlement Analysis in be amplified for the benefit of future readers.

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Very truly yours,  !

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F.E. Richart,Jr.

FER/b W.J. Emmons Professor of Civil Engineering s

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