ML20210B246
| ML20210B246 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon, FitzPatrick  |
| Issue date: | 06/23/1983 |
| From: | Costantino C NRC |
| To: | Reich M NRC |
| Shared Package | |
| ML16340C148 | List:
|
| References | |
| FOIA-86-151 NUDOCS 8609180009 | |
| Download: ML20210B246 (4) | |
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i ATTACHMENT NO 3 DATE: June 23, 1983 T0:
M. Reich FROM:
C. J. Costantino
SUBJECT:
Trip Report for IDVP Technical-Interchange Meeting of June 8-10, 1983 held at R. L. Cloud & Associates On June 8, 9, and 10, a staff team consisting of J. Knight, Assistant Director for Components and. Structures Engineering of NRC, B. Jagannath of SGEB/NRC and C. J. Costantino of BNL attended a techncal interchange meeting with the Independent Design Verification Program (IDVP) staff and PGE/Bechtel Diablo Canyon Project (DCP) staff. The areas discussed were the ITR reports issued by the IDVP associated with soils and soil related activities, namely, ITR 13, 16, 39 and 40. After lengthy discussions between the IDVP staff and the audit team, the following areas of concern were mentioned.
BACKFILL STRENGTH PARAMETERS ITR 39 presents a summary of the dynamic lateral stress analysis for the 0
Intake Structure, in which a soil friction angle of 45 is used to represent the strength of the backfill soil. The value was arrived at in the following fashion.
First, the sample blow counts taken from the.
boring logs were noted to vary from 14 to about 100 blows / foot. This range of blow counts was then compared to similar results for a very dense, clean, well graded sand, obtained from standard references, i
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The audit team disagrees with this conclusion for several reasons.
First, the blow count data obtained from the boring logs was for a different sample (3" 00) and hammer size / drop (325 lbs.,'18 in.) than that of the Standard Penetration Test- (2" OD split spoon sampler,140 hammer, 30 inch drop). THe SPT data is required to compare with the standard data. Secondly, the backfill is a gravelly soil with a clay / silt binder. The triaxial test data presented for this material by HLA indicates a much lower friction angle. Thirdly, the placement criteria for the backfill specifies a minimum of 95% relative compaction. This ordinary placement criteria.will not lead to a very -
dense condition for the backfill.
It was stated at the meeting that the reason for using this high friction angle is to somehow account for the known cohesion of the backfill which cannot be accounted for in the formula for lateral earth force computation friction.
It is-the feeling of the audit team that rather than use this formula, the complete analysis be used for the earth forces, including the effects of both cohesion and ~ friction angle.
DYNAMIC LATERAL EARTH FORCES In ITR 39, the lateral earth forces are computed using a pseudodynamic Rankine analysis.
In addition to the friction angle problem for the backfill mentioned previously, the IDVP did not include the effects of j
the peak vertical acceleration in the force computation. The justifi-j' cation for this emission mentioned at the meeting is that:
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The fault zone is located close to the site leading to significant differences in arrival times of the peak horizontal and vertical acceleration, and,
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M. Reich 3-June.23, 1983 b.- For such strong motion records, the peak g's of both pulses decay rapidly with time, and multiple peaks of the same magnitude will not occur.
It is the opinion of the audit team that this assumption is questionable '
when using such an approximate method of anlaysis and further justifica-
- tion is required. Of more importance, nowhere in the ITR is the overall sliding factor of safety mentioned, so as to make impossible the assess-ment of the impact of this assumption.
In addition, the IDVP used some comparisons with stress distributions 1
obtained for braced excavations in their. analysis. Again, it is the opinion of the audit team that such a comparison has no place in the analysis for lateral stress distribution from backfill placed against such a rigid structure.
ROCK BEARING CAPACITY It is the opinion of the audit team that an insufficient assessment of the bearing capacity of the bedrock was made by the IDVP.
Firstly, a single triaxial strength test was.made by HLA (actually two tests at the same confining pressure leading' to similar results) from which strength was derived. Unfortunately at least two, and preferably three such~
tests, each at different confining pressures, must be made to assess the choice for cohesion and friction angle for the rock used by HLA. Short 4
of this data, only the strength from that single test can be utilized.
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o M. Reich June 23, 1983 The data presented by the IDVP'from their separate calculations of the rock test data is incorrect and should be removed.
In addition, the single piece of data from the literature mentioned in ITR 39 (which is ten times higher than the test data) should not be used to assess the bearing capacity. This rock is normally expected to be extremely variable, and some average data from other sites has no bearing on this analysis without extensive justification.
Again, since overall safety factors are not calculated in the ITR's, no assessment of the impact of these judgments can be made.
It should be noted that no dynamic bearing capacity calculations were made for the Intake Structure.
CONCLUSIONS Aside from the specific comments _ mentioned above, it is the recommendation of the audit team that a single ITR be issued, tying
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together all the soil / rock related activities, and including the overall assessments of bearing capacity, earth forces and safety so that the impact of the assumptions made in the various analyses can be suitably judged.
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