ML20077H647

Requests Compaction Requirements for Category I Backfill, to Be Placed Around Piping & Similar Conduits,Be Changed from Average 97% Max Dry Density,Per ASTM D1557,to Average of 95%.Change Will Be Implemented by 830901

ML20077H647
Person / Time
Site:	Vogtle
Issue date:	08/05/1983
From:	Foster D GEORGIA POWER CO.
To:	Adensam E Office of Nuclear Reactor Regulation
References
NUDOCS 8308110177
Download: ML20077H647 (4)

Text

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.. Georgia Power Company 333 Piedmont Avenue Atfanta, Georgta 30308 Telephone 404 526-7726 Mading Address-Post Olbee Box 4545 Atlanta. Georgia 30302 h Georgia Power D. O. Foster the sauthern enxtoc sys:ern Vice President and Genera: Manager Vogtte Proiect August 5, 1983 Elinor G. Adensam, Chief Licensing Branch No. 4 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555 NRC Docket Nubmers 50-424 and 50-425 Construction Permit Numbers CPPR-108 and CPPR-109 Vogtle Electric Generating Plant - Units 1 and 2 Compaction Around Pipes in Category 1 Backfill

Dear Ms. Adensam:

At this stage of the backfilling operation at the Vogtle site, Georgia Power Company's contractor personnel are experiencing difficulty in achieving the 97 percent compaction of Category 1 backfill around buried piping. As a result of this problem, we are requesting that the compaction requirements for Category 1 backfill to be placed around piping and similar- conduits be changed from an average of 97 percent of the maximum dry density determined in accordance with ASTM D1557 to an average of 95 percent.

The reason for requesting this change is the great difficulty GPC field personnel have experienced in attempting to backfill around pipes in Category 1 backfill areas. The initial program developed to accomplish this task used wooden tampers since the pipes were typically so closely spaced that conventional backfilling equipment could not be used between them. Pipes were laid directly on the ground or concrete mudmats and 4 inch lifts were compacted between pipes by means of the wooden tampers.

While the required 97 percent compaction was achieved using this wooden tamper method, GPC field found the procedure prohibitively slow and expensive. In

. addition, the coatings on the piping were frequently damaged when inadvertently struck by the wooden tampers. Compaction using the wooden tamper method was further complicated by the pipes bsing placed on angle frame supports (see attachment A) in the trenches to provide access for welding prior to backfilling.

Backfilling the resulting 12 inch space beneath the pipes using the wooden tamper method was impossible since the backfill directly beneath the pipe could not be reached. Even if the 12 inch space could be backfilled.using lean concrete to-the bottom of the pipe, the wooden tamper method would remain a difficult procedure to implement.

8308110177 830805 PDR ADOCK 05000424 PDR h @Of l l

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+8 Ms. Elinor G. Adensam August 5, 1983 Page 2 The second method developed for trench backfill is the vibration method in

! which concrete sand is saturated and compacted using concrete vibrators. It is this method which our proposed change in criteria addresses. By vibrating the concrete sand, good compaction is achieved all around the pipe without the need for lean concrete, with minimum potential for damage to pipes and in a reasonably rapid manner. With this method 97 percent compaction cannot ~

be consistently achieved but 95 percent compaction can be achieved.. While

, some areas may have to be reworked and retested in order to meet the 95 percent compaction criteria, we feel this method is the best solution. '

The technical justification for reducing the compaction criteria in the localized area surrounding pipes or similar conduits is the-following: ,

o The static and dynamic design properties of 95 percent and 97 percent compacted backfill are essentially the same and the properties of 95 percent compacted backfill are consistent with those assumed for the  !

design of the power block structures.

o All material to be compacted by this method is located above the water

, table so that liquefaction of the soil is -not a concern. Maximum water i table is at elevation 165'-0" while the lowest piping is at approximately elevation 200'-0".

o At most, a few percent of the entire power block backfill would be '

modi fied.

o Material at 95% would not be placed directly beneath Category 1 structures.

There may be limited areas where the pipes exi t the building where material

! at 95% may be used under the edge of Category 1 structures.

o Structures settlement would not be increased.

It should be noted that the backfill testing to date has been performed on

, the in-situ soil (sands and silty sands)-but the properties of the backfill sands and the concrete sand to be used are so similar that no differentiation -

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i need be made.

As has been indicated, we are proposing to use batch plant' sand compacted to an average of 95 percent with no more than 10 percent of the- tests below 95 percent and no test below 93 percent in Category 1 backfill areas around both-

' Category l'and~ Category 2 piping. The' compaction criteria' proposed is the usame as the' criteria which has been approved for the Category 1 backfill area ~ north of the turbine building. This proposed change would require revision to FSAR

' section :2.5.4.5.2. . A sketch of a typical pipe trench backfill situation is provided in attachment A.

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Ms. Elinor G. Adensam August 5, 1983 Page 3 A proposed revision to FSAR section 2.5.4.5.2 is shown below:

The localized area around buried piping and similar conduits is compccted with Category 1 backfill sand and silty sand or other sands with similar properties to an average of 95 percent of the maximum density determined by ASTM D1557 with no tests below 93 percent and not more than 10 percent of the tests between 93 and 95 percent. Typically, this localized area consists of backfill one foot above, one foot below, and a maximum of 5 feet on either side of buried piping or similar conduits. Only a few percent of the total power block backfill will utilize this compaction criteria. All such areas are located above the water table so that the factor of safety against liquefaction is not affected. Sand compacted to an average of ~

95 percent in the limited areas around piping and similar conduits will not affect the structural integrity of any Category 1 structures.

Sand c~ompacted to an average of 95 percent will have static and dynamic properties consistent with those properties assumed for design of power block structures and piping.

In summary, we are propasing a localized change in the Category 1 backfill compaction criteria to provide an economical and workable method for the installation of buried piping and similar conduits. The overall effect on the backfill resulting from this change will be negligible. We plan to implement this change in compaction critieria in these localized areas by September 1,1983, unless we hear from you to the contrary.

Should you have any questions, please inquire.

Sincerely, -

D. O. Foster 00F:sb xc: R. A. Thomas ,-

0. Batum M. Malcom L. T. Gucwa H. H. Gregory, III J. A. Bailey M. A. Miller J. P. O'Reilly W. S. Sanders G. F. Trowbridge

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