ML19258A086
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DISTRIBUTION:
JUN 16 E2 Doc!.et File - DCD 016 DE:HGEB RDG. File Docket Nes. 50-329/330 MEMOP#!Dutt FOR: Elinor Adensam, Chief Licensing Branch f4 Division of Licensing FROM:
George Lear, Chief Hydrologic and Geotechnical Engineering Branch Division of Engineering
SUBJECT:
QUESTIONS, POSIfMNS AND REVIEW C0'tMENTS ON COP. '
APRIL 22, 1982 SUBt(ITTAL Plant Name: Midland Plant, Units 1 and 2 Licensing Stage: OL Responsible reanch: Licensing Branch #4, D. Hood, R. Hernan, LP'4's Review Status: Continuing We have enclosed the review coments of the GES staff and its Consultants on the April 22, 1982 submittal by the Applicant concerning the Borated Water Storage Tanks and Service WaterPump Structure underpinning work.
(Letter to H. Denton from J. W. Cook dated April 22, 1982).
The enclosure indicate the staff's two major areas of difference with the Applicant are (1) having measured vertical deflections (differential settlements) control the underrinning work rather than an unreasonably large strain criterion and (2) the Applicant's apparent reluctance to fully comply with the staff's past reccmendations on construction de-waitring that were previously transmitted in the April 2,1982 letter froi. R. Tedesco to J. Cook on construction dewatering for the Service Wate! Pump Structure underpinning work We recomend contact with the Applicant to resolve these differences followine a reasonable period for Consumers and its consultant to review the enclosed evaluation.
This input was prepared by Joseph Kane.
Original signed by L. W. Hell.63 George Lear, Chief Hydrologic and Geotechnical 8206:'a o401 820616 Engineering Branch CF (UDCK 05000 29 Division of Engineering m,_.
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Midlend Plar.t, Units 1 and 2 Doc.ket Numbers : 50-329/330
Subject:
Geatechnical Engineering Evaluation of Reference 1 Prepared by: Jose; a D. Kane, HGEB, DE, NRR Reference 1: April 22,1982 letter from J. W. Cook to H. R. Denton on Responses to the NRC Staff Request for Additional Information Required for Completion of Staff Review of the Borated Water Storage Tank and Underpinning of the Service Water Pump Structure The following comments and questions are based on the reviews of Reference 1 by the Geotechnical Engineering Section Staff, HGEB, DE and its consultants, Dr. S. Poulos, Geotechnical Engineers, Inc. and H. Singh, U. S. Army Corps of Engineers.
Q.l.
(Issue 1, Page 2, Par. 3) Provide the range in layer thicknesses that the oil-impregnated sand will be placed beneath BWST IT-60 tank and the construction controls to be required for its placement and compaction.
Q.2 (Issue 2, Page 3, Par. 2) Averaging the strain over a 20-foot gage length is not acceptable to the Staff because this averaging could lead to underestimating stresses and unacceptable cracking.
Installing shorter length gages over the 20-foot length is recommended.
The Staff's concern with the single 20-foot gage 1c.gth is further discu ssed in Q.5.
Q.3 (Issue 2, Page 3, Par. 3) As a minimum, the BWST ring beams should be monitored for increasing strains at a frequency of at least once a year, following the initial 5 year period of plant operation.
Q.4 (Issues 1 and 2, Pages 5 and 6).
The Applicant's responses to issues 1 and 2 are inadequate with respect to the basis for adopting the soil spring stiffness of 4,000 KCF and with respect to determining the effects
- of differential settlement on the existing SWPS.
The Applicant should either justify the adoption of the soil spring stiffness value of 4000 KCF or alternately use a stiffness of K = 400 KCF for the glacial till, a value which is considered reasonable and acceptable to the Staff and its consultants.
Q.5 (Issue 3, Page 6). The proposed 5/16-inch displacement (extension) criterion over a 20-foot gage length is not acceptable to the Staff or its consultants. More gages of snorter lengths would be preferable to permit identification of the more highly stressed sections. The Staff and its consultants recognize the advantages of the proposed strain monitoring program but consider measurenent of the vertical differential settlement, similar to what is being carried out for the Auxiliary Building underpinning work, to be the more positive and sensitive construction control that would permit corrective action to be taken before overstressing the SWPS would occur.
For these reasons the Staff requires that underpinning of the SWPS be controlled by monitoring of vertical differential settlement to tolerable limits established before starting this work.
Q.6 (Issue 6 Page 7). The Applicant's response to issue 6 does not provide the calculations for sliding resistance of the SWPS under seismic loading which were requested at the March 16 through 19, 1982 design audit.
For this reason Item 2.2 of Enclosure 8 to the May 25, 1982 letter from D. G. Eisenhut to J. W. Cook again requests this information.
, Q.7 (Issue 13. Pages 10-12).
The following changes and additions should be made to the Applicant's response to issue 13.
On 5th line, Page 10, the word " solely" should be deleted.
a.
b.
On 2nd line, Par. 3, Page 11, the word " generally" should be deleted. At the en.1 of this paragraph add tne following: The correlation between the pier or plate load test results and the penetration tests performed on the foundation soils will be used to correct the correlation graphs and to judge the suitability of the bearing stratum.
Last paragraph, Page 11, should be revised to incorporate the c.
following changes. The zone of influence should be defined by extending lines downward at a slope of 1 horizontal (H) to 1 vertical (V) from the edge of the footing into the foundation t r-: c < a soils.
If the foundation soil is cohesionless, a braded exca-vation is required if the excavation must proceed more than 6-inches below the adjacent pier or, if not an immediately adja-cent pier, then 6-inches below the intersection of the pier footing with the lH to lV zone of influence slope. Movements of adjacent piers shall be monitored as the excavation proceeds to 18-inches or less.
Excavations shall be stopped and construction procedures modified if measured movements are larger than anticipated.
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, Q.8 (Issue 14, Page 12).
The modifications and additions which were required for the pier load test procedures for the Auxiliary Building (Enclosure 2 to the May 25, 1932 letter from D. G. Eisenhut to J. W.
Cook, Par. 4) are also required in the procedures for the Service Water Pump Structure.
In addition, if the very dense sandy alluvium is ultimately accepted as the foundation for a portion of the SWPS underpinning piers, then either a p'er or a plate load test should also be conducted on this foundation material.
Q.9 (Issue 18, Pages 13-15). The following comments and questions are numbered in identical order to the numbering of the contingency plan items given in response to issue 18:
1.c.
What procedure is to be followed that will permit a single well failure to be identified from the total system?
2.b.
It is unclear what level will be equalized and the time it will take to complete this action.
What occurrence (e.g., settlement measurement, etc.) triggers this reaction to uncontrolled groundwater flow?
3.a and 3.b.
Is the equipment for carrying out techniques such as
./
forepooling or speeling or grouting to stop ground loss in readiness at the plant site? If not, what time frame is required to make it available?
4.a.
Include limits on maximum depth of excavation and zone of influence and requirements for bracing.
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, 4.b.
A required increase in bearing area of underpinning piers is a significant change. hat requires notification of Region III, 5.
Recording of excessive pier settlement requires an evaluation of its cause and notification of Region III before proceeding with other piers.
6.
The use of wedges and plates wr 'd be the routine method to stop movement in the event of a jack failure.
7.
A loss in functioning of the important northerly benchmarks would require underpinning work to be stopped until the bench-marks were restored and elevations confirmed.
8.
Prior to ' implementing the listed i; ems of 8a, 8b and 8c the underpinning work should be stopped and the existing excavation faces carefully supported.
The contingency plan should be revised to incorporate the above Staff's comments and Applicant's responses.
Q.10 (Issue 19, Pages 15-16).
The following comments should be incorporated into the notes controlling the checking or adjusting of jacking loads.
Jacking will be controlled to limit settlements to acceptance criteria values identified on SWPS-14 (Still to be established by the Applicant and evaluated by the Staff).
Wedges and plates will be used to prevent unacceptable movement in the event of a jack failure, both during pier construction and during application of final jacking loads.
.. During the construction of Piers 1, 2 and 3 the jacks will be monitored at least at the start of every shift and daily during holidays and weekends. More frequent checking and jacking is required until the rate of load decrease is small enough and sufficiently stabilized to permit checking once during each shift.
Q.11 (Issue 20, Paje 16).
The above comments on jacking control and monitoring frequency are applicable to the transfer of the jacking load into the pennanent underpinning wall.
Provide the actual value of the " predetermined rate".
Q.12 (Issue 24, Page 19).
It is unclear from the Applicant's response whether or not Consumers intends to comply with the Staff's recom-mendation (April 2,1982 letter from R. Tedesco to J. Cook, " Staff Concurrence for Installation and Operation of Construction Dewatering and Observation Wells for the Service Water Pump Structure", Enclosure 3, Page 4) to require extension of the six previously proposed piezomete s to at least elevation 570. The Staff does not have a problem if the Applicant chooses to add piezometers to the original six and terminate these additional piezometers at "an elevation no lower than approximately l' foot above the undisturbed natural soil."
However, the Staff still requires that the bottom elevation of the original six piezometers be drilled to at least elevation 570.
The Staff dnes not accept the Applicant's statements on controlling the groundwater level in the SWPS area during underpinning construction for the following reasons:
...,, a.
Drawing the water level down to approximately the interface of the fill and natural soil is not a realistic control. Completed borings show this interface surface and soil conditions to be highly variable in the immediate area of the underpinning work with the interface level ranging from Elevation 605 to Elevation 583.
b.
Identification of the soil type at the bottom of the dewatering well does not provide assurances that blow outs will not occur at the base of oier excavations because this information does not address the > aoblem of pervious layer stratification and continuity and imperviot s layers of insufficient thickness.
Frr the above reasons, the Staff reiterates its position that there should be a control on the upper phreatic surface which requires a minimum 2-foot depth between the upper phreatic surface being controlled by dewatering and the bottom of any underpinning excavation at any given time. As a minimum, the six originally proposed piezometer locations are to be used to verify that the groundwater is being maintained to this level during underpinning.
It is recognized that localized temporary dewatering techniques such as sumping may be necessary to produce hydrostatically relieved conditions in areas of entrapped water.
Q.13 (Fig. SWPS-14 ).
A correction to Nota 9 is needed to indicate that all instrumentation and material identified in the Monitoring Matrix
,. is to be Q-listed unless otherwise shown not to be required. A separate request of the Applicant to provide the following draw *. 3s identified on Fig. SWPS-14 has been made.
Drawing fios.
Subject C-2040 thru C-2043-11 Crack "onitoring Requirements C-2003 and C-2004 Building Settlement Monitoring Requirements C-2035 and C-2036 Details of Wall and Pier Settlement Monitoring 1.
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