ML20041E205

Forwards Trip Repts 3 & 4 of 820224-26 Meeting in Bethesda, MD Re Underpinning Plans for Svc Water Pump Structure

ML20041E205
Person / Time
Site:	Midland
Issue date:	03/03/1982
From:	Poulos S GEI CONSULTANTS, INC. (FORMERLY GEOTECHNICAL ENGINEER
To:	Kane J Office of Nuclear Reactor Regulation
References
CON-NRC-03-82-092, CON-NRC-3-82-92 81907-5, NUDOCS 8203100244
Download: ML20041E205 (5)

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Subject:

Trip Report Nos. 3 and 4 - Bethesda Meeting of February 24, 25, 26, 1932 Midland Plant Underpinning Contract No. NRC-03-82-092

Dear Mr. Kane:

On February 24 and 25 a meeting was held to discuss under-pinning plans for the service water pump structure. On February 26, 1982 an audit for License Condition 5 of the auxiliary building underpinning was held.

Enclosure (1), Trip Report No. 3, is a list of unresolved issues for the service water pump structure.

Enclosure (2), Trip Report No. 4, is a list of unresolved issues for the auxiliary building.

Sincerely yours, GEOTECHNICAL ENGINEERS INC.

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Steve J. Poulos Principal SJP:ms Encl.

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.8203100244 820303 PDR ADOCK 05000329 A PDR 1

1 Trip Report No. 3 MEETING OF FEBRUARY 24, 25, 1982 SERVICE WATER PUMP STRUCTURE MIDLAND PLANT UNDERPINNING CONTRACT NRC-03-82-092 4

Project 81907 Geotechnical Engineers Inc. March 3, 1982 The following items remain unresolved subsequent to our 4 meeting in Bethesda relative to underpinning of the Service Water Pump Structure.

1. Subgrade moduli that were used for the seismic analysis were presented in very general form. The test data and other assumptions and equations used tor estimating these moduli should be provided.

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2. Provide the remedies that are available to prevent further movement if the maximum allowable movements are reached.

3. Provide the out-of-plane forces for which the wall was designed.

4. Clarify the method used for designing the vertical bolts between the structure and the underpinning wall.

5. Describe the dewatering system to be used to lower the water level to the hard clay.

6. Provide location, depths, and types of piezometers for' monitoring groundwater level to ensure that it has been drawn down below excavation level before excavation to that level.

Enclosure (1)

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7. Select telltale locations at which differential settle-ments and strain in the concrete wili be measured during underpinning. State precision of measurement and type of instrument. State frequency of readings and evaluation of readings before, during, and shortly after under-pinning.

8. Provide limits of movements of strain and differential settlement that will (1) trigger review and (2) trigger a stop of construction and start remedial action.

9. State who is responsible for accepting the bearing stra-tum by direct inspection.

10. Provide the quantitative method for evaluating the suitability of the dense alluvium.

11. State the limits of thickness of lean concrete under the piers and the maximum difference in elevation between adjacent piers. Review borings and select a bearing ele-vation low enough to eliminate, for the most part, the need for elevation differences.

12. One pier on hard clay should be carefully load te sted (like a pile load test) to about 20% above its expected lock-off load. Which pier will be tested?

13. Ilow often will load on piers be checked during the progress of the work? Who has this responsibility?

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Trip Report No. 4 AUDIT OF FEBRUARY 26, 1982 AUXILIARY BUILDING MIDLAND PLANT UNDERPINNING CONTRACT NRC-03-82-092 Project 81907 Geotechnical Engineers Inc. March 2, 1982 The following is a list of issues left unresolved af ter the audit on February 26, 1982 of the Electrical Penetration Areas and the Control Tower. The audit pertained principally to License Condition 5.

1. A new sequence of construction should be submitted. Some important details on the sequence previously provided have been altered. The support under the EPA at the east and west ends was to be installed prior to advancing drif t beyond that point. This sequence is not given in the presently available documents.

2. Strain gages should be mounted in the zones where highest stress changes are expectd to occur in the main auxiliary building during underpinning. Tolerable limits of move-ment and frequency of reading and evaluation before and during critical stages of underpinning should be provided.

3. Remedial measures that are available to the contractor if excessive settlements, deflection, or concrete strain are measured should be provided. The sequence of construc-tion and the location of the drifts and piers should be selected to ensure that acceptable remedial actions are possible in a short time if the movements are excessive.

4. Tne NRC reviewers were to study the (a) proposed spring constants, (b) the proposed critical monitoring points, and (c) proposed tolerable movements and provide a response to Consumers Power.

Enclosure (2)

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5. Jacking load adjustment criteria are to be provided by applicant. Frequency of-checks on jacking loads are to be included.

6. Time lapse between observed excessive reading and action

. for an emergency situation should be given.

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- NOTE: Items 3, 5, 6, 7, and 8 of Trip Report No. 2 dated February _8, 1982 should be followed up. These items were not covered during the February 26 audit.

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