ML19316B116
| ML19316B116 | |
| Person / Time | |
|---|---|
| Site: | Bailly |
| Issue date: | 05/28/1980 |
| From: | Shorb E NORTHERN INDIANA PUBLIC SERVICE CO. |
| To: | Youngblood B Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8006110331 | |
| Download: ML19316B116 (6) | |
Text
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O Northern Indiana Public Service Company
> q'!!nta General Ottees l 5265 Hor.2%i Avenue l Hammond. Ind:ana 46325 l Tel.: 853-5200 (219)
NII EUGENE M. SHORB May 28,1980 n., v. c ' '" ' ' ' ' " '
Mr. B. J. koungblood, Chief Licensing Branch No.1 Division of Licensing U. S. Nuclear Regulatory Commission Wa shington, D. C.
20555
Dear Mr. Youngblood:
Your letter dated May 22, 1980, transmitted Request for Ad.litional Information No. 362. 30 regarding the Bailly Pile Foundation. This is in addition to Mr. R. L. Tedesco's letter dated May 16, 1980, to v;hich we responded on May 27, 1980.
Forty copies of the additional information requested are attached.
ery truly yours, V
EMS: cgs Attachment
\\ 80 0 6110 33, p
r REQUEST NUMBER 362.30 We transmitted a question (Item 362.1) to you in our letter dated June 22, 1978, requesting additional information regarding pile group capacity; you responded to this matter in your letter dated July 14, 1978.
In reviewing Figure 362.1-4 of your July 1978 response, we note that you assume a soil density of 130 pounds per cubic foot'in your analysis of the capability of a pile group to resist uplift. This soil density appears to be a total soil unit weight.
However, when construction dewatering operations are stopped, the ground water level will rise above the tops of the piles, thereby totally submerging the soil resisting uplift.
Accordingly, provide justification for using the total unit weight of the soil rather than the submerged unit weight when calculating the weight of soil resisting uplift. Provide the minimum factors of safety for pile group uplift using the submerged unit weight of soil.
Revise your July 1978 response to our Item 362.1 of 1978 as required.
State the minimum length of pile embedment to achieve the required factors of safety for pile group uplift. ' Indicate how your pile placement criteria will achieve this minimum pile embedment length.
RESPONSE
The uplift loads for the Bailly Foundation piles coulddevelop during the postulated design basis earthquake. These loads would be applied very rapidly and are considered transient in nature.
The response of the soil under these rapid loads will take place under undrained conditions and the total unit weight should be used when calculating i
the weight of soil resisting uplift.
Therefore, the case using the submerged unit weight of the soil is not appropriate and was not considered.
In the July 14, 1978 response, an analytical study of the uplift capacity of pile groups, based on the results of uplift pile load tests (Ref. 3), was described. The analytical model used assumes that thesonly resistance to the applied uplift loads comes from the dead weight of a truncated pyramid of soll as shown in Figure 362.1-4 of the July 14, 1978 response. Since the loads are applied very
c7.
1 rapidly, the water in the soil pores will not have sufficient time to drain, and thus the entire mass of soil'together with the pore water will move as a unit.
It is therefore concluded that the total weight of soil nid water will participate in resisting the applied uplift loads. Thus, the use of the total unit weight of the soil in the comput.ation of group uplift capacities is justified.
The analytical model used to evaluate the group uplift capacities is conservative for the following reasons:
1.
It does not take into consideration the shear resistance along the soil failure surface, i.e.,
at the surface of the truncated soil pyramid.
2.- It does not take into consideration the soil suction that would develop at the base of the pile group as it is pulled out (See vesic 1971).
3.
It does not take into consideration the weight of overburden soil.
As can be seen from Figure 362.1-1 in the July 14, 1978 response, all the pile groups which are subjected to uplift loads are located at the' corners of the various buildings.
Thus, each such' pile group has two exterior sides where the soil above the base of the mat ranges from 32 feet to 46 feet.
The weight of the backfill outside the building will offer additional resistance to uplift, for which no credit is taken.
t
4.
The analysis assumes that each pile group can move upwards independent of the rest of the piles.
In fact, the piles are tied together with a thick reinforced concrete mat.
Therefore, the upward pile movements will be controlled by the mat acting as a unit, leading to redistribution of uplift loads as the mat deflects. The analytical model provides the minimum possible uplift capacity, if each group could act independently.
In preparinc the response to Question 362.1 (1978), other methods of analyses were also examined in evaluating group sq? lift capacity. One method which is widely accepted (Meyerhoff,1957) assumes that the pile group fails as a block with shear stresses acting along the perimeter. The'results of such analyses provide much greater capacities than those obtained by the analysis used in response to Question 362.1 (1978). Therefore, ir Miould be realized that the analytical model used to evaluate group uplift capacities was selected to provide the minimum possible capacity (the maximum conservatism).
In summary, it has been shown that:
1.
The use of the total unit weight in conjunction with the
/ Analytical model demonstrated in Figare 362.1-4 is justified.
2.
The analytical procedure used to compute the uplift pile capacities is conservative.
_4 The pile lengths assumed in the analyses for pile group capacities in the response to Question 362.1 are in good agreement with pile lengths achieved during the indicator pile driving program. For example, in the analysis of group uplift capacities in the Auxiliary Building we used a pile length of 50 feet. The 40 piles driven in the heave monitoring cluster had embedded lengths greater than 55 feet.
Indicator Pile SA-135, which is located near the southern end of the group considered for uplift, has an embedded length of 57 feet, which is also greater than the pile length used for computations.
Similarly, in the Reactor Building, the pile length used for computations was 35 feet (See Table 362.1-4).
Pile RD-49, which is located 7.5 feet east of the cluster considered for uplift, will have an embedded length of 37 feet af ter excavation to elevation of -6 feet, which is greater than the assumed length.
Indicator piles RWD-01, RWD-04 and RWD-09, located in the area of the Radwaste Building where uplift loads are expected, have embedment lee gths of approximately 28 feet or more.
Again, this is more than the length of 25 feet assumed for computation of uplift capacities.
The extensive indicator pile program and soil borings taken throughout the Category I areas have defined the top of the bearing stratum and N sith the present as. illustrated l above, the piles driven criteria have always exceeded' the minimum embedment depths required.
It is expected that the production piles will also be driven to similar depths as those achieved during the indicator pile program.
As production pile driving is progressing the embedment depth of piles that may be subjected to uplift will be reviewed by a qualified geotechnical engineer to assure that sufficient emt
'J.2 d lengths is provided. Piles not meeting this minimum embedment will be redriven to provide the required embedment length.
1.
Vesic. A. S. (1971), " Breakout Resistance of Objects Embedded in Ocean Bottom," Journal of the Soil Mechanics and Foundation Division, ASCE, Vol. 97, No. SM9.
2.
Meyerhoff, G.
G., " Compaction of Sands and Bearing Capacity of Piles," ASCE, Journal of Soil Mechanics and Foundations Division, Dec. 1959.
3.
Report SL-3629, " Design, Analysis and Installation of Driven H-Pile Foundation", March 8, 1978, Chapter 5.
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