ML20210C426

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Interim Technical Rept,Diablo Canyon Unit 1,IDVP,Soils Rept - Intake Structure Bearing Capacity & Lateral Earth Pressure,Rev 0,ITR 39,by Rl Cloud Assoc,830225, Marked Up Rept Evaluation
ML20210C426
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Site: Diablo Canyon Pacific Gas & Electric icon.png
Issue date: 07/14/1983
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FOIA-86-151 NUDOCS 8609180331
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Text

_. -..._ -.

O Report Evaluation by NRC Staff Report

Title:

Interim Technical Report, Diablo Canyon Unit 1, Independent Design Verification Program, Soils Report - Intake Structure Bearing Capacity and Lateral Earth Pressure, Revision 0, ITR #39, by Robert L. Cloud Associates, Inc., February 25',

1983.

IDVP Designati_on:

P105-4-839-039, Revision 0 Originator:

Robert L. Cloud Associates, Inc.

Submitted By: Teledyne Engineering Services NRC Docket Number:

50-275

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I.

INTRODUCTION

~

Interim Technical Report Number 39 (ITR #39) was prepared by Robert L. Cloud Associates Inc., (RLCA), for the Independent Desi.gn Verification Program (IDVP) of the Diablo Canyon Nuclear Power Plant (DCNPP) for the Hosgri seismic criteria.

Teledyne Engineering Services (TES), who is the program manager for this IDVP, issued this ITR (Reference 1).

The following evaluation of ITR #39 was prepared by the NRC staff and incorpo-rates review comments of NRC's consultant, Brookhaven National Laboratory (BNL).

During their review, the staff had telephone discussions with RLCA in April and May, 1983, and conducted a technical audit of the references quoted in ITR

  1. 39 on June 8 through 10, 1983, at the offices of RLCA.

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DIABLO CANYON SER APP 3

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i The firm of Harding Lawson Associates (HLA) performed the geotechnical work for the intake structure.

ITR #39 presents RLCA's review of HLA's work on bearing capacity and lateral earth and water pressures for the intake structure.

As a result of the IOVP review, an error and open item report, E0I 1112, which identified the discrepancy in the location of borings, was issued. Appendix A of this report and ITR #39 present resolution of EDI 1112.

2.

SUMMARY

OF REPORT Interim Technical Report No. 39 (Reference 1)

The intake structure is a reinforced concrete building founded on a grout mudmat that was poured directly over the bedrock.

Soil material has been backfilled along three sides of the structure to plant grade. The fourth side of the structure has no backfill and admits seawater to the intake pumps.

Several years after the intake structure was constructed, HLA reanalyzed it as a part of.the Hosgri evaluation (1978) of the DCNPP. As a part of the IDVP, RLCA reviewed HLA's work on lithology and bearing capacity of the rock beneath the intake-structure-and laterai earth and water pressures on the walls of the intake structure.

RLCA's findings are presented in ITR #39.

2.1 Litholoay of Rock

~

All the borings at the intake structure were drilled down to the top of bedrock and provided information on the depth to bedrock. To define the strength of the rock beneath the intake structure, HLA used data from a 1968 study of the cooling water intake and discharge lines at the DCNPP.

In this study, two un-consolidated undrained shear strength (UU) tests were performed on samples of tuff recovered from the borings drilled for the cooling water intake line.

Both of these tests were conducted at the same confining pressure and yielded i

comparable results (See Figure No. 4 of ITR #39).. For the bedrock at the intake i

structure, HLA assigned strength parameters of 3 ksf for cohesion and 30* for angle of internal friction. The mohr circle plot for the above UU test data is below the envelope for the assigned strength parameters; i.e., strength

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07/14/83 2

DIABLO CANYON SER APP 3 o

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definedbyk.heHLA-assignedparametersarehigherthanthe-strengthmeasured

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in the UU tests.

HLA inspected the foundation excavation for the intake structure in 1972 and their inspection memo describes the bedrock as " moderately hard, moder-ately strong tuff and shale with minor weathering."

3 RLCA verified HLA's work on lithology of the bedrock by verifying location of borings, grade elevation, bedrock depth and description of rock samples from the borings drilled for the cooling water lines.

RLCA compared informa-tion on the above factors from the 1968 study of HLA field logs and a HLA report.

j Table 2 of ITR #39, presents the result of this RLCA verification. The loca-tion of borings No. 18 through 22 were shown in the HLA report as along the

" Discharge Line" whereas they were actually along the " Intake Line'!.. Error and Open Item report No. 1112 documented and classified this error as Class D, Deviation error, with no significant impact on design. The error was rectified (see Appendix A). With this correction, RLCA concluded that HLA used_a con-sistent set of data in their evaluation.

i i

RLCA reviewed the HLA test data and found it acceptable. To validate the HLA-assigned strength parameters for the bedrock at the intake structure, RLCA compared them with the strength paramet'ers recommended by HLA for the bedrock at the turbine building and Outdoor Water Storage Tanks of the DCNPP l

(See Figure No. 4 of ITR #39).

RLCA compared the compressive strength from I

the laboratory tests (UU) by HLA (15.0 ksf) with the compressive strength quoted in the literature for tuff (76 ksf).

Considering the above and description of the bedrock in HLA's site visit memo, RLCA concluded that the i

strength values from HLA's tests (UU) can be considered as low-bound value for the overall bedrock and HLA's glefinition of the strength of the rock is reason-able and acceptable.

I i

2.2 Bearino Capacity of the Rock For the bedrock at the intake structure HLA recommended an allowable bearing capacity of 33 ksf, for the following assumed foundations:

i 07/13/83 3

DIABLO CANYON APP. 3 l

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o 3 ft wide, long strip footing, 7 ft depth of embedmont 70 pcf buoyant unit weight of fill shear strqngth of rock C = 3 ksf, 9 = 30*

factor oi safety = 3 ultimate bearing capacity 99 ksf HLA did not estimate the settlement of the structure.

RLCA estimated the settlement of the structure as mentioned below.

RLCA computed the ultimate bearing capacity of the bedrock at the intake structure using a range of strength parameters for the bedrock as follows:

Footing size, ft x ft 211 x 102 211 x 103 211 x 103 Embedmont ft 49 49 49 Death to water table, ft 17 17 17 Fill density, pcf 120 120 120 Rock strength-C ksf 3

10 38 9 degrees 30 40 0

. -Ultimate bearing capacity, ksf 320 1,963 219 Based on the above parametric study RLCA concluded that the HLA recommended allowable bearing capacity of 33 ksf determined by shear failure criterion, is conservative and acceptable.

RLCA estimated the settlement of the intake structure using a Young's modulus (500 ksi) and Poisson's ratio (0.39) obtained from the geophysical tests per-formed for the Outdoor Water Storage Tanks (ITR #16).

RLCA estimated that a 33 ksf uniform bearing pressure (maximum allowable pressure) results in 0.75 in. settlement. A differential live load of 23 ksf will cause a 0.5 in, of differential settlement.

RLCA states that the differential live load in the intake structure will be less than 23 ksf so settlement will not control the allowable bearing capacity of the bedrock beneath the intake structure.

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07/13/83 4

DIABLO CANYON APP. 3

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RLCA concluded that HLA's recommendation of 33 ksf allowable bearing pressure for the bedrock under the intake structure is acceptable.

2.3 Lateral Pressures 2.3.1 Analysis by HLA In 1978, HLA drilled borings in the backfill material around the intake struc-ture and performed laboratory tests on soil samples recovered from the borings.

HLA used this data in developing soil properties for Hosgri qualification analyses of the DCNPP.

For the backfill material, HLA assigned a unit weight of 127 pcf and shear strength parameters of 35' for angle of internal friction and zero for' cohesion.

For the static loading condition HLA calculated the lateral at-rest earth pres--

sure on the intake structure walls. The equivalent fluid densities were 55 pcf above the ground water table (mean sea level) and 90 pcf below the water table.

For the dynamic loading condition, the lateral active earth pressure on the wall was calculated using the Hononobe-0kabe method as simplified by Seed and Whitman (Reference 2). This computed lateral force was multiplied by a factor, 3, te compensate for the simplified assumptions in the analyses. This resulted in a uniform dynamic lateral earth pressure of (86)H psf, where H is the height of the wall.

HLA computed the dynamic water force using Westergaard theory as modifi.ed by Matsuo and O'Hara (explained in Reference 2). This resulted in a uniform dynamic. water pressure of (14)h psf where h is the depth of water.

HLA calculated lateral pressure only for the portion of wall above the bedrock (36 ft high), whereas the bottom of the foundation is approximately 13 ft below the top of the bedrock (49 ft total depth of embedmont on 3 sides of the structure).

07/33/83 5

DIA8LO CANYON APP. 3

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To summarize, the lateral earth and water pressures on the intake structure walls, calculated by HLA resulted in a total lateral force of 158 kips /ft

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of wall. Cee Figure No. 5 of ITR #39 for details.

1 2.3.2 Analysis 8y RLCA Based on the HLA data (1978), reviewed in ITR #13.-RLCA assigned shear strength parameters of zero for cohesion and 45 degrees for angle of internal friction for the backfill material.

For the static loading condition RLCA calculated the lateral active earth pressure. This resulted in a lateral active earth pressure coefficient of

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0.17.

z Thedynamyclateralactiveearthpressureonthewallwascalculatedusing MononobpabemethodasmodifiedbySeedandWhitman(Reference 2).

In their analysis, RLCA assumed the vertical component of the Hosgri earthquake accele-ration to be zero. Also, RLCA computed the dynamic active earth pressure coef-fi,ciant'far marthquakes of peak horizontal acceleration of 0.75g and 2/3 of 0.75g and stated that the actual seismic Condition would be bounded by these two limits.

It should be noted that the dynamic pressure was calculated for the active earth -

condition whereas the intake structure walls are rigid and do not result in the active earth condition.

RLCA chose to compensate for the rigidity of the wall by using a pressure distribution pattern generally used in braced excavation (Terzaghi and Peck, Reference 3) to compute lateral earth pressure.

The dynamic water pressure was computed using the same method as was used by l

HLA.

To summarize, the lateral earth and water pressures calculated by RLCA resulted l

in a total lateral. force of 161 kips /ft of wall for 0.75 g earthquake and 89 l

kips /ft of wall for 2/3 of 0.75 g earthquake.

See figure 5 of ITR #39 for l'

details.

Because the results of RLCA analyses and HLA analyses are c' lose, i

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DIABLO CANYON SER APP 3 i

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w RLCA concluded that HLA's analyses of lateral pressures on the intake structure is acceptable.

i 3.

EVALUATION BY NRC STAFF 3.1 Lithology of the Rock i

The NRC staff agrees with RLCA's conclusion on HLA's date,rmination of depth' to bedrock at the intake structure. The strength properties of the bedrock (c = 3 ksf, 9 = 30*), assigned by HLA, are based on judgement after consider-ing:

UU test data on tuff, strength parameters developed for the bedrock at the turbine building, strength values quoted in the literature for tuff and

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description of bedrock in HLA's site visit meno.

These parameters are judged to be reasonable and are accepted by the staff.

I For the backfill material, HLA assigned shear strength parameters of 35* for

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i angle of internal friction and zero for cohesion. RLCA assigned shear strength parameters of 45* for engle of internal friction and zero for cohesian. The staff concurs with the parameters assigned by HLA, but does not agree with the parameters assigned by RLCA. An angle of internal friction of 45' is very high for.a compacted backfill material.

RLCA has not presented a valid justifica-i J

tion for their assumption.

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i During an audit meeting at RLCA's office, the staff examined construction drawings which showed that the foundation was supported on a mudmat that was poured directly against the bedrock. The bottom of the foundation is approxi-mately 13 ft below the top of bedrock and the space between the outer walls of the intake structure and the face of the excavation in bedrock was filled with concrete up to the top of the bedrock. The walls can therefore be considered as bearing against the face of excavation for lateral pressure determinations.

i 3.2 Bearina Capacity i

l HLA recommended an ultimate bearing capacity of 99 ksf for the bedrock beneath a

i the intake structure.

RLCA evaluated the ultimate bearing capacity of the bed-

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rock for a range of rock strength parameters to demonstrate the conservatism 07/14/83 7

DIABLO CANYON SER APP 3

in HLA's recommendation. During the technical audit meeting at RLCA's office, the staff was informed by the RLCA representatives that the maximum static bearing pressure under the intake structure is 10.16 ksf and there is a local maximum bearing pressure of 26 ksf, under a pier.

Considering the low bearing pressures initially imposed on the bedrock the staff concludes that the bearing capacity, as controlled by shear failure of the supporting bedrock, is satis-factory.

j RLCA estimated the rate of settlement of the intake structure to be 0.022 inch per ksf. Considering the low bearing pressure, the settlement will not be detrimental to the structure.

J 3.3 Lateral Pressure The staff has the following comments on the lateral pressure analyses by both HLA and RLCA.

i 3.3.1 Staff Comments on HLA's Analysis The at-rest earth pressure coefficient used for static loadings by HLA, K, = 0.44, is less than that normally used for a compacted backfill.

The Seed-Whitman simplified equation (Reference 2) used by HLA for comput-ing the dynamic active earth pressure yields unconservative results for earthquakes of horizontal acceleration greater than 0.4 g.

HLA multiplied the computed dynamic active earth pressure by a factor of 3 to compensate for the simplified assumptions. This factor, 3, was

" selected on the basis of judgement" only.

There is no known rational basis for using this factor.

i 3.3.2 Staff Comments on RLCA Analysis 4

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For static loadings, RLCA evaluated the lateral earth pressure for active r

soil condition.

For rigid walls, the lateral earth pressures should be B

computed for the at i'est soil condition.

1 For the Hosgri SSE, the vertical component of the acceleration was assumed i

to be zero. The staff recommends using a vertical component of accelera-tion equal to 2/3 of the horizontal component of acceleration.

ALCA computed the dynamic active lateral pressure using Mononbe and Okabe method, as modified by Seed and Whitman (Reference 2).

RLCA combined this i

computed dynamic active earth pressure coefficient with the pressure distribution pattern used for braced. excavations (Reference 3) and obtained lateral earth pressures on the rigid walls of the intaka structure under dynamic conditions. The dynamic active earth pressure calculated by Mononobe and Okabe method is based on limit-equilibrium condition and is i

l generally used in the profession for earthquakes of peak acceleration less than 0.4 g.

For rigid walls, which do not result in active soil condition, the computed active lateral force is muliplied by factors ranging from L

1.5 and higher to compensate for the assumed active earth condition.

There is no.known guideline for selecting this factor.

Since the Hosgri qualifica-tion earthquake for this plant is unusually high' (peak horizontal accelera-tion of 0.75 g) the lateral pressure under dynamic conditions should be l

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evaluated by a more accurate method (such as finite element method). Tbe staff does not concur with the RLCA procedure. The RLCA has not demon-strated that the computed lateral earth forces on the intake structure walls under the dynamic loading conditions are reasonable. It has also not demon-l strated conservatism in the analysis.

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RLCA and HLA calculated lateral earth and water pressures on the wall l

above the bedrock only. The lateral pressures should be computed

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down to the bottom of the foundation so that the lateral forces on the l

intake structure, required for the sliding analysis, can be computed.

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DIABLO CANYON APP. 3 I

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4.

Conclusions The NRC staff has reviewed'ITR #39 prepared by RLCA and conclude:

1.

Shear strength parameters receumended by HLA for the bedrock and backfill material at the intake structure, although based on minimal data, are judged reasonable and are acceptable to the staff. The staff does not agree with the strength parameters for the backfill material used in RLCA's analyses.

2.

Evaluation of the bearing capacity of the bedrock beneath the intake structure was based on assigned rock shear strength parameters. Con-sidering the low rock bearing pressure (10 ksf maximum over most of the foundation and 25 ksf peak under a pier), the staff judges that the rock bearing capacity is satisfactory.

3.

RLCA's assessment of lateral earth and water pre:sures on the, intake structure walls is not acceptable.

Section 3.3 of this report presents stef* cc-- ats.

During the audit meeting, RLCA agreed to revise ITR #39 to address staff comments.

4.

Total lateral force at the foundation level should be computed to deter-mine the factor of safety against sliding of the intake structure. The safety margin available in sliding should be used to check the effect o approximations and assumptions used in computing lateral earth pressures.

References 1.

Interim Technical Report, Diablo Canyon Unit 1, Independent Design l

Verification Program, Soils Report - Intake Structure Bearing Capacity and Lateral Earth Pressure, Revision 0. ITR #39, by Robert L. Cloud.

Associates Inc., February 25, 1983.

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07/13/83 10 DIABLO CANYON APP. 3

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Conclusions 4

The NRC staff has reviewed ITR #39 prepared by RLCA and conclude:

1.

Shear strength parameters recompended by HLA for the bedrock and backfill material at the intake structure, although based on minimal data, are judged reasenable and are acceptable to the staff. The staff does r.ot agree with the strength parameters for the backfill material used in RLCA's analyses.

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2.

Evaluation of the bearing capacity of the bedrock beneath the intake structure was based on assigned rock shetr strength parameters. Con-sidering the low rock bearing pressure (10 ksf maximum over nost of the foundation and 26 ksf peak under a pier), the staff judges tnat the rock bearing capacity is satisfactory.

I 3.

RLCA's assessment of lateral earth and water pressures on the, intake structure walls is not acceptable. Section 3.3 of this report presents staff comments. During the audit meeting, RLCA agreed to revise ITR F39 to address staff comments.

4.

Total lateral force at the foundation level should be computed to deter-mine the factor of safety against sliding of the int 4ke structure. The safety margin available in sliding should be used to check the effect of approximations and assumptions used in computing lateral earth pressures.

I Refarences 1.

Interim Technical Report, Diablo Canycn Unit 1 Indeoendent Ocsign Verification Program, Soils Report - Intake Structure Bearing Capacity and Lateral Earth Pressure, Revision 0, ITR #39, by Robert L. Cloud.

Associates Inc., February 25, 1983.

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01/13/83 10 M ABLO CANYON AFP. 3

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Seed H.

E., anc Whitman, R.V., " Design of Earth Aitaining Structures for Dynamic Lo, ads " ASCE Speciality Conference o.1 Lateral Strestes and Earth Retaining Structures, 1970.

3.

Terzaghi, K., and Peck;, R. S., "Sc11 Mechanics in Er.gineering Practice,"

John Wiley ar.d Sons, Inc., New York, 1967.

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APPENDIX A t

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APPENDIX A EDI Status - Soils Report 1

Intake Structure, Bearing Capacity and Lateral Earth Pressure i

EDI Action Physical File No.

Subject Rev.

Date 8y Type Required Mad.

1112 Rering location inconsis-0 12/29/82 RLCA DIR BLCA tencies 1

12/29/82 RLCA PPRR/0IP YES 2

1/5/83 TES PRR/0IP PGandE 3

2/15/83 TES OIR RLCA 4

2/15/83 RLCA PPRR/DEV TES 5

2/22/83 TES PRR/DEV TES 6

2/22/63 TES CR None No YY

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STATUS: Status is indicated ny the type of classification of latest report received by PGandE:

(

O; OIR - Open Ites Report ER - Error Report A - Class A Error

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PPRR - Potential Program Resolution Report CR - Completion Report E - Class B Error PRR - Program Resolution Report C1 - closed ites C - Class C Error D

PER - Potential Error Report DEV - Deviation B - Class D Error 8

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5 OIP - Open Item with future action by PGandE 8

PHYSICAL. MDO: Physical modification required to resolve the issue. Black entry indicates that M.

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