Dewey DamSeismic Assessment

2005 Tri-Service Infrastructure SystemsConference

St. Louis, MO

Huntington DistrictHuntington District

Site Location

Project Description• Homogeneous Earth Dam• 118' Tall; 913' Long• On John's Creek• Completed in 1949

Typical Embankment Section

Station 3+50

Clay

Sands and Silts

Rock Toe

Filter Blanket

Elev. 718’

Seasonal Pool Elev. 650’

Project Description

Profile Along Dam Centerline

ClayEmbankment

Foundation Sands

720

690

660

630

600

570

0+00 1+00 2+00 3+00 4+00 5+00 6+00 7+00 8+00 9+00

ApproximateTop of Rock

Existing Groundline Cut-Off TrenchExcavation

Project Description

350'

50'

Seismic Assessment

� Intermediate SeismicAssessment 1995

�Feature DesignMemorandum 1997

�SPT & CPT Tests 1996-98

�Seismic AssessmentReport 1998

View of Downstream Area

Seismic Assessment

1998 Seismic Analysis Report

Conclusions• Remediation Cost � $13 MillionRecommendations• Site Specific Seismic Study

(2000)• Additional Field Work (1999)• Hydro-fracture Potential (1999)• Specific Design Criteria

(pending)

Seismic Assessment

TARA – FLAC Comparison

• Incorporated the TARA model into FLAC• Obtained Parameters used by Dr. Finn• Completed 1998 TARA Analysis using

FLAC• Dr. Finn Reviewed & Concurred with

Results

TARA – FLAC Comparison

TARA – FLAC Comparison

TARAStatic

Analysisw/ Gravity

SeismicAnalysis

w/o Gravity

DeformationAnalysis

w/ Gravity

FLAC

All Combinedw/ Gravity

EX_ 5 Values-2.000E+00-1.000E+000.000E+001.000E+002.000E+003.000E+004.000E+005.000E+006.000E+007.000E+00

Sand BlanketRock Toe DrainEmbankmentFoundation # 1Foundation # 2Foundation # 3Foundation # 4Foundation # 5Foundation # 6

Idealized Cross-SectionTARA – FLAC Comparison

RegionUnit

WeightsUndrainedStrength

DrainedStrength

CleanSand

ResidualStrength

ShearModulus

PWP1

Modelγm

(pcf)γsat

(pcf)φ

(deg)c

(ksf)φ'

(deg)c'

(ksf)(N1)60 cresidual

(ksf)K2max Kr

Embankment 127 130 18 2.0 29.0 0.0 -- -- 60-80 --Filter Blanket -- 130 16 1.8 34.0 0.0 -- -- 60 --Toe Drain 110 110 -- -- 38.0 0.0 -- -- 61 --Foundation #1 -- 133 16 1.8 34.0 0.0 16 0.7 27 0.0366-0.0389Foundation #2 -- 133 16 1.8 34.0 0.0 15 0.6 27 0.0316-0.0323Foundation #3 -- 133 16 1.8 34.0 0.0 14 0.5 27 0.0279-0.0287Foundation #4 -- 128 21 0.6 30.0 0.0 13 0.4 27 0.0043-0.0087Foundation #5 -- 128 21 0.6 30.0 0.0 11 0.3 27 0.0035-0.0071Foundation #6 -- 128 21 0.6 30.0 0.0 9 0.2 27 0.0034-0.0081Foundation #7 -- 128 21 0.6 30.0 0.0 5 0.1 27 0.0027-0.00781C1= 0.76; C2 = 0.53

A CBD

E

F

G H

TARA

FLAC

A CBD

EF

TARA – FLAC Comparison

FLAC PWP Calibration

• FLAC Modeling Calibrated with TimeHistory and ENC.

• Results for both analyses shown forcomparison.

TARA

FLACTime History

FLACENC

TARA – FLAC Comparison

Max. shear strain increment0.00E+004.00E-018.00E-011.20E+001.60E+002.00E+002.40E+002.80E+00

Contour interval= 2.00E-01

Time History

ENC

Shear StrainContours

TARA – FLAC Comparison

Excess PWP RatioContours

TARA – FLAC Comparison

Time History

ENC

0.00E+001.00E-012.00E-013.00E-014.00E-015.00E-016.00E-017.00E-018.00E-019.00E-01

Existing Condition Analyses

• New Design Earthquake, Mw = 5.5,PGA=0.17

• Three Time Histories• Improved Characterization of Foundation• Undrained Strengths in Embankment• Review and Concurrence by Dr. Finn

-0.25

-0.20

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0 2 4 6 8 10Time (sec)

Acc

eler

atio

n (g

)

SyntheticMiramichiNahanni

Design Time HistoriesExisting Condition Analyses

Maximum Displacement 0.25 feet

Existing Condition Analyses

Deformations

Max. shear strain increment0.00E+005.00E-041.00E-031.50E-032.00E-032.50E-033.00E-03

Contour interval= 5.00E-04

Existing Condition Analyses

Shear Strain

Excess PWP Ratio_

0.00E+001.00E-012.00E-013.00E-014.00E-015.00E-016.00E-017.00E-018.00E-019.00E-01

Max. shear strain increment0.00E+002.50E-035.00E-037.50E-031.00E-021.25E-021.50E-021.75E-022.00E-022.25E-02

Contour interval= 2.50E-03

Post Earthquake SF = 1.6

Existing Condition Analyses

Limit Equilibrium

• OBE Mw = 5.0 w/ PGA=0.09g• New Design MCE Mw = 5.5 w/ PGA =

0.17g• TARA OBE used Mw = 5.5 w/ PGA =

0.09g– System Stable w/ Excess PWP < 13%

• FLAC New MCE– System Stable w/ Excess PWP < 25%

1998 TARA Analyses for OBE

SHAKE/TARA Analyses

Distance and Magnitude

(USBR)

Summary• TARA model incorporated into FLAC• FLAC analyses compare well with TARA• New existing condition analyses indicate a

stable dam because:– Reduced earthquake magnitude– Use of undrained strengths in embankment– Improved foundation characterization

• Dr. Finn reviewed and concurred with results.

Recommendations

• Remediation of Dewey Dam unwarrantedat this time.

• Further assessment warranted only uponadvancement of the state-of-the-art.

• Prepare a comprehensive seismic analysisreport incorporating the present study.

EE NN GG NN EEII EE RR SS

FullerMossbargerScott &May

FullerMossbargerScott &May

Teaming to Provide Practical Solutions to Complex Problems

Huntington District