liquefaction evaluations at doe sites_1
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LIQUEFACTION EVALUATIONS ATDOE SITES
M. Lewis, M. McHood, R. Williams, B. GutierrezOctober 25, 2011
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Agenda
Background
Purpose and Objective
Liquefaction Methods
Site Evaluations
Aging
Conclusions
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Background
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Liquefaction at DOE Sites
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Background
Liquefaction evaluations are required at allDOE sites
Methods have evolved over the years, butthere is currently only one consensusmethodology;
Youd et al., 2001
Two other methods have emerged in the lastfew years; Cetin et al., 2004
Idriss & Boulanger, 2008
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Background
Youd et al., was the result of two workshops(NCEER/NSF) held in the late 1990s, culminatingin a NCEER report and a ASCE publication in2001. The method is widely used.
Cetin et al., was the result of several doctoraldissertations and evaluations at University ofCalifornia-Berkeley. It culminated in a ASCEpublication in 2004.
Idriss & Boulanger is the result of several MS &doctoral dissertations and evaluations atUniversity of California-Davis. It culminated inan EERI Monograph in 2008.
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Background
There is currently ongoing discussion in theprofession regarding the Cetin et al., andIdriss & Boulanger methods.
There is no such discussion regarding Youd etal.
This presentation will present results from
each for comparison. We will also present results from the SRS site-
specific methodology for comparison to Youdet al.
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Purpose & Objectives
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Liquefaction at DOE Sites
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Purpose & Objectives
The overall purpose is to present and showdifferences in each of the methodologies(Youd, Cetin, and Idriss & Boulanger) withrespect to liquefaction factor of safety (FS)
Comparisons will be shown of variousparameters along with some discussion
An added comparison will be made betweenthe SRS site-specific and Youd methodologiesto introduce a potential aging correction
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Liquefaction Methods
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Liquefaction at DOE Sites
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Liquefaction Evaluation
Methods Youd et al., 2001
Only consensus liquefaction method NSF/NCEER Workshops in the 1990s
ASCE Geotechnical Journal October 2001 Cetin et al., 2004
Re-evaluated some key case histories ASCE Geotechnical Journal December 2004
Idriss & Boulanger 2008 EERI Monograph 12 (MNO-12) SRS site-specific, 2008
Results from site-specific laboratory testing
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Liquefaction Methods
For this comparative evaluation the Seed & Idrisssimplified equation will be used to calculate theearthquake demand.
Each of the four methods will utilize the specificrecommendations of each method for the variousparameters (e.g., rd, MSF, CN, and K ).
The evaluation with the 3 methods will utilize resultsfrom the standard penetration test (SPT), using the
method-specific triggering relationship. The added comparison between the SRS and Youd
methods will utilize the triggering relationshipsdeveloped for the Cone Penetration Test (CPT).
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Liquefaction Methods
Just a reminder, the Seed/Idriss simplifiedequation;
The safety factor against liquefaction isdefined as;
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d
vo
vo
vo
ave rg
aCSR
'
max
'65.0
age7.5 KKKMSF
CSR
CRRFS
d
vo
vo
vo
ave rg
aCSR max''
65.0
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Liquefaction Methods
Where;
CSR is the earthquake demand
CRR is the soils capacity (resistance or strength)
MSF the magnitude scaling factor
K a correction for static shear stress (set to 1 for thiscomparison)
K a correction for overburden pressure
Kage a correction for age (set to 1 for the comparison ofthe 3 methods)
vo and vo effective and total overburden pressures
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Liquefaction Methods
Stress Reduction Coeff. (rd)
Cetin et al., lower at all
depths shown
Youd et al., varies with depth
Idriss & Boulanger changes
with earthquake M and depth
Cetin et al., changes with
depth, M, amax and Vs
Site response analysis
eliminates these differences
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Liquefaction Methods
MSF Comparison
All three show similartrends
All three are equal at Mw =7.5
At Mw > 6.5, differences are
minimal
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Liquefaction Methods
K Correction
Significant differences atshallow depths
Values vary withoverburden pressure andrelative density (DR)
Most level-groundevaluations are atoverburden pressures < 3.5to 4 tsf
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Liquefaction Methods
SPT CN Correction
All relationships converge
at o
= 1 tsf
Relationships at o < 4 tsfare very similar
At o > 6 tsf, differences
can be important
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SPT Triggering Relationships
18Idriss & Boulanger, 2010
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SPT Triggering Relationships
19Adapted from Idriss & Boulanger, 2010
0.226
0.205
0.156
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Triggering Relationships(most important difference)
CRR at (N1)60cs = 5
I/B:Y = 0.087/0.068 =1.28
C:Y = 0.048/0.068 = 0.71
CRR at (N1)60cs = 10
I/B:Y = 0.118/0.115 = 1.03 C:Y = 0.072/0.115 = 0.63
CRR at (N1)60cs = 20
I/B:Y = 0.205/0.226 =0.91
C:Y = 0.156/0.226 = 0.69
CRR at (N1)60cs = 30
I/B:Y = 0.48/0.6 = 0.8 C:Y = 0.338/0.6 = 0.56
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Savannah River Site; F, Z, and K areas
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Site Evaluations
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SRS Generalized Profile
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GWT varies by area;K 55 ft, F 80 ft, Z 55 ft
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SRS Seismic Demand
Two earthquakes are utilized
Deterministic
Mw = 7.2, pga = 0.1g Charleston 50th (C50)
Probabilistic
Mw = 6.6, pga = 0.2g Design Basis Event (DBE)
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SRS F-Area
Mw=7.2, pga=0.1g Mw=6.6, pga=0.2g
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80
85
90
95
100
105
110
0.0 1.0 2.0 3.0 4.0 5.0 6.0
D
epth(ft)
Safety Factor
Youd I/B Cetin
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85
90
95
100
105
110
0.0 1.0 2.0 3.0 4.0 5.0 6.0
D
epth(ft)
Safety Factor
Youd I/B Cetin
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SRS Z-Area
Mw=7.2, pga=0.1g Mw=6.6, pga=0.2g
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50
60
70
80
90
100
110
0.0 1.0 2.0 3.0 4.0 5.0 6.0
D
epth(ft)
Safety Factor
Youd I/B Cetin
50
60
70
80
90
100
110
0.0 1.0 2.0 3.0 4.0 5.0 6.0
D
epth(ft)
Safety Factor
Youd I/B Cetin
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SRS Results
In general; Cetin results in lower FS
Youd and Idriss/Boulanger are comparable
Neglecting very high FS; I/B is about 9% of Youd with a ~ 20% for the C50 (Mw = 7.2)
I/B is about 12% of Youd with a ~ 21% for the DBE (Mw =6.6)
Cetin is about -44% of Youd with a ~ 24% for the C50 (Mw= 7.2)
Cetin is about -30% of Youd with a ~ 27% for the DBE (Mw= 6.6)
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Paducah (PDGP)
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Site Evaluations
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Paducah Seismic Demand
Mw = 7.5, pga = 0.48g
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Paducah Generalized Profile
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GWT assumed at 10 ft
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PDGP; SB-01, 02, 03, 05, 06
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0
10
20
30
40
50
60
0.0 1.0 2.0 3.0
Depth(ft)
Safety Factor
Youd I/B Cetin
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PGDP Results
In general, the results for each of the threemethods are much closer, however;
Cetin results in lower FS
Youd and Idriss/Boulanger are comparable
Overall;
Idriss/Boulanger is about -4% of Youd with a ~
26% (16 of 22 [73%] analyses within 20% of Youd) Cetin is about -35% of Youd with a ~ 22% results
(6 of 23 [26%] analyses within 20% of Youd)
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Savannah River Site
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Aging
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Aging (SRS)
Compare Youd et al., (2001) to the SRSmethodology
SRS methodology based on site-specific
testing (CRR and K ); no attempt was madeto correct for disturbance
Most other parameters (CN, MSF, rd) followrecommendations of Youd
Difference in computed FS can be attributedto aging
Compare results for CPT in K-Area
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Strength Gain vs Age
39Lewis et al., 2008
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50
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0.0 1.0 2.0 3.0 4.0 5.0 6.0
Depth(ft)
FS
KC7
SRS DBE Youd DBE
KC
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0.0 1.0 2.0 3.0 4.0 5.0 6.0
Depth(ft)
FS
KC7
SRS C50 Youd C50
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55
60
65
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0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60
Depth(ft
)
SRS/Youd (KC7)
C50/Youd C50 DBE/Youd DBE
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Aging (SRS)
The results for CPT KC7 would indicate thefollowing;
For the DBE (Mw = 6.6, pga = 0.2g);
Ratio of SRS/Youd ranges from about 1.1 to 2.4, witha mean ~ 1.4 (say ~ 1.1 to 1.2 from 55 to 80 ft)
For the C50 (Mw = 7.2, pga = 0.1g);
Ratio of SRS/Youd ranges from about 1 to 2.3, with amean ~ 1.3 (say ~ 1.1 to 1.2 from 55 to 85 ft)
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Strength Gain vs Age; SRS
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Conclusions
For the evaluations shown; Youd et al., is the only consensus liquefaction evaluation method
and is still recommended for use Site-specific correlations (SRS) can be extremely valuable
(expensive and time consuming) More than one tool (e.g., SPT, CPT) is recommended for
liquefaction evaluations Youd et al., and Idriss/Boulanger are comparable In general, Cetin et al., results in significantly lower FS than either
Youd et al., and Idriss/Boulanger
For SRS soils, an aging correction factor appears appropriatewhen using the Youd et al., relationship (which is for Holocenesoils)
Upcoming workshops specifically targeting resolution betweenIdriss/Boulanger and Cetin et al., methods would be very helpfulin resolving differences