liquefaction hazard mapping -...
TRANSCRIPT
Liquefaction Hazard Mapping
Keith L. KnudsenSenior Engineering GeologistCalifornia Geological Survey –Seismic Hazard Mapping ProgramApril 20, 2006
Topics
Liquefaction hazard mapping (regional)
CGS approachOther approachesFuture CGS approaches
Comments on site-specific studiesQ & A
San Francisco “Zones of Required Investigation” for liquefaction &
landsliding (1:24,000)
Liquefaction - how does it work?
from University of Washington soil liquefaction web site
3 Ingredients for liquefactionLoose granular deposits Saturation Strong shaking
(Probabilistic PGA -10% exceedance in 50 years)
Consequences of liquefaction
Lateral spreadingSettlementFlow failureLoss of bearing capacityGround oscillation
Basis for CGS Liquefaction Zones of Required Investigation (ZORIs)Past occurrencesBoring logs (mainly SPT)
Geotechnical propertiesLoose sand & silt (Q deposits)Simplified procedure
GeologyUncompacted artificial fillHolocene deposits
Historical-high ground waterGround shaking (pga, magnitude)
Boring Log DatabaseOver 13,500 boringsOver 300,000 recordsOver 100 citiesBoring log info available for download on our web site! Northern California Database
Principal Parameters
4780
860
6042
80
8019
02000400060008000
10000
blow co
unt
dry de
nsity
grain si
ze
% mois
ture
void ra
tio
Geotechnical Parameter
Num
ber
of R
ecor
ds
Penetration resistance - Nfield to (N1)60 or (N1)60,cs
Resisting forces - CRR from (N1)60
Driving forces - CSR = 0.65(amax/g)(σ/σ’)rd
Factor of Safety - FS=CRR/CSRIf FS <1 then liquefaction (triggering) likely
Geotechnical Criteria for Liquefaction Zone –Simplified Procedure
Nfield to (N1)60
CRR from (N1)60
CSR = 0.65(amax/g)(σ/σ’)rd
FS=CRR/CSRIf FS<1 then liquefaction likely to be triggered
Geotechnical Criteria for Liquefaction Zone –Simplified Procedure
Hydrograph for a Santa Clara Valley monitoring well (modified from Figure 3-2, Reymers and Hemmeter, 2001)
Ground water - through time
Defining margin of liquefaction zone of required investigation
Qhf Qpf
Liquefaction zoneboundary
Top of Pleistocene
GW
saturated HolocenesedimentQpf
Qhf
Geologic Criteria for Liquefaction Zone
GEOLOGIC AGE PEAK GROUNDACCELERATION
HISTORICAL-HIGH GROUND
WATER
LATEHOLOCENE
(HISTORICALFLOODPLAINS,ESTUARIES)
>10% g <40 FT
HOLOCENE (< 11,000 YEARS) >20% g <30 FT
LATEPLEISTOCENE
(11,000-15,000YEARS)
>30% g <20 FT
Liquefaction Zoning - Issues & Limitations
Use available geotechnical data Any layer liquefies (triggers) -> area included in zoneZone is binary -> in or outHistorical-high ground water is usedFree faces and slopes – no special attention
Zones of Required
Investigation (liquefaction, landsliding,
surface rupture)
Guidelines and Criteria by CGS
SP 117SP 117SP 118SP 118
Important Publications from Southern Important Publications from Southern California Implementation CommitteesCalifornia Implementation Committees
(www.scec.org)(www.scec.org)
pga’sfrom reports:
(on CGS SHZP website)
Mode magnitude
anddistance
De-aggregated from PSHA
(in reports on web)
New CGS approaches to zoningPast occurrencesDeformation based – in areas with sufficient subsurface dataAreas with little boring data – grid based
Proximity to water body or streamAge of depositsAreas with free faces
(N1)60 min - Borings (only liquefiable textures)
Modern Latest Holocene
Holocene Latest Pleistocene
024
68
1012
141618
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
N160_min
# of
bor
ings
rep_age = Modern n = 39
Lognormal Distribution forModern
0
5
10
15
20
25
30
35
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
N160_min
# of
bor
ings
rep_age = Latest Holocene n = 70Lognormal Distribution forLatest Holocene
0
20
40
60
80
100
120
140
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
N160_min
# of
bor
ings
rep_age = Holocene n = 361
Lognormal Distribution forHolocene
0
1
2
3
4
5
6
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
N160_min
# of
bor
ings
rep_age = Latest Pleistocene n = 23Lognormal Distribution forLatest Pleistocene
(N1)60 - Layers (only liquefiable textures)
0
2
4
6
8
10
12
14
16
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
N160_min
# of
laye
rs
Modern
Lognormal Distribution for Modern
liquefiable textures only
0
5
10
15
20
25
30
35
40
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
N160_min
# of
laye
rs
Latest Holocene
Lognormal Distribution for LatestHolocene
liquefiable textures only
0
50
100
150
200
250
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
N160_min
# of
laye
rs
Holocene
Lognormal Distribution forHolocene
liquefiable textures only
0
5
10
15
20
25
30
35
40
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95
N160_min
# of
laye
rs
Latest Pleistocene
Lognormal Distribution for LatestPleistocene
liquefiable textures only
Modern Latest Holocene
Holocene Latest Pleistocene
(N1)60 - Layers (all textures)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80 90 100
N160_min
Cum
ulat
ive
Freq
uenc
y (%
)
age = Modern n = 153
age = Latest Holocene n = 254
age = Holocene n = 1651
age = Latest Pleistocene to Holocene n = 90
age = Latest Pleistocene n = 388
Lognormal Distribution for All
0 5 10 15 20 25 30 355
10
15
20
25
30
35
40
45
50
55
60
0.0250.050.10.20.30.40.50.60.70.80.911.11.21.31.41.51.6
N1,60,cs
CSR,
%Limiting shear strain, Wu 2002
5 10 15 20 25 30 35 40
N1,60,cs
5
10
15
20
25
30
35
40
45
50
55
60C
SR
,%
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
0.055
0.06
Volumetric strain, Wu 2002
Shear strain (%) - layers
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Shear Strain (%)
Cum
ulat
ive
Freq
uenc
y (%
)
age = Modern n = 29age = Latest Holocene n = 82age = Holocene n = 616age = Latest Pleistocene to Holocene n = 42age = Latest Pleistocene n = 150age = All n = 919
How good is the data? (Penetration tests)
Nm (ASTM D1586) Blow count Spt equivalent1 OD = 2.0" 29 28 272 OD < 2.5" 26 253 OD = or > 2.5" and < 3.0" 24 234 UNK or NULL 22 211 OD = 2.0" 20 192 OD < 2.5" 18 173 OD = or > 2.5" and < 3.0" 16 154 UNK or NULL 14 131 OD = 2.0" 12 112 OD < 2.5" 10 93 OD = or > 2.5" and < 3.0" 8 74 UNK or NULL 6 5
5 Sampler or hammer rejected; n160 is not calculated. 4 3 Force is not evaluated.
6
Data run prior to 4/20/00 or current data with "stealth" samplers or bad hammers. n160 calculated in error.
2 1
Rank of pen test
Type
of s
ampl
er re
cord
ed
Calculated force is betw een 5418 and 3150 pound-inches; n160 is
calculated.
Calculated force is > 5418 or < 3150 pound-inches; n160 is NULL
Force is assumed to be 4200 pound-inches, i.e. liquefy is applying the default mass and/or fall values of 140 lb. 30 in.; n160 is calculated.
Other approaches to regional liquefaction hazard mapping
Mw 7.4 Izmit, Turkey 1999 earthquake.
Mw 7.9 1906 San Francisco earthquake.
New Quaternary geologic mapping
USGS OFR 2006-10371:24,000
Quaternary map units (37 units)
New liquefaction susceptibility mapping
USGS OFR 2006-10371:24,000
Past occurrences
available USGS OFR 2000-444
Relationship between Quaternary map units & liquefaction susceptibility
Holzer et al., 2002
Holzer et al., 2002
M7.1 & M6.6 Earthquakes
LPI = Liquefaction
Potential Index
Liquefaction HazardHolzer et al., 2002
Site-specific investigations
From Seed et al., 2001
Site-specific investigationsConsult available mapsHistorical occurrences nearby?Age of sediment?Borings – collect & document quality dataGeologic interpretation – cross sections
Liquefaction triggering?Deformation?Consequences of deformation?Mitigation (& testing)Document & describe your approach, interpretations & results
Penetration Test Comparisons: Modified California Versus Standard Penetration Test
Jacqueline D.J. BottKeith L. KnudsenCharles R. Real
Review of N1,60 calculation
N1,60 = Nm.CE.CN.CR.CB. CS
Where Nm = measured blows (using SPT sampler)CE = Correction for hammer energy efficiencyCN = overburden correction factor (to 1 atm,)CR = correction for “short” rod lengthCB = Correction for borehole diameterCS = Correction for non-standard sampler
Conversion to SPT-equivalent from non-standard samplers
N=N’(WH/4200)(2.02-1.3752)/(OD2-ID2)(Burmister, 1948)
N=N’(WH/4200)(2/OD2)(LaCroix & Horn, 1973)
where N = SPT-equivalent blow countN’ = measured blow countWH = hammer mass (lbs) x fall distance (in)OD = outer diameter of non-standard sampler (in)ID = inner diameter of non-standard sampler (in)
Conversion factors for MCS to SPT-equivalent blowsUsing CGS Definition of MCS: ID = 2.0 in (1.875 in with liners) & OD = 2.5 in.
0.77 Burmister (1948)0.64 LaCroix & Horn (1973)
Other definition of MCS: ID = 2.5 in (2.4 with liners) & OD = 3.0 in
0.65 Burmister (1948)0.44 LaCroix & Horn (1973)
How?Compare consecutive samples (MCS & SPT) from same lithologic layer in same boring, that are within 5 ft of each other.Direct comparison of two such values cancels out factors often not reported by consultants such as hammer energy, borehole diameter, etc. Only overburden (and rod length for shallow samples) will be different so also compare N1,60’s
MLCLSM
MCS
SPT
<5 ft
MCS
MCS
SPT
SPT
<5 ft <5 ft
MCS-SPT MCS-MCS SPT-SPT
Consecutive samples taken in same lithologic layerin same boring, separated by 5 ft or less
MCS vs SPT - SFBA
0 20 40 60 80BLOW_COUNT
0
20
40
60
80
NM
0 20 40 60 80N1602
0
20
40
60
80
N16
01
Raw blows Converted to N1,60’s
MCS sample
SPT
sample
MCS Blows
SPT
Blow
s
N1,
60
N1,60 from MCS
N1,
60 f
rom
SPT
N=129
0
20
40
60
80
0 20 40 60 800
20
40
60
80
0 20 40 60 80Adjusted N1,60’s from MCS Blows
N16
0’s
fro m
SPT
Blow s
Y=0.45x + 9.16Do not use
MCS-SPT LS regression - SFBA
SPT vs SPT - SFBARaw blows Converted to N1,60’s
Deeper sample
Shallowe
rsa
mple
0 20 40 60 80NM1
0
20
40
60
80
NM
2
S P T B lo w s fo r S F B A d a ta ( 1 = d e e p e s t)
0 20 40 60 80N1601
0
20
40
60
80
N16
02
N 1 6 0 's f r o m S P T B lo w s fo r S F B A (1 = d
SPT Blows
SPT
Blow
s
N1,60
N1,
60
N=1121
Rogers (defines ModCal as 3” OD)
In Feb. or May, 2006 Environmental & Engineering Geoscience
Conclusions so far...When liquefaction is a concern USE SPTThere is a large scatter in blow count data - both for SPT and MCSCGS conversion from MCS to SPT-equivalent (N1,60) gives more consistent results for SFBA than for LA Basin. Is MCS defined differently in the two locations? Is this a function of the geology? Or related to something else?
New Probabilistic
Tools for Liquefaction Triggering Evaluation
SPT & CPT probabilistic triggering
Shear wave
velocity evaluation
– now probabilistic
Estimated horizontal
displacement
Free face ratio
Slope
T15
Earthquake magnitude
Distance to rupture
D5015
F15Youd et al. (2002) 6 parameter
Bardet et al. (1999) 4 parameter
Lateral Spreading
Predicting lateral spread displacements
Free facelog DH = -16.713+(1.532*M)-(1.406*logR*)-
(0.012*R)+(0.592*logW)+(0.540*logT15)+(3.413*log(100-F15))-(0.795*log(D5015+0.1mm))
Sloping groundlog DH = -16.213+(1.532*M)-(1.406*logR*)
(0.012*R)+(0.338*logS)+(0.540*logT15)+(3.413*log(100-F15))-(0.795*log(D5015+0.1mm))
(Youd et al., 2002)
“A Semi-empirical Model for the Estimation of Maximum Horizontal Displacement Due to Liquefaction-induced
Lateral Spreading”
Faris et al., 2003&
this conference
DPI
Hmax = exp(1.0443 ln(DPImax) + 0.0046 ln(α) + 0.0029 Mw)
Faris, 2003
Faris, 2003
Modified Chinese Criteria –being debated
From Seed et al., 2001
Predicting consequences
Liquefaction-related web sitesCalifornia Geological Survey – SHZP
http://www.conservation.ca.gov/cgs/shzp/New USGS/CGS liquefaction web site
http://sfgeo.wr.usgs.gov
San Francisco Bay Area susceptibility mapshttp://earthquakes.usgs.gov/regional/nca/qmap/
Association of Bay Area Governmentshttp://www.abag.ca.gov/bayarea/eqmaps/liquefac/liquefac.html
Soil Liquefaction – University of Washingtonhttp://www.ce.washington.edu/~liquefaction/html/main.html
Southern CA Implementation Committee doc. http://www.scec.org/resources/catalog/hazardmitigation.html#land
Liquefaction Engineering Resourceshttp://earthquake.geoengineer.org/liquefaction.html
DocumentsCGS SHZP evaluation reports – on web siteRecommended procedures for implementation of DMG Special Publication 117 - Guidelines for analyzing and mitigating liquefaction in CA [www.scec.org]Youd, T.L., and 20 others, 2001, Liquefaction resistance of soils: Summary Report from the 1996 NCEER and 1998 NCEER/NSF Workshops on Evaluation of Liquefaction Resistance of Soils: Journal of Geotechnical and Geoenvironmental Engineering, 127(10), p. 817-833.Seed, R. B., Cetin, K. O., Moss, R. E. S., Kammerer, A. M., Wu, J.,Pestana, J. M. and Riemer, M. F., 2003, Recent advances in soil liquefaction engineering and seismic site response evaluation: International Conference and Symposium on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, paper SPL-2, San Diego, California, 71p. Idriss, I.M., and Boulanger, R.W., 2004, Semi-empirical procedures for evaluating liquefaction potential during earthquakes: 11th SDEE and 3rd ICEGE, Univ of CA, Berkeley, 2004