Liquefaction Hazard Mapping Keith L. Knudsen Senior Engineering Geologist California Geological Survey Seismic Hazard Mapping Program April 20, 2006
Topics Liquefaction hazard mapping (regional) CGS approach Other approaches Future CGS approaches Comments on sitespecific studies Q & 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 liquefaction Loose granular deposits Saturation Strong shaking (Probabilistic PGA - 10% exceedance in 50 years)
Consequences of liquefaction Lateral spreading Settlement Flow failure Loss of bearing capacity Ground oscillation
Basis for CGS Liquefaction Zones of Required Investigation (ZORIs) Past occurrences Boring logs (mainly SPT) Geotechnical properties Loose sand & silt (Q deposits) Simplified procedure Geology Uncompacted artificial fill Holocene deposits Historical-high ground water Ground shaking (pga, magnitude)
Boring Log Database Over 13,500 borings Over 300,000 records Over 100 cities Boring log info available for download on our web site! Northern California Database Principal Parameters Number of Records 10000 8000 6000 4000 2000 0 8019 4780 860 6042 80 blow count dry density grain size Geotechnical Parameter % moisture void ratio
Geotechnical Criteria for Liquefaction Zone Simplified Procedure Penetration resistance - N field to (N 1 ) 60 or (N 1 ) 60,cs Resisting forces - CRR from (N 1 ) 60 Driving forces - CSR = 0.65(a max /g)(σ/σ )r d Factor of Safety - FS=CRR/CSR If FS <1 then liquefaction (triggering) likely
Geotechnical Criteria for Liquefaction Zone Simplified Procedure N field to (N 1 ) 60 CRR from (N 1 ) 60 CSR = 0.65(a max /g)(σ/σ )r d FS=CRR/CSR If FS<1 then liquefaction likely to be triggered
Ground water - through time Hydrograph for a Santa Clara Valley monitoring well (modified from Figure 3-2, Reymers and Hemmeter, 2001)
Defining margin of liquefaction zone of required investigation Liquefaction zone boundary GW Qhf Qhf Top of Pleistocene Qpf Qpf saturated Holocene sediment
Geologic Criteria for Liquefaction Zone GEOLOGIC AGE PEAK GROUND ACCELERATION HISTORICAL- HIGH GROUND WATER LATE HOLOCENE (HISTORICAL FLOODPLAINS, ESTUARIES) >10% g <40 FT HOLOCENE (< 11,000 YEARS) >20% g <30 FT LATE PLEISTOCENE (11,000-15,000 YEARS) >30% g <20 FT
Liquefaction Zoning - Issues & Limitations Use available geotechnical data Any layer liquefies (triggers) -> area included in zone Zone is binary -> in or out Historical-high ground water is used Free faces and slopes no special attention
Zones of Required Investigation (liquefaction, landsliding, surface rupture)
Guidelines and Criteria by CGS SP 118 SP 117
Important Publications from Southern California Implementation Committees (www.scec.org)
pga s from reports: (on CGS SHZP web site)
Mode magnitude and distance De-aggregated from PSHA (in reports on web)
New CGS approaches to zoning Past occurrences Deformation based in areas with sufficient subsurface data Areas with little boring data grid based Proximity to water body or stream Age of deposits Areas with free faces
(N 1 ) 60 min - Borings (only liquefiable textures) # of borings 18 16 14 12 10 8 6 4 2 rep_age = Modern n = 39 Lognormal Distribution for Modern # of borings 35 30 25 20 15 10 5 rep_age = Latest Holocene n = 70 Lognormal Distribution for Latest Holocene 0 0 5 10 15 20 25 30 35 40 45 50 55 N160_min 60 65 70 75 80 85 90 95 5 10 15 20 25 30 35 40 45 50 55 N160_min 60 65 70 75 80 85 90 95 Modern Latest Holocene # of borings 140 120 100 80 60 40 rep_age = Holocene n = 361 Lognormal Distribution for Holocene # of borings 6 5 4 3 2 rep_age = Latest Pleistocene n = 23 Lognormal Distribution for Latest Pleistocene 20 1 0 0 5 10 15 20 25 30 35 40 45 50 55 N160_min 60 65 70 75 80 85 90 95 5 10 15 20 25 30 35 40 45 50 55 N160_min 60 65 70 75 80 85 90 95 Holocene Latest Pleistocene
(N 1 ) 60 -Layers (only liquefiable textures) 16 Modern 40 Latest Holocene # of layers 14 12 10 8 6 Lognormal Distribution for Modern liquefiable textures only # of layers 35 30 25 20 15 Lognormal Distribution for Latest Holocene liquefiable textures only 4 10 2 5 0 0 5 10 15 20 25 30 35 40 45 50 55 N160_min 60 65 70 75 80 85 90 95 5 10 15 20 25 30 35 40 45 50 55 N160_min 60 65 70 75 80 85 90 95 Modern Latest Holocene 250 Holocene 40 Latest Pleistocene # of layers 200 150 100 Lognormal Distribution for Holocene liquefiable textures only # of layers 35 30 25 20 15 Lognormal Distribution for Latest Pleistocene liquefiable textures only 50 10 5 0 0 5 10 15 20 25 30 35 40 45 50 55 N160_min 60 65 70 75 80 85 90 95 5 10 15 20 25 30 35 40 45 50 55 N160_min 60 65 70 75 80 85 90 95 Holocene Latest Pleistocene
(N 1 ) 60 -Layers (all textures) 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 10 20 30 40 50 60 70 80 90 100 Cumulative Frequency (%) 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 N160_min
Limiting shear strain, Wu 2002 60 CSR, % 55 50 45 40 35 30 25 20 15 1.6 1.5 1.4 1.3 1.2 1.1 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.05 0.025 10 5 0 5 10 15 20 25 30 35 N 1,60,cs
Volumetric strain, Wu 2002 CSR,% 60 55 50 45 40 35 30 25 20 15 10 0.06 0.055 0.05 0.045 0.04 0.035 0.03 0.025 0.02 0.015 0.01 0.005 5 5 10 15 20 25 30 35 40 N 1,60,cs
Shear strain (%) - layers 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Cumulative Frequency (%) age = Modern n = 29 age = Latest Holocene n = 82 age = Holocene n = 616 age = Latest Pleistocene to Holocene n = 42 age = Latest Pleistocene n = 150 age = All n = 919 Shear Strain (%)
How good is the data? (Penetration tests) Type of sampler recorded Nm (ASTM D1586) Blow count Spt equivalent 1 OD = 2.0" 29 28 27 2 OD < 2.5" 26 25 3 OD = or > 2.5" and < 3.0" 24 23 4 UNK or NULL 22 21 1 OD = 2.0" 20 19 2 OD < 2.5" 18 17 3 OD = or > 2.5" and < 3.0" 16 15 4 UNK or NULL 14 13 1 OD = 2.0" 12 11 2 OD < 2.5" 10 9 3 OD = or > 2.5" and < 3.0" 8 7 4 UNK or NULL 6 5 5 Rank of pen test Calculated force is betw een 5418 and 3150 pound-inches; n160 is calculated. Force is assumed to be 4200 poundinches, i.e. liquefy is applying the default mass and/or fall values of 140 lb. 30 in.; n160 is calculated. Calculated force is > 5418 or < 3150 pound-inches; n160 is NULL 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
Other approaches to regional liquefaction hazard mapping Mw 7.9 1906 San Francisco earthquake. Mw 7.4 Izmit, Turkey 1999 earthquake.
New Quaternary geologic mapping USGS OFR 2006-1037 1:24,000
Quaternary map units (37 units)
New liquefaction susceptibility mapping USGS OFR 2006-1037 1:24,000 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 Hazard Holzer et al., 2002
Site-specific investigations From Seed et al., 2001
Site-specific investigations Consult available maps Historical occurrences nearby? Age of sediment? Borings collect & document quality data Geologic 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. Bott Keith L. Knudsen Charles R. Real
Review of N 1,60 calculation N 1,60 = Nm.C E.C N.C R.C B.C S Where Nm = measured blows (using SPT sampler) C E = Correction for hammer energy efficiency C N = overburden correction factor (to 1 atm,) C R = correction for short rod length C B = Correction for borehole diameter = Correction for non-standard sampler C S
Conversion to SPT-equivalent from non-standard samplers N=N (WH/4200)(2.0 2-1.375 2 )/(OD 2 -ID 2 ) (Burmister, 1948) N=N (WH/4200)(2/OD 2 ) (LaCroix & Horn, 1973) where N = SPT-equivalent blow count N = measured blow count WH = 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 blows Using 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 N 1,60 s
Consecutive samples taken in same lithologic layer in same boring, separated by 5 ft or less MCS-SPT MCS-MCS SPT-SPT MCS MCS SPT <5 ft SM <5 ft CL <5 ft ML SPT MCS SPT
MCS vs SPT - SFBA Raw blows Converted to N 1,60 s 80 80 SPT sample SPT Blows NM 60 40 20 N 1,60 from SPT N1601 N 1,60 60 40 20 0 0 20 40 60 80 BLOW_COUNT MCS Blows 0 0 20 40 60 80 N1602 N 1,60 from MCS MCS sample N=129
MCS-SPT LS regression - SFBA 80 80 N160 s from SPT Blows 60 60 40 40 20 20 0 0 Y=0.45x + 9.16 Do not use 0 20 40 60 80 Adjusted N 1,60 s from MCS Blows
SPT vs SPT - SFBA Raw blows Converted to N 1,60 s 80 SPT Blows for SFBA data (1=deepest) 80 N160's from SPT Blows for SFBA (1=d Shallower sample SPT Blows NM2 60 40 20 N1602 N 1,60 60 40 20 0 0 20 40 60 80 SPT Blows NM1 0 0 20 40 60 80 N1601 N 1,60 Deeper sample 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 SPT There is a large scatter in blow count data - both for SPT and MCS CGS conversion from MCS to SPTequivalent (N 1,60 ) 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
Distance to rupture Earthquake magnitude T15 D5015 F15 Slope Free face ratio Lateral Spreading Estimated horizontal displacement Youd et al. (2002) 6 parameter Bardet et al. (1999) 4 parameter
Predicting lateral spread displacements Free face log D H = -16.713+(1.532*M)-(1.406*logR*)- (0.012*R)+(0.592*logW)+(0.540*logT 15 )+(3.413*log (100-F 15 ))-(0.795*log(D50 15 +0.1mm)) Sloping ground log D H = -16.213+(1.532*M)-(1.406*logR*) (0.012*R)+(0.338*logS)+(0.540*logT 15 )+(3.413*log( 100-F 15 ))-(0.795*log(D50 15 +0.1mm)) (Youd et al., 2002)
A Semi-empirical Model for the Estimation of Maximum Horizontal Displacement Due to Liquefaction-induced Lateral Spreading DPI Faris et al., 2003 & this conference
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 sites California 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 maps http://earthquakes.usgs.gov/regional/nca/qmap/ Association of Bay Area Governments http://www.abag.ca.gov/bayarea/eqmaps/liquefac/liquefac.html Soil Liquefaction University of Washington http://www.ce.washington.edu/~liquefaction/html/main.html Southern CA Implementation Committee doc. http://www.scec.org/resources/catalog/hazardmitigation.html#land Liquefaction Engineering Resources http://earthquake.geoengineer.org/liquefaction.html
Documents CGS SHZP evaluation reports on web site Recommended 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: 11 th SDEE and 3 rd ICEGE, Univ of CA, Berkeley, 2004