Liquefaction Hazard Mapping. Keith L. Knudsen Senior Engineering Geologist California Geological Survey Seismic Hazard Mapping Program

Transcription

1 Liquefaction Hazard Mapping Keith L. Knudsen Senior Engineering Geologist California Geological Survey Seismic Hazard Mapping Program April 20, 2006

2 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)

3 Liquefaction - how does it work? from University of Washington soil liquefaction web site

4 3 Ingredients for liquefaction Loose granular deposits Saturation Strong shaking (Probabilistic PGA - 10% exceedance in 50 years)

5 Consequences of liquefaction Lateral spreading Settlement Flow failure Loss of bearing capacity Ground oscillation

6 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)

7 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 blow count dry density grain size Geotechnical Parameter % moisture void ratio

8 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

9 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

10 Ground water - through time Hydrograph for a Santa Clara Valley monitoring well (modified from Figure 3-2, Reymers and Hemmeter, 2001)

11 Defining margin of liquefaction zone of required investigation Liquefaction zone boundary GW Qhf Qhf Top of Pleistocene Qpf Qpf saturated Holocene sediment

12 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

13 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

14 Zones of Required Investigation (liquefaction, landsliding, surface rupture)

15 Guidelines and Criteria by CGS SP 118 SP 117

16 Important Publications from Southern California Implementation Committees (

17 pga s from reports: (on CGS SHZP web site)

18 Mode magnitude and distance De-aggregated from PSHA (in reports on web)

19 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

20 (N 1 ) 60 min - Borings (only liquefiable textures) # of borings rep_age = Modern n = 39 Lognormal Distribution for Modern # of borings rep_age = Latest Holocene n = 70 Lognormal Distribution for Latest Holocene N160_min N160_min Modern Latest Holocene # of borings rep_age = Holocene n = 361 Lognormal Distribution for Holocene # of borings rep_age = Latest Pleistocene n = 23 Lognormal Distribution for Latest Pleistocene N160_min N160_min Holocene Latest Pleistocene

21 (N 1 ) 60 -Layers (only liquefiable textures) 16 Modern 40 Latest Holocene # of layers Lognormal Distribution for Modern liquefiable textures only # of layers Lognormal Distribution for Latest Holocene liquefiable textures only N160_min N160_min Modern Latest Holocene 250 Holocene 40 Latest Pleistocene # of layers Lognormal Distribution for Holocene liquefiable textures only # of layers Lognormal Distribution for Latest Pleistocene liquefiable textures only N160_min N160_min Holocene Latest Pleistocene

22 (N 1 ) 60 -Layers (all textures) 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

23 Limiting shear strain, Wu CSR, % N 1,60,cs

24 Volumetric strain, Wu 2002 CSR,% N 1,60,cs

25 Shear strain (%) - layers 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 (%)

26 How good is the data? (Penetration tests) Type of sampler recorded Nm (ASTM D1586) Blow count Spt equivalent 1 OD = 2.0" OD < 2.5" OD = or > 2.5" and < 3.0" UNK or NULL OD = 2.0" OD < 2.5" OD = or > 2.5" and < 3.0" UNK or NULL OD = 2.0" OD < 2.5" OD = or > 2.5" and < 3.0" UNK or NULL 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

27 Other approaches to regional liquefaction hazard mapping Mw San Francisco earthquake. Mw 7.4 Izmit, Turkey 1999 earthquake.

28 New Quaternary geologic mapping USGS OFR :24,000

29 Quaternary map units (37 units)

30 New liquefaction susceptibility mapping USGS OFR :24,000 Past occurrences available USGS OFR

31 Relationship between Quaternary map units & liquefaction susceptibility

32 Holzer et al., 2002

33 Holzer et al., 2002 M7.1 & M6.6 Earthquakes LPI = Liquefaction Potential Index

34 Liquefaction Hazard Holzer et al., 2002

35 Site-specific investigations From Seed et al., 2001

36 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

37 Penetration Test Comparisons: Modified California Versus Standard Penetration Test Jacqueline D.J. Bott Keith L. Knudsen Charles R. Real

38 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

39 Conversion to SPT-equivalent from non-standard samplers N=N (WH/4200)( )/(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)

40 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 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)

41 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

42 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

43 MCS vs SPT - SFBA Raw blows Converted to N 1,60 s SPT sample SPT Blows NM N 1,60 from SPT N1601 N 1, BLOW_COUNT MCS Blows N1602 N 1,60 from MCS MCS sample N=129

44 MCS-SPT LS regression - SFBA N160 s from SPT Blows Y=0.45x Do not use Adjusted N 1,60 s from MCS Blows

45 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 NM N1602 N 1, SPT Blows NM N1601 N 1,60 Deeper sample N=1121

46 Rogers (defines ModCal as 3 OD) In Feb. or May, 2006 Environmental & Engineering Geoscience

47 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?

48 New Probabilistic Tools for Liquefaction Triggering Evaluation

49 SPT & CPT probabilistic triggering

50 Shear wave velocity evaluation now probabilistic

51 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

52 Predicting lateral spread displacements Free face log D H = (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(D mm)) Sloping ground log D H = (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(D mm)) (Youd et al., 2002)

53 A Semi-empirical Model for the Estimation of Maximum Horizontal Displacement Due to Liquefaction-induced Lateral Spreading DPI Faris et al., 2003 & this conference

54 Hmax = exp( ln(dpimax) ln(α) Mw) Faris, 2003

55 Faris, 2003

56 Modified Chinese Criteria being debated From Seed et al., 2001

57 Predicting consequences

58 Liquefaction-related web sites California Geological Survey SHZP New USGS/CGS liquefaction web site San Francisco Bay Area susceptibility maps Association of Bay Area Governments Soil Liquefaction University of Washington Southern CA Implementation Committee doc. Liquefaction Engineering Resources

59 Documents CGS SHZP evaluation reports on web site Recommended procedures for implementation of DMG Special Publication Guidelines for analyzing and mitigating liquefaction in CA [ 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 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