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Transcript of Evaluating liquefaction & lateral spreading in interbedded ... · Evaluating liquefaction & lateral...
Evaluating liquefaction & lateral spreading in
interbedded sand, silt, and clay deposits
using the cone penetrometer
5th International Conference on Geotechnical & Geophysical Site Characterization (ISC’5)
Jupiters Gold Coast, Queensland, Australia – September 5-9, 2016
Ross W. Boulanger, PhD, PE
Professor, Director of CGM
Diane M. Moug Sean K. Munter Jason T. DeJongAdam B. Price
The problem
Current liquefaction evaluation procedures (triggering & consequences) appear to have a tendency to over-predict liquefaction effects in interbedded sand, silt, and clay deposits
Example: Çark Canal in 1999 M=7.5 Kocaeli earthquake
Absence of visible ground deformations despite an estimated PGA of 0.4g (Youd et al. 2009)
Photo: Brady Cox
Example: Çark Canal in 1999 M=7.5 Kocaeli earthquake
Absence of visible ground deformations despite an estimated PGA of 0.4g (Youd et al. 2009)
The problem
Current liquefaction evaluation procedures (triggering & consequences) appear to have a tendency to over-predict liquefaction effects in interbedded sand, silt, and clay deposits
Examples include:
Çark Canal & Cumhuriyet Avenue in 1999 M=7.5 Kocaeli earthquake (Youd et al. 2009)
Sites in Taiwan in 1999 M=7.6 Chi-Chi earthquake (Chu et al. 2007 & 2008)
Gainsborough Reserve & Riccarton areas of Christchurch, New Zealand in the 2010-11 Canterbury Earthquake Sequence (Beyzaei et al. 2015, Stringer et al. 2015, van Ballegooy et al. 2014, 2015)
Tendency to over-predict liquefaction effects, while conservative, but can have significant economic implications
Computing a few 10’s of cm of lateral displacement or a few cm of settlement can lead to ground improvement or structural strengthening efforts
Today's presentation
Identify possible reasons for over-prediction of liquefaction effects in interbedded deposits:
Brief remarks on transitions, thin-layers, & graded bedding
List factors of primary concern
Describe three related research projects:
Axisymmetric cone penetration with the MIT-S1 constitutive model (Moug et al. 2016)
Cyclic strength correlations for intermediate soils (Price et al. 2015)
Evaluation of liquefaction effects at Çark Canal (Munter et al. 2017)
Concluding remarks
Factors affecting prediction of liquefaction effectsin interbedded deposits
Transition & thin-layer corrections
Measurements of qt & fs influenced by soils within 10 to 30 diameters around the tip
Transition
*
tH
t thin
qK
q
Thin layer:
Modified from Robertson & Fear (1995)
Transition & thin-layer corrections
Thin-layer effects from field data are smaller than those from elastic solutions and greater than those from nonlinear simulations (Van den Berg et al. 1996, Walker & Yu 2010)
Graded bedding
Problem: Graded bedding rather than distinct interfaces (e.g., erosional contacts)
Ripples of sand, silt and clay in Dead Sea sediments(http://woostergeologists.scotblogs.wooster.edu/2012/03/)
Graded beds with flame structures in fine grained layers (Permian, Inyo County, CA)(Tim D. Cope, http://acad.depauw.edu/~tcope/index.html)
Factors Part 1: Limitations in site characterization tools & procedures
Interface transitions
Penetration resistance (e.g., qt ) in sand is reduced near interfaces with clays or silts. Icvalues increase in the sandy soils and decrease in the clays/silts near the interface
Thin-layer effects
Penetration resistance (e.g., qt ) reduced throughout sand layers less than about 1 m thick (with clays/silts on either side of the layer)
Graded bedding
Penetration data may not differentiate between distinct interfaces & graded transitions in soil types. Transition and thin layer effects in graded deposits are not well understood
Continuity of lenses
Large horizontal spacing of explorations may not enable the lateral continuity of weak or liquefiable layers to be evaluated or quantified
Saturation
Presumption of 100% saturation below the groundwater table may underestimate cyclic strengths for partially saturated zones
Factors Part 2: Limitation in correlations for liquefaction
Triggering correlations
Triggering correlations are not well constrained for intermediate soils with certain FC and PI combinations
Strain correlations
Correlations for estimating peak shear or post-liquefaction reconsolidation strains have been developed primarily from data for clean sands, although data for other soil types is becoming more plentiful
Factors Part 3: Limitations from analysis methods & neglected mechanisms
Spatial variability
The assumption that liquefiable layers are laterally continuous can contribute to over-estimation of liquefaction effects. Composite strength from nonliquefied and liquefied zones may limit deformations.
Thick crust layers
Thick crust layers can reduce surface manifestations of liquefaction at depth in areas without lateral spreading
Dynamic response
Liquefaction of loose layers in one depth interval may reduce seismic demand on soils in other depth intervals
Geometry & scale
The 2D or 3D scale of a deformation mechanism affects the dynamic response and role of spatial variability
Diffusion of excess pore pressures
Transient seepage may increase or decrease ground deformations depending on stratigraphy, permeability contrasts, geometry, seismic loading, & other factors
Concluding remarks
Key factors grouped in three categories:
Limitations in site characterization tools & procedures
Limitations in correlations for triggering and shear/volumetric strains
Limitations in analysis approaches
For most case histories:
Several factors likely contribute to any observed over-prediction of liquefaction effects
Contribution of each factor will depend on the specific situation & analysis method
Related study #1:Direct cone penetration model
Simulation of cone penetration in intermediate soils
Direct cone penetration model with ALE formulation & MIT-S1 constitutive model (Pestana & Whittle 1999) implemented in FLAC to enable modeling of intermediate soil types
Current efforts focused on validation; example for anisotropic Boston Blue clay in the paper
Related study #2:Developing cyclic strength correlations
for intermediate soils
Cyclic strength correlations for intermediate soils
Cyclic DSS strengths for PI = 0, 6, & 20 mixtures of silica silt & Kaolin
Cyclic strength correlations for intermediate soils
Comparisons are conditional on the same depositional process, recognizing all other factors are different (e.g., void ratio, critical state line, compressibility)
Want comparisons conditional on cone penetration resistance
Cyclic strength correlations for intermediate soils
Calibrate the MIT-S1 model to monotonic responses over a range of stresses & OCRs
Cyclic strength correlations for intermediate soils
Simulated qt using indirect modeling (cavity expansion); results to be updated with full model & validated against centrifuge data
CRRs conditional on (simulated) qt more useful for practice
Related study #3:Çark canal case history
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Youd et al. (2009)
Absence of visible ground cracking or deformation despite an estimated PGA 0.4g
Several buildings settled up to 100 mm suggesting liquefaction or cyclic softening occurred, but sand boils were not observed
Photo:
Brady Cox
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Youd et al. (2009)
Current liquefaction susceptibility analyses with MLR model for lateral spreading predicted significant deformations
Newmark analysis with key stratum as clay correctly predicts small displacements
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Youd et al. (2009)
"At the Çark Canal and Cumhuriyet Avenue sites, …the absence of lateral spread at these sites indicates that these [liquefiable] layers were most likely discontinuous lenses with sufficient shear resistance in the discontinuities [clays] to prevent lateral spread."
Çark Canal: CPT and borehole data
Canal is a channelized segment of a meandering river
CPT and boring data binned by geologic strata & soil type
Data at peer.berkeley.edu/publications/…/cark/index.html
1D Liquefaction Vulnerability Indices
Integration of various response measures versus depth
Shear strains, volumetric strains, FSliq, …
May include weighting factors based on depth
Commonly applied to individual SPT borings or CPT soundings
Implicitly assumes horizontal layering (hence the 1D assumption)
Examples
Liquefaction Potential Index, LPI (Iwasaki 1978)
Lateral Displacement Index, LDI (e.g., Tokimatsu and Asaka 1998, Zhang et al. 2004)
Liquefaction Severity Number, LSN (Van Ballegooy et al. 2014)
Reconsolidation settlement, Sv-1D (e.g., Ishihara and Yoshimine 1992, Zhang et al. 2002)
Results for Çark Canal based on two methods:
LD's based on procedure by Zhang et al. (2004) which uses the triggering correlation of Robertson & Wride (1998)
LDI's based on procedure in Idriss & Boulanger (2008) based on Ishihara & Yoshimine (1992) and the triggering correlation of Boulanger & Idriss (2015)
Çark Canal: 1D LDI & LD analyses
Results for CPT 1-23 without any adjustments and with application of transition & thin-layer corrections and a site-specific fines content calibration
Top
max
Bottom
dz
Çark Canal: 1D LDI & LD analyses
Results for CPT 1-23 without any adjustments and with application of transition & thin-layer corrections and a site-specific fines content calibration
Top
max
Bottom
dz
Çark Canal: 1D LDI & LD analyses
Results for CPT 1-23 without any adjustments and with application of transition & thin-layer corrections and a site-specific fines content calibration
Top
max
Bottom
dz
Çark Canal: 1D LDI & LD analyses
Results for CPT 1-23 without any adjustments and with application of transition & thin-layer corrections and a site-specific fines content calibration
Top
max
Bottom
dz
Çark Canal in 1999 M=7.5 Kocaeli earthquake
LD results over-predict liquefaction effects, even with transition corrections
Çark Canal in 1999 M=7.5 Kocaeli earthquake
LDI results over-predict liquefaction effects, even with all corrections applied
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Nonlinear deformation analyses using FLAC 7.0 (Itasca 2011)
24,000 zones with typical thicknesses of 10 cm
Compliant base & free-field boundaries
Input (outcrop) motion: Sakarya 090 recording scaled to PGA = 0.40g
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Two-category model for this deposit of channel sands and overbank clays based on a transition probability geostatistical approach (Carle 1999)
Silty sand: sills of 23% and 40%, horizontal mean lengths of 5 m and 10 m, and vertical mean lengths of 0.16 m and 0.26 m
Realizations conditional on the two CPTs near the channel sides
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Data binned by stratum and soil type, and inspected for vertical or lateral trends
Sand-like portion of stratum:
23-40% depending on Ic criteria
median qc1Ncs 90 w/o corrections, and 115 w/ corrections
Clay-like portion of stratum: median su 50 kPa
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Fill:
Mohr Coulomb model with c' = 5 kPa, f' = 39°
Interlayered fine grained sediments with silty sand lenses:
Clays: Mohr Coulomb model with su = 50 kPa, fu = 0°
Silty sands: PM4Sand (Boulanger & Ziotopoulou 2015) calibrated for qc1Ncs = 90 or 115
Dense silts and sands:
PM4Sand calibrated for qc1Ncs = 250
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Realization B10-3 (40% sand, Lx = 10 m, Ly = 0.26 m)
Çark Canal in 1999 M=7.5 Kocaeli earthquake
Realization B10-Long-1 (40% sand, Lx = 10 m, Ly = 0.26 m)
Çark Canal in 1999 M=7.5 Kocaeli earthquake
NDA results are in the range of deformations that might not be visually detectable at this site
Çark Canal – Concluding remarks
A site underlain by interbedded soils along Çark Canal developed no visible ground cracking or deformations in the 1999 M=7.5 Kocaeli earthquake despite an estimate PGA of 0.4 g, as documented in Youd et al. (2009).
1D Lateral Displacement Index (LD & LDI) analyses using two current approaches:
Over-predicted the potential for liquefaction effects
Incorporating transition & thin-layer corrections along with a site-specific fines content calibration reduced the degree of over-prediction (but did not eliminate it)
Nonlinear dynamic analyses with stochastic realizations of the interbedded liquefiable and nonliquefiable sediments:
Produced small to moderate deformations
Were consistent with the lack of visible damage for this site
Support Youd et al.'s (2009) conclusion that shear resistance from the nonliquefiable soils between lenses of liquefiable soils must have been sufficient to prevent lateral spreading
Concluding remarks
Concluding remarks
Currently-used liquefaction evaluation procedures & practices can have a tendency to over-predict liquefaction effects in interbedded sand, silt, and clay deposits.
Factors of primary concern were identified & are discussed in the paper
Importance of each factor depends on the specific situation & analysis approach employed
Reexamination of Çark Canal in the 1999 M=7.5 Kocaeli earthquake illustrated the overlapping roles of several factors:
Corrections to CPT data for transition & interface effects
Spatial variability of interbedded deposits
Dynamic versus simplified analyses
2D versus 1D geometry
Other factors may have contributed, but are difficult to assess based on existing data
Advancing liquefaction evaluation procedures for interbedded deposits will require:
Mix of experimental, theoretical, and field studies to address the various factors of concern
Reevaluation of case histories with due consideration to all contributing factors
Three projects working toward this goal were introduced & are discussed in the paper
Acknowledgments
Discussions with numerous colleagues & friends, including Jon Bray, Brady Cox, Misko Cubrinovski, I. M. Idriss, Bruce Kutter, Ken Stokoe, and Sjoerd van Ballegooy.
Assistance by Chris Krage and Ana Maria Parra Bastidas
Financial support from the California Department of Water Resources (CADWR) and National Science Foundation (NSF)