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


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


Calibrate the MIT-S1 model to monotonic responses over a range of stresses & OCRs


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


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


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


LD results over-predict liquefaction effects, even with transition corrections


LDI results over-predict liquefaction effects, even with all corrections applied


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


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


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


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


Realization B10-3 (40% sand, Lx = 10 m, Ly = 0.26 m)


Realization B10-Long-1 (40% sand, Lx = 10 m, Ly = 0.26 m)


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)

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