performance of improved ground

PPEEEERR

2002 PEER Annual Meeting

Performance of Improved Ground

Elizabeth A. Hausler and Nicholas Sitar

Acknowledgements

U.S.- Japan Cooperative Research Program for Urban Earthquake Disaster Mitigation, NSF, Award No. CMS-0070278

Earthquake Engineering Research Centers Program, NSF, Award No. EEC-9701568

Public Works Research Institute, Japan Port and Airport Research Institute, Japan University of California, Davis Center for Geotechnical

Modeling Hayward Baker

1964 Niigata Earthquake Case History

Unimproved, up to 50 cm settlement (Watanabe, 1966)

Improved with vibroflotation, 2-3cm settlement (Fudo Corp., 1964)

1995 Kobe Earthquake Case History

Portopialand, Port Island, improved with vibro-rod (Fudo Corp., 1995)

Unimproved area

2001 Nisqually Earthquake Case History

Home Depot, improved with VR stone columns

Unimproved

Field Case Histories by EarthquakeEarthquake Year No. Sites Magnitude

Nisqually, Washington 2001 >8 6.8 MW921 Chi-Chi, Taiwan 1999 >1 7.6 MWKocaeli, Turkey 1999 6 7.4 MWKagoshimaken Hoku, Japan 1997 1 6.3 JMAHyogoken Nanbu, Japan 1995 50 6.9 MWSanriku Haruka Oki, Japan 1994 1 7.5 JMAHokkaido Toho Oki, Japan 1994 4 8.1 JMANorthridge, California 1994 5 6.7 MWHokkaido Nansei Oki, Japan 1993 4 7.8 JMAKushiro Oki, Japan 1993 3 7.8 JMALoma Prieta, California 1989 12 6.9 MWNihonkai Chubu, Japan 1983 2 7.7 JMAMiyagiken Oki, Japan 1978 1 7.4 JMATokachi Oki, Japan 1968 2 6.8 GRNiigata, Japan 1964 4 7.3 GR

Hausler, E.A. and Sitar, N., (2001). “Performance of Soil Improvement Techniques in Earthquakes”, Fourth International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, Paper 10.15, March 26 - 31. www.ce.berkeley.edu/~hausler/casehistories.html

Field Case Histories by Method

Method

Performance (Acceptable/

Unacceptable)

Average Increase in N1,60

Densification through vibration and compactionSand compaction piles 26 / 5 11Deep dynamic compaction 15 / 0 5Vibrorod/Vibroflotation 11 / 6 13Stone columns 7 / 1 8Preloading 5 / 0 5Compaction grouting 1 / 1 n/aTimber displacement piles 1 / 0 n/aDissipation of excess pore water pressureGravel drains 5 / 0 7Sand drains 5 / 0 9Wick or paper drains 2 / 0 n/aRestraining effect through inclusionsDeep soil mixing 4 / 1 n/aDiaphragm walls 0 / 1 n/aStiffening through chemical or cement additionJet grouting 5 / 0 n/aChemical grouting 1 / 0 n/a

Results of Case History Analysis

Field case histories indicate that sites with ground improvement experience less ground deformation than adjacent, unimproved areas

10 % of the case histories received inadequate performance designation, most commonly because there was a significant lateral spreading hazard present or the improvement was not deep enough

Most field case histories, however, lack sufficient quantitative information on building settlement, vertical ground strain, and degree, depth, and lateral extent of ground improvement

How Deep? How Wide?

H

H

Zc

? ?? ?

?? ? ?

Approach

Compile field case histories of sites with liquefaction mitigation that have been shaken by an earthquake

Review available design guidelines for remediation zone geometry

Review previous physical model studies with ground improvement

Perform centrifuge-based shaking table tests to study the influence of remediation zone geometry on performance of a structure on embedded shallow foundation

Develop the design guideline using case histories and physical model studies

Experience and Guidelines -- Depth

In U.S., common to determine depth using SPT, CPT, or Vs measurements in deterministic simplified liquefaction triggering analysis (Seed and Idriss, 1971, Youd and Idriss, 1997, Cetin, 2000); sometimes, assessment of potential settlement using Ishihara and Yoshimine (1992) or Tokimatsu and Seed (1987), or more detailed site response analysis is done

In Japan, similar procedures, emphasis on lab testing, Road and Bridge Code specifies maximum 20m depth for liquefaction hazard evaluation

Field case histories: 45% of cases with sufficient data were improved through the full potentially liquefiable thickness

Experience and Guidelines – Lateral Extent

Lateral extent should be equal to improved depth (Mitchell, case histories)

Lateral extent should include the zone that influences the stability of the structure (Iai, laboratory tests and numerical modeling) or is affected by seepage

Lateral extent equal to 2/3 liquefiable thickness, but at least 5m and no greater than 10m (Japanese Fire Code)

Field case histories: 20% (5 of 25) of cases with sufficient data were improved laterally to a distance equal to the improved depth

Tests at PWRI – Field Scale Prototype

85%

Dr =

.3H20m

132m

18m

20m=100%H

16m

14m=70%H6m=30%H

Dr = 35% Keisa

8m x 18m, 96 kPa

4 6 8 10 12 14 16 18 20 22 24 26 28 30 320.2

0.1

0

0.1

0.2

time (s)

A1 (g)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 280.2

0.1

0

0.1

0.2

time (s)

A26 (g)

6.6m radius centrifugespinning @ 60g

rigid model container Kobe Port Island 83m depth record, NSscaled to 0.16g, 0.37g PGA

Tests at UC Davis – Field Scale Prototype

85%

Dr =

.3H20m

132m

32m

20m=100%H

16m

14m=70%H6m=30%H

Dr = 30% Nevada Sand

8m x 8m, 96 kPa

4 6 8 10 12 14 16 18 20 22 24 26 28 30 320.2

0.1

0

0.1

0.2

time (s)

A1 (g)

0 2 4 6 8 10 12 14 16 18 20 22 24 26 280.2

0.1

0

0.1

0.2

time (s)

A26 (g)

9.1m radius centrifugespinning @ 40g

flexible shear beammodel container

Kobe Port Island 83m depth record, NSscaled to 0.16g, 0.75g PGA

16m

Parameters varied

Depth of improvement (100%H, 70%H, 30%H, 0%H) Lateral extent of improvement relative to depth of

improvement Static stress condition (2D vs. 3D) Soil (Nevada, Keisa) Relative density of liquefiable soil (Dr,initial = 30%, 35%,

50%) PGA, frequency, and energy content of the input motion

(scaled Kobe Port Island 83m depth wave, changed centrifuge shakers)

Normalized Settlement vs. Improved Depth

PWRI 0.16gUCD 0.16g


PWRI 0.16gUCD 0.16g

Liu + Dobry 0.2g


PWRI 0.16gUCD 0.16g

Liu + Dobry 0.2g PWRI 0.37g

PWRI02 Large Event Movie

85%

Dr =

.7H

.3H

4m

8m

12m

16m

20m

70%H

30%H


PWRI 0.16gUCD 0.16g

Liu + Dobry 0.2g PWRI 0.37g


PWRI 0.16gUCD 0.16g

Liu + Dobry 0.2g PWRI 0.37gUCD 0.75g

Below the 70% Improved Depth Block16 to 20m BGS, Initial Dr = 30%


PWRI 0.16gUCD 0.16g


Tokachi Port Movie

85%

Dr =

.7H

.3H

4m

8m

12m

16m

20m

70%H

30%H


PWRI 0.16gUCD 0.16g


Tokachi Port Blast


PWRI 0.16gUCD 0.16g


Tokachi Port Blast

UCD 0.75g, 0.63g, Dr=50%

Most Influential Factors

Initial relative density of liquefiable soil Energy/intensity of the input motion Confining stress (structure) Confining stress (depth of soil) Confining stress (layering of improved and

unimproved ground)

Vertical Strain by Layer

85%.3H

.3H

By Layer Comparison with Empirical Relation

Shamoto, Zhang, Tokimatsu based on emin, einitial, maximum shear strain

PWRI dataUCD data

Lessons Learned – Low Levels of Shaking

Vertical ground strain decreases with increasing improved zone depth

Settlement is not totally eliminated with improvement through full liquefiable thickness

Lessons Learned – High Levels of Shaking

Vertical ground strain DOES NOT NECESSARILY decrease with increasing improved zone depth

Settlement is still significant with improvement through full liquefiable thickness; differential settlement possible

Acceleration measured on the structure is highest for the case with the improvement through the full liquefiable thickness

Modeling Underway…

Corinne Cipière, UC Berkeley

Using FLIP (Port and Airport Research Institute)

performance of improved ground

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