performance of improved ground
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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PPEEEERR
2002 PEER Annual Meeting
Performance of Improved Ground
Elizabeth A. Hausler and Nicholas Sitar
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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
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1964 Niigata Earthquake Case History
Unimproved, up to 50 cm settlement (Watanabe, 1966)
Improved with vibroflotation, 2-3cm settlement (Fudo Corp., 1964)
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1995 Kobe Earthquake Case History
Portopialand, Port Island, improved with vibro-rod (Fudo Corp., 1995)
Unimproved area
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2001 Nisqually Earthquake Case History
Home Depot, improved with VR stone columns
Unimproved
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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
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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
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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
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How Deep? How Wide?
H
H
Zc
? ?? ?
?? ? ?
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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
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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
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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
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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
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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
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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)
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Normalized Settlement vs. Improved Depth
PWRI 0.16gUCD 0.16g
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Normalized Settlement vs. Improved Depth
PWRI 0.16gUCD 0.16g
Liu + Dobry 0.2g
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Normalized Settlement vs. Improved Depth
PWRI 0.16gUCD 0.16g
Liu + Dobry 0.2g PWRI 0.37g
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PWRI02 Large Event Movie
85%
Dr =
.7H
.3H
4m
8m
12m
16m
20m
70%H
30%H
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Normalized Settlement vs. Improved Depth
PWRI 0.16gUCD 0.16g
Liu + Dobry 0.2g PWRI 0.37g
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Normalized Settlement vs. Improved Depth
PWRI 0.16gUCD 0.16g
Liu + Dobry 0.2g PWRI 0.37gUCD 0.75g
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Below the 70% Improved Depth Block16 to 20m BGS, Initial Dr = 30%
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Normalized Settlement vs. Improved Depth
PWRI 0.16gUCD 0.16g
Liu + Dobry 0.2g PWRI 0.37gUCD 0.75g
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Tokachi Port Movie
85%
Dr =
.7H
.3H
4m
8m
12m
16m
20m
70%H
30%H
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Normalized Settlement vs. Improved Depth
PWRI 0.16gUCD 0.16g
Liu + Dobry 0.2g PWRI 0.37gUCD 0.75g
Tokachi Port Blast
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Normalized Settlement vs. Improved Depth
PWRI 0.16gUCD 0.16g
Liu + Dobry 0.2g PWRI 0.37gUCD 0.75g
Tokachi Port Blast
UCD 0.75g, 0.63g, Dr=50%
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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)
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Vertical Strain by Layer
85%.3H
.3H
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By Layer Comparison with Empirical Relation
Shamoto, Zhang, Tokimatsu based on emin, einitial, maximum shear strain
PWRI dataUCD data
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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
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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
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Modeling Underway…
Corinne Cipière, UC Berkeley
Using FLIP (Port and Airport Research Institute)