Post on 13-Oct-2020
Building Near Faults: Soil-Fault-Structure Interaction
Nicolas K. Oettle, Ph.D., P.E.
Jonathan D. Bray, Ph.D., P.E. University of California, Berkeley
Funding: National Science Foundation
Grant No. 926473
Acknowledgements
Overview
Four Topics: • Effects of Past Earthquakes • 2011 Tohoku Earthquake • Dynamic Modeling • Mitigation Strategies
• Conclusions
:: 1906 San Francisco Earthquake (Lawson, 1908)
• Faults rupture up to several meters at the ground surface • Which disturbs structures and the built environment • This study addresses engineering in fault zones
:: Chi-Chi (Taiwan) Earthquake, 3 to 4.5 m of reverse fault slip (GEER)
Fault-Soil-Structure Interaction
Structural damage from earthquake fault rupture
Deformed Ground Surface
:: (Anastasopoulos et al., 2008) Fault
Fault-Soil-Structure Problem
Bedrock fault ruptures through soil with overlying structure
Soil Ductility (Bray et al., 1994)
• Showed that soil failure strain is large controlling factor in soil response
• Critical in estimating damage to earthen dams
Geotechnical Centrifuge Tests (Bransby et al., 2008)
Light Load: q = 37 kPa
Heavy Load: q = 91 kPa
• Fault-soil-structure interaction in geotechnical centrifuge • Showed importance of structure
Numerical Model of SFSI (Anastasopoulos et al., 2008)
• Numerical SFSI model for evaluating fault rupture in soil • Advanced the state-of-the-art in simulation capabilities
Building in fault zones is still controversial
Project Motivation
• Study the fundamentals of boundary deformation problems • Analyze dynamic effects of near-field fault slip rate • Evaluate mitigation strategies for structures in fault zones
:: Darfield Earthquake (Quigley et al., 2011)
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0.7
30 35 40 45 50 55 60
Ver
tical
Dis
plac
emen
t at S
urfa
ce (m
)
Original Horizontal Position (m)
RupturedSoil
UnrupturedSoil
Deformed GroundSurface
Pulse Time History
Structure
Pulse Time History(Rigid Boundary)
orApplied Stress from1-D Site Response
(Deformable)
Soil
Bedrock
FixedBoundary
Not to Scale
2011 Tohoku Earthquake Effects of Past Earthquakes
Mitigation Strategies Dynamic Modeling
Collaborators: Jonathan Bray Paper: Oettle, N.K. and Bray, J.D. 2013, JGGE, 139:10, 1637–1647.
Collaborators: Jonathan Bray, Keith Kelson, Kazuo Konagai Paper: Oettle, N.K. et al. 2013. 2013 Geo-Congress.
Collaborators: Jonathan Bray Paper: Oettle, N.K. and Bray, J.D. 2013. JGGE, 139:11, 1864–1874.
Collaborators: Jonathan Bray, Douglas Dreger Paper: Oettle, N.K., Bray, J.D., and Dreger, D.S. Submitted: Soil Dynamics and Earthquake Engineering.
Evolution of Surface Expression
• Observation: response localizes with increasing displacement • Idea: Faults with prior seismicity could begin with localized
displacement
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35 40 45 50 55In
crem
enta
l Dis
plac
emen
t (m
)Original Horizontal Position (m)
0-0.3 m 0.6-0.9 m 2.1-2.4 m
Soil
Fault
Numerical Model
Shear Strain
Mesh
A numerical model was developed to study this effect
Elastic-perfectly plastic
Friction interface
Structural Model
7-10 kPa/floor
Model structures included three- and six-story steel moment frames attached to a reinforced-concrete mat foundation
10 m wide bays
Constitutive Model
Yield surface:
Flow rule:
:: (Beaty, 2009)
Hardening law (hyperbolic):
Validation
0.00.20.40.60.81.01.21.41.61.82.0
20 30 40 50 60 70
Ver
tical
Dis
plac
emen
t at S
urfa
ce (m
)
Original Horizontal Position (m)
Dots - Centrifuge TestSolid Lines - Numerical Model
1.87 m vert.base offset
0.98 m vert.base offset
0.7 m vert.base offset
Numerical model was validated with centrifuge data
Boundary Deformation Induced Localization
Zone of High Stress Ratio
Principal Stresses
Fault Movement
Surface Deformation
• Shear band formation propagates upward with increasing displacement
• Initial K0 stress state altered to failure stress state
Shear Band Boundary Deformation
The Effect from Previous Ruptures
• Fault rupture may already be localized – Weakened shear zone – Existing stress state
:: 1906 San Francisco Earthquake (Lawson, 1908)
Effect of Historical Seismicity
• Assumed continuation of prior earthquake • More localized deformation field
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Ver
tical
Dis
plac
emen
t at S
urfa
ce (m
)
Original Horizontal Position (m)
RupturedSoil
UnrupturedSoil
Effect of Prior Ruptures on SSI
Without prior rupture: • Broad deformation • Fault splitting
With prior rupture: • Localized displacement • Foundation separation
Boundary Displacement Required for Localization
Compression
• Based on several numerical models • Depends on soil height, failure strain, fault type
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20
40
60
80
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120
140
0% 5% 10% 15%
Soi
l Thi
ckne
ss /
Req
uire
d V
ertic
alB
ase
Offs
et
PS Compression (Loading) Failure Strain
Solid - Reverse FaultDashed - Normal Fault
Normal and Reverse Fault Stress Fields
Zone of High Stress Ratio
Shear BandPrincipal Stresses
Fault Movement
Graben
Plane StrainCompression
Unloading
Zone of High Stress Ratio
Surface Deformation
Shear Band
Zone of High Stress Ratio
ShearBand
Principal Stresses
Fault Movement
Surface Deformation
Plane StrainExtension Loading
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-50
0
50
100
0 50 100 150 200
t = (σ
1-σ 3
)/2(k
Pa)
s = (σ1+σ3)/2 (kPa)
Reverse FaultStress Path
Normal FaultStress Path
InitialStress
PeakStress Ratio
CriticalState
Stress Ratio
Stress PathDirections
Fundamentally different stress fields for normal and reverse faults Stress Paths: Reverse:
Normal:
Required Boundary Deformation Controlled by field stress path failure strain
0
20
40
60
80
100
120
140
0% 5% 10% 15%
Soi
l Thi
ckne
ss /
Req
uire
d V
ertic
alB
ase
Offs
et
PS Compression (Loading) Failure Strain
Solid - Reverse FaultDashed - Normal Fault
0
20
40
60
80
100
120
140
0% 5% 10% 15% 20%
Soi
l Thi
ckne
ss /
Req
uire
d V
ertic
alB
ase
Offs
et
Stress Path-Dependent Failure Strain
Solid - Reverse FaultDashed - Normal Fault
• Developed the potential importance of prior fault ruptures • Elucidated the correct mechanics of fault rupture
mechanisms in soil
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30 35 40 45 50 55 60
Ver
tical
Dis
plac
emen
t at S
urfa
ce (m
)
Original Horizontal Position (m)
RupturedSoil
UnrupturedSoil
Deformed GroundSurface
Pulse Time History
Structure
Pulse Time History(Rigid Boundary)
orApplied Stress from1-D Site Response
(Deformable)
Soil
Bedrock
FixedBoundary
Not to Scale
2011 Tohoku Earthquake Effects of Past Earthquakes
Mitigation Strategies Dynamic Modeling
Collaborators: Jonathan Bray Paper: Oettle, N.K. and Bray, J.D. 2013, JGGE, 139:10, 1637–1647.
Collaborators: Jonathan Bray, Keith Kelson, Kazuo Konagai Paper: Oettle, N.K. et al. 2013. 2013 Geo-Congress.
Collaborators: Jonathan Bray Paper: Oettle, N.K. and Bray, J.D. 2013. JGGE, 139:11, 1864–1874.
Collaborators: Jonathan Bray, Douglas Dreger Paper: Oettle, N.K., Bray, J.D., and Dreger, D.S. Submitted: Soil Dynamics and Earthquake Engineering.
2011 Tohoku Aftershock
Site
Down
Fault
Ridge
Up
Three years ago, a fault ruptured through this ridge
Site Geology
The tertiary ridge overlies cretaceous bedrock
Field Deformation Measurements
:: (Karabacak et al., 2011)
Terrestrial LiDAR fault deformation on ridge by Prof. Kazuo Konagai of the University of Tokyo
Field Deformation Measurements
LiDAR measured 3D deformation field as determined from the original pool elevation
Conceptual Site Geometry
Pool/Gym
Tertiary RidgeSedimentary Rocks
CretaceousAbukuma Bedrock
Not to Scale
South
1.2 m
A tertiary ridge overlying cretaceous bedrock with the pool and gymnasium on the ridge, above the fault
Numerical Modeling • At least 20 m of deformable media is necessary to deform
the ground surface this broadly • Elasto-plastic analysis indicates 2% or higher axial failure
strain without prior ruptures matches the LiDAR data • Subsequent geophysics confirm this model
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-1.0
-0.8
-0.6
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-0.2
0.0
35 45 55 65
Vert
ical
Dis
plac
emen
t (m
)
Original Horizontal Position (m)
2% (or higher) Failure Strain Needed
5 m
50 m
20 m
Improved Building Performance
:: (GEER, 2011)
• 20 m of deformable media changed surface expression of the boundary deformation problem from localized to broad
• Ridge likely had no previous ruptures at this location • Other areas with soft sediments on this fault ruptured
discretely and likely had prior ruptures
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30 35 40 45 50 55 60
Ver
tical
Dis
plac
emen
t at S
urfa
ce (m
)
Original Horizontal Position (m)
RupturedSoil
UnrupturedSoil
Deformed GroundSurface
Pulse Time History
Structure
Pulse Time History(Rigid Boundary)
orApplied Stress from1-D Site Response
(Deformable)
Soil
Bedrock
FixedBoundary
Not to Scale
2011 Tohoku Earthquake Effects of Past Earthquakes
Mitigation Strategies Dynamic Modeling
Collaborators: Jonathan Bray Paper: Oettle, N.K. and Bray, J.D. 2013, JGGE, 139:10, 1637–1647.
Collaborators: Jonathan Bray, Keith Kelson, Kazuo Konagai Paper: Oettle, N.K. et al. 2013. 2013 Geo-Congress.
Collaborators: Jonathan Bray Paper: Oettle, N.K. and Bray, J.D. 2013. JGGE, 139:11, 1864–1874.
Collaborators: Jonathan Bray, Douglas Dreger Paper: Oettle, N.K., Bray, J.D., and Dreger, D.S. Submitted: Soil Dynamics and Earthquake Engineering.
Dynamic Modeling
• Very near fault ground motions • Based on numerical work by
Dreger et al. (2011) • Slip rate 0.5 to 1.0 m/s
:: Dreger et al. (2011)
Deformed GroundSurface
Pulse Time History
Structure
Pulse Time History(Rigid Boundary)
orApplied Stress from1-D Site Response
(Deformable)
Soil
Bedrock
FixedBoundary
Not to Scale
-300
-200
-100
0
100
200
300
Acce
lera
tion
(cm
/s2 ) This Study
Dregeret al. (2011)
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20
40
60
80
Velo
city
(cm
/s)
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10
20
30
40
17 18 19 20 21
Dis
plac
emen
t (cm
)
Time (s)
Change in Soil Stresses
• Very unusual site response due to fling-type motions • Could cause tension in soil if fast enough slip velocity
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1.60
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100
150
200
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300
350
0.0 0.1 0.2 0.3 0.4 0.5 0.6
Bou
ndar
y V
eloc
ity (m
/s)
Stre
ss (k
Pa)
Time (s) Reverse Fault, 0.8 m/s
σyy
σxx
Vboundary
Increase in Fault Diversion • Free-field solution not changed considerably • A dynamic analysis influences the amount of building
movement
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1.0
0.2 0.4 0.6 0.8 1 1.2
Mov
emen
t of S
truct
ure
as F
ract
ion
ofP
seud
o-S
tatic
Mov
emen
t
Slip Velocity (m/s)
Pseudo-StaticDisplacement
Dynamic Displacement
Free-FieldBoundary Condition
Pseudostatic: 0.8 m/s:
Structural Mass
Increasing the size of the structure decreases building movement
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1.0
0 20 40 60 80 100 120
Mov
emen
t of S
truct
ure
as F
ract
ion
ofP
seud
o-S
tatic
Mov
emen
t
Mat Pressure (kPa)
Pseudo-Static Displacement
Dynamic Displacement
• Fault rupture dynamics can have a moderate affect on the predicted soil-structure interaction
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30 35 40 45 50 55 60
Ver
tical
Dis
plac
emen
t at S
urfa
ce (m
)
Original Horizontal Position (m)
RupturedSoil
UnrupturedSoil
Deformed GroundSurface
Pulse Time History
Structure
Pulse Time History(Rigid Boundary)
orApplied Stress from1-D Site Response
(Deformable)
Soil
Bedrock
FixedBoundary
Not to Scale
2011 Tohoku Earthquake Effects of Past Earthquakes
Mitigation Strategies Dynamic Modeling
Collaborators: Jonathan Bray Paper: Oettle, N.K. and Bray, J.D. 2013, JGGE, 139:10, 1637–1647.
Collaborators: Jonathan Bray, Keith Kelson, Kazuo Konagai Paper: Oettle, N.K. et al. 2013. 2013 Geo-Congress.
Collaborators: Jonathan Bray Paper: Oettle, N.K. and Bray, J.D. 2013. JGGE, 139:11, 1864–1874.
Collaborators: Jonathan Bray, Douglas Dreger Paper: Oettle, N.K., Bray, J.D., and Dreger, D.S. Submitted: Soil Dynamics and Earthquake Engineering.
Design Strategies for Mitigation
1. Spread fault deformation 2. Design structure to move 3. Divert the fault
Design Strategies: Engineered Fill
Limited ShearBand Propagation
Fault Movement
Distributed Ground Deformation
Spreading ofFault MovementDuctile
EngineeredFill
500
1,000
1,500
2,000
2,500
0 0.3 0.6 0.9
Mom
ent i
n 2n
d Fl
oor (
kN·m
)
Vertical Fault Displacement (m)
Stiff Previously Ruptured Native Soil
More DuctileEngineered Fill
Less DuctileEngineered Fill
Yielding
• Engineered fill spreads fault deformation • Note: first plastic behavior in structure typically bending in
beams at beam-column joints
Design Strategies: Mat Foundations
Thick mats support structure and limit distress to superstructure
Thinner Mat Columns
Floor Beams
Thicker Mat
Design Strategies: Mat Foundations
500
1,000
1,500
2,000
2,500
0 1 2 3
Mom
ent i
n 2n
d Fl
oor (
kN·m
)
Mat Thickness (m)
0 m 0.05 m 0.1 m0.2 m 0.3 m 0.6 m
Reverse Fault
Vertical Fault Displacement:
Yield Moment
• Increasing mat thickness decreases structural loads • Can decrease structural distress to elastic levels or
to life-safety levels
Design Strategies: Mat Foundations
Thick mats are resilient to complex fault deformation
Thick MatFoundation
Fault 2Fault 1
Design Strategies: Fault Diversion
:: 1999 Kocaeli Earthquake (Lettis et al., 2000)
Heavy structures diverted fault rupture in Kocaeli
Design Strategies: Fault Diversion
Ground improvement diverts well located faults
Reverse Fault
Soil
Ground�Improvement
Six-storyStructure
Normal FaultSoil
Diaphragm Wall
Three-storyStructure
Tiebacks
Design Strategies: Fault Diversion
Structural walls can divert well located faults
Design Strategies: Fault Diversion
Reverse Fault
Soil
Anchors
Three-storyStructure
Ground anchors can hold a building to one side of a fault
Design Strategies: Fault Diversion
Fault
Seismic Gap
Structure
Excavation
Gaps or soft ground can accommodate fault displacement
Mitigation strategies can work and come in a variety of styles
Conclusions
• Historic seismicity affects soil-fault-structure interaction • Can explain localized fault deformation observed • Japan showed how soil can spread fault rupture • Slip rate also affects the boundary deformation solution • Safe structural design in fault zones is achievable
• Spread fault deformation • Design structure to move • Divert the fault