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Seismic Earth Pressures on Below Grade Seismic Earth Pressures
on Below Grade Retaining WallsRetaining Walls
Tom Boardman, PE, GE SVRT/VTA Line Segment ProjectTom Boardman,
PE, GE SVRT/VTA Line Segment ProjectPEER/UC Berkeley Seismic Earth
Pressures Workshop June 8, 2006PEER/UC Berkeley Seismic Earth
Pressures Workshop June 8, 2006
Oakland
Hayward Fault
San Andreas Fault
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Cross Section Through Future UCross Section Through Future
U--Wall StructureWall Structure
20 ft
37 ft
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San JoseSan JoseAirportAirport
Hayward Fault MHayward Fault Mww 7.25, PGA ~0.6g7.25, PGA
~0.6g
General Location of Future UGeneral Location of Future
U--WallsWalls
SVRT/VTA Project Location (Looking East)SVRT/VTA Project
Location (Looking East)
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References: Wood (1973) and References: Wood (1973) and Clough
& Clough & Fragaszy Fragaszy (1977)(1977)
UU--Wall Damage During 1971 San Fernando Wall Damage During 1971
San Fernando EqEq
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BFS Design Criteria for UBFS Design Criteria for U--WallsWalls
UU--Walls are classified as either Walls are classified as either
yieldingyielding or or rigidrigid wallswalls
Top of Top of yieldingyielding UU--Wall moves a distance of
0.004H or greater Wall moves a distance of 0.004H or greater during
loading (during loading ( = 1 inch for H = 20 feet)= 1 inch for H =
20 feet)-- Yielding walls designed using active earth pressures for
staticYielding walls designed using active earth pressures for
staticloads and loads and MononobeMononobe--Okabe (MOkabe (M--O)
procedure for seismic loadsO) procedure for seismic loads
Top of Top of rigidrigid UU--Wall moves less than 0.004HWall
moves less than 0.004H-- Rigid walls designed using atRigid walls
designed using at--rest (rest (KoKo) earth pressures for ) earth
pressures for static loads and 1.5 x Mstatic loads and 1.5 x M--0
forces for seismic loads0 forces for seismic loads-- Rigid walls
are designed to behave in ductile mannerRigid walls are designed to
behave in ductile manner
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Project Earth PressuresProject Earth Pressures
MononobeMononobe--Okabe Okabe PPAEAE = 0.5= 0.5HH22KKAEAE Clayey
sands to sandy clays but assume Clayey sands to sandy clays but
assume cohesionlesscohesionless soil soil
with with ~32 degrees~32 degrees Flat backfill; include wall
friction; and PGA ~ 0.6gFlat backfill; include wall friction; and
PGA ~ 0.6g
Shallow water table; increased seismic pressures due to
inertiaShallow water table; increased seismic pressures due to
inertial l effects of saturated backfill per effects of saturated
backfill per EbelingEbeling & Morrison (1992)& Morrison
(1992)
Design MDesign M--O seismic pressure of 40H (O seismic pressure
of 40H (psfpsf) with maximum at top ) with maximum at top of wall
(i.e of wall (i.e inverted triangleinverted triangle))
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SoilSoil--Structure Interaction (FLAC)Structure Interaction
(FLAC)Mesh and StructureMesh and Structure
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SoilSoil--Structure Interaction (FLAC)Structure Interaction
(FLAC)
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SoilSoil--Structure Interaction (FLAC)Structure Interaction
(FLAC)
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SoilSoil--Structure Interaction (FLAC)Structure Interaction
(FLAC)
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SoilSoil--Structure Interaction (FLAC)Structure Interaction
(FLAC)Top of Wall DisplacementsTop of Wall Displacements
Top Left Wall
Top Right Wall
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Free Field Displacements from SHAKE AnalysisFree Field
Displacements from SHAKE Analysis
Free field shear Free field shear strain ~ 0.2%strain ~ 0.2%
El Centro SHAKE Run @ t = 11.1 sec
0
2
4
6
8
10
12
14
16
18
20
0 0.1 0.2 0.3 0.4
Relative Horizontal Displacement (in)
D
e
p
t
h
(
f
t
)
EC @ 11.1 sec
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Comparison of Total Horizontal Earth PressuresComparison of
Total Horizontal Earth Pressures
0
5
10
15
20
0 500 1000 1500 2000 2500
Total Horizontal Earth Pressure (psf)
D
e
p
t
h
(
f
e
e
t
)
1979 El CentroMotion (Max Values)
Flexible Wall DesignValues
Rigid Wall DesignValues
El Centro Motion at t =11.1 sec
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What Other Approaches Could We Have Used?What Other Approaches
Could We Have Used?
Seismic slope stability analysisSeismic slope stability
analysis
GazetasGazetas et al. (2004) elastic based solutionset al.
(2004) elastic based solutions
Davis (2003) approach for rigid underground lifeline
structuresDavis (2003) approach for rigid underground lifeline
structures
OstadanOstadan and White (1998) approach for rigid basement
wallsand White (1998) approach for rigid basement walls
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Seismic Slope StabilitySeismic Slope Stability
Solve for wall pressure (p) that results in FS > 1Solve for
wall pressure (p) that results in FS > 1
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GazetasGazetas et al. (2004)et al. (2004)
Elastic based solutions and chartsElastic based solutions and
charts
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Davis (2003) ApproachDavis (2003) Approach
Simplified approach for dSimplified approach for deep (elastic)
soil conditions, to allow for eep (elastic) soil conditions, to
allow for seismic shear waves to radiate away from structure
resulting in seismic shear waves to radiate away from structure
resulting in lower lower estimates for earth pressures on rigid
basement walls.estimates for earth pressures on rigid basement
walls.
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OstadanOstadan & White (1998) Approach& White (1998)
Approach
Soil Soil
Rigid Subgrade
Rigid basement walls and mat bearing on rigid Rigid basement
walls and mat bearing on rigid subgradesubgrade. SHAKE and . SHAKE
and SASSI were used by SASSI were used by OstadanOstadan &
White (1998) to develop normalized seismic & White (1998) to
develop normalized seismic pressure profile. Allows designer to
evaluate the effect of nonpressure profile. Allows designer to
evaluate the effect of nonlinear soil linear soil properties and
different ground motions on seismic earth pressurproperties and
different ground motions on seismic earth pressures.es.
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Comparison of Total Horizontal Earth PressuresComparison of
Total Horizontal Earth Pressures
0
5
10
15
20
0 500 1000 1500 2000 2500
Total Horizontal Earth Pressure (psf)
D
e
p
t
h
(
f
e
e
t
)
Flexible Wall Design Values
Rigid Wall Design Values
Ostadan&White (1998) ElCentro Motion
Davis (2003) G = f(z)
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Conclusions & OpinionsConclusions & Opinions Design
pressures of 40H (Design pressures of 40H (psfpsf) are conservative
for ) are conservative for flexibleflexible UU--Walls in the Walls
in the
SVRT/VTA Line Segment. Value of 40H is likely on the high side
SVRT/VTA Line Segment. Value of 40H is likely on the high side due
to due to including inertial effects of saturated soils and by not
using including inertial effects of saturated soils and by not
using undrainedundrainedshear strengths of sandy clays during
seismic loading.shear strengths of sandy clays during seismic
loading.
SSI FLAC modeling was useful to study seismic displacement
behavSSI FLAC modeling was useful to study seismic displacement
behavior of ior of UU--Wall, though additional analyses necessary
to evaluate earth preWall, though additional analyses necessary to
evaluate earth pressures.ssures.
Either the Davis (2003) or Either the Davis (2003) or
OstadanOstadan and White (1998) approaches for rigid and White
(1998) approaches for rigid basement walls have promise and should
be considered for final dbasement walls have promise and should be
considered for final design.esign.
The PEER/UC Berkeley research should provide commentary on how
wThe PEER/UC Berkeley research should provide commentary on how
wall all flexibility affects seismic pressures. Is the current BFS
of 1.flexibility affects seismic pressures. Is the current BFS of
1.5xMO for 5xMO for rigidrigid walls with wall deflections <
0.4% reasonable?walls with wall deflections < 0.4%
reasonable?
Seismic Earth Pressures on Below Grade Retaining WallsCross
Section Through Future U-Wall StructureSVRT/VTA Project Location
(Looking East)U-Wall Damage During 1971 San Fernando EqBFS Design
Criteria for U-WallsProject Earth PressuresSoil-Structure
Interaction (FLAC)Mesh and StructureSoil-Structure Interaction
(FLAC)Soil-Structure Interaction (FLAC)Soil-Structure Interaction
(FLAC)Soil-Structure Interaction (FLAC)Top of Wall
DisplacementsFree Field Displacements from SHAKE AnalysisComparison
of Total Horizontal Earth PressuresWhat Other Approaches Could We
Have Used?Seismic Slope StabilityGazetas et al. (2004)Davis (2003)
ApproachOstadan & White (1998) ApproachComparison of Total
Horizontal Earth PressuresConclusions & Opinions
