field testing to determine realistic geotechnical parameters · 2015. 12. 29. · realistic...
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Field Testing to Determine Realistic Geotechnical Parameters
J. Ryan ShaferNichols Consulting Engineers
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Agenda
Why direct measurement methods might be appropriate?Background on plate load test (PLT)Some limitations to the PLTA case history on the UC Berkeley Campus for use of the Footing Load Test (FLT)Concluding remarks
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Applicability
Projects increasingly using more demanding modeling that require greater accuracy.Highly variable subsurface conditions can make it difficult to estimate foundation stiffness and bearing capacities.
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Plate Load Test
Plate Size Typically 1’X1’
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Good Applications of PLT
Fairly uniform subsurface conditions within the influences of planned foundations (2B to 3B)Plate is seated at expected foundation levelsProgram should include variable plate sizes and depths for extrapolation to larger footing sizes and different depthsEconomical approach for direct measurement method
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Limitations of PLT
Limited stress influence due to small plate sizesSites with variable or stratified subsurface conditions (i.e. compressible layer just below stress influence of PLT)Does not fully capture real footing behavior
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Example of Stress Influence
0
5
10
15
20
0 1000 2000 3000 4000 5000 6000
Stress (psf)D
epth
(ft)
5X5 FTG
1X1 FTG
2B
2B
STIFF CLAY
ROCK
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Case History
UC Berkeley Stanley Hall Biosciences Facility
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Seismic Setting
Hayward Fault
Liquefaction
Landslides
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Stanley Hall
UC Berkeley Campus
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Stanley Hall Looking East
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Site Conditions
Fill and colluvium over Franciscan Bedrock (shale and graywacke sandstone)Shale bedrock predominantly in the east, very fractured and weathered, and generally soft rockGraywacke sandstone in the west becoming hard and more competent with depthOld Strawberry Creek stream channelShallow groundwaterAbout 500 feet to Hayward Fault
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Geologic Mapping of Bottom of Basements
?
?
?
? ? ?
S O U T H W A L L
DONNER LAB
GRAYWACKESANDSTONE
BRECCIATED
MUDSTONE
AND SHALE
INTERBEDDEDSANDSTONE AND SHALE
CARBONACEOUS
SHEARED AND
SERPENTINITE
SHALE WITH
Colluvium
Legend:
Mudstone/Shale
GraywackeSandstone
Fill
South Wall
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Geologic Mapping
T
P
390.00
380.00
370.00
360.00
350.00
340.00
330.00
320.00
310.00
300.00
T
T
T
T
T
T
P
T
T
T
T
T T
T
T
T
T
T
T
ELEVATIONIN FEET
SOUTH WALL ELEVATION
ColluviumLegend: Mudstone/Shale GraywackeSandstone
Fill
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Geotechnical Uncertainties -Franciscan Rock
Difficult to estimate engineering properties of highly heterogeneous rock based on traditional boring data and laboratory tests
Subgrade modulus (foundation stiffness)Bearing capacity
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Foundation Stiffness Relationships
)5.1
5.0(1
mm
Bkk v
s+
= 21 )
21(
BBkk vs+
=Cohesive Soil Cohesionless Soil
Relationships Used (NFEC Design Manual 7.02)
FEMA 356 Relationship
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Bearing Capacities
Conservatively based on historical, presumptive, and/or empirical valuesDifficult to assign material properties to Franciscan sandstone and shale that can be incorporated into traditional bearing capacity relationships
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Implications?
What is a conservative subgrade modulus?Actual modulus is stiffer may result in damage to shear wall elementsActual modulus is softer may result in damage to building frame
Conservative bearing capacities that will likely perform well but may be costing the project with larger footings with increasing seismic demands
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Why the Footing Load Test (FLT) was conceived?
Large seismic demandsDifficult to determine the stiffness and bearing capacity for heterogeneous Franciscan sandstone and shale Many buildings on campus are founded in Franciscan rockImprove design for future campus buildings with direct measure of stiffness and bearing capacity of full size footings founded in Franciscan rock
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
The Plan
Construct full size square footings (2.5, 4, and 6 feet) founded in sandstone and shale in basement levels of the active excavation of Stanley Hall
Perform load tests to cyclically impact footings using a Pile Load Tester (PLT) with loads up to 800 kips
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
FLT Location Plan
Western Footings
(Sandstone)
Eastern Footings (Shale)
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FLTs Amidst Construction
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25Test Apparatus
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
25,000kg mass on heavy coiled
springs
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
6’X6’4’X4’
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Load Versus Displacement (2.5' x 2.5')
-5.5
-4.5
-3.5
-2.5
-1.5
-0.5
0 100 200 300 400 500 600 700 800Load (Kips)
Dis
plac
emen
t (in
ch)
Maximum Displacement
Residual Displacement
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
30
EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Load Versus Displacement (4' x 4')
-1.5
-1
-0.5
00 100 200 300 400 500 600 700 800
Load (Kips)D
ispl
acem
ent (
inch
)
Maximum Displacement
Residual Displacement
31
EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Load Versus Displacement (6' x 6')
-0.5
-0.4
-0.3
-0.2
-0.1
00 100 200 300 400 500 600 700 800
Load (Kips)D
ispl
acem
ent (
inch
)
Maximum Displacement
Residual Displacement
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Summary of Load Tests
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
00 20 40 60 80 100
Bearing Pressure (ksf)
Max
imum
Dis
plac
emnt
(inc
hes)
FLT TEST 2.5x2.5 Footing
FLT TEST 4x4 Footing
FLT TEST 6x6 Footing
Original Recommendation: Kb =(900 / B) kcf for 2.5x2.5 Footing
Original Recommendation: Kb =(900 / B) kcf for 4x4 Footing
Original Recommendation: Kb =(900 / B) kcf for 6x6 Footing
New Recommendation: Kv1=3000kcf, Disp.<0.5in; Kv1=750 kcf,0.5<Disp.<1.5; for 2.5x2.5 Footing
New Recommendation: Kv1=3000kcf, Disp.<0.5in; Kv1=750 kcf,0.5<Disp.<1.5; for 4x4 Footing
New Recommendation: Kv1=3000kcf, Disp.<0.5in; Kv1=750 kcf,0.5<Disp.<1.5; for 6x6 Footing
33
EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
What Was Gained?
Original Recommendation: Kv1=900 kcfAfter FLT: Kv1=3000 kcf (<1/2 inch), 750 kcf(1/2 to 1.5 inch), plastic after 1.5 inchOriginal Recommendation: Ultimate Bearing Capacity (UBC) = 26,000 psfAfter FLT: UBC = 30,000 to 70,000 psfCost Savings to Next Campus Building
34
EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
Concluding Remarks
As seismic modeling and demands increase there is a shift towards ultimate load vs. displacement.Provide more realistic geotechnical recommendations because often it is not clear what is conservative.Direct measurements methods such as the PLT or FLT can help achieve these goals.
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EERI TechnicalSeminar Series
Impact of Soil-Structure Interaction on Response of StructuresSeminar 1: Practical Applications to Shallow Foundations
THE END
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