Static TestingStatic Testing••ExpensiveExpensive
••Time consumingTime consuming
Dynamic Pile Testingwith the
Pile Driving Analyzer ®
Dynamic Pile Testingwith the
Pile Driving Analyzer ®
© 2002, Pile Dynamics, © 2002, Pile Dynamics, IncInc..Quality Assurance for Deep FoundationsQuality Assurance for Deep Foundations
DYNAMIC TESTING
• Research began at Case Institute of Technology (Cleveland) in 1964 under G. Goble
• Developed “Case Method” – “PDA”– Pile capacity from pile top measurements
• WEAP (Wave Equation Analysis Program)
• CAPWAP (CAse Pile Wave Analysis Program
DYNAMIC METHODS
• Do not hinder pile driving• Are much less expensive than static tests• Can test many piles (a representative
sample)
Case Method – PDA• CONSTRUCTION CONTROL
– Test sample of production piles to insure capacity over entire project.
• DESIGN– Can be cost effective to test for pile capacity as a
function of penetration• Lower penetration to reach design capacity.
• REPLACE OR SUPPLEMENT STATIC TESTS– For large capacity piles– Offshore environments
Case Method – PDA
• RESULTS– Hammer performance
• Compute transferred energy, efficiency• Monitor effects of changes in hammer cushion, helmet and pile
cushion
– Pile stresses• Compressive (hard driving)• Tensile (easy driving)
– Pile integrity– Pile capacity
GRLWEAP• INPUT
– Hammer properties– Hammer and pile cushion properties– Helmet weight– Pile Properties– Soil Properties
• Quakes, damping, resistance distribution
• OUTPUT– Resistance vs. blow count– Stresses vs. pile length/blow count– Transferred hammer energy
CAPWAP
• PROCEDURE:1. Input soil model (quakes, damping, etc.)2. Use measured velocity as input3. Compute pile top force4. Compare computed force to measured force5. Modify soil model as necessary until field and
measured force are in agreement
CAPWAP
• OUTPUT:1. Ultimate capacity and distribution2. Stresses vs. pile length3. Quakes4. Damping factors Used to refine
GRLWEAP
Dynamic Testing BenefitsDynamic Testing BenefitsDynamic Testing Benefits
•• More information in less time (reduces delays):More information in less time (reduces delays):•• Confirms pile capacity design Confirms pile capacity design
•• EvaluatesEvaluates integrity, stresses, hammer energyintegrity, stresses, hammer energy
•• Improves quality control Improves quality control
••(test more piles; tests “problem piles”)(test more piles; tests “problem piles”)
•• Rational means to reduce pile costsRational means to reduce pile costs•• shorter piles or fewer piles (lower S.F.)shorter piles or fewer piles (lower S.F.)
•• Significantly less cost than static testSignificantly less cost than static test
CaseCase MethodMethod1958: first thesis 1958: first thesis
1964: field testing began under 1964: field testing began under direction ofdirection of DrDr. G.G. . G.G. GobleGoble
W
measure measure
Compute from measurementsCompute from measurements
•• hammer performance hammer performance
•• driving stressesdriving stresses
•• pile integrity pile integrity
•• capacitycapacity
“Monitoring”
“Dynamic Load testing”
Motion is measured Motion is measured by accelerometersby accelerometers
strainstraingagegage FF(t)(t)
accelerometeraccelerometer
vv(t)(t)
Dynamic Pile TestingDynamic Pile TestingDynamic Pile Testing
Load is appliedLoad is appliedby impacting ramby impacting ram
Load is measured byLoad is measured bystrain transducersstrain transducers
Strain Strain transducertransducer
AccelerometerAccelerometer
STRAIN
ACCELERATION
PDA testingdata acquisition
PDA testingdata acquisition
“PDA”“PDA”“PDA”
Pile Driving Analyzer ®
Hammer PerformanceHammer Performance
Why is it important?Why is it important?•• Contractor productivityContractor productivity
•• Sufficient for pile installationSufficient for pile installation to to designdesign depth and/or to required depth and/or to required capacitycapacity
Energy = ∫ Fv (dt)
Efficiency = Efficiency = Em / ErEm / ErEm = Measured Transf. EnergyEm = Measured Transf. EnergyEr = Rated EnergyEr = Rated Energy
0%0% 20%20% 40%40% 60%60% 80%80% 100%100%
20%20% 80%80%cabled drop hammerscabled drop hammers
60%60%30%30% diesel hammersdiesel hammers
40%40% 70%70%air or steam hammersair or steam hammers
60%60% 100%100%hydraulic drop hammershydraulic drop hammers
Efficiencies on concrete piles are lower ~ 10%Efficiencies on concrete piles are lower ~ 10%
Hammer performance and Hammer performance and cushion evaluation cushion evaluation
Driving StressesDrivingDriving StressesStressesKnowing stresses leads to steps to reduce risk of pile damage due to:
• Compression stress
• at both Top and Bottom
• Tension stress (concrete piles)
• Bending, Alignment
Knowing stresses leads to steps to Knowing stresses leads to steps to reduce risk ofreduce risk of pile damage due to:pile damage due to:
•• Compression stressCompression stress
•• at both Top and Bottomat both Top and Bottom
•• Tension stressTension stress (concrete piles)(concrete piles)
•• Bending, AlignmentBending, Alignment
PDA testingdata acquisition
PDA testingdata acquisition
Average force is proportional Average force is proportional and reasonable; 2 sensors can and reasonable; 2 sensors can
compensate large bendingcompensate large bending
Codes:Codes: Allowable Driving StressesAllowable Driving Stresses
USA - AASHTOSteel piles
90% of yield strength for steel
Concrete pilesCompression: (85% of c.strength) - prestressTension (PS): prestress + (50% of t.strength)
Compression: 85% of c.strengthTension (RR): 70% of yield of reinforcement
Pile integrityProblem:
Broken piles have low capacity
Detect damage by:
• blow count record , or very long piles
• visually (above ground, closed pipes)
• extraction
• Electronically ( PDA or PIT )
• or static load test
PilePile integrityintegrityProblem: Problem:
Broken piles have low capacityBroken piles have low capacity
Detect damage by:Detect damage by:
•• blow count record , or very long pilesblow count record , or very long piles
•• visually (above ground, closed pipes)visually (above ground, closed pipes)
•• extractionextraction
•• Electronically ( PDA or PIT )Electronically ( PDA or PIT )
•• or static load testor static load test
IntegrityIntegrityIntegrity•• Magnitude of damageMagnitude of damage•• LocationLocation
Normal time return (pile length OK)
Small damage
blow1
2
3
4
Integrity by PDA dynamic testing
Early return indicates shorter pile length
Large damage
Small damage
Large damage
blow
1
2
3
4
toetop
New toepile shorter
Start of damageStart of damage
Major damageMajor damagePile failed at pickup point. Pile failed at pickup point. Due to early handling, or Due to early handling, or low concrete strength, or low concrete strength, or
uneven toe stress (uneven toe stress (limerocklimerock))
Extraction reveals Extraction reveals damagedamage
12001200 psi prestresspsi prestress5000 5000 psi f’c psi f’c driven at 7 daysdriven at 7 days
β Condition100100 UniformUniform
80 80 -- 100100 Slight damageSlight damage60 60 -- 8080 Significant damageSignificant damage
<60<60 BrokenBroken
BETA guidelinesBETA guidelines
Capacity of broken piles Capacity of broken piles is meaninglessis meaningless
CapacityCapacity• At time of testing• vs depth during drive• resistance distribution
– CAPWAP ®
•• At time of testingAt time of testing•• vsvs depth during drivedepth during drive•• resistance distributionresistance distribution
–– CAPWAP CAPWAP ®®
PDA testingPDA testingdata interpretationdata interpretation
Easy drivingEasy driving Hard drivingHard driving
Pile as it encounters rock
Toe reflection in tension
(relatively easy driving)
Toe reflection in compression
(relatively hard driving)
End of Drive
Restrike (8 days)
Low shaft resistance
Increased shaft resistance
(setup)
PDA testingPDA testingdata interpretationdata interpretation
EOD 85 tonEOD 85 ton
BOR 1D BOR 1D -- 189 ton189 ton
BOR 75D BOR 75D -- 286 ton286 ton
Restrike testing -fine grained soilsRestrike testing -fine grained soils
log timelog time
capa
city
capa
city
1 da
y1
day
10 d
ays
10 d
ays
100
days
100
days
1000
day
s10
00 d
ays
Technically desirable
Technically desirableEconomically desirable
Economically desirable
Restrike testing generally underRestrike testing generally under--taken 1 to 10 days after installationtaken 1 to 10 days after installation
Restrike testing -fine grained soilsRestrike testing -fine grained soils
log timelog time
capa
city
capa
city
1 da
y1
day
10 d
ays
10 d
ays
100
days
100
days
1000
day
s10
00 d
ays
Technically desirable
Technically desirableEconomically desirable
Economically desirable
Restrike testing generally underRestrike testing generally under--taken 1 to 10 days after installationtaken 1 to 10 days after installation
CAPWAP METHODCAPWAP METHOD
1 Set up pile model and assume soil model for Rshaft and Rtoe
1 Set up pile model and assume soil model for Rshaft and Rtoe
RshaftRRshaftshaft
RtoeRRtoetoe5 Go to step 25 Go to step 2
4 Adjust 4 Adjust RRshaftshaft andand RRtoetoe
3 Compare 3 Compare FFcc with measured with measured FFmm
2 Apply one measured curve (2 Apply one measured curve (vvmm););Calculate complementary Calculate complementary FFcc
vvmm FFccFFmm
Repeat until match Repeat until match is satisfactoryis satisfactory
First try (poor)
Final match (good)
CAPWAP
Adjustments
….. is an iterative process
CAPWAP match can be obtained by computer in
fully automatic way!
PDA testing + CAPWAP leads to calculated load - set curve
PDA testing + CAPWAP PDA testing + CAPWAP leads to calculated load leads to calculated load -- set curveset curve
Drilled Shaft TestingDrilled Shaft Testing
PDAPDA
Alternate: Alternate: use hydraulic jawsuse hydraulic jaws
•• Drop weightDrop weight
•• SizeSize
•• drop mechanismdrop mechanism
•• GuidesGuides
•• CushionCushion
•• Pile Pile preparationpreparation
•• Sensor Sensor AttachmentAttachment
Loading guideLoading guide
20 ton ram20 ton ram(free drop)(free drop)
static tests planned for 70 shafts (1.5 m OD) to 2000 tons static tests planned for 70 shafts (1.5 m OD) to 2000 tons
WestgateWestgate Freeway, Australia, 1982Freeway, Australia, 1982
MalaysiaMalaysia
30 ton drop weight30 ton drop weight
40 ton weight 40 ton weight -- PhilippinesPhilippines
“Big Newton” “Big Newton” in honor of in honor of
Sir Isaac’s F=maSir Isaac’s F=ma
“APPLE” “APPLE” -- AA PPreferred referred PPile ile LLoad oad EEvaluatorvaluator
OhioOhio
GRL drop hammerGRL drop hammer
(fuel pump removed (fuel pump removed from a diesel hammer)from a diesel hammer)
Plywood cushionPlywood cushion
OhioOhio
GRL drop hammer >GRL drop hammer >
(fuel pump removed (fuel pump removed from a diesel hammer)from a diesel hammer)
Drilled Shaft tests Drilled Shaft tests -- Milwaukee StadiumMilwaukee Stadium
•• CSL tests found 15 shafts with soft toesCSL tests found 15 shafts with soft toes
•• Capacity was questionedCapacity was questioned
•• Quote for 2 static tests was $200,000 Quote for 2 static tests was $200,000 $100,000 per test$100,000 per test
•• Quote for 15 PDA tests was $45,000 Quote for 15 PDA tests was $45,000 $3,000 per test$3,000 per test
•• Client tested all 15 shafts with PDA Client tested all 15 shafts with PDA total cost savings: $155,000total cost savings: $155,000
Vibrator clampsVibrator clampsto free releaseto free releasethe ramthe ram
Ram guideRam guide
20 ton ram20 ton ram
42” drilled shaft42” drilled shaft
Drilled Shaft Testing in MilwaukeeDrilled Shaft Testing in MilwaukeeDrilled Shaft Testing in Milwaukee
Vibrator supportVibrator supportpostsposts
Steel pinSteel pin
2000 ton 2000 ton RuRu
Improvised Drop Hammer made Improvised Drop Hammer made on site: scrap steel bits in tube on site: scrap steel bits in tube (not ideal, but it worked)(not ideal, but it worked)
RultRult requiredrequired2000 ton 2000 ton 4000 4000 kipskips
CAPWAPCAPWAP
RultRult requiredrequired2000 ton 2000 ton 4000 4000 kipskips
4 blows in PDA test in Milwaukee4 blows in PDA test in Milwaukee( 20 ton drop weight )( 20 ton drop weight )
Stress OKStress OK RultRult OKOK
Milwaukee testsMilwaukee tests
PIT done before and PIT done before and after PDA testing after PDA testing for every shaft.for every shaft.
(2 examples shown)(2 examples shown)
PIT results show no PIT results show no damage to shaft due to damage to shaft due to PDA testing and PDA testing and improved toe bearing.improved toe bearing.
Before
Before
After
After
Increased toe resistance
Conclusions,Conclusions,PDA testing on drilled shafts:PDA testing on drilled shafts:
•• proven worldwide application now proven worldwide application now
•• uses available or easyuses available or easy--toto--make drop hammers make drop hammers and minimal pile preparationand minimal pile preparation
•• confirms capacity, even at large loadsconfirms capacity, even at large loads
•• reduced testing time and large cost savings reduced testing time and large cost savings (cost 10 to 30 times less than static cost) (cost 10 to 30 times less than static cost)
PDA ConclusionsPDA ConclusionsPDA Conclusions
• PDA with CAPWAP evaluates capacity at low cost for driven piles, drilled shafts,
& augercast piles
• PDA gives extra valuable information (integrity, stresses, hammer energy)
• PDA potentially saves time or pile length in favorable site conditions
• Improves quality control by more pile tests
•• PDA with CAPWAP evaluates capacity at PDA with CAPWAP evaluates capacity at low cost for driven piles, drilled shafts, low cost for driven piles, drilled shafts,
&& augercastaugercast pilespiles
•• PDA gives extra valuable information PDA gives extra valuable information (integrity, stresses, hammer energy)(integrity, stresses, hammer energy)
•• PDA potentially saves time or pile length in PDA potentially saves time or pile length in favorable site conditionsfavorable site conditions
•• Improves quality control by more pile testsImproves quality control by more pile tests
SPT Testing and Analysis
(Standard Penetration Test)
SPT Testing and AnalysisSPT Testing and Analysis
(Standard Penetration Test)(Standard Penetration Test)
SPT Purpose:SPT Purpose:
•• NN--value (strength)value (strength)
•• Retrieve soil sampleRetrieve soil sample
“Standard” Penetration Testing“Standard” Penetration Testing“Non“Non--standard” variablesstandard” variables
• Hammers– Safety– Automatic– Donut
• Operators– Manual– Semi-automatic– Automatic
• Drill Rods– Size– Length
• Hammers– Safety– Automatic– Donut
• Operators– Manual– Semi-automatic– Automatic
• Drill Rods– Size– Length
•• Lift MechanismsLift Mechanisms–– CatheadCathead--roperope–– CatheadCathead diameterdiameter–– Spooling WinchSpooling Winch–– Chain Driven Chain Driven
•• Drill MethodsDrill Methods–– Hollow Stem AugersHollow Stem Augers–– Drilling FluidsDrilling Fluids
•• Split Tube SamplerSplit Tube Sampler–– ShapeShape–– Liners or notLiners or not
Why measure?Why measure?
•• Due to “nonDue to “non--standard” SPT systems, standard” SPT systems, energy delivered can be highly variableenergy delivered can be highly variable
•• Energy transfer affects N Energy transfer affects N -- value value •• Soil strength estimated from N Soil strength estimated from N -- valuevalue
–– (used in static analysis to estimate capacity)(used in static analysis to estimate capacity)
•• Obtain normalized N Obtain normalized N -- value ( Nvalue ( N60 60 ))•• Improve reliability of soil analysisImprove reliability of soil analysis•• EvaluateEvaluate Liquifaction Liquifaction (ASTM D 6066)(ASTM D 6066)
SPT Energy TestingSPT Energy Testing
Energy TransferEnergy Transfer
Hammer Type EFV avg C.O.VOne stdTwo std Samples
Cathead-rope 63 12 55 – 7147 – 79 15
CME automatic 75 9 67 – 8359 – 91 10
Spooling winch 35 8 31 – 39 3Hydraulic auto 69 15 59 – 79 5Donut 43 22 34 – 52 3Other Auto 49 13 42 - 56 6
Data from GRL compiled by Utah StateData from GRL compiled by Utah State
Comparison of StudiesComparison of Studies
Hammer Study EFV avg C.O.V.
Safety Utah State 63 12
Flordia DOT 66 11
Automatic Utah State 75 9
Flordia DOT 80 8
Normalized N valueNormalized N value
NN60 60 ==NNmm * E* Emm
{{ WhWh (60%) }(60%) }
Wh Wh (60%) = (60%) = AverageAverage Energy Energy
NNmm = Measured N= Measured N
EEmm = Measured Energy= Measured Energy
Why measure on SPT?Why measure on SPT?• Energy is variable; affects N - value • Soil strength estimated by N - value
– (used in static analysis to estimate capacity)• Obtain normalized N - value ( N60 )
• Improves reliability of soil analysis• Evaluate Liquifaction (ASTM D 6066)
•• Energy is variable; affects N Energy is variable; affects N -- value value •• Soil strength estimated by N Soil strength estimated by N -- valuevalue
–– (used in static analysis to estimate capacity)(used in static analysis to estimate capacity)•• Obtain normalized N Obtain normalized N -- value ( Nvalue ( N60 60 ))
•• Improves reliability of soil analysisImproves reliability of soil analysis•• EvaluateEvaluate Liquifaction Liquifaction (ASTM D 6066)(ASTM D 6066)
What is the benefit?What is the benefit?
ConclusionsConclusions• Great potential benefit to industry due to
SPT testing– Better uniformity– Spot problem rigs– Improve predictions using N values– Adjust procedures to get uniform energy
• Great potential benefit to industry due to SPT testing– Better uniformity– Spot problem rigs– Improve predictions using N values– Adjust procedures to get uniform energy
The EndThe End
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