PDA Testing : 1997 Proper Practice

1973

1982

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1965

1997PDA Testing :

© 2015, Pile Dynamics, Inc.

Proper Practice

2007

1958

2014

Luckily, no fatalities but sure slows job down

NOTHING is more important than your safety!

If you perceive something as unsafe, don’t do it

Watch where you stand (particularly during lifts) and plan an exit strategy in anticipation.

“Case Method” requires measuring Force ( F ) and Velocity ( V ) versus time at same point on pile (usually near top).

Pile Testing

Convert STRAIN ( ε ) to F

F (t) = E A ε (t)

Convert ACCELERATION to V V (t) = a(t) dt

Testing of any pile type

Solution to meet all needs:

lightweight strain and acceleration transducers

PR acc PE acc

Not good for steel-to-steel

Need good sensors in good conditionPE acc – rugged, better in very cold temps, any pile typePR acc - any pile type, better for steel-to-steel impactsStrains - handle with care

“Rain proof”

In-house• 7 to 11 week survival at

near-surface conditions• Nominal 70 ft (7 day test)• One failed at 140 ft• Survived 320 ft for 7 days• Failed at 460 ft

• Test all sensors BEFORE attaching sensors to the pile

• Tap the strain and acceleration sensors to see response (select by TRIGGER channel)

Do NOT excessively beat on PR gages!

( can also deform strain transducers! )

PDA testing - data acquisition

• Need Minimum 2 strains per pile to compensate for bending

– Place symmetrically about neutral axis– Need 4 strains to assess 2 axis bending



Use drilling template

Plastic anchorsNOT acceptable(gave poor data)

Proper attachment for concrete piles

Important

Gap

AXIAL !


How to put on sensors (piles or shafts)Axial with pile~2 diameters from top

restrike – at convenient locationFirmly bolted


Avoid – “cracks” (gaps make false strain readings)– welds (particularly spiral welded)– section changes

CAL TEST ( “CT” ) • save this input, verify calibration of the PDA itself

(but NOT of sensors)

• cal test also determines if PDA is functional

• VMX and MEX • for known inputs• give known outputs ±2%

Unacceptable

( power noise )

PAX - Balance

•PAX ( 8G ) have 10,000 µε total range (huge)

• PAX shows test range available (+3000 to -3000 µε)(PAK has 2000 µε range)

• PAX says “OK” then is OK to test

8G - Balance

wireless

cables

BN 1

BN 2

BN 3

Pile plastically yielding changes balance

Put sensors near pile head

Support cable weight

~2 D


Damaged Cables are by far the largest cause of repairs;

Wireless eliminates cables

~2 DRadio

Transmit

wireless PDA “smart sensors” know their calibration

Do not climb to attach

sensors or cables

Sensor-Transmitter Protection

• H-piles – no issue

• H-piles – no issue• Pipe piles – use protectors


• H-piles – no issue• Pipe piles – use protectors• Concrete piles – protectors

or - sensors in indentations


Attached on uniform Attached in indent

604 k597 k

Why Wireless?Eliminates cable

reliabilityaids site logistics easy clean up (no cable in the mud)

Allows attaching on ground speeds testing process properly attached

Easy to transport – very lightweight

PAX – allows 2 strain and 2 acceleration8G – allows up to 16 channels of data (any type)

Pile

Site

APile

Site B

Pile Driving Analyzer ®

Aircardwith

Internet

Internet connection

Experienced Engineer controls PDA as if on-site; monitors pile in real time.

CAPWAP analysis starts immediately after testing.

Later same day

Office

SiteLink ® - Remote PDA USA Patent #6,301,551

PAX Remote SiteLink® Operation

• PDA is operated by office engineer (improve efficiency)• Some site assistance• Improves scheduling of tests• Faster results, reduced cost testing• Likins, G, Hermansson, I, Kightley, M, Cannon, J, Klingberg, D, March, 2009. “Advances in Dynamic

Foundation Testing Technology”. Geotechnical Special Publication No. 185. American Society of Civil Engineers: pp. 591-598.

PAX

Diesels onlyRadios only

8G

35

Sampling rate

Recommendation: 200 ms for most tests8G:

select 200 msec

PAX:

5 kHz @ 1K

10kHz @ 2K

20kHz @ 4K

PAK:

5kHz @ 1K (record length)

Minimum 2 strains per pile (symmetrical)to compensate bending


2 strains compensate bending

Bending caused by bad alignment

Even with large bending, the two velocities are very similar.

2 strain and 1 acceleration are minimum2 strain and 2 acceleration are recommendedimportant

Minimum 2 strains to compensate for

bending in pile

bending

Avg F is OK

Minimum 2 strains per pile (symmetrical)to compensate bending

• Use 4 strains for drilled shafts • place at 90o in pairs at 180o

• F1 and F2 opposite, F3 and F4 opposite• Use 4 strains for spiral weld pipes

( if problems with data )• (EX-9 shows benefit for sprial pipes)


V1 reduced by cosine of angle from axial


• Pile properties (at sensor location)– Area AR– “Diameter” @sensor location circumference– Length (from sensors to toe) LE– Material properties

• Density SP• Modulus EM• Wavespeed WS

• EM = ρ c2 = (SP / g) WS2

– Embedment (LP) for CAPWAP– Uniform?


• Steel• SP, WS and EM known

• Concrete• SP known• WS and EM unknown

– measure WS

• Timber• SP, WS and EM unknown

– measure SP and WS!


Typical concrete WS is 4,000 m/s or 13,000 ft/s, but varies according to concrete strength and age

Approx. guide below, but WS needs to be measured

E = f (f’c) 0.5 : WS = ( E/ρ )0.5 = f ( f’c )0.25

f'c f'c EM-dyn EM-dyn WS-dyn WS-dynpsi MPa ksi MPa ft/sec m/s

2,000 14 2,804 19,518 9,249 2,8303,000 21 3,434 23,883 10,235 3,1314,000 28 3,965 27,575 10,999 3,3645,000 35 4,434 30,831 11,630 3,5576,000 42 4,857 33,772 12,172 3,7237,000 49 5,246 36,477 12,650 3,8698,000 56 5,608 38,997 13,080 4,0019,000 63 5,948 41,361 13,470 4,120

10,000 70 6,270 43,600 13,830 4,230

Concrete/Timber - find WS ?

Rise to rise Peak to peak

RISE

PEAK

How to find WS ?

Rise to rise

Peak to peak

WS 3911 m/s

BN 3

WS 3911 m/s

BN 2045

Variable wavespeed

Use ← or → to adjust WC

WC 3556 m/s

BN 2045

WS still 3911 m/s

PDA testing - data interpretation


8G – PDA-S

Use “Blow by Blow Auto Edit”Set “Blow by Blow Edit” before saving

Drilled shafts with casing Concrete filled steel pipe piles

(common practice)H pile full length in grout/concrete

Testing Uniform Composite Piles

Because of higher impedance - can activate more capacityduring restrike cases when setup causes refusal

Why or when do we want to test concrete filled piles?

Concrete: Ac, ρc Steel: As, ρs

Uniform Composite Piles

Average Density ρ = (Ac ρc + As ρs) / (Ac + As)

Average Modulus EM = (Ac Ec + As Es) / (Ac + As)

estimate WS = √{EM/ρ} (if see WS from test, use it)

Example: concrete filled pipe

• Concrete strain = Steel strain this is required !

•if high percent steel, attach to steel “windows” make significant (bad) stress concentration effect (do not make windows)

•if low percent steel, (use “windows”) attach to concrete

EAsteel / EAtotal < 10%

Important

Protect pile top with plywood cushion

Concrete filled pipeMust hit thru concrete

213 mm x 8.2 mm pipes (8 3/8” x 0.322 pipes)

circumference 668 mm (26.3 inch), so 42% steel removed Steel is about 50% of EA and 44% of EA/c

No windows 140 mm (5.5”) Windows

Sensors on steel Sensors on concrete

badgood

Testing drilled shaftsBuild up pile top, plywood cushion

Reduces excavationProtects reinforcing

Remove after testing

Drop weight 1%, 2%, …5% of Ru(2% helps activate end bearing)

Four strains standard: To assess data quality by 180o pairs

To give backup (few blows allowed)

Poor top preparation

Use template for drilling holesSurface not flat.

Poor attachment leads to bad data (damage sensor?)

42 inch nom. shaft

25% increase AR

Sensors just below transition NOT ideal; strain not fully

engaged, proportionality lost

Ideal extension is 1D diameter and 2D high

Ideal

2

3 4

1

24

3

1

4?

3? Know which are opposite !

Pay attention to details ! 4 strains allow backup and assess data quality

Turn off mate if one fails

Important

Strain

Accelerometer

Pile Velocity

Force

TraditionalF = ma

Top transducer

F

V

Single ram only

Thick cushion

APPLE IVWith 56 kips25,500 kg

250 kN

Thin cushion

PDA Testing : 1997 Proper Practice

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