Proper Practice. 2015, Pile Dynamics, Inc.

Transcription

1 PDA Testing : Proper Practice , Pile Dynamics, Inc.

2 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.

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

4 Testing of any pile type Convert STRAIN ( ε ) to F F (t) = E A ε (t) Convert ACCELERATION to V Solution to meet all needs: lightweight strain and acceleration transducers V (t) = a(t) dt

5 PR acc PE acc Not good for steel-to-steel Need good sensors in good condition PE acc rugged, better in very cold temps, any pile type PR acc - any pile type, better for steel-to-steel impacts Strains - handle with care

6 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

7 PDA testing - data acquisition 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! )

8 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

9 PDA testing - data acquisition Use drilling template

10 Plastic anchors NOT acceptable (gave poor data)

11

12 Proper attachment for concrete piles Important Gap

13 NO

14 PDA testing - data acquisition AXIAL!

15 PDA testing - data acquisition How to put on sensors (piles or shafts) Axial with pile ~2 diameters from top restrike at convenient location Firmly bolted Avoid cracks (gaps make false strain readings) welds (particularly spiral welded) section changes

16 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 )

17 PAX - Balance PAX ( 8G ) have 10,000 µε total range (huge) PAX shows test range available (+3000 to µε) (PAK has 2000 µε range) PAX says OK then is OK to test

18 8G - Balance wireless cables

19 PDA testing - data acquisition

20 BN 1 BN 2 Pile plastically yielding changes balance BN 3

21 PDA testing - data acquisition Put sensors near pile head ~2 D Support cable weight

22 Damaged Cables are by far the largest cause of repairs; Wireless eliminates cables ~2 D Radio Transmit

23 wireless PDA smart sensors know their calibration Do not climb to attach sensors or cables

24 Sensor-Transmitter Protection H-piles no issue

25 Sensor-Transmitter Protection H-piles no issue Pipe piles use protectors

26 Sensor-Transmitter Protection H-piles no issue Pipe piles use protectors Concrete piles protectors or - sensors in indentations

27 Attached on uniform Attached in indent 597 k 604 k

28 Why Wireless? Eliminates cable reliability aids 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 acceleration 8G allows up to 16 channels of data (any type)

29 SiteLink - Remote PDA USA Patent #6,301,551 Pile Driving Analyzer Pile Site A Internet connection Aircard with Internet Later same day Site B Pile Experienced Engineer controls PDA as if on-site; monitors pile in real time. Office CAPWAP analysis starts immediately after testing.

30 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, Advances in Dynamic Foundation Testing Technology. Geotechnical Special Publication No American Society of Civil Engineers: pp

31 PAX Diesels only Radios only

32 35 8G

33 Sampling rate Recommendation: 200 ms for most tests 8G: select 200 msec PAX: 5 1K 2K 4K PAK: 1K (record length)

34 PDA testing - data acquisition Minimum 2 strains per pile (symmetrical) to compensate bending

35 2 strains compensate bending Avg F is OK Minimum 2 strains to compensate for bending in pile Bending caused by bad alignment bending Even with large bending, the two velocities are very similar. important 2 strain and 1 acceleration are minimum 2 strain and 2 acceleration are recommended

36 PDA testing - data acquisition Minimum 2 strains per pile (symmetrical) to compensate bending Use 4 strains for drilled shafts place at 90 o in pairs at 180 o 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)

37 PDA testing - data acquisition V1 reduced by cosine of angle from axial

38 PDA testing - data acquisition

39 PDA testing - data acquisition

40 PDA testing - data acquisition

41 PDA testing - data acquisition Pile properties (at sensor location) Area AR location circumference Length (from sensors to toe) LE Material properties Density SP Modulus EM Wavespeed WS EM = ρ c 2 = (SP / g) WS 2 Embedment (LP) for CAPWAP Uniform?

42 PDA testing - data acquisition 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!

43 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 f'c f'c EM-dyn EM-dyn WS-dyn WS-dyn psi MPa ksi MPa ft/sec m/s 2, ,804 19,518 9,249 2,830 3, ,434 23,883 10,235 3,131 4, ,965 27,575 10,999 3,364 5, ,434 30,831 11,630 3,557 6, ,857 33,772 12,172 3,723 7, ,246 36,477 12,650 3,869 8, ,608 38,997 13,080 4,001 9, ,948 41,361 13,470 4,120 10, ,270 43,600 13,830 4,230 E = f (f c) 0.5 : WS = ( E/ρ ) 0.5 = f ( f c ) 0.25

44 Concrete/Timber - find WS? PEAK RISE Rise to rise Peak to peak

45 How to find WS? Rise to rise Peak to peak

46 PDA testing - data interpretation Variable wavespeed WS still 3911 m/s WS 3911 m/s BN 3 WS 3911 m/s BN 2045 WC 3556 m/s BN 2045 Use or to adjust WC

47 PDA testing - data interpretation

48 PDA testing - data interpretation Use Blow by Blow Auto Edit Set Blow by Blow Edit before saving 8G PDA-S

49 Testing Uniform Composite Piles Drilled shafts with casing Concrete filled steel pipe piles (common practice) H pile full length in grout/concrete Why or when do we want to test concrete filled piles? Because of higher impedance - can activate more capacity during restrike cases when setup causes refusal

50 Uniform Composite Piles Example: concrete filled pipe Concrete: Ac, ρc Steel: As, ρs 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)

51 Concrete filled pipe Protect pile top with plywood cushion Must hit thru concrete Concrete strain = Steel strain this is required! Important 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 EA steel / EA total < 10%

52 good bad No windows Sensors on steel 140 mm (5.5 ) Windows Sensors on concrete 213 mm x 8.2 mm pipes (8 3/8 x pipes) circumference 668 mm (26.3 inch), so 42% steel removed Steel is about 50% of EA and 44% of EA/c

53 Testing drilled shafts Build up pile top, plywood cushion Reduces excavation Protects reinforcing Remove after testing Drop weight 1%, 2%, 5% of Ru (2% helps activate end bearing) Four strains standard: To assess data quality by 180 o pairs To give backup (few blows allowed)

54 Poor top preparation Use template for Surface not flat. drilling holes Poor attachment leads to bad data (damage sensor?)

55 Ideal extension is 1D diameter and 2D high 42 inch nom. shaft 25% increase AR Sensors just below transition NOT ideal; strain not fully engaged, proportionality lost

56 Pay attention to details! 4 strains allow backup and assess data quality Ideal 4 Important 2 4 3? Know which are opposite! 2 Turn off mate if one fails 4? 3

57 Traditional F = ma Top transducer Force Pile Velocity Single ram only F V Accelerometer Strain

58 APPLE IV With 56 kips 25,500 kg 250 kn Thick cushion Thin cushion